Medicine - kembara Xtra

Published on: August 25, 2026

Infectious Disease and Microbiology - Acanthamoeba Species

Infectious Disease and Microbiology - Acanthamoeba Species Basics Acanthamoeba is a genus of free-living protozoa that is widely distributed in the environment. Several species have been associated with human infection, including A. astronyxis, A. castellanii, A. culbertsoni, A. divionensis, A. glebae, A. griffini, A. healyi, A. hatchetti, A. palestinensis, A. polyphaga, and A. rhysodes. These organisms do not require a human or animal host to complete their life cycle and can persist independently in environmental sources. Acanthamoeba species exist as both trophozoites and cysts. The trophozoite is the active, feeding form, whereas the cyst is more resistant to environmental stress and contributes to the organism’s persistence in unfavorable conditions.

Microbiologic Characteristics Acanthamoeba species are free-living protozoa with a worldwide environmental distribution. They are commonly encountered in soil, dust, freshwater, brackish water, sewage, hot tubs, and other moist environments. Their ability to form resistant cysts allows them to survive under conditions that would eliminate many other microorganisms. The organisms are relatively resistant to standard concentrations of chlorine used in drinking water and swimming pools, which helps explain their persistence in treated water systems.

Epidemiology Acanthamoeba infections occur worldwide because the organisms are ubiquitous in the environment. Human exposure is common, but clinical disease is relatively uncommon and usually develops when the organism gains access to susceptible tissues. Acquisition may occur through inhalation, contamination of damaged skin, or direct contact with contaminated soil or water. Contact lens–associated infection is particularly important. Using tap water, nonsterile saline, or contaminated lens-cleaning solutions can introduce Acanthamoeba onto the corneal surface. Although disseminated and central nervous system disease primarily affects immunocompromised or debilitated patients, infection can occasionally occur in people without an obvious underlying immune defect.

Major Clinical Infections Acanthamoeba produces three particularly important clinical syndromes: granulomatous amebic encephalitis, keratitis, and chronic cutaneous or soft-tissue disease. Granulomatous amebic encephalitis is typically seen in patients with impaired immunity. The illness usually has an insidious and progressive course rather than the abrupt presentation seen with many bacterial or viral encephalitides. Neurologic symptoms may evolve over more than a week and can continue for several weeks or months before diagnosis. Acanthamoeba keratitis usually occurs after corneal trauma or in contact lens users. Contaminated cleaning solutions, tap-water rinsing of lenses, swimming while wearing lenses, and poor contact lens hygiene are important risk factors. The keratitis may resemble herpes simplex keratitis because dendritic or pseudodendritic corneal lesions can occur. Acanthamoeba can also cause chronic skin and soft-tissue infection. Manifestations include persistent ulcerative lesions, abscesses, plaques, or erythematous nodules. Cutaneous disease is particularly important in immunocompromised patients and may sometimes accompany disseminated infection.

Granulomatous Amebic Encephalitis Granulomatous amebic encephalitis is a severe, usually subacute or chronic central nervous system infection. It occurs most often in individuals with major underlying illness or impaired cellular immunity. The presentation is variable and can include progressive headache, behavioral changes, altered mental status, focal neurologic deficits, seizures, ataxia, cranial nerve abnormalities, and eventually coma. Because the disease evolves slowly, the diagnosis may initially be confused with brain tumor, fungal infection, tuberculosis, or another chronic encephalitis. The prognosis is generally poor, particularly when diagnosis is delayed.

Acanthamoeba Keratitis Keratitis is one of the most clinically recognizable Acanthamoeba infections and often occurs in otherwise healthy individuals. The strongest risk factor is contact lens use, particularly when lenses are exposed to nonsterile water. Important exposures include rinsing lenses or lens cases with tap water, swimming or showering while wearing lenses, using contaminated cleaning products, or poor lens-case hygiene. Patients may develop severe eye pain, photophobia, tearing, redness, and reduced visual acuity. Pain may be disproportionately severe compared with the initial clinical appearance. Early disease may show punctate epithelial abnormalities or dendritiform lesions and can therefore be mistaken for herpes simplex keratitis. As infection progresses, stromal inflammation and a characteristic ring-shaped corneal infiltrate may develop. Early recognition is important because delayed treatment can lead to corneal destruction and permanent visual impairment.

Cutaneous and Disseminated Disease Cutaneous Acanthamoeba infection may present with slowly progressive erythematous papules, nodules, ulcers, or abscess-like lesions. These lesions can be chronic and may involve the face, trunk, or extremities. In markedly immunocompromised patients, skin disease may represent part of disseminated infection. Organisms can spread hematogenously to other sites, including the central nervous system. Persistent unusual skin lesions in an immunocompromised patient should therefore prompt consideration of opportunistic free-living amebic infection.

Diagnosis Diagnosis depends on identifying the organism in tissue or clinical specimens. Acanthamoeba may be cultured using specialized media, although culture is not always rapidly available. Cysts or trophozoites can sometimes be demonstrated directly in tissue specimens. Brain tissue, corneal tissue, or corneal scrapings may show the organism on histopathologic examination. Useful stains include silver-methenamine and periodic acid–Schiff stains. Organisms may rarely be visualized in fresh cerebrospinal fluid, but CSF examination has relatively low sensitivity. For keratitis, corneal scrapings or biopsy specimens may be evaluated using microscopy, culture, histopathology, and polymerase chain reaction. PCR can provide highly useful confirmation when available. Serologic testing has little clinical value and is generally not useful for establishing the diagnosis.

Diagnostic Approach to Keratitis Acanthamoeba should be strongly suspected in a contact lens wearer with severe keratitis, especially when symptoms persist despite antibacterial or antiviral therapy. A particularly suggestive pattern is severe ocular pain combined with a history of contact lens exposure to tap water or recreational water. Corneal scraping should be obtained for microbiologic evaluation when the diagnosis is suspected. PCR, culture, and direct visualization can all contribute to confirmation.

Differential Diagnosis Granulomatous encephalitis may resemble other chronic or subacute central nervous system infections, including fungal meningitis or encephalitis, tuberculosis, toxoplasmosis, and other free-living amebic infections. Neoplastic and inflammatory neurologic disorders may also mimic the presentation. Acanthamoeba keratitis can be confused with herpes simplex keratitis, bacterial keratitis, fungal keratitis, and other causes of corneal ulceration. Chronic cutaneous disease may mimic fungal infection, atypical mycobacterial infection, bacterial abscesses, inflammatory dermatoses, or malignancy.

Treatment Treatment of Acanthamoeba infection can be difficult because the organisms have both trophozoite and cyst forms, and the cysts are relatively resistant to therapy. For granulomatous amebic encephalitis, no single standardized regimen has been proven consistently effective. Therapy generally uses combinations of agents with demonstrated in vitro or reported clinical activity. Drugs that have activity against Acanthamoeba include pentamidine, azole antifungals, sulfonamides, flucytosine, and, to a lesser extent, amphotericin B. Combination therapy is usually favored for serious systemic or neurologic disease because monotherapy is unlikely to be reliably effective. Treatment should be individualized with infectious disease and neurologic expertise whenever possible.

Treatment of Acanthamoeba Keratitis Keratitis generally requires prolonged topical combination therapy. Older regimens included topical propamidine combined with neomycin, gramicidin, and polymyxin. Modern treatment commonly relies heavily on topical biguanides because they have activity against both trophozoites and cysts. Frequently used agents include: • Polyhexamethylene biguanide at approximately 0.02% • Chlorhexidine at approximately 0.02% These may be combined with diamidines such as propamidine in selected cases. Treatment is often prolonged because viable cysts may persist even after initial clinical improvement. Severe disease or inadequate response may require ophthalmologic surgical management, including corneal transplantation in selected cases.

General Prevention Prevention is especially important because Acanthamoeba is widespread and difficult to eliminate completely from the environment. Contact lens users should use only sterile, commercially prepared solutions for lens cleaning, rinsing, and storage. Tap water should never be used to clean or store contact lenses or lens cases. Contact lenses should generally be removed before swimming, showering, entering hot tubs, or participating in water activities unless appropriate protective measures are used. Lens cases should be cleaned according to manufacturer instructions, allowed to dry completely, and replaced regularly. Standard precautions are sufficient for hospitalized patients because routine person-to-person spread is not a major mode of transmission. Avoiding exposure of open wounds or vulnerable tissues to contaminated warm freshwater may also reduce risk.

High-Yield Clinical Pattern Contact lens wearer ● Severe eye pain ● Exposure of lenses to tap water, swimming water, or contaminated cleaning solution → Think Acanthamoeba keratitis.

High-Yield Neurologic Pattern Immunocompromised patient ● Slowly progressive encephalitis over days to weeks ● Granulomatous CNS disease → Consider Acanthamoeba granulomatous amebic encephalitis.

High-Yield Diagnostic Features Acanthamoeba may be identified by: • Corneal scraping or biopsy • Brain or skin biopsy • Specialized culture • Histopathology • PCR Serologic testing: → Generally not useful.

Exam Essentials Organism type:

→ Free-living protozoan Distribution:

→ Worldwide Environmental reservoirs:

→ Soil, freshwater, brackish water, dust, sewage, and hot tubs Major infections:

→ Granulomatous amebic encephalitis, keratitis, and chronic cutaneous disease Major risk group for encephalitis:

→ Immunocompromised or debilitated patients Major risk factor for keratitis:

→ Contact lens use with contaminated or nonsterile water exposure Keratitis may mimic:

→ Herpes simplex keratitis Important diagnostic methods:

→ Corneal scraping, biopsy, culture, histopathology, and PCR Useful histologic stains:

→ Periodic acid–Schiff and silver-methenamine stains Serology:

→ Not clinically useful Important topical agents for keratitis:

→ Biguanides such as chlorhexidine or polyhexamethylene biguanide Key prevention:

→ Use only sterile solutions for contact lens care and avoid tap-water exposure.

Published on: August 25, 2026

Infectious Disease and Microbiology - Absidia corymbifera

BASICS

Genus

Absidia

Species

Absidia corymbifera is the principal species of Absidia historically recognized as pathogenic to humans.

It was previously referred to as:

Absidia ramosa

In more recent taxonomic classifications, organisms historically called Absidia corymbifera have been reclassified, but the older name is still encountered in medical literature.

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MICROBIOLOGIC CHARACTERISTICS

Absidia corymbifera is a:

• Filamentous fungus

• Mold

• Member of the order Mucorales

Its morphology resembles other mucormycetes such as Rhizopus.

Characteristic microscopic features include:

• Broad hyphae

• Hyaline appearance

• Pauciseptate or nonseptate hyphae

• Hyphal diameter approximately 6–15 μm

The hyphae commonly branch at relatively wide angles, as is typical of mucormycetes.

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CULTURE CHARACTERISTICS

The fungus grows rapidly in culture.

Typical growth may be visible within:

Approximately 4 days

Colonies are often:

• Light gray

• Grayish-brown

• Woolly or cotton-like

It can grow over a relatively broad temperature range, approximately:

25–45°C

Rapid growth helps distinguish mucormycetes from many slower-growing molds.

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EPIDEMIOLOGY

Absidia corymbifera is:

Ubiquitous in the environment.

It can be found in:

• Soil

• Decaying organic matter

• Plant material

• Environmental debris

Because it is widely distributed, its isolation from a nonsterile specimen does not always indicate invasive disease.

It may occasionally represent:

Environmental contamination or colonization.

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MODE OF ACQUISITION

The most common route of acquisition is believed to be:

Inhalation of airborne sporangiospores.

Other routes can include:

• Direct inoculation into damaged skin

• Traumatic implantation

• Contamination of wounds

The route of exposure influences the clinical syndrome that develops.

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RISK FACTORS

Severe invasive infection occurs predominantly in patients with impaired host defenses.

Important risk factors include:

• Profound neutropenia

• Hematologic malignancy

• Hematopoietic stem-cell transplantation

• Solid-organ transplantation

• Prolonged corticosteroid therapy

• Severe immunosuppression

• Advanced HIV infection

• Uncontrolled diabetes mellitus

• Diabetic ketoacidosis

• Major trauma or burns

• Iron overload

• Deferoxamine exposure

The risk rises substantially when several of these factors coexist.

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PATHOGENESIS

Like other mucormycetes, Absidia can invade blood vessels.

Angioinvasion produces:

• Thrombosis

• Tissue ischemia

• Infarction

• Necrosis

This explains the rapidly progressive and destructive nature of mucormycosis.

Vascular invasion also facilitates:

Hematogenous dissemination to distant organs.

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INFECTIONS

Absidia corymbifera is an uncommon cause of:

Mucormycosis

Clinical disease may involve many organ systems.

Major forms include:

• Rhinocerebral mucormycosis

• Pulmonary mucormycosis

• Cutaneous mucormycosis

• Disseminated mucormycosis

Less common manifestations include:

• Central nervous system infection

• Meningitis

• Post-traumatic infection

• Deep soft-tissue infection

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RHINOCEREBRAL MUCORMYCOSIS

Rhinocerebral disease typically begins in the:

Nasal cavity or paranasal sinuses

and may extend rapidly into:

• Orbit

• Facial structures

• Skull base

• Brain

It is classically associated with:

Poorly controlled diabetes and diabetic ketoacidosis.

Possible symptoms include:

• Facial pain

• Headache

• Nasal congestion

• Fever

• Periorbital swelling

• Diplopia

• Visual loss

Black necrotic tissue involving the nasal mucosa or palate is a major warning sign.

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PULMONARY MUCORMYCOSIS

Pulmonary disease occurs especially in:

• Neutropenic patients

• Patients with hematologic malignancies

• Transplant recipients

Symptoms may include:

• Fever

• Cough

• Dyspnea

• Pleuritic chest pain

• Hemoptysis

Pulmonary infection can rapidly invade blood vessels and cause:

• Pulmonary infarction

• Massive hemorrhage

• Dissemination

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CUTANEOUS MUCORMYCOSIS

Cutaneous infection may follow:

• Trauma

• Burns

• Contaminated dressings

• Surgery

• Direct inoculation

Lesions may begin as:

• Erythema

• Swelling

• Painful plaques

and progress to:

• Ulceration

• Necrosis

• Black eschar

Localized cutaneous disease can extend deeply into:

• Subcutaneous tissue

• Fascia

• Muscle

• Bone

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DISSEMINATED MUCORMYCOSIS

Dissemination occurs most often in patients with severe immunosuppression.

The infection may spread hematogenously to:

• Brain

• Liver

• Spleen

• Kidneys

• Heart

• Skin

Disseminated disease carries a very high mortality rate.

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CENTRAL NERVOUS SYSTEM DISEASE

CNS involvement may occur by:

• Direct extension from rhinocerebral infection

• Hematogenous dissemination

• Rarely, traumatic inoculation

Meningitis after severe head injury has been described but is uncommon.

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DIAGNOSIS

Diagnosis requires a combination of:

• Clinical suspicion

• Histopathology

• Culture

Because mucormycosis progresses rapidly, treatment should not be delayed while waiting for definitive culture results when clinical suspicion is high.

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CULTURE

Culture can identify the organism.

However:

A positive culture alone does not always prove invasive infection because the organism may be an environmental contaminant.

Conversely:

A negative culture does not exclude mucormycosis.

Tissue examination is therefore very important.

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HISTOPATHOLOGY

Characteristic tissue findings include:

• Broad hyphae

• Irregular width

• Pauciseptate or nonseptate appearance

• Wide-angle branching

• Angioinvasion

• Tissue necrosis

Demonstration of fungal invasion into tissue or blood vessels strongly supports true invasive disease.

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DIFFERENTIAL DIAGNOSIS

Important fungal differentials include:

• Rhizopus

• Mucor

• Lichtheimia

• Cunninghamella

• Aspergillus

• Fusarium

A particularly important distinction is:

Mucormycetes:

→ Broad, irregular, pauciseptate hyphae with wide-angle branching

Aspergillus:

→ Narrower, regularly septate hyphae with acute-angle branching

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TREATMENT

Mucormycosis is a medical and surgical emergency.

Successful management depends on three major principles:

1. Prompt antifungal therapy

2. Aggressive surgical debridement when feasible

3. Correction of underlying predisposing factors

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FIRST-LINE ANTIFUNGAL THERAPY

A lipid formulation of amphotericin B is generally preferred for invasive mucormycosis.

Typical dosing:

Liposomal amphotericin B approximately 5 mg/kg/day IV

Higher doses may be considered in selected severe infections, particularly CNS disease.

Historically, amphotericin B deoxycholate was used at:

Approximately 1–1.5 mg/kg/day

However, lipid formulations are generally preferred because they permit higher dosing with less nephrotoxicity.

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POSACONAZOLE

Posaconazole has activity against many mucormycetes.

It may be used as:

• Step-down therapy

• Salvage therapy

• An alternative when amphotericin B cannot be continued

Older regimens used:

Posaconazole approximately 800 mg/day

Modern dosing depends on formulation and should follow current prescribing guidance.

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ISAVUCONAZOLE

Isavuconazole is another important agent active against mucormycetes.

It may be considered for:

• Primary treatment in selected patients

• Step-down therapy

• Salvage treatment

Choice between amphotericin B, posaconazole, and isavuconazole depends on:

• Disease severity

• Site of infection

• Renal function

• Drug interactions

• Antifungal susceptibility

• Clinical response

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SURGICAL MANAGEMENT

Surgery is often crucial.

Aggressive debridement is especially important in:

• Rhinocerebral disease

• Cutaneous disease

• Necrotic soft-tissue infection

• Localized pulmonary disease in selected patients

Necrotic tissue has poor blood supply, limiting delivery of systemic antifungal therapy.

Therefore:

Antifungal therapy alone may be insufficient when extensive necrotic tissue remains.

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REVERSAL OF UNDERLYING RISK FACTORS

Whenever possible:

• Correct diabetic ketoacidosis

• Control hyperglycemia

• Reduce or discontinue corticosteroids

• Reduce immunosuppression

• Treat neutropenia

• Discontinue deferoxamine

• Correct severe metabolic abnormalities

Recovery of neutrophil function can be particularly important for survival.

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DURATION OF THERAPY

There is no single fixed duration.

Treatment is generally continued until:

• Clinical signs resolve

• Radiographic abnormalities improve substantially

• Surgical disease is controlled

• Immunosuppression has improved when possible

Therapy frequently lasts:

Several weeks to months

rather than a predetermined total cumulative dose.

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GENERAL PREVENTION

There is no vaccine.

Preventive strategies focus on reducing susceptibility and exposure.

Important measures include:

• Avoid unnecessary immunosuppression

• Optimize management of HIV infection

• Control diabetes

• Avoid prolonged severe neutropenia when possible

• Minimize corticosteroid exposure

• Avoid deferoxamine in patients at risk when alternatives are appropriate

• Protect wounds from environmental contamination

⸻

PROGNOSIS

Prognosis depends strongly on:

• Site of infection

• Speed of diagnosis

• Extent of tissue invasion

• Degree of immunosuppression

• Ability to surgically remove infected tissue

• Reversal of underlying risk factors

Localized cutaneous disease generally has a better prognosis than:

• Pulmonary disease

• Rhinocerebral disease with CNS extension

• Disseminated mucormycosis

Delayed therapy markedly worsens outcomes.

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HIGH-YIELD MICROBIOLOGY

Absidia corymbifera:

• Mold

• Mucorales

• Broad hyphae

• Pauciseptate or nonseptate

• Hyaline

• Rapidly growing

• Environmental organism

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HIGH-YIELD PATHOLOGY

Broad, irregular, pauciseptate hyphae

Wide-angle branching

Angioinvasion

→ Think mucormycosis

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HIGH-YIELD CLINICAL PATTERN

Immunocompromised patient

Rapidly progressive necrotic infection

Broad nonseptate fungal hyphae

→ Think Mucorales infection

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HIGH-YIELD RISK PATTERN

Diabetic ketoacidosis

Facial pain/sinus disease

Black necrotic nasal or palatal lesion

→ Rhinocerebral mucormycosis

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EXAM ESSENTIALS

Organism:

→ Absidia corymbifera

Older name:

→ Absidia ramosa

Organism type:

→ Filamentous mold

Order:

→ Mucorales

Hyphae:

→ Broad, hyaline, pauciseptate/nonseptate

Typical hyphal width:

→ Approximately 6–15 μm

Growth:

→ Rapid

Major route of infection:

→ Inhalation of spores

Major disease:

→ Mucormycosis

Common forms:

→ Rhinocerebral, pulmonary, cutaneous, disseminated

Major risk group:

→ Immunocompromised patients

Important pathogenic mechanism:

→ Angioinvasion with thrombosis and tissue necrosis

Diagnosis:

→ Tissue histopathology + culture

Preferred major antifungal class:

→ Amphotericin B, especially lipid formulations

Important alternatives/step-down agents:

→ Posaconazole or isavuconazole

Critical additional treatment:

→ Surgical debridement

Major management principle:

→ Reverse underlying immunosuppression or metabolic risk factors whenever possible

Published on: August 25, 2026

Infectious Disease and Microbiology - Yersinia enterocolitica Infections

BASICS

Description

Yersinia enterocolitica is a gram-negative coccobacillus that causes gastrointestinal and occasionally systemic infection.

The genus Yersinia includes:

• Yersinia pestis — causes plague

• Yersinia enterocolitica

• Yersinia pseudotuberculosis

Yersinia species are facultative anaerobes.

Y. enterocolitica most commonly causes:

• Acute enterocolitis

• Terminal ileitis

• Mesenteric adenitis

• Enteric fever–like illness

• Septicemia in high-risk patients

• Rare focal extraintestinal infections

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EPIDEMIOLOGY

Y. enterocolitica occurs worldwide.

It has historically been reported more frequently in:

• Northern Europe

• Parts of North America

• South America

• Africa

• Asia

In some European countries, Yersinia has been among the more commonly identified bacterial foodborne pathogens.

Disease is especially common in:

Young children, particularly those younger than 5 years.

Acute enterocolitis is the most frequent clinical presentation in this age group.

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TRANSMISSION

Y. enterocolitica infection is usually acquired through ingestion of contaminated food or water.

Important routes include:

• Contaminated pork

• Undercooked pork products

• Untreated water

• Contaminated food

• Contact with infected animals

• Rarely, contaminated blood products

Pigs are an especially important reservoir.

⸻

ANIMAL RESERVOIRS

Natural reservoirs include:

• Pigs

• Rodents

• Rabbits

• Sheep

• Cattle

• Horses

• Dogs

• Cats

Pork exposure is one of the most important epidemiologic clues.

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RISK FACTORS

Important risk factors include:

• Consumption of raw or undercooked pork

• Exposure to untreated water

• Young age

• Advanced age

Severe or invasive disease is more likely in patients with:

• Iron overload

• Hemochromatosis

• Beta-thalassemia

• Severe anemia

• Cirrhosis

• Diabetes mellitus

• Malignancy

• Immunocompromising conditions

⸻

IRON OVERLOAD — HIGH YIELD

Yersinia has a particularly important relationship with iron.

Patients with excess body iron have a substantially increased risk of severe Y. enterocolitica infection.

Examples include:

• Hemochromatosis

• Thalassemia

• Repeated blood transfusions

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DESFERRIOXAMINE

Patients receiving desferrioxamine, also called deferoxamine, are at particularly high risk for invasive Yersinia infection.

Why?

Yersinia can use iron bound to deferoxamine as a growth-promoting siderophore.

Therefore:

Iron overload + deferoxamine therapy + fever or abdominal symptoms

→ Strongly consider invasive Yersinia infection.

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TRANSFUSION-ASSOCIATED INFECTION

Y. enterocolitica can rarely contaminate stored red blood cell products.

This occurs because the organism can:

• Survive refrigerated temperatures

• Multiply during prolonged blood storage

Transfusion of heavily contaminated blood can cause:

• Acute fever

• Hypotension

• Septic shock

• Hemolysis

• Disseminated intravascular coagulation

This is a rare but important transfusion-associated bacterial infection.

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GENERAL PREVENTION

Prevention focuses on reducing exposure to animal reservoirs and contaminated food.

Important measures include:

• Cook pork thoroughly

• Avoid raw or undercooked pork

• Prevent cross-contamination during food preparation

• Use safe drinking water

• Practice careful hand hygiene

• Wash hands after handling raw pork or animals

• Use appropriate food-processing and slaughtering practices

Blood-storage and transfusion safety measures also help reduce transfusion-associated infection.

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ETIOLOGY

Y. enterocolitica is:

• Gram negative

• Facultatively anaerobic

• Non–lactose fermenting

• Urease positive

It belongs to the family Enterobacterales.

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PATHOPHYSIOLOGY

After oral ingestion, the organism reaches the terminal ileum.

It invades the intestinal mucosa and preferentially localizes in:

Peyer’s patches

The organism then spreads to:

Mesenteric lymph nodes

This explains the characteristic combination of:

• Terminal ileitis

• Mesenteric adenitis

• Right lower quadrant abdominal pain

The presentation may closely resemble acute appendicitis.

⸻

INCUBATION PERIOD

Symptoms usually begin approximately:

4–7 days after exposure

The possible range may be roughly:

1–11 days

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CLINICAL MANIFESTATIONS

Y. enterocolitica produces several important clinical syndromes.

These include:

• Acute enterocolitis

• Terminal ileitis

• Mesenteric adenitis

• Pseudoappendicitis

• Enteric fever–like illness

• Bacteremia/septicemia

• Focal extraintestinal disease

• Postinfectious reactive arthritis

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ACUTE ENTEROCOLITIS

This is the most common presentation.

It occurs particularly in:

Young children.

Symptoms may include:

• Fever

• Diarrhea

• Abdominal pain

• Nausea

• Vomiting

Stools may contain:

• Leukocytes

• Mucus

• Occasionally blood

The diarrhea is usually self-limited.

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PSEUDOAPPENDICITIS

One of the most important clinical associations is:

Yersinia → pseudoappendicitis

Older children and adults may develop:

• Right lower quadrant abdominal pain

• Fever

• Terminal ileitis

• Mesenteric lymphadenitis

This may closely mimic:

Acute appendicitis

A patient may even undergo surgery before the infectious diagnosis becomes apparent.

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MESENTERIC ADENITIS

Yersinia can infect mesenteric lymph nodes and produce:

• Enlarged lymph nodes

• Necrotizing lymphadenitis

• Right lower quadrant abdominal pain

This syndrome is especially associated with:

Y. enterocolitica and Y. pseudotuberculosis.

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TERMINAL ILEITIS

Inflammation of the terminal ileum may resemble:

• Crohn disease

• Appendicitis

• Other inflammatory bowel disorders

Clinical presentation can include:

• Fever

• Abdominal pain

• Diarrhea

• Right lower quadrant tenderness

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ENTERIC FEVER–LIKE ILLNESS

Some patients develop a systemic febrile syndrome characterized by:

• Fever

• Headache

• Abdominal pain

• Malaise

This can resemble typhoid or another systemic enteric infection.

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SEPTICEMIA

Y. enterocolitica bacteremia is uncommon but potentially severe.

It occurs mainly in high-risk patients with:

• Iron overload

• Cirrhosis

• Diabetes

• Malignancy

• Severe anemia

• Immunosuppression

• Very young or advanced age

Clinical manifestations may include:

• High fever

• Hypotension

• Septic shock

• Multiorgan dysfunction

Mortality is substantial in invasive disease.

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EXTRAINTESTINAL INFECTIONS

Rare focal infections may include:

• Abscesses

• Osteomyelitis

• Septic arthritis

• Endocarditis

• Meningitis

• Hepatic infection

These usually occur in patients with major underlying disease or bacteremia.

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PHYSICAL EXAMINATION

There are no pathognomonic examination findings.

Possible findings include:

• Fever

• Abdominal tenderness

• Right lower quadrant tenderness

• Signs of dehydration

• Signs of sepsis in invasive disease

In pseudoappendicitis, the abdominal examination may strongly resemble appendicitis.

⸻

DIAGNOSIS

Diagnosis depends on the clinical syndrome and microbiologic testing.

Possible specimens include:

• Stool

• Blood

• Mesenteric lymph nodes

• Tissue from affected sites

⸻

STOOL CULTURE

Stool culture can identify Y. enterocolitica in patients with enterocolitis.

Because Yersinia is not always recovered on routine culture conditions, the laboratory should be informed when infection is suspected.

Special culture approaches may improve recovery.

Yersinia can grow at low temperatures, a characteristic sometimes exploited using:

Cold enrichment

⸻

STOOL FINDINGS

Possible stool findings include:

• Fecal leukocytes

• Mucus

• Occult or visible blood

Fecal shedding may continue for:

Several weeks after symptoms resolve.

⸻

BLOOD CULTURES

Blood cultures should be obtained when:

• Bacteremia is suspected

• The patient is toxic

• There is hypotension

• Significant comorbidity is present

• There is iron overload

• Transfusion-associated sepsis is suspected

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LYMPH NODE CULTURE

In patients undergoing surgery for presumed appendicitis, culture of:

• Mesenteric lymph nodes

• Terminal ileal tissue

may reveal Yersinia.

⸻

SEROLOGY

Serologic testing can support diagnosis, particularly in selected extraintestinal or postinfectious syndromes.

However:

• It is not routinely available everywhere

• Cross-reactivity occurs

• Interpretation can be difficult

Cross-reactions may occur between:

• Y. enterocolitica

• Y. pseudotuberculosis

• Other bacteria

Agglutinating antibodies usually appear early and decline over several months.

⸻

MOLECULAR TESTING

Modern multiplex gastrointestinal PCR panels may detect Y. enterocolitica directly from stool in some laboratories.

Advantages include:

• Rapid detection

• Greater sensitivity than conventional culture in some settings

However, culture remains useful when:

• Antimicrobial susceptibility testing is required

• Public-health investigation is needed

• Confirmation of invasive disease is important

⸻

DIFFERENTIAL DIAGNOSIS

Depending on presentation, consider:

• Acute appendicitis

• Crohn disease

• Campylobacter enteritis

• Salmonellosis

• Shigellosis

• Enteroinvasive E. coli

• Clostridioides difficile infection

• Mesenteric adenitis from other causes

• Typhoid fever

• Viral gastroenteritis

For right lower quadrant pain:

Yersinia should be remembered as a classic infectious cause of pseudoappendicitis.

⸻

TREATMENT

Most uncomplicated gastrointestinal infections are:

Self-limited

Therefore, antimicrobial treatment is not routinely required for mild uncomplicated enterocolitis.

The most important management is:

• Hydration

• Electrolyte replacement

• Supportive care

⸻

WHEN TO CONSIDER ANTIBIOTICS

Antibiotic treatment is appropriate in:

• Severe enterocolitis

• Complicated gastrointestinal infection

• Bacteremia

• Septicemia

• Extraintestinal infection

• Immunocompromised patients

• Patients with major comorbidities

• Patients with iron overload and systemic disease

⸻

ANTIMICROBIAL OPTIONS

Active agents may include:

• Trimethoprim-sulfamethoxazole

• Fluoroquinolones

• Third-generation cephalosporins

• Doxycycline

• Aminoglycosides in selected severe cases

Choice should be based on:

• Disease severity

• Site of infection

• Susceptibility results

• Patient age

• Pregnancy status

• Local resistance patterns

⸻

SEVERE SEPTICEMIA

For severe invasive infection, regimens may include:

Ceftriaxone

with or without:

Gentamicin

or a fluoroquinolone such as:

Ciprofloxacin

Therapy should be individualized according to susceptibility testing and clinical response.

⸻

UNCOMPLICATED ENTEROCOLITIS

Antibiotics generally provide limited benefit in uncomplicated disease because:

• The illness is usually self-limited

• Symptoms often resolve spontaneously

Therefore:

Mild diarrhea + stable patient

→ Supportive treatment is usually sufficient.

⸻

SUPPORTIVE CARE

Important measures include:

• Oral rehydration

• Intravenous fluids when necessary

• Electrolyte replacement

• Nutritional support

• Antipyretics when appropriate

Severe dehydration or systemic illness may require hospitalization.

⸻

REACTIVE ARTHRITIS

One of the most important postinfectious complications is:

Reactive arthritis

It typically develops after the gastrointestinal illness has begun to resolve.

Symptoms may include:

• Painful swollen joints

• Oligoarthritis

• Lower-extremity predominance

The arthritis is sterile.

Yersinia is one of the classic gastrointestinal triggers of reactive arthritis.

⸻

HLA-B27

Reactive arthritis is more likely and may be more severe in patients who are:

HLA-B27 positive.

This association is particularly high yield.

⸻

ANKYLOSING SPONDYLITIS

Rarely, Yersinia infection has been associated with later development or triggering of:

• Sacroiliitis

• Spondyloarthritis

• Ankylosing spondylitis

This association is strongest in genetically susceptible patients, particularly those with HLA-B27.

⸻

Infectious Disease and Microbiology - Yellow Fever

BASICS

Description

Yellow fever is an acute mosquito-borne viral infection caused by the yellow fever virus. Clinical illness ranges from an asymptomatic or mild febrile syndrome to a severe systemic disease characterized by jaundice, hepatic injury, hemorrhage, renal dysfunction, shock, and multiorgan failure.

The term “yellow” refers to the jaundice that develops in severe disease.

⸻

EPIDEMIOLOGY

Yellow fever occurs primarily in tropical regions of:

• Sub-Saharan Africa

• Tropical South America

Transmission occurs mainly in areas located approximately between 15° north and 15° south of the equator.

The infection may occur as:

• Sporadic cases

• Local outbreaks

• Large epidemics

The true incidence is substantially higher than the number of reported cases because many infections are mild, unrecognized, or occur in areas with limited surveillance.

Historically, Africa has accounted for the majority of cases and deaths.

Travel-associated risk varies according to:

• Destination

• Season

• Vaccination status

• Mosquito exposure

• Local outbreak activity

Transmission has traditionally been highest:

• In parts of West Africa during the rainy season

• In parts of Brazil and South America during periods of increased mosquito activity

⸻

RISK FACTORS

Major risk factors include:

• Residence in or travel to an endemic region

• Lack of yellow fever vaccination

• Mosquito exposure

• Travel during periods of increased mosquito activity

• Outdoor activities without appropriate mosquito precautions

• Travel to areas experiencing an outbreak

Unvaccinated travelers entering endemic regions are at greatest risk.

⸻

ETIOLOGY

Yellow fever is caused by:

Yellow fever virus

The virus is:

• An enveloped RNA virus

• A member of the Flaviviridae family

• Related to other flaviviruses such as dengue, Zika, West Nile, and Japanese encephalitis viruses

⸻

TRANSMISSION

Yellow fever is transmitted through the bite of infected mosquitoes.

Important mosquito vectors include:

• Aedes species

• Haemagogus species in the Americas

Humans and nonhuman primates participate in transmission cycles.

Three epidemiologic transmission patterns are recognized:

1. Sylvatic or jungle cycle

The virus circulates between mosquitoes and nonhuman primates.

Humans become infected when they enter forested environments.

2. Intermediate or savannah cycle

Occurs mainly in Africa.

Mosquitoes transmit infection between humans and nonhuman primates in areas between jungle and urban environments.

3. Urban cycle

The virus is transmitted from:

Human → Aedes aegypti mosquito → Human

This cycle can produce large urban outbreaks.

⸻

PATHOPHYSIOLOGY

After an infected mosquito bite, the virus initially replicates in local tissues and regional lymph nodes.

Viremia subsequently develops and the virus disseminates through the bloodstream.

Important organs affected include:

• Liver

• Kidneys

• Heart

• Adrenal glands

• Spleen

Severe hepatic injury produces:

• Jaundice

• Impaired clotting-factor synthesis

• Coagulopathy

Hemorrhage is promoted by:

• Thrombocytopenia

• Platelet dysfunction

• Reduced hepatic production of coagulation factors

• Disseminated intravascular coagulation in severe disease

⸻

INCUBATION PERIOD

The incubation period is generally:

3–6 days

Symptoms usually begin abruptly.

⸻

CLINICAL COURSE

Yellow fever traditionally progresses through three clinical phases:

1. Infection phase

2. Remission phase

3. Intoxication phase

Not every patient progresses through all three phases.

Most infections are mild or asymptomatic.

⸻

INFECTION PHASE

The illness usually begins suddenly with:

• High fever

• Chills

• Severe headache

• Myalgias

• Back pain

• Malaise

• Prostration

• Nausea

• Vomiting

Patients may also develop:

• Photophobia

• Arthralgia

• Loss of appetite

This phase usually lasts approximately 3–4 days.

⸻

REMISSION PHASE

After several days of fever, symptoms may temporarily improve.

The patient may become:

• Afebrile

• Less symptomatic

• Apparently recovering

This remission may last:

• Several hours

• Up to approximately 1–2 days

Most patients recover during this stage.

A minority, however, progress to severe disease.

⸻

INTOXICATION PHASE

Patients who enter the toxic phase become severely ill.

Fever returns and systemic organ dysfunction develops.

Important manifestations include:

• Jaundice

• Severe hepatic dysfunction

• Renal failure

• Hemorrhage

• Hypotension

• Shock

• Myocarditis

• Encephalopathy

This is the most dangerous phase of yellow fever.

⸻

HEMORRHAGIC MANIFESTATIONS

Bleeding may occur from:

• Gums

• Nose

• Gastrointestinal tract

• Venipuncture sites

• Other mucosal surfaces

Clinical manifestations include:

• Petechiae

• Purpura

• Hematemesis

• Melena

• Hematochezia

Vomiting of dark blood has historically been called:

“Black vomit”

This is a classic manifestation of severe yellow fever.

⸻

HEPATIC MANIFESTATIONS

Severe liver involvement produces:

• Jaundice

• Markedly elevated aminotransferases

• Coagulopathy

• Hepatic dysfunction

A useful clue is that AST may become markedly elevated, sometimes exceeding ALT because of both hepatic and extrahepatic tissue injury.

Severe hepatic failure is associated with poor prognosis.

⸻

RENAL MANIFESTATIONS

Renal involvement may cause:

• Oliguria

• Acute kidney injury

• Azotemia

• Proteinuria or albuminuria

Severe patients may require renal replacement therapy.

⸻

CARDIAC INVOLVEMENT

Myocarditis may occur.

Possible manifestations include:

• Bradycardia

• Arrhythmias

• ECG abnormalities

• Reduced cardiac function

• Cardiovascular collapse

⸻

RELATIVE BRADYCARDIA

A classic clinical finding is:

High fever + unexpectedly slow pulse

This is called:

Faget sign

pulse-temperature dissociation.

It is suggestive but not specific for yellow fever.

⸻

NEUROLOGIC MANIFESTATIONS

Severe or late disease can cause:

• Confusion

• Agitation

• Delirium

• Seizures

• Encephalopathy

• Coma

Neurologic abnormalities generally indicate severe systemic illness.

⸻

PHYSICAL EXAMINATION

Possible findings include:

• Fever

• Relative bradycardia

• Conjunctival injection

• Jaundice

• Abdominal tenderness

• Hepatomegaly

• Petechiae

• Purpura

• Mucosal bleeding

• Gastrointestinal bleeding

• Hypotension

• Signs of shock

Severe cases may progress to:

• Acute respiratory distress syndrome

• Multiorgan failure

• Coma

⸻

DIAGNOSIS

Diagnosis requires consideration of:

Compatible illness + epidemiologic exposure

Important questions include:

• Recent travel

• Residence in an endemic area

• Vaccination status

• Mosquito exposure

• Local yellow fever outbreaks

• Timing of illness after travel

Laboratory confirmation is especially important because many infections can resemble yellow fever.

⸻

LABORATORY FINDINGS

Common nonspecific findings include:

• Leukopenia

• Thrombocytopenia

• Elevated AST and ALT

• Elevated bilirubin

• Prolonged coagulation studies

• Evidence of DIC

• Metabolic acidosis

• Elevated creatinine

• Azotemia

• Proteinuria or albuminuria

Severe thrombocytopenia and hepatic dysfunction increase the risk of hemorrhage.

⸻

PCR

During the early viremic phase, yellow fever viral RNA may be detected by:

RT-PCR

PCR is most useful early in illness while viremia is present.

Availability may be limited to specialized or public-health laboratories.

⸻

SEROLOGY

Serologic diagnosis commonly relies on detection of:

Yellow fever-specific IgM antibodies

IgM can be detected using assays such as:

ELISA

Interpretation may be complicated by cross-reactivity with other flaviviruses, including:

• Dengue

• Zika

• West Nile virus

• Japanese encephalitis virus

Previous flavivirus vaccination may also complicate serologic interpretation.

Confirmation may require specialized neutralization testing.

⸻

TISSUE TESTING

In fatal or diagnostically difficult cases, viral antigen can be demonstrated by:

• Immunohistochemistry

• Molecular testing

Possible tissues include:

• Liver

• Kidney

• Myocardium

⸻

LIVER BIOPSY

Liver biopsy should generally be avoided during acute severe yellow fever because of the major risk of:

Fatal hemorrhage

This is an important clinical point.

⸻

PATHOLOGY

Characteristic hepatic abnormalities include:

• Hepatocyte apoptosis

• Steatosis

• Midzonal hepatic necrosis

Classic eosinophilic apoptotic hepatocytes are known as:

Councilman bodies

The midzonal pattern of hepatic injury is a characteristic pathologic feature of yellow fever.

⸻

ECG FINDINGS

Possible ECG abnormalities include:

• Sinus bradycardia

• ST-T abnormalities

• Other changes associated with myocarditis

⸻

DIFFERENTIAL DIAGNOSIS

Yellow fever can resemble many tropical and systemic infections.

Important differential diagnoses include:

• Dengue

• Severe malaria

• Leptospirosis

• Viral hepatitis

• Typhoid fever

• Ebola virus disease

• Marburg virus disease

• Lassa fever

• Rift Valley fever

• Crimean-Congo hemorrhagic fever

• South American viral hemorrhagic fevers

• Other causes of acute hepatic failure

Travel history is essential for narrowing the differential.

⸻

TREATMENT

There is currently no established specific antiviral therapy for yellow fever.

Treatment is therefore:

SUPPORTIVE

Patients with severe disease require careful management of organ dysfunction.

⸻

SUPPORTIVE CARE

Important measures include:

• Fluid resuscitation

• Electrolyte correction

• Oxygen support

• Hemodynamic monitoring

• Treatment of hypoglycemia

• Correction of metabolic acidosis

• Renal support

• Management of hemorrhage

• Mechanical ventilation when necessary

Severely ill patients should receive intensive-care management.

⸻

SHOCK

Treatment may require:

• Careful intravenous fluid resuscitation

• Vasopressors when hypotension persists

• Monitoring of urine output

• Correction of acid-base abnormalities

• Treatment of concurrent organ failure

Fluid therapy must be balanced carefully because capillary leak and organ dysfunction can predispose to pulmonary edema.

⸻

COAGULOPATHY

Significant bleeding or severe coagulation abnormalities may require:

• Fresh frozen plasma

• Other blood products when clinically indicated

• Vitamin K in selected patients

Management should be guided by active bleeding and coagulation studies.

⸻

RENAL FAILURE

Severe acute kidney injury may require:

Hemodialysis or another form of renal replacement therapy.

⸻

RESPIRATORY FAILURE

Patients who develop:

• Severe hypoxemia

• ARDS

• Respiratory failure

may require:

• Endotracheal intubation

• Mechanical ventilation

⸻

MEDICATION PRECAUTIONS

Avoid medications that increase bleeding risk.

In particular, avoid:

• Aspirin

• Other salicylates

• NSAIDs when significant hemorrhagic risk exists

Acetaminophen may also require caution in severe hepatic injury because of potential hepatotoxicity.

Medication selection should therefore be individualized in patients with hepatic dysfunction.

⸻

ADMISSION

Hospitalization is generally appropriate for patients with suspected clinically significant yellow fever, particularly outside endemic settings.

Urgent admission is required when there is:

• Jaundice

• Hemorrhage

• Hypotension

• Renal dysfunction

• Altered mental status

• Respiratory compromise

• Severe vomiting

• Evidence of multiorgan disease

Severe cases require ICU care.

⸻

PREVENTION

Prevention relies on two major strategies:

1. Vaccination

2. Mosquito-bite avoidance

⸻

YELLOW FEVER VACCINE

The yellow fever vaccine is a:

Live attenuated 17D vaccine

It is highly effective.

A single dose produces protective immunity in the great majority of recipients.

Protection generally develops within approximately:

10 days

Current international guidance recognizes that a single dose provides long-lasting protection for most people.

Routine booster vaccination every 10 years is no longer required for most individuals, although additional doses may be recommended in selected circumstances.

⸻

INTERNATIONAL CERTIFICATE OF VACCINATION

Some countries require proof of yellow fever vaccination for:

• Entry from endemic countries

• Travel through high-risk areas

• Prevention of importation into regions capable of sustaining transmission

The International Certificate of Vaccination or Prophylaxis generally becomes valid:

10 days after primary vaccination

Under current International Health Regulations, the certificate is generally considered valid for the lifetime of the vaccinated person.

Travelers should verify the current entry requirements of their destination before travel.

⸻

MOSQUITO-BITE PREVENTION

Travelers should use:

• EPA- or locally approved insect repellents

• Long sleeves

• Long trousers

• Permethrin-treated clothing or equipment when appropriate

• Window screens

• Air conditioning

• Mosquito nets where needed

Mosquito precautions remain important even after vaccination because mosquitoes transmit many diseases other than yellow fever.

⸻

VACCINE ADVERSE EFFECTS

Most vaccine reactions are mild.

Common reactions include:

• Headache

• Myalgia

• Low-grade fever

• Local injection-site discomfort

Serious reactions are extremely rare.

⸻

YELLOW FEVER VACCINE-ASSOCIATED NEUROLOGIC DISEASE

Rare neurologic complications include:

• Encephalitis

• Meningoencephalitis

• Guillain-Barré-like syndromes

• Other neurologic syndromes

Symptoms generally develop within days to several weeks following vaccination.

The risk is very low but is higher in certain age groups.

⸻

YELLOW FEVER VACCINE-ASSOCIATED VISCEROTROPIC DISEASE

This is an extremely rare but potentially fatal complication in which the vaccine strain produces an illness resembling severe wild-type yellow fever.

Features may include:

• High fever

• Hypotension

• Liver injury

• Thrombocytopenia

• Respiratory failure

• Multiorgan dysfunction

Risk is increased in certain patients, including:

• Older adults

• Individuals with significant thymus disorders

Because of its severity, vaccination should be based on careful risk-benefit assessment when risk factors are present.

⸻

VACCINE CONTRAINDICATIONS AND PRECAUTIONS

Because yellow fever vaccine is live attenuated, caution is required in patients with significant immune dysfunction.

Contraindications or major precautions may include:

• Severe immunosuppression

• Certain thymus disorders

• Severe allergy to vaccine components

• Infancy below the recommended vaccination age

• Pregnancy in situations where exposure risk is low

Decisions should be individualized according to:

Risk of yellow fever exposure vs risk of vaccination.

⸻

HIV

People living with HIV require individualized assessment.

Vaccination may be considered in selected patients who:

• Are clinically stable

• Do not have severe immunosuppression

• Have adequate CD4 counts

Severely immunocompromised patients generally should not receive a live yellow fever vaccine.

⸻

PREGNANCY

Pregnancy is generally considered a precaution rather than an absolute contraindication when yellow fever exposure is significant.

If travel to a high-risk area can be postponed, postponement may be preferred.

If travel cannot be avoided and the risk of yellow fever is substantial, vaccination may be considered after individualized risk-benefit assessment.

⸻

PROGNOSIS

Most infected individuals either remain asymptomatic or recover from the initial febrile illness.

Patients who progress to the intoxication phase have a substantially worse prognosis.

Mortality in severe yellow fever may reach approximately:

20–50%

Death usually results from:

• Shock

• Hepatic failure

• Renal failure

• Hemorrhage

• Multiorgan dysfunction

⸻

IMMUNITY AFTER INFECTION

Survivors generally develop:

Strong, long-lasting immunity

Recurrent yellow fever after natural infection is extremely unusual.

⸻

COMPLICATIONS

Important complications include:

• Fulminant hepatitis

• Severe jaundice

• Coagulopathy

• DIC

• Gastrointestinal hemorrhage

• Acute kidney injury

• Myocarditis

• Arrhythmias

• Shock

• ARDS

• Encephalopathy

• Seizures

• Multiorgan failure

Secondary bacterial infections may complicate prolonged severe illness.

⸻

HIGH-YIELD CLINICAL PATTERN

Traveler from tropical Africa or South America

Fever

Jaundice

Hemorrhage

Renal dysfunction

→ Think yellow fever

⸻

HIGH-YIELD DISEASE COURSE

Initial fever and myalgias

↓

Temporary improvement

↓

Return of fever + jaundice + hemorrhage + organ failure

→ Intoxication phase of yellow fever

⸻

HIGH-YIELD PHYSICAL SIGN

High fever + relative bradycardia

→ Faget sign

⸻

HIGH-YIELD PATHOLOGY

Midzonal hepatic necrosis

Councilman bodies

→ Characteristic of yellow fever

⸻

HIGH-YIELD DIAGNOSTIC APPROACH

Early illness:

→ RT-PCR

Later illness:

→ Yellow fever IgM serology

Remember:

Flavivirus serology can cross-react.

⸻

HIGH-YIELD PREVENTION

Most effective preventive measure:

→ Yellow fever vaccination

Additional essential measure:

→ Mosquito-bite prevention

⸻

EXAM ESSENTIALS

Causative agent:

→ Yellow fever virus

Virus family:

→ Flaviviridae

Genome:

→ RNA

Vector:

→ Mosquito

Major urban vector:

→ Aedes aegypti

Major endemic regions:

→ Sub-Saharan Africa and tropical South America

Incubation period:

→ Approximately 3–6 days

Classic severe manifestations:

→ Fever + jaundice + hemorrhage

Characteristic pulse finding:

→ Relative bradycardia / Faget sign

Characteristic liver pathology:

→ Midzonal necrosis

Characteristic apoptotic hepatocytes:

→ Councilman bodies

Diagnostic test during viremia:

→ RT-PCR

Important later diagnostic test:

→ IgM serology

Specific antiviral therapy:

→ None established

Main treatment:

→ Supportive care

Major prevention:

→ Live attenuated yellow fever vaccine

Vaccine type:

→ 17D live attenuated vaccine

Time for primary vaccine certificate to become valid:

→ 10 days

Routine 10-year booster for most people:

→ No longer required

Severe-stage mortality:

→ Approximately 20–50%

Major complications:

→ Hepatic failure, hemorrhage, renal failure, shock, ARDS, multiorgan failure

Published on: August 25, 2026

Infectious Disease and Microbiology - Whipple’s Disease

Infectious Disease and Microbiology - Whipple’s Disease

Basics

Description

Whipple’s disease is a rare, chronic, multisystem infection caused by Tropheryma whipplei. The disease classically affects the small intestine but can involve many organs, including the joints, central nervous system, heart, lungs, liver, kidneys, and lymphatic system.

Typical manifestations include:

Weight loss
Chronic diarrhea
Malabsorption
Abdominal pain
Lymphadenopathy
Migratory arthralgia or arthritis
Neurologic abnormalities

Untreated disease can be fatal, particularly when the central nervous system or heart is involved.

⸻

Epidemiology

Whipple’s disease is very uncommon.

Only a relatively small number of clinically recognized cases have been reported worldwide, with most cases described in:

Western Europe
North America

The disease most often affects:

Middle-aged adults
Men much more commonly than women
Historically, white European populations

Exposure to T. whipplei appears to be much more common than actual Whipple’s disease, suggesting that host immune factors contribute strongly to disease development.

⸻

Risk Factors

Important associations include:

Male sex
Middle age
Possible occupational or environmental exposure to sewage or wastewater
Certain abnormalities in cell-mediated immune responses
Immunosuppressive therapy

Symptoms may worsen dramatically after treatment with:

Corticosteroids
Other immunosuppressive agents

This can occur when Whipple’s disease has been mistaken for an inflammatory or rheumatologic disorder.

⸻

Genetics

Certain host genetic factors have been investigated, including associations with specific HLA patterns.

Older literature described an association with HLA-B27, although no single genetic marker is sufficiently specific to diagnose or predict Whipple’s disease.

⸻

Etiology

The causative organism is:

Tropheryma whipplei

It is:

A gram-positive actinomycete-related bacterium
Intracellular
Non-acid-fast
Detectable by periodic acid-Schiff staining in infected tissue

The organism can be found in several tissues, including:

Small bowel
Lymph nodes
Heart valves
Synovium
Brain
Liver
Lungs
Kidneys

⸻

Pathophysiology

T. whipplei infects macrophages and accumulates within tissues.

In the small intestine, infected macrophages infiltrate the lamina propria and interfere with normal intestinal architecture and nutrient absorption.

This produces:

Villous dysfunction
Malabsorption
Steatorrhea
Weight loss
Nutritional deficiencies

The organism can disseminate hematogenously or through lymphatic pathways to multiple organs.

A notable feature is that the tissue response may be relatively weak despite substantial organism burden.

⸻

Clinical Course

Whipple’s disease often evolves through two broad phases.

Prodromal Phase

This stage may last for years.

The most characteristic early symptoms are:

Migratory arthralgias
Intermittent arthritis

Joint symptoms often precede gastrointestinal symptoms by several years.

The arthritis is typically:

Migratory
Episodic
Nondestructive
Seronegative

⸻

Established Systemic Disease

Later, patients may develop:

Weight loss
Chronic diarrhea
Steatorrhea
Abdominal pain
Fever
Lymphadenopathy
Neurologic disease
Cardiac involvement

The interval between early joint symptoms and overt gastrointestinal disease may be several years.

⸻

Gastrointestinal Manifestations

Classic gastrointestinal features include:

Chronic diarrhea
Steatorrhea
Abdominal pain
Abdominal distention
Weight loss
Malabsorption

Occult gastrointestinal blood loss may occur.

Frank hematochezia is uncommon.

Consequences of malabsorption may include:

Anemia
Vitamin deficiencies
Hypoalbuminemia
Coagulopathy from vitamin K deficiency
Muscle wasting

⸻

Musculoskeletal Manifestations

Joint disease is one of the most important early clues.

Typical features include:

Migratory arthralgia
Intermittent arthritis
Large-joint involvement
Nondestructive course

Joint symptoms may precede intestinal disease by years.

This pattern can lead to misdiagnosis as:

Rheumatoid arthritis
Reactive arthritis
Other inflammatory arthritides

Immunosuppressive therapy given for an incorrect rheumatologic diagnosis may accelerate progression.

⸻

Constitutional Features

Patients may develop:

Fever
Fatigue
Malaise
Cachexia
Muscle wasting

Hypotension may occur in advanced disease.

⸻

Lymphatic and Reticuloendothelial Manifestations

Possible findings include:

Peripheral lymphadenopathy
Abdominal lymphadenopathy
Hepatomegaly
Splenomegaly

Lymph nodes are often enlarged but not necessarily painful.

⸻

Skin Manifestations

Skin hyperpigmentation may occur.

This can be related to:

Chronic illness
Nutritional abnormalities
Adrenal dysfunction

⸻

Neurologic Involvement

Central nervous system involvement is particularly important because it worsens prognosis and increases relapse risk.

Neurologic manifestations may include:

Cognitive impairment
Dementia
Personality change
Depression
Confusion
Cerebellar ataxia
Seizures
Nystagmus
Myoclonus
Supranuclear ophthalmoplegia

Hypothalamic involvement may produce:

Polydipsia
Hyperphagia
Decreased libido
Amenorrhea
Sleep abnormalities

⸻

Characteristic Neurologic Signs

A particularly characteristic but uncommon feature is:

Oculomasticatory myorhythmia

This consists of rhythmic eye movements accompanied by synchronous movements of the jaw or facial muscles.

When present, it is highly suggestive of CNS Whipple’s disease.

⸻

Ocular Manifestations

Possible ocular findings include:

Uveitis
Retinitis
Ophthalmoplegia
Nystagmus

⸻

Cardiac Manifestations

Cardiac involvement may include:

Endocarditis
Pericarditis
Myocarditis
Valvular disease

T. whipplei is an important cause of:

Culture-negative endocarditis

Importantly, Whipple endocarditis may occur without obvious:

Diarrhea
Weight loss
Classic intestinal manifestations

Patients may present only with:

Heart murmur
Embolic events
Heart failure
Constitutional symptoms

⸻

Pulmonary Manifestations

Possible respiratory manifestations include:

Dyspnea
Pleural effusion
Pulmonary infiltrates

These findings are usually nonspecific.

⸻

Adrenal and Endocrine Manifestations

Adrenal involvement may produce features of adrenal insufficiency.

Possible findings include:

Hypotension
Hyperpigmentation
Weakness
Electrolyte abnormalities

⸻

Physical Examination

Possible examination findings include:

Cachexia
Muscle wasting
Abdominal distention
Ascites
Hepatomegaly
Splenomegaly
Peripheral lymphadenopathy
Hyperpigmentation
Cardiac murmur
Neurologic deficits

Oral nutritional abnormalities may include:

Glossitis
Angular cheilitis

⸻

Diagnosis

Diagnosis requires a combination of:

Clinical suspicion
Histopathology
Molecular testing

The classic diagnostic approach is:

Small-bowel biopsy showing PAS-positive macrophages

with confirmation by:

PCR for T. whipplei

⸻

Laboratory Findings

Possible laboratory abnormalities include:

Anemia
Leukocytosis
Lymphopenia
Thrombocytosis
Elevated inflammatory markers
Hypoalbuminemia
Prolonged prothrombin time
Nutritional deficiencies

Prolonged PT may result from:

Vitamin K malabsorption

Eosinophilia may occasionally occur but is not a characteristic finding.

⸻

Cerebrospinal Fluid

In CNS disease, CSF may demonstrate:

Pleocytosis
Elevated protein

However, routine CSF findings are nonspecific.

PCR of CSF for T. whipplei is much more important when neurologic disease is suspected.

⸻

Small-Bowel Biopsy

Upper gastrointestinal endoscopy with multiple duodenal or jejunal biopsies is a classic diagnostic procedure.

Histology typically demonstrates:

Foamy macrophages within the lamina propria containing PAS-positive material

Multiple biopsies should be obtained because involvement can be patchy.

⸻

Histopathology

The hallmark finding is:

PAS-positive macrophages in the lamina propria

The macrophages contain magenta-staining intracellular material derived from the organism.

Additional confirmation with:

Immunohistochemistry
PCR

helps distinguish Whipple’s disease from other conditions with PAS-positive macrophages.

⸻

PCR

PCR is highly useful for detecting T. whipplei DNA.

Samples may include:

Small-bowel tissue
Lymph-node tissue
Synovial tissue
Cardiac valve tissue
CSF
Blood

Saliva and stool PCR may also detect the organism.

However:

Positive saliva or stool PCR alone does not establish Whipple’s disease

because asymptomatic carriage can occur.

⸻

CNS Testing

When CNS involvement is suspected:

CSF PCR should be performed

even if neurologic symptoms are subtle.

CNS infection may persist despite apparent gastrointestinal improvement.

⸻

Culture

T. whipplei can be cultured in specialized laboratories.

However:

Growth is slow
Culture is technically difficult
It is not routinely required for diagnosis

⸻

Serology

Serologic testing is generally not useful for routine diagnosis.

Antibody responses may be unreliable and can occur in asymptomatic carriers.

⸻

Imaging

Imaging findings are usually nonspecific.

Possible studies include:

Chest radiography

May show:

Pleural effusion
Nonspecific pulmonary abnormalities

Abdominal CT

May demonstrate:

Mesenteric lymphadenopathy
Bowel-wall abnormalities
Ascites

Brain MRI

May show nonspecific abnormalities on:

T1
T2
FLAIR sequences

Imaging cannot reliably establish the diagnosis.

⸻

Differential Diagnosis

Whipple’s disease can mimic numerous gastrointestinal, infectious, rheumatologic, and neurologic disorders.

Important differentials include:

Celiac disease
Inflammatory bowel disease
Small-bowel lymphoma
Sarcoidosis
Mycobacterial infection
HIV enteropathy
Reactive arthritis
Autoimmune disease
Familial Mediterranean fever
Infective endocarditis
Hyperthyroidism
Neurosarcoidosis
Neurosyphilis
Neurodegenerative disease

⸻

Whipple’s Disease vs Mycobacterium avium Complex

Both conditions can show macrophage infiltration of the small intestine.

However:

Whipple’s disease

→ PAS-positive macrophages

→ Acid-fast stain negative

Mycobacterium avium complex

→ Acid-fast organisms present

This is a useful diagnostic distinction.

⸻

Treatment Principles

Whipple’s disease requires prolonged antimicrobial therapy because the organism:

Disseminates widely
Can involve the CNS
May persist intracellularly
Can relapse years after treatment

Therapy should include agents with:

Good CNS penetration

even when neurologic symptoms are absent.

⸻

Initial Treatment

A commonly used approach begins with a CNS-penetrating intravenous antibiotic for approximately 2 weeks.

Options may include:

Ceftriaxone
Meropenem

The purpose is to rapidly reduce systemic and CNS organism burden.

More prolonged initial IV treatment may be considered for:

Endocarditis
CNS disease
Relapse
Severe disseminated infection

⸻

Long-Term Treatment

After induction therapy, prolonged oral treatment is required.

Historically, trimethoprim-sulfamethoxazole was widely used.

However, contemporary practice increasingly favors regimens such as:

Doxycycline plus hydroxychloroquine

for prolonged therapy because of concerns regarding intrinsic or acquired resistance patterns and relapse with trimethoprim-sulfamethoxazole.

Treatment often continues for approximately:

12 months or longer

depending on disease site and response.

Specialist infectious-disease management is strongly recommended.

⸻

Doxycycline Plus Hydroxychloroquine

A commonly used oral combination is:

Doxycycline
Hydroxychloroquine

Hydroxychloroquine alkalinizes the phagolysosome and improves the activity of doxycycline against intracellular T. whipplei.

Long courses are required.

Monitoring is necessary for hydroxychloroquine toxicity, particularly:

Retinal toxicity
Cardiac effects in selected patients

⸻

CNS Disease

Neurologic Whipple’s disease requires especially aggressive and prolonged treatment.

Important considerations include:

CNS-penetrating induction therapy
Long-term antimicrobial treatment
Serial neurologic evaluation
CSF PCR monitoring in selected cases

Relapse may occur years later.

⸻

Endocarditis

Whipple endocarditis should be treated with prolonged antimicrobial therapy.

Valve replacement may be necessary if there is:

Severe valve destruction
Heart failure
Persistent infection
Major hemodynamic compromise

Not every case automatically requires valve surgery; management depends on standard endocarditis surgical indications.

⸻

Corticosteroids

Corticosteroids are generally not routine treatment for Whipple’s disease.

They may occasionally be considered in selected severe inflammatory complications under specialist supervision.

Unrecognized Whipple’s disease can worsen substantially when immunosuppressive therapy is administered without effective antimicrobial treatment.

⸻

Immune Reconstitution Inflammatory Syndrome

After antimicrobial therapy begins, some patients develop paradoxical inflammatory worsening.

This may present with:

High fever
New inflammatory lesions
Clinical deterioration despite microbiologic treatment

This resembles an immune reconstitution inflammatory syndrome.

It appears particularly in patients with neurologic involvement or prior immunosuppression.

⸻

Jarisch-Herxheimer-Like Reaction

A transient inflammatory reaction has occasionally been described shortly after antibiotic initiation.

Possible manifestations include:

Fever
Chills
Clinical worsening

Careful observation is appropriate, particularly during initial therapy.

⸻

Follow-Up

Long-term follow-up is essential.

Monitoring should include:

Weight
Gastrointestinal symptoms
Neurologic status
Joint symptoms
Cardiac findings
Nutritional status

PCR may help assess treatment response in selected cases.

Histologic abnormalities can persist after successful therapy, so persistent PAS-positive macrophages do not always indicate active infection.

⸻

Relapse

Relapse is a major concern.

It may occur:

Months later
Years later
Even after apparently successful treatment

Relapse commonly involves:

The central nervous system

Therefore new neurologic symptoms in a previously treated patient should prompt urgent investigation.

⸻

Diet and Nutritional Support

No specific diet treats Whipple’s disease.

However, malabsorption may require replacement of:

Fat-soluble vitamins
Iron
Folate
Vitamin B12
Electrolytes
Protein and calories

Nutritional rehabilitation is important in severely wasted patients.

⸻

Prognosis

With appropriate diagnosis and prolonged antimicrobial treatment, prognosis is generally favorable.

Without treatment, the disease is ultimately fatal.

Poorer outcomes are associated with:

CNS involvement
Delayed diagnosis
Severe cardiac disease
Relapse
Inappropriate immunosuppression

⸻

Complications

Important complications include:

Severe malabsorption
Cachexia
Vitamin deficiencies
Neurologic deterioration
Dementia
Seizures
Ophthalmoplegia
Culture-negative endocarditis
Heart failure
Pericarditis
Myocarditis
Relapse

⸻

High-Yield Clinical Pattern

Years of migratory arthralgia followed by weight loss and chronic diarrhea

→ Think Whipple’s disease

⸻

High-Yield Diagnostic Pattern

Small-bowel biopsy + PAS-positive foamy macrophages

→ Strongly suggestive of Whipple’s disease

Confirmation:

→ T. whipplei PCR

⸻

High-Yield Cardiac Pattern

Culture-negative endocarditis + negative routine cultures + systemic or arthritic history

→ Consider Tropheryma whipplei

⸻

High-Yield Neurologic Pattern

Cognitive decline + ophthalmoplegia + myoclonus in systemic Whipple’s disease

→ CNS involvement

Characteristic finding:

→ Oculomasticatory myorhythmia

⸻

Exam Essentials

Causative organism:

→ Tropheryma whipplei

Organism type:

→ Actinomycete-related gram-positive bacterium

Classic patient:

→ Middle-aged man

Classic early manifestation:

→ Migratory arthralgia/arthritis

Classic later manifestations:

→ Weight loss + diarrhea + malabsorption

Classic biopsy:

→ PAS-positive macrophages in small-bowel lamina propria

Acid-fast stain:

→ Negative

Confirmatory test:

→ PCR for T. whipplei

Important cardiac manifestation:

→ Culture-negative endocarditis

Important neurologic complication:

→ CNS Whipple’s disease

Characteristic neurologic sign:

→ Oculomasticatory myorhythmia

Treatment principle:

→ Initial CNS-penetrating antibiotics followed by prolonged oral therapy

Important clinical warning:

→ Immunosuppressive therapy can markedly worsen undiagnosed disease

Major long-term concern:

→ Relapse, particularly in the CNS

Published on: August 25, 2026

Infectious Disease and Microbiology - Warts

Infectious Disease and Microbiology - Warts

Basics

Description

Warts, or verrucae, are benign proliferative lesions of the skin or mucous membranes caused by human papillomavirus (HPV) infection.

Transmission occurs through:

Direct skin-to-skin contact
Sexual contact
Contact with contaminated surfaces or objects
Autoinoculation from one body site to another

Warts may be broadly divided into:

Cutaneous warts
Anogenital warts
Respiratory papillomatosis

⸻

Epidemiology

Warts are common and affect roughly 7–10% of the population.

Cutaneous warts are seen most often in:

Children
Adolescents
Young adults

They are especially common among people who regularly handle:

Meat
Poultry
Fish

because repeated minor trauma facilitates viral inoculation.

Anogenital HPV infection is among the most common sexually transmitted infections worldwide.

⸻

Risk Factors

Important risk factors include:

Repeated skin trauma
Meat, poultry, or fish handling
Atopic dermatitis
Immunosuppression
Defects in cell-mediated immunity
Unprotected sexual contact
Multiple sexual partners
Men who have sex with men
Contact with a partner who has anogenital HPV infection

Immunocompromised patients may develop:

Numerous lesions
Larger lesions
Refractory lesions
More frequent recurrence

⸻

Etiology

Warts are caused by human papillomaviruses, a large group of double-stranded DNA viruses with tropism for squamous epithelium.

There are more than 200 recognized HPV types.

Important associations include:

HPV 6 and 11

→ Cause most genital warts

HPV 16 and 18

→ High-risk oncogenic types strongly associated with:

Cervical cancer
Anal cancer
Penile cancer
Vulvar cancer
Vaginal cancer
Oropharyngeal cancer

Genital warts themselves are usually caused by low-risk HPV types, particularly 6 and 11.

⸻

Pathophysiology

HPV gains entry through microscopic breaks in the skin or mucosa.

It infects basal keratinocytes and induces epithelial proliferation.

As infected cells migrate toward the surface, viral replication increases and produces the characteristic wart architecture.

Warts may persist for months or years, but immune recognition can eventually cause spontaneous regression.

⸻

General Prevention

Prevention includes:

Avoiding direct contact with visible warts
Avoiding picking, scratching, or shaving over warts
Wearing footwear in communal showers and pool areas
Avoiding sharing razors or personal items
Practicing safer sex
Using condoms, while recognizing that condoms do not completely prevent HPV transmission because uncovered skin may remain infectious
HPV vaccination

⸻

HPV Vaccination

Modern HPV vaccination is one of the most important preventive measures.

The currently used vaccine in many countries is the 9-valent HPV vaccine, which protects against HPV types:

It protects against both:

Genital warts
HPV-associated cancers

Vaccination is most effective when given before exposure to HPV.

Routine vaccination is generally recommended beginning in early adolescence, with catch-up vaccination also recommended for older adolescents and young adults according to national guidelines.

Vaccination prevents new infection but does not treat existing warts or established HPV infection.

⸻

Pregnancy Considerations for Vaccination

HPV vaccine is not a live vaccine.

However, routine administration during pregnancy is generally deferred.

If a dose is given inadvertently during pregnancy, this is not considered an indication for pregnancy termination.

Remaining doses can usually be completed after pregnancy.

⸻

Clinical Types

Common Warts

Common warts, or verruca vulgaris, typically appear as:

Firm papules
Hyperkeratotic surface
Rough or cauliflower-like texture

Common locations include:

Hands
Fingers
Elbows
Knees
Periungual areas

They may occur anywhere.

⸻

Plantar Warts

Plantar warts occur on the soles of the feet.

Typical features include:

Pain with pressure
Thickened keratotic surface
Disruption of normal skin lines
Small thrombosed capillaries appearing as black dots
Pinpoint bleeding when pared

They may be confused with calluses.

⸻

Flat Warts

Flat or juvenile warts are typically:

Small
Smooth
Flat-topped
Multiple

They are commonly seen on:

Face
Hands
Shins

They are especially common in children and adolescents.

⸻

Filiform Warts

Filiform warts are:

Thin
Finger-like
Pedunculated

They often occur on:

Face
Eyelids
Lips
Neck

Because cosmetic outcome matters, treatment should minimize scarring.

⸻

Anogenital Warts

Anogenital warts are also called:

Condylomata acuminata

They may appear as:

Small papules
Papillary lesions
Pedunculated growths
Large cauliflower-like masses

Possible sites include:

Vulva
Vagina
Cervix
Penis
Scrotum
Perineum
Perianal region
Anal canal
Urethral meatus

Most are caused by HPV 6 and 11.

⸻

Cervical HPV Infection

Cervical HPV infection may produce:

No visible lesion
Low-grade squamous intraepithelial lesion
High-grade squamous intraepithelial lesion
Cervical intraepithelial neoplasia

Persistent infection with high-risk HPV types is the major cause of cervical cancer.

The presence of external genital warts does not by itself imply cervical cancer.

⸻

Respiratory Papillomatosis

Recurrent respiratory papillomatosis is usually associated with HPV 6 and 11.

It is most often seen in children but can also occur in adults.

Possible manifestations include:

Hoarseness
Chronic voice change
Stridor
Respiratory distress
Upper-airway obstruction

Lesions most commonly involve the larynx and may recur repeatedly.

⸻

Diagnosis

Most warts are diagnosed clinically from their characteristic appearance.

Routine laboratory testing is usually unnecessary.

Important questions include:

Duration
Number of lesions
Prior treatment
Immunosuppression
Sexual history for anogenital lesions
Rapid growth
Bleeding
Ulceration
Pain
Failure to respond to treatment

⸻

Biopsy

Biopsy should be considered when a lesion is:

Atypical
Pigmented
Ulcerated
Indurated
Rapidly growing
Bleeding spontaneously
Large
Refractory to therapy

It is also particularly useful in:

Immunocompromised patients
Patients in whom malignancy cannot be excluded

⸻

HPV Testing

HPV typing is not routinely used to diagnose ordinary cutaneous or genital warts.

Molecular tests are primarily used in cervical cancer screening and selected anogenital disease evaluation.

Methods may include:

PCR
Nucleic acid hybridization
Other molecular assays

⸻

Acetic Acid Testing

Dilute acetic acid may cause HPV-infected epithelium to become white.

This is known as:

Acetowhitening

However, the finding is nonspecific and should not be used alone to diagnose HPV infection.

⸻

Histopathology

Typical histologic findings include:

Papillomatosis
Acanthosis
Hyperkeratosis
Parakeratosis

Koilocytes may be present, particularly in genital lesions.

A koilocyte is a squamous epithelial cell with:

Perinuclear clearing
Nuclear enlargement
Nuclear irregularity

It reflects HPV-related cytopathic change.

⸻

Differential Diagnosis

Cutaneous warts may resemble:

Callus
Corn
Seborrheic keratosis
Actinic keratosis
Molluscum contagiosum
Squamous cell carcinoma
Other keratinizing skin tumors

Anogenital lesions may resemble:

Molluscum contagiosum
Condylomata lata of secondary syphilis
Skin tags
Pearly penile papules
Vestibular papillomatosis
Squamous neoplasia

Atypical anogenital lesions should be assessed carefully before destructive treatment.

⸻

Natural History

Many warts resolve spontaneously.

In immunocompetent children, a substantial proportion disappear within:

1 year
2 years

Spontaneous regression reflects development of effective cell-mediated immunity.

Anogenital warts can also regress without treatment.

However, treatment may be desired because of:

Pain
Bleeding
Irritation
Cosmetic concerns
Sexual transmission concerns
Functional interference
Psychological distress

⸻

Treatment Principles

No treatment guarantees eradication of latent HPV infection.

Most therapies remove visible lesions rather than eliminate all infected cells.

Therefore:

Recurrence is common

Treatment is individualized according to:

Wart type
Location
Number
Size
Patient age
Pregnancy
Immune status
Cosmetic considerations
Patient preference

⸻

Cutaneous Warts

Salicylic Acid

Salicylic acid is one of the most commonly used first-line treatments for cutaneous warts.

It works by:

Keratolysis
Gradual removal of infected epithelium

Treatment usually requires repeated application for several weeks.

Before application:

Soak the wart
Pare excess keratin if appropriate
Apply the preparation carefully to the lesion

This is particularly useful for:

Common warts
Plantar warts
Palmar warts

⸻

Cryotherapy

Cryotherapy with liquid nitrogen is another standard treatment.

It causes tissue destruction through freezing.

It is commonly used for:

Common warts
Plantar warts
Genital warts

Treatment may be repeated every few weeks.

Adverse effects include:

Pain
Blistering
Erosion
Temporary pigment changes
Hypopigmentation
Hyperpigmentation
Rare scarring

Pigment alteration is particularly relevant in darker skin.

⸻

Pediatric Considerations

For younger children, salicylic acid is often favored because cryotherapy can be painful.

Treatment is generally unnecessary if:

Lesions are asymptomatic
They are not spreading rapidly
Cosmetic concerns are minimal

Spontaneous resolution is common.

⸻

Flat Warts

Possible treatments include:

Topical retinoids
Selected keratolytic therapy
Cryotherapy in carefully selected lesions

Treatment on the face should be conservative because of the risk of:

Scarring
Pigment alteration

⸻

Recalcitrant Cutaneous Warts

For persistent lesions, options may include:

Intralesional immunotherapy
Curettage
Electrosurgery
Laser therapy
Selected topical immune-modifying therapies

Management is often best individualized by dermatology.

⸻

Treatment of External Anogenital Warts

Treatment may be:

Patient-applied

Clinician-administered

Choice depends on the lesion and patient preference.

⸻

Imiquimod

Imiquimod is a topical immune-response modifier.

It can be used for external anogenital warts.

It promotes local cytokine production and antiviral immune activity.

Potential adverse effects include:

Erythema
Burning
Erosion
Local irritation

Treatment may require several weeks.

⸻

Podofilox

Podofilox, also called podophyllotoxin, is a patient-applied antimitotic treatment for external genital warts.

It causes local tissue necrosis.

It should not be used:

Internally
During pregnancy

Patients should receive careful instructions to avoid application to normal surrounding skin.

⸻

Trichloroacetic Acid

Trichloroacetic acid, or TCA, is a clinician-applied chemical destructive therapy.

It may be used for:

External genital warts
Vaginal lesions
Selected anal lesions

The solution is applied directly to the wart until a white frost develops.

Possible adverse effects include:

Burning
Pain
Ulceration if excessive amounts are applied

⸻

Cryotherapy for Anogenital Warts

Liquid nitrogen cryotherapy is effective for external genital warts.

Advantages include:

Rapid lesion destruction
No systemic drug exposure
Use during pregnancy when needed

Repeated treatments may be required.

⸻

Surgical Treatment

Surgical approaches are useful for:

Large lesions
Extensive lesions
Refractory disease
Lesions requiring immediate removal

Methods include:

Scissor excision
Curettage
Electrosurgery
Laser ablation

Potential disadvantages include:

Pain
Scarring
Need for anesthesia
Recurrence

⸻

Anal Warts

External perianal warts can be managed similarly to other external genital warts.

Patients with lesions involving the anal canal should generally undergo expert evaluation because internal disease may require:

Anoscopy
Biopsy
Specialist treatment

⸻

Cervical Warts

Visible cervical lesions require specialist evaluation.

Before destructive treatment, it is important to exclude:

High-grade squamous intraepithelial lesions
Cervical malignancy

Management should follow cervical screening and colposcopy guidelines.

⸻

Vaginal Warts

Potential treatments include:

Cryotherapy
TCA
Surgical approaches when needed

Treatment should be performed carefully to avoid injury to surrounding mucosa.

⸻

Urethral Meatus Warts

Small external lesions may be treated with:

Cryotherapy
Other specialist-directed destructive techniques

Warts extending into the urethra may require urologic evaluation.

⸻

Oral Warts

Oral HPV lesions do not always require treatment.

Treatment may be considered when lesions are:

Painful
Traumatized
Growing
Functionally problematic
Cosmetically concerning

Options include:

Excision
Cryotherapy
Electrosurgery
Laser therapy

Persistent oral lesions should be examined carefully to exclude neoplasia.

⸻

Respiratory Papillomatosis Treatment

Recurrent respiratory papillomatosis is usually managed by otolaryngology.

Treatment may include:

Endoscopic debulking
Laser therapy
Microdebrider techniques
Selected intralesional or systemic adjunctive therapies

Repeated procedures are often necessary because recurrence is common.

Airway obstruction can be life-threatening.

⸻

Partner Management

Sex partners of patients with genital warts do not require treatment unless they have visible lesions.

However, partners may benefit from:

STI screening
HPV education
Vaccination if eligible
Counseling about transmission

Condoms reduce but do not eliminate HPV transmission.

⸻

Follow-Up

Follow-up depends on:

Lesion type
Treatment used
Immune status
Recurrence

Patients with genital warts should continue routine cervical cancer screening according to age and national recommendations.

Having external genital warts does not automatically require more frequent cervical screening than otherwise indicated.

⸻

Prognosis

The prognosis is generally excellent.

Many cutaneous warts resolve spontaneously.

Treatment often works but recurrence is common because:

HPV may persist in surrounding clinically normal tissue
Latent infection can reactivate

Recurrence does not necessarily represent reinfection.

⸻

Complications

Possible complications include:

Pain
Bleeding
Secondary bacterial infection
Cosmetic disfigurement
Recurrence
Extensive disease in immunosuppressed patients

High-risk HPV infection can lead to:

Cervical intraepithelial neoplasia
Cervical cancer
Anal cancer
Penile cancer
Vulvar and vaginal cancer
Oropharyngeal cancer

Genital warts caused by HPV 6 and 11 themselves are generally not considered precancerous lesions.

⸻

Pregnancy

Genital warts may enlarge during pregnancy because of:

Hormonal changes
Increased vascularity
Altered immunity

They may also become:

More friable
More prone to bleeding

Treatment options that can be used during pregnancy include selected clinician-administered therapies such as:

Cryotherapy
TCA

Agents such as podofilox should be avoided.

Cesarean delivery is not routinely performed solely to prevent neonatal HPV transmission. It may be considered when massive genital lesions obstruct the birth canal or would cause excessive bleeding during vaginal delivery.

⸻

High-Yield Comparison

Common wart

→ Rough hyperkeratotic papule

→ Usually hands and fingers

Plantar wart

→ Sole of foot

→ Painful

→ Black thrombosed capillary dots

Flat wart

→ Smooth, flat-topped papules

→ Often multiple

Genital wart

→ Condyloma acuminatum

→ Usually HPV 6 or 11

High-risk oncogenic HPV

→ HPV 16 and 18 among the most important types

Respiratory papillomatosis

→ Usually HPV 6 and 11

→ Hoarseness/stridor

⸻

High-Yield Clinical Approach

Child with rough papules on fingers

→ Common warts

Painful lesion on sole + black dots

→ Plantar wart

Multiple smooth facial papules in adolescent

→ Flat warts

Cauliflower-like genital lesions

→ Condylomata acuminata

Genital wart + atypical pigmentation/ulceration

→ Biopsy before routine destructive therapy

Immunocompromised patient + extensive refractory warts

→ Consider specialist evaluation and biopsy of atypical lesions

Hoarseness + recurrent laryngeal papillomas in child

→ Recurrent respiratory papillomatosis

⸻

Exam Essentials

Cause of warts:

→ Human papillomavirus

Virus type:

→ Double-stranded DNA virus

Most common genital-wart types:

→ HPV 6 and 11

Major oncogenic types:

→ HPV 16 and 18

Classic plantar-wart clue:

→ Thrombosed capillaries/black dots

First-line treatment for many cutaneous warts:

→ Salicylic acid or cryotherapy

Common patient-applied genital-wart therapies:

→ Imiquimod or podofilox

Clinician-applied genital-wart therapies:

→ Cryotherapy or TCA

Genital warts are usually caused by:

→ Low-risk HPV

HPV vaccine treats existing warts:

→ No

HPV vaccination prevents:

→ New infection with vaccine-covered HPV types

Best prevention of HPV-associated cancer:

→ Vaccination plus appropriate screening

Recurrence after treatment:

→ Common

External genital warts mean cervical cancer is present:

→ No

Published on: August 25, 2026

Infectious Disease and Microbiology - Viral Hepatitis

Infectious Disease and Microbiology - Viral Hepatitis

Basics

Description

Viral hepatitis refers to inflammation and injury of the liver caused by hepatotropic viruses, particularly hepatitis A, B, C, D, and E viruses.

Disease may be:

Acute and self-limited
Chronic and progressive
Fulminant, with massive hepatic necrosis and acute liver failure

The likelihood of chronic infection varies greatly by virus. HAV and HEV usually cause acute disease only, whereas HBV, HCV, and HDV may cause chronic infection.

Fulminant hepatitis is characterized by severe hepatic necrosis with rapid development of liver failure, coagulopathy, and encephalopathy.

⸻

Major Hepatitis Viruses

The principal hepatotropic viruses are:

Hepatitis A virus (HAV)
Hepatitis B virus (HBV)
Hepatitis C virus (HCV)
Hepatitis D virus (HDV)
Hepatitis E virus (HEV)

Hepatitis G virus has historically been described, but it is not considered a major cause of clinically significant chronic hepatitis.

Other viruses that can cause hepatitis include:

Epstein-Barr virus
Cytomegalovirus
Herpes simplex virus
HIV
Adenovirus
Measles virus
Enteroviruses

⸻

Epidemiology

Hepatitis A

HAV has a worldwide distribution.

Transmission is predominantly:

Fecal-oral

Common sources include:

Contaminated food
Contaminated water
Close household contact
Outbreaks in congregate settings

Sexual transmission, particularly with oral-anal exposure, may also occur.

Chronic infection does not occur.

⸻

Hepatitis B

HBV remains a major global infection.

Major routes of transmission include:

Blood exposure
Sexual transmission
Injection drug use
Needlestick exposure
Perinatal transmission
Vertical transmission
Contaminated blood products where screening is inadequate

The probability of chronic infection is strongly related to age at acquisition.

Neonatal or perinatal infection

→ Very high risk of chronicity

Adult-acquired infection

→ Most immunocompetent adults clear the infection spontaneously

This age-dependent difference is one of the most important features of HBV infection.

⸻

Hepatitis C

HCV is predominantly a blood-borne infection.

Important routes include:

Injection drug use
Shared injection equipment
Needlestick injuries
Unscreened blood transfusion
Organ transplantation from an infected donor
Perinatal transmission
Sexual transmission, although less efficient than with HBV

Without treatment, chronic infection develops in a substantial proportion of infected individuals.

⸻

Hepatitis D

HDV is a defective RNA virus that requires hepatitis B surface antigen (HBsAg) for its life cycle.

Therefore:

No HBV → no HDV infection

HDV occurs in two patterns:

Coinfection

HBV and HDV are acquired at the same time.

Superinfection

HDV infects a person who already has chronic HBV infection.

Superinfection is generally associated with more severe disease and a greater risk of chronic liver injury.

⸻

Hepatitis E

HEV resembles HAV epidemiologically.

Transmission is mainly:

Fecal-oral

Large outbreaks are especially associated with:

Contaminated water
Poor sanitation
Developing regions

Most infections are acute and self-limited, although chronic HEV can occur in selected immunocompromised patients.

HEV deserves special attention during pregnancy because severe disease may occur, particularly later in gestation.

⸻

Risk Factors

Hepatitis A

Important risk factors include:

Travel to areas with poor sanitation
Household or close contact with an infected person
Men who have sex with men
Drug use
Homelessness
Occupational or institutional exposure in selected settings
Contaminated food or water exposure

⸻

Hepatitis B

Important risk factors include:

Unprotected sexual contact
Multiple sexual partners
Men who have sex with men
Injection drug use
Occupational blood exposure
Hemodialysis
Household exposure to chronic HBV
Birth in or immigration from endemic regions
Perinatal exposure
Repeated blood-product exposure
HIV infection

⸻

Hepatitis C

Major risk factors include:

Injection drug use
Sharing injection equipment
Needlestick injury
Blood transfusion before modern screening
Hemodialysis
HIV infection
Tattoos or piercings performed with inadequately sterilized equipment
Organ transplantation from an infected donor

Intranasal drug use may also pose risk when blood-contaminated equipment is shared.

⸻

Hepatitis D

Risk factors are essentially those of HBV because HDV depends on HBV infection.

⸻

Hepatitis E

Risk factors resemble HAV and include:

Contaminated water
Poor sanitation
Travel to endemic areas

Zoonotic transmission can also occur in some regions.

⸻

Prevention

Hepatitis A Prevention

The most important strategies are:

Handwashing
Safe food handling
Clean water
Improved sanitation
Vaccination

HAV vaccine is highly effective and is routinely used in many countries.

It is particularly important for:

Travelers to endemic regions
People with chronic liver disease
Men who have sex with men
People who use drugs
Certain occupational or outbreak settings

Post-exposure prophylaxis may involve:

HAV vaccination
Immune globulin in selected high-risk individuals

The exact choice depends on age, immune status, liver disease, and timing of exposure.

⸻

Hepatitis B Prevention

HBV vaccination is one of the most effective preventive measures in infectious disease.

Vaccination is recommended broadly, including routine infant vaccination and vaccination of nonimmune adults.

Particularly important groups include:

Healthcare workers
Hemodialysis patients
Injection drug users
Sexual contacts of infected persons
People with multiple sexual partners
Travelers to endemic areas
Household contacts of chronic HBV carriers

After a significant exposure in a nonimmune person, post-exposure prophylaxis may include:

Hepatitis B immune globulin
HBV vaccination

depending on vaccination status and the source patient.

⸻

Hepatitis C Prevention

There is currently no vaccine for HCV.

Prevention relies on:

Avoiding shared needles
Sterile injection practices
Safe blood screening
Avoiding shared razors or blood-contaminated personal items
Appropriate occupational precautions
Safer sex in higher-risk situations

⸻

Hepatitis D Prevention

There is no separate widely used HDV vaccine.

However:

HBV vaccination prevents HDV infection

because HDV cannot establish infection without HBV.

⸻

Hepatitis E Prevention

Prevention relies mainly on:

Safe drinking water
Sanitation
Proper food handling
Avoidance of contaminated water

An HEV vaccine exists in limited geographic availability but is not routinely available worldwide.

⸻

Etiology and Virology

HAV

HAV is:

An RNA virus
Non-enveloped
A member of the Picornaviridae family

It does not cause chronic infection.

⸻

HBV

HBV is:

A partially double-stranded DNA virus
A member of the Hepadnaviridae family
Enveloped

Important viral markers include:

HBsAg
Anti-HBs
Anti-HBc
HBeAg
Anti-HBe
HBV DNA

⸻

HCV

HCV is:

An enveloped RNA virus
A member of the Flaviviridae family

Multiple genotypes exist, although modern direct-acting antiviral therapy has reduced the practical importance of genotype in many treatment settings.

⸻

HDV

HDV is:

A small RNA virus
Dependent on HBsAg from HBV for its envelope

Therefore it can occur only in a patient infected with HBV.

⸻

HEV

HEV is:

A non-enveloped RNA virus in blood
Structurally quasi-enveloped during some phases of infection
Classified within the Hepeviridae family

Most human disease is acute.

⸻

Pathophysiology

The liver injury in viral hepatitis is largely mediated by the host immune response to infected hepatocytes, rather than direct viral destruction alone.

Typical pathologic changes include:

Lobular inflammation
Mononuclear-cell infiltration
Hepatocyte degeneration
Hepatocyte necrosis
Kupffer-cell hyperplasia
Cholestasis

In severe disease, extensive hepatic necrosis can result in:

Coagulopathy
Hypoglycemia
Encephalopathy
Multiorgan dysfunction
Acute liver failure

⸻

Clinical Presentation

The clinical manifestations of acute viral hepatitis are often similar regardless of the specific virus.

Many infections are asymptomatic or anicteric.

The illness may be divided into:

Prodromal phase
Icteric phase
Convalescent or posticteric phase

⸻

Prodromal Phase

The prodrome usually precedes jaundice by approximately several days to 1–2 weeks.

Symptoms may include:

Fatigue
Malaise
Anorexia
Nausea
Vomiting
Fever
Headache
Myalgias
Arthralgias
Altered taste
Altered smell
Cough
Coryza

Some patients report aversion to cigarettes or certain foods.

⸻

Icteric Phase

As jaundice develops, some constitutional symptoms may improve.

Features may include:

Jaundice
Dark urine
Pale stools
Pruritus
Right upper quadrant discomfort
Hepatomegaly
Tender liver

Not all patients become visibly jaundiced.

⸻

Physical Examination

Possible findings include:

Jaundice
Hepatomegaly
Right upper quadrant tenderness
Splenomegaly
Cervical lymphadenopathy

Splenomegaly and lymphadenopathy occur in a minority of patients.

In severe disease, look for:

Confusion
Asterixis
Bleeding
Hypotension
Signs of cerebral edema
Evidence of acute liver failure

⸻

Incubation Periods

Approximate incubation periods are:

HAV

→ 15–50 days

HBV

→ Approximately 1–6 months

HCV

→ Approximately 2 weeks to 6 months

HDV

→ Depends on HBV coinfection or superinfection

HEV

→ Approximately 2–8 weeks

Incubation periods overlap and should not be used alone for diagnosis.

⸻

Laboratory Findings in Acute Viral Hepatitis

Common findings include:

Markedly elevated ALT
Markedly elevated AST
Hyperbilirubinemia
Mild alkaline phosphatase elevation
Relative lymphocytosis
Atypical lymphocytes
Mild leukopenia early in illness

Aminotransferases may rise before jaundice appears.

In hepatocellular injury:

ALT and AST are usually disproportionately elevated compared with alkaline phosphatase.

⸻

Bilirubin

When jaundice develops, bilirubin may rise substantially.

Both conjugated and unconjugated fractions may increase, although conjugated hyperbilirubinemia is common in clinically significant hepatitis.

⸻

Prothrombin Time and INR

A prolonged:

PT/INR

is an important marker of impaired hepatic synthetic function.

This is especially important in acute hepatitis because a rising INR may signal:

Acute liver failure

Aminotransferase levels alone do not reliably indicate severity.

A falling ALT in a deteriorating patient can actually be ominous if it reflects massive hepatocyte loss.

⸻

Albumin

Albumin may remain relatively preserved in acute disease because of its long half-life.

Low albumin is more suggestive of:

Chronic liver disease
Prolonged severe illness
Poor synthetic function

⸻

Hypoglycemia

Hypoglycemia can occur in severe or fulminant hepatitis because of impaired hepatic glucose regulation.

It is an important marker of severe disease.

⸻

Hepatitis A Diagnosis

The key test for acute HAV is:

IgM anti-HAV

This indicates recent or acute infection.

IgG anti-HAV

Indicates:

Previous infection
Vaccination
Immunity

HAV does not cause chronic hepatitis.

⸻

Hepatitis B Serology

HBV serology is particularly important and frequently tested.

HBsAg

Hepatitis B surface antigen

Indicates current HBV infection.

It appears early after infection.

Persistence for more than 6 months supports chronic infection.

⸻

Anti-HBs

Antibody to hepatitis B surface antigen

Indicates immunity.

It can result from:

Recovery from natural infection
Vaccination

⸻

Anti-HBc

Antibody to hepatitis B core antigen

This indicates exposure to actual HBV infection.

It is not produced by vaccination alone.

IgM anti-HBc

Suggests:

Acute infection
Recent infection
Sometimes an acute flare of chronic HBV

Total or IgG anti-HBc

Usually persists for life after natural infection.

⸻

HBV Window Period

An important examination concept is the window period.

During this period:

HBsAg has disappeared
Anti-HBs has not yet appeared

The key marker may therefore be:

IgM anti-HBc

⸻

HBeAg

HBeAg generally indicates:

Active viral replication
Higher infectivity

However, some HBV variants replicate actively without detectable HBeAg, so modern assessment relies heavily on:

HBV DNA

⸻

HBV DNA

HBV DNA measured by PCR reflects:

Viral replication

It is crucial for:

Assessing disease activity
Deciding treatment
Monitoring response
Evaluating transmission risk

⸻

High-Yield HBV Serologic Patterns

Vaccinated

HBsAg: negative

Anti-HBc: negative

Anti-HBs: positive

→ Immune from vaccination

⸻

Resolved natural infection

HBsAg: negative

Anti-HBc: positive

Anti-HBs: positive

→ Past infection, now immune

⸻

Acute HBV

HBsAg: positive

IgM anti-HBc: positive

Anti-HBs: negative

→ Acute infection

⸻

Chronic HBV

HBsAg: positive for >6 months

Anti-HBc: positive

Anti-HBs: negative

→ Chronic infection

⸻

Hepatitis C Diagnosis

Initial screening is usually performed with:

Anti-HCV antibody

However, anti-HCV indicates exposure and does not distinguish:

Active infection
Resolved infection
Successfully treated infection

Therefore a positive antibody test must be followed by:

HCV RNA

to determine whether active infection is present.

⸻

HCV RNA

HCV RNA can become detectable very early after infection, before antibodies develop.

Therefore:

Recent exposure + negative antibody does not exclude acute HCV

HCV RNA should be checked if acute infection is suspected.

⸻

HCV Genotype

Genotyping historically played a major role in treatment selection.

With modern pan-genotypic direct-acting antiviral regimens, genotype is less important than it once was, although it may still influence management in selected situations.

⸻

Hepatitis D Diagnosis

Diagnosis may include:

Anti-HDV antibodies
HDV RNA

HDV RNA confirms active replication.

Because HDV requires HBV, patients should also undergo a complete HBV evaluation.

⸻

Hepatitis E Diagnosis

Testing may include:

IgM anti-HEV
HEV RNA

IgM anti-HEV supports recent infection.

HEV RNA is especially useful in:

Immunocompromised patients
Suspected chronic infection

⸻

Imaging

Ultrasound is not usually needed to diagnose uncomplicated viral hepatitis.

However, it may be useful to:

Exclude biliary obstruction
Evaluate liver morphology
Assess portal or hepatic vessels
Look for ascites
Assess chronic liver disease

Doppler ultrasound may be added when vascular disease is a consideration.

⸻

Liver Biopsy

Liver biopsy is rarely required in straightforward acute viral hepatitis.

It may be considered when:

Diagnosis is uncertain
Autoimmune hepatitis is suspected
Chronic hepatitis requires staging
Another liver disease needs exclusion

Noninvasive fibrosis assessment has replaced biopsy for many chronic hepatitis patients.

⸻

Differential Diagnosis

The differential diagnosis of acute hepatitis includes:

Drug-induced liver injury
Acetaminophen toxicity
Alcohol-associated hepatitis
Autoimmune hepatitis
Ischemic hepatitis
Sepsis-associated liver injury
Biliary obstruction
Wilson disease
EBV
CMV
HSV hepatitis
Leptospirosis

Clinical context and targeted testing are essential.

⸻

Treatment of Hepatitis A

There is no specific antiviral therapy for uncomplicated HAV.

Treatment is supportive and includes:

Hydration
Adequate nutrition
Antiemetics if needed
Avoidance of hepatotoxic substances
Monitoring for acute liver failure

Most patients recover completely.

⸻

Treatment of Acute Hepatitis B

Most immunocompetent adults with uncomplicated acute HBV recover spontaneously and do not require antiviral therapy.

Antiviral treatment is considered for:

Severe acute hepatitis
Protracted severe disease
Acute liver failure

Potent nucleos(t)ide analogues such as:

Tenofovir
Entecavir

are generally preferred when antiviral treatment is indicated.

⸻

Treatment of Chronic Hepatitis B

Modern first-line oral agents generally include potent drugs with a high barrier to resistance, particularly:

Tenofovir disoproxil fumarate
Tenofovir alafenamide
Entecavir

Pegylated interferon may be used in selected patients.

Older drugs such as lamivudine are used much less frequently because resistance develops readily.

The major goals are:

Suppression of HBV DNA
Prevention of cirrhosis
Prevention of liver failure
Reduction of hepatocellular carcinoma risk
HBeAg seroconversion when applicable
Ideally, loss of HBsAg

⸻

Treatment of Hepatitis C

The historical interferon-ribavirin regimens are now largely obsolete.

Modern HCV treatment uses:

Direct-acting antiviral agents (DAAs)

These regimens are:

Oral
Shorter
Better tolerated
Highly effective

Common modern pan-genotypic regimens include combinations such as:

Sofosbuvir/velpatasvir
Glecaprevir/pibrentasvir

Most appropriately treated patients can achieve cure rates exceeding 95%.

⸻

Sustained Virologic Response

The goal of HCV therapy is:

Sustained virologic response (SVR)

This means HCV RNA remains undetectable after completion of therapy, typically assessed at least 12 weeks afterward.

SVR is considered a virologic cure.

⸻

Treatment of Hepatitis D

Treatment of HDV has historically relied on pegylated interferon alfa in suitable patients.

Newer targeted therapies are becoming available in some regions, and specialist management is recommended.

The older statement that interferon gamma is standard therapy is not current practice.

⸻

Treatment of Hepatitis E

Most immunocompetent patients require only:

Supportive care

Chronic HEV may occur in immunocompromised patients, particularly transplant recipients.

Management may include:

Reduction of immunosuppression when possible
Ribavirin in selected chronic cases under specialist guidance

⸻

Fulminant Hepatitis

Fulminant hepatitis refers to acute severe hepatic injury with:

Coagulopathy
Encephalopathy
No established preexisting cirrhosis

Patients may develop:

Cerebral edema
Hypoglycemia
Renal failure
Metabolic disturbances
Bleeding
Multiorgan failure

These patients require urgent admission to a liver-transplant-capable center.

⸻

Liver Transplantation

Liver transplantation may be life-saving in:

Acute liver failure
Decompensated cirrhosis
Selected hepatocellular carcinoma
End-stage chronic viral hepatitis

Early transplant referral is essential in fulminant disease.

⸻

Hepatitis A Complications

Most HAV infections resolve completely.

Possible complications include:

Prolonged cholestatic hepatitis
Relapsing hepatitis
Rare acute liver failure

HAV does not become chronic.

⸻

Hepatitis B Complications

Chronic HBV may lead to:

Chronic hepatitis
Fibrosis
Cirrhosis
Portal hypertension
Liver failure
Hepatocellular carcinoma

HBV can cause hepatocellular carcinoma even in the absence of cirrhosis.

Extrahepatic manifestations include:

Polyarteritis nodosa
Glomerulonephritis
Serum-sickness-like syndrome
Arthralgias
Cryoglobulinemia

⸻

Hepatitis C Complications

Chronic HCV may lead to:

Progressive fibrosis
Cirrhosis
Portal hypertension
Liver failure
Hepatocellular carcinoma

Important extrahepatic associations include:

Mixed cryoglobulinemia
Membranoproliferative glomerulonephritis
Porphyria cutanea tarda
Lichen planus
B-cell lymphoma
Insulin resistance and diabetes

⸻

Hepatitis D Complications

HDV infection may accelerate HBV-associated liver disease.

Superinfection can produce:

Severe acute hepatitis
Rapid progression of fibrosis
Cirrhosis
Liver failure

HDV is generally more severe than HBV infection alone.

⸻

Hepatitis E and Pregnancy

One of the classic high-yield features of HEV is severe disease during pregnancy.

In certain endemic settings, particularly with some HEV genotypes, pregnant women—especially in the second and third trimesters—have an increased risk of:

Fulminant hepatitis
Acute liver failure
Maternal death
Fetal complications

This association is particularly important in examinations.

⸻

High-Yield Comparison

HAV

→ RNA

→ Fecal-oral

→ Acute only

→ No chronic infection

→ Vaccine available

HBV

→ DNA

→ Blood, sexual, perinatal

→ Acute or chronic

→ Vaccine available

→ Can cause cirrhosis and hepatocellular carcinoma

HCV

→ RNA

→ Mainly blood-borne

→ High rate of chronic infection

→ No vaccine

→ Curable with direct-acting antivirals

HDV

→ RNA

→ Requires HBV

→ Coinfection or superinfection

→ Prevented by HBV vaccination

HEV

→ RNA

→ Fecal-oral

→ Usually acute

→ Particularly severe in pregnancy

⸻

High-Yield Clinical Approach

Acute hepatitis + recent contaminated food/water exposure

→ Think HAV or HEV

Acute hepatitis + sexual/blood exposure

→ Think HBV

Injection drug use + chronic hepatitis

→ Think HCV

HBsAg-positive patient with unexpectedly severe hepatitis

→ Consider HDV

Pregnant patient + acute hepatitis after travel to endemic region

→ Consider HEV

Positive anti-HCV

→ Confirm active disease with HCV RNA

HBsAg negative + anti-HBs positive + anti-HBc negative

→ Vaccinated

HBsAg negative + anti-HBs positive + anti-HBc positive

→ Resolved natural HBV infection

HBsAg positive + IgM anti-HBc positive

→ Acute HBV

HBsAg positive for >6 months

→ Chronic HBV

HBV window period

→ IgM anti-HBc may be the key positive marker

⸻

Exam Essentials

HAV transmission:

→ Fecal-oral

HAV chronic infection:

→ Does not occur

HAV acute diagnostic marker:

→ IgM anti-HAV

HBV type:

→ DNA virus

HBV vaccination marker:

→ Anti-HBs only

Marker of natural HBV exposure:

→ Anti-HBc

HBV window-period marker:

→ IgM anti-HBc

HBV replication marker:

→ HBV DNA

HBeAg:

→ Usually indicates increased replication/infectivity

HCV screening test:

→ Anti-HCV antibody

HCV active infection test:

→ HCV RNA

HCV chronicity:

→ Common if untreated

Modern HCV treatment:

→ Direct-acting antivirals

HCV cure endpoint:

→ Sustained virologic response

HDV requirement:

→ HBV/HBsAg

Best prevention of HDV:

→ HBV vaccination

HEV transmission:

→ Fecal-oral

HEV major high-risk group for severe disease:

→ Pregnant women

Severe acute hepatitis marker:

→ Rising PT/INR

Fulminant hepatitis + encephalopathy:

→ Urgent liver-transplant-center referral

Published on: August 25, 2026

Infectious Disease and Microbiology - Viral Hepatitis

Infectious Disease and Microbiology - Viral Hepatitis

Basics

Description

Viral hepatitis refers to inflammation and injury of the liver caused by hepatotropic viruses, particularly hepatitis A, B, C, D, and E viruses.

Disease may be:

Acute and self-limited
Chronic and progressive
Fulminant, with massive hepatic necrosis and acute liver failure

The likelihood of chronic infection varies greatly by virus. HAV and HEV usually cause acute disease only, whereas HBV, HCV, and HDV may cause chronic infection.

Fulminant hepatitis is characterized by severe hepatic necrosis with rapid development of liver failure, coagulopathy, and encephalopathy.

⸻

Major Hepatitis Viruses

The principal hepatotropic viruses are:

Hepatitis A virus (HAV)
Hepatitis B virus (HBV)
Hepatitis C virus (HCV)
Hepatitis D virus (HDV)
Hepatitis E virus (HEV)

Hepatitis G virus has historically been described, but it is not considered a major cause of clinically significant chronic hepatitis.

Other viruses that can cause hepatitis include:

Epstein-Barr virus
Cytomegalovirus
Herpes simplex virus
HIV
Adenovirus
Measles virus
Enteroviruses

⸻

Epidemiology

Hepatitis A

HAV has a worldwide distribution.

Transmission is predominantly:

Fecal-oral

Common sources include:

Contaminated food
Contaminated water
Close household contact
Outbreaks in congregate settings

Sexual transmission, particularly with oral-anal exposure, may also occur.

Chronic infection does not occur.

⸻

Hepatitis B

HBV remains a major global infection.

Major routes of transmission include:

Blood exposure
Sexual transmission
Injection drug use
Needlestick exposure
Perinatal transmission
Vertical transmission
Contaminated blood products where screening is inadequate

The probability of chronic infection is strongly related to age at acquisition.

Neonatal or perinatal infection

→ Very high risk of chronicity

Adult-acquired infection

→ Most immunocompetent adults clear the infection spontaneously

This age-dependent difference is one of the most important features of HBV infection.

⸻

Hepatitis C

HCV is predominantly a blood-borne infection.

Important routes include:

Injection drug use
Shared injection equipment
Needlestick injuries
Unscreened blood transfusion
Organ transplantation from an infected donor
Perinatal transmission
Sexual transmission, although less efficient than with HBV

Without treatment, chronic infection develops in a substantial proportion of infected individuals.

⸻

Hepatitis D

HDV is a defective RNA virus that requires hepatitis B surface antigen (HBsAg) for its life cycle.

Therefore:

No HBV → no HDV infection

HDV occurs in two patterns:

Coinfection

HBV and HDV are acquired at the same time.

Superinfection

HDV infects a person who already has chronic HBV infection.

Superinfection is generally associated with more severe disease and a greater risk of chronic liver injury.

⸻

Hepatitis E

HEV resembles HAV epidemiologically.

Transmission is mainly:

Fecal-oral

Large outbreaks are especially associated with:

Contaminated water
Poor sanitation
Developing regions

Most infections are acute and self-limited, although chronic HEV can occur in selected immunocompromised patients.

HEV deserves special attention during pregnancy because severe disease may occur, particularly later in gestation.

⸻

Risk Factors

Hepatitis A

Important risk factors include:

Travel to areas with poor sanitation
Household or close contact with an infected person
Men who have sex with men
Drug use
Homelessness
Occupational or institutional exposure in selected settings
Contaminated food or water exposure

⸻

Hepatitis B

Important risk factors include:

Unprotected sexual contact
Multiple sexual partners
Men who have sex with men
Injection drug use
Occupational blood exposure
Hemodialysis
Household exposure to chronic HBV
Birth in or immigration from endemic regions
Perinatal exposure
Repeated blood-product exposure
HIV infection

⸻

Hepatitis C

Major risk factors include:

Injection drug use
Sharing injection equipment
Needlestick injury
Blood transfusion before modern screening
Hemodialysis
HIV infection
Tattoos or piercings performed with inadequately sterilized equipment
Organ transplantation from an infected donor

Intranasal drug use may also pose risk when blood-contaminated equipment is shared.

⸻

Hepatitis D

Risk factors are essentially those of HBV because HDV depends on HBV infection.

⸻

Hepatitis E

Risk factors resemble HAV and include:

Contaminated water
Poor sanitation
Travel to endemic areas

Zoonotic transmission can also occur in some regions.

⸻

Prevention

Hepatitis A Prevention

The most important strategies are:

Handwashing
Safe food handling
Clean water
Improved sanitation
Vaccination

HAV vaccine is highly effective and is routinely used in many countries.

It is particularly important for:

Travelers to endemic regions
People with chronic liver disease
Men who have sex with men
People who use drugs
Certain occupational or outbreak settings

Post-exposure prophylaxis may involve:

HAV vaccination
Immune globulin in selected high-risk individuals

The exact choice depends on age, immune status, liver disease, and timing of exposure.

⸻

Hepatitis B Prevention

HBV vaccination is one of the most effective preventive measures in infectious disease.

Vaccination is recommended broadly, including routine infant vaccination and vaccination of nonimmune adults.

Particularly important groups include:

Healthcare workers
Hemodialysis patients
Injection drug users
Sexual contacts of infected persons
People with multiple sexual partners
Travelers to endemic areas
Household contacts of chronic HBV carriers

After a significant exposure in a nonimmune person, post-exposure prophylaxis may include:

Hepatitis B immune globulin
HBV vaccination

depending on vaccination status and the source patient.

⸻

Hepatitis C Prevention

There is currently no vaccine for HCV.

Prevention relies on:

Avoiding shared needles
Sterile injection practices
Safe blood screening
Avoiding shared razors or blood-contaminated personal items
Appropriate occupational precautions
Safer sex in higher-risk situations

⸻

Hepatitis D Prevention

There is no separate widely used HDV vaccine.

However:

HBV vaccination prevents HDV infection

because HDV cannot establish infection without HBV.

⸻

Hepatitis E Prevention

Prevention relies mainly on:

Safe drinking water
Sanitation
Proper food handling
Avoidance of contaminated water

An HEV vaccine exists in limited geographic availability but is not routinely available worldwide.

⸻

Etiology and Virology

HAV

HAV is:

An RNA virus
Non-enveloped
A member of the Picornaviridae family

It does not cause chronic infection.

⸻

HBV

HBV is:

A partially double-stranded DNA virus
A member of the Hepadnaviridae family
Enveloped

Important viral markers include:

HBsAg
Anti-HBs
Anti-HBc
HBeAg
Anti-HBe
HBV DNA

⸻

HCV

HCV is:

An enveloped RNA virus
A member of the Flaviviridae family

Multiple genotypes exist, although modern direct-acting antiviral therapy has reduced the practical importance of genotype in many treatment settings.

⸻

HDV

HDV is:

A small RNA virus
Dependent on HBsAg from HBV for its envelope

Therefore it can occur only in a patient infected with HBV.

⸻

HEV

HEV is:

A non-enveloped RNA virus in blood
Structurally quasi-enveloped during some phases of infection
Classified within the Hepeviridae family

Most human disease is acute.

⸻

Pathophysiology

The liver injury in viral hepatitis is largely mediated by the host immune response to infected hepatocytes, rather than direct viral destruction alone.

Typical pathologic changes include:

Lobular inflammation
Mononuclear-cell infiltration
Hepatocyte degeneration
Hepatocyte necrosis
Kupffer-cell hyperplasia
Cholestasis

In severe disease, extensive hepatic necrosis can result in:

Coagulopathy
Hypoglycemia
Encephalopathy
Multiorgan dysfunction
Acute liver failure

⸻

Clinical Presentation

The clinical manifestations of acute viral hepatitis are often similar regardless of the specific virus.

Many infections are asymptomatic or anicteric.

The illness may be divided into:

Prodromal phase
Icteric phase
Convalescent or posticteric phase

⸻

Prodromal Phase

The prodrome usually precedes jaundice by approximately several days to 1–2 weeks.

Symptoms may include:

Fatigue
Malaise
Anorexia
Nausea
Vomiting
Fever
Headache
Myalgias
Arthralgias
Altered taste
Altered smell
Cough
Coryza

Some patients report aversion to cigarettes or certain foods.

⸻

Icteric Phase

As jaundice develops, some constitutional symptoms may improve.

Features may include:

Jaundice
Dark urine
Pale stools
Pruritus
Right upper quadrant discomfort
Hepatomegaly
Tender liver

Not all patients become visibly jaundiced.

⸻

Physical Examination

Possible findings include:

Jaundice
Hepatomegaly
Right upper quadrant tenderness
Splenomegaly
Cervical lymphadenopathy

Splenomegaly and lymphadenopathy occur in a minority of patients.

In severe disease, look for:

Confusion
Asterixis
Bleeding
Hypotension
Signs of cerebral edema
Evidence of acute liver failure

⸻

Incubation Periods

Approximate incubation periods are:

HAV

→ 15–50 days

HBV

→ Approximately 1–6 months

HCV

→ Approximately 2 weeks to 6 months

HDV

→ Depends on HBV coinfection or superinfection

HEV

→ Approximately 2–8 weeks

Incubation periods overlap and should not be used alone for diagnosis.

⸻

Laboratory Findings in Acute Viral Hepatitis

Common findings include:

Markedly elevated ALT
Markedly elevated AST
Hyperbilirubinemia
Mild alkaline phosphatase elevation
Relative lymphocytosis
Atypical lymphocytes
Mild leukopenia early in illness

Aminotransferases may rise before jaundice appears.

In hepatocellular injury:

ALT and AST are usually disproportionately elevated compared with alkaline phosphatase.

⸻

Bilirubin

When jaundice develops, bilirubin may rise substantially.

Both conjugated and unconjugated fractions may increase, although conjugated hyperbilirubinemia is common in clinically significant hepatitis.

⸻

Prothrombin Time and INR

A prolonged:

PT/INR

is an important marker of impaired hepatic synthetic function.

This is especially important in acute hepatitis because a rising INR may signal:

Acute liver failure

Aminotransferase levels alone do not reliably indicate severity.

A falling ALT in a deteriorating patient can actually be ominous if it reflects massive hepatocyte loss.

⸻

Albumin

Albumin may remain relatively preserved in acute disease because of its long half-life.

Low albumin is more suggestive of:

Chronic liver disease
Prolonged severe illness
Poor synthetic function

⸻

Hypoglycemia

Hypoglycemia can occur in severe or fulminant hepatitis because of impaired hepatic glucose regulation.

It is an important marker of severe disease.

⸻

Hepatitis A Diagnosis

The key test for acute HAV is:

IgM anti-HAV

This indicates recent or acute infection.

IgG anti-HAV

Indicates:

Previous infection
Vaccination
Immunity

HAV does not cause chronic hepatitis.

⸻

Hepatitis B Serology

HBV serology is particularly important and frequently tested.

HBsAg

Hepatitis B surface antigen

Indicates current HBV infection.

It appears early after infection.

Persistence for more than 6 months supports chronic infection.

⸻

Anti-HBs

Antibody to hepatitis B surface antigen

Indicates immunity.

It can result from:

Recovery from natural infection
Vaccination

⸻

Anti-HBc

Antibody to hepatitis B core antigen

This indicates exposure to actual HBV infection.

It is not produced by vaccination alone.

IgM anti-HBc

Suggests:

Acute infection
Recent infection
Sometimes an acute flare of chronic HBV

Total or IgG anti-HBc

Usually persists for life after natural infection.

⸻

HBV Window Period

An important examination concept is the window period.

During this period:

HBsAg has disappeared
Anti-HBs has not yet appeared

The key marker may therefore be:

IgM anti-HBc

⸻

HBeAg

HBeAg generally indicates:

Active viral replication
Higher infectivity

However, some HBV variants replicate actively without detectable HBeAg, so modern assessment relies heavily on:

HBV DNA

⸻

HBV DNA

HBV DNA measured by PCR reflects:

Viral replication

It is crucial for:

Assessing disease activity
Deciding treatment
Monitoring response
Evaluating transmission risk

⸻

High-Yield HBV Serologic Patterns

Vaccinated

HBsAg: negative

Anti-HBc: negative

Anti-HBs: positive

→ Immune from vaccination

⸻

Resolved natural infection

HBsAg: negative

Anti-HBc: positive

Anti-HBs: positive

→ Past infection, now immune

⸻

Acute HBV

HBsAg: positive

IgM anti-HBc: positive

Anti-HBs: negative

→ Acute infection

⸻

Chronic HBV

HBsAg: positive for >6 months

Anti-HBc: positive

Anti-HBs: negative

→ Chronic infection

⸻

Hepatitis C Diagnosis

Initial screening is usually performed with:

Anti-HCV antibody

However, anti-HCV indicates exposure and does not distinguish:

Active infection
Resolved infection
Successfully treated infection

Therefore a positive antibody test must be followed by:

HCV RNA

to determine whether active infection is present.

⸻

HCV RNA

HCV RNA can become detectable very early after infection, before antibodies develop.

Therefore:

Recent exposure + negative antibody does not exclude acute HCV

HCV RNA should be checked if acute infection is suspected.

⸻

HCV Genotype

Genotyping historically played a major role in treatment selection.

With modern pan-genotypic direct-acting antiviral regimens, genotype is less important than it once was, although it may still influence management in selected situations.

⸻

Hepatitis D Diagnosis

Diagnosis may include:

Anti-HDV antibodies
HDV RNA

HDV RNA confirms active replication.

Because HDV requires HBV, patients should also undergo a complete HBV evaluation.

⸻

Hepatitis E Diagnosis

Testing may include:

IgM anti-HEV
HEV RNA

IgM anti-HEV supports recent infection.

HEV RNA is especially useful in:

Immunocompromised patients
Suspected chronic infection

⸻

Imaging

Ultrasound is not usually needed to diagnose uncomplicated viral hepatitis.

However, it may be useful to:

Exclude biliary obstruction
Evaluate liver morphology
Assess portal or hepatic vessels
Look for ascites
Assess chronic liver disease

Doppler ultrasound may be added when vascular disease is a consideration.

⸻

Liver Biopsy

Liver biopsy is rarely required in straightforward acute viral hepatitis.

It may be considered when:

Diagnosis is uncertain
Autoimmune hepatitis is suspected
Chronic hepatitis requires staging
Another liver disease needs exclusion

Noninvasive fibrosis assessment has replaced biopsy for many chronic hepatitis patients.

⸻

Differential Diagnosis

The differential diagnosis of acute hepatitis includes:

Drug-induced liver injury
Acetaminophen toxicity
Alcohol-associated hepatitis
Autoimmune hepatitis
Ischemic hepatitis
Sepsis-associated liver injury
Biliary obstruction
Wilson disease
EBV
CMV
HSV hepatitis
Leptospirosis

Clinical context and targeted testing are essential.

⸻

Treatment of Hepatitis A

There is no specific antiviral therapy for uncomplicated HAV.

Treatment is supportive and includes:

Hydration
Adequate nutrition
Antiemetics if needed
Avoidance of hepatotoxic substances
Monitoring for acute liver failure

Most patients recover completely.

⸻

Treatment of Acute Hepatitis B

Most immunocompetent adults with uncomplicated acute HBV recover spontaneously and do not require antiviral therapy.

Antiviral treatment is considered for:

Severe acute hepatitis
Protracted severe disease
Acute liver failure

Potent nucleos(t)ide analogues such as:

Tenofovir
Entecavir

are generally preferred when antiviral treatment is indicated.

⸻

Treatment of Chronic Hepatitis B

Modern first-line oral agents generally include potent drugs with a high barrier to resistance, particularly:

Tenofovir disoproxil fumarate
Tenofovir alafenamide
Entecavir

Pegylated interferon may be used in selected patients.

Older drugs such as lamivudine are used much less frequently because resistance develops readily.

The major goals are:

Suppression of HBV DNA
Prevention of cirrhosis
Prevention of liver failure
Reduction of hepatocellular carcinoma risk
HBeAg seroconversion when applicable
Ideally, loss of HBsAg

⸻

Treatment of Hepatitis C

The historical interferon-ribavirin regimens are now largely obsolete.

Modern HCV treatment uses:

Direct-acting antiviral agents (DAAs)

These regimens are:

Oral
Shorter
Better tolerated
Highly effective

Common modern pan-genotypic regimens include combinations such as:

Sofosbuvir/velpatasvir
Glecaprevir/pibrentasvir

Most appropriately treated patients can achieve cure rates exceeding 95%.

⸻

Sustained Virologic Response

The goal of HCV therapy is:

Sustained virologic response (SVR)

This means HCV RNA remains undetectable after completion of therapy, typically assessed at least 12 weeks afterward.

SVR is considered a virologic cure.

⸻

Treatment of Hepatitis D

Treatment of HDV has historically relied on pegylated interferon alfa in suitable patients.

Newer targeted therapies are becoming available in some regions, and specialist management is recommended.

The older statement that interferon gamma is standard therapy is not current practice.

⸻

Treatment of Hepatitis E

Most immunocompetent patients require only:

Supportive care

Chronic HEV may occur in immunocompromised patients, particularly transplant recipients.

Management may include:

Reduction of immunosuppression when possible
Ribavirin in selected chronic cases under specialist guidance

⸻

Fulminant Hepatitis

Fulminant hepatitis refers to acute severe hepatic injury with:

Coagulopathy
Encephalopathy
No established preexisting cirrhosis

Patients may develop:

Cerebral edema
Hypoglycemia
Renal failure
Metabolic disturbances
Bleeding
Multiorgan failure

These patients require urgent admission to a liver-transplant-capable center.

⸻

Liver Transplantation

Liver transplantation may be life-saving in:

Acute liver failure
Decompensated cirrhosis
Selected hepatocellular carcinoma
End-stage chronic viral hepatitis

Early transplant referral is essential in fulminant disease.

⸻

Hepatitis A Complications

Most HAV infections resolve completely.

Possible complications include:

Prolonged cholestatic hepatitis
Relapsing hepatitis
Rare acute liver failure

HAV does not become chronic.

⸻

Hepatitis B Complications

Chronic HBV may lead to:

Chronic hepatitis
Fibrosis
Cirrhosis
Portal hypertension
Liver failure
Hepatocellular carcinoma

HBV can cause hepatocellular carcinoma even in the absence of cirrhosis.

Extrahepatic manifestations include:

Polyarteritis nodosa
Glomerulonephritis
Serum-sickness-like syndrome
Arthralgias
Cryoglobulinemia

⸻

Hepatitis C Complications

Chronic HCV may lead to:

Progressive fibrosis
Cirrhosis
Portal hypertension
Liver failure
Hepatocellular carcinoma

Important extrahepatic associations include:

Mixed cryoglobulinemia
Membranoproliferative glomerulonephritis
Porphyria cutanea tarda
Lichen planus
B-cell lymphoma
Insulin resistance and diabetes

⸻

Hepatitis D Complications

HDV infection may accelerate HBV-associated liver disease.

Superinfection can produce:

Severe acute hepatitis
Rapid progression of fibrosis
Cirrhosis
Liver failure

HDV is generally more severe than HBV infection alone.

⸻

Hepatitis E and Pregnancy

One of the classic high-yield features of HEV is severe disease during pregnancy.

In certain endemic settings, particularly with some HEV genotypes, pregnant women—especially in the second and third trimesters—have an increased risk of:

Fulminant hepatitis
Acute liver failure
Maternal death
Fetal complications

This association is particularly important in examinations.

⸻

High-Yield Comparison

HAV

→ RNA

→ Fecal-oral

→ Acute only

→ No chronic infection

→ Vaccine available

HBV

→ DNA

→ Blood, sexual, perinatal

→ Acute or chronic

→ Vaccine available

→ Can cause cirrhosis and hepatocellular carcinoma

HCV

→ RNA

→ Mainly blood-borne

→ High rate of chronic infection

→ No vaccine

→ Curable with direct-acting antivirals

HDV

→ RNA

→ Requires HBV

→ Coinfection or superinfection

→ Prevented by HBV vaccination

HEV

→ RNA

→ Fecal-oral

→ Usually acute

→ Particularly severe in pregnancy

⸻

High-Yield Clinical Approach

Acute hepatitis + recent contaminated food/water exposure

→ Think HAV or HEV

Acute hepatitis + sexual/blood exposure

→ Think HBV

Injection drug use + chronic hepatitis

→ Think HCV

HBsAg-positive patient with unexpectedly severe hepatitis

→ Consider HDV

Pregnant patient + acute hepatitis after travel to endemic region

→ Consider HEV

Positive anti-HCV

→ Confirm active disease with HCV RNA

HBsAg negative + anti-HBs positive + anti-HBc negative

→ Vaccinated

HBsAg negative + anti-HBs positive + anti-HBc positive

→ Resolved natural HBV infection

HBsAg positive + IgM anti-HBc positive

→ Acute HBV

HBsAg positive for >6 months

→ Chronic HBV

HBV window period

→ IgM anti-HBc may be the key positive marker

⸻

Exam Essentials

HAV transmission:

→ Fecal-oral

HAV chronic infection:

→ Does not occur

HAV acute diagnostic marker:

→ IgM anti-HAV

HBV type:

→ DNA virus

HBV vaccination marker:

→ Anti-HBs only

Marker of natural HBV exposure:

→ Anti-HBc

HBV window-period marker:

→ IgM anti-HBc

HBV replication marker:

→ HBV DNA

HBeAg:

→ Usually indicates increased replication/infectivity

HCV screening test:

→ Anti-HCV antibody

HCV active infection test:

→ HCV RNA

HCV chronicity:

→ Common if untreated

Modern HCV treatment:

→ Direct-acting antivirals

HCV cure endpoint:

→ Sustained virologic response

HDV requirement:

→ HBV/HBsAg

Best prevention of HDV:

→ HBV vaccination

HEV transmission:

→ Fecal-oral

HEV major high-risk group for severe disease:

→ Pregnant women

Severe acute hepatitis marker:

→ Rising PT/INR

Fulminant hepatitis + encephalopathy:

→ Urgent liver-transplant-center referral

Published on: August 25, 2026

Infectious Disease and Microbiology - Typhus

Infectious Disease and Microbiology - Typhus

Basics

Description

Typhus refers to a group of rickettsial infections characterized primarily by acute fever, headache, systemic illness, and often a rash.

The major forms are:

Epidemic typhus — classic or louse-borne typhus
Murine typhus — endemic or flea-borne typhus
Scrub typhus — mite-borne infection
Brill-Zinsser disease — recrudescence of previous epidemic typhus

Although these illnesses share several clinical features, they differ in their causative organisms, vectors, reservoirs, geographic distribution, and severity.

⸻

Etiology

Typhus infections are caused by small, obligate intracellular bacteria.

Important organisms include:

Rickettsia prowazekii → epidemic typhus
Rickettsia typhi → murine typhus
Orientia tsutsugamushi → scrub typhus
Reactivation of R. prowazekii → Brill-Zinsser disease

⸻

Vectors and Reservoirs

Epidemic Typhus

Organism: Rickettsia prowazekii

Vector:

→ Human body louse

Major reservoir:

→ Humans

Flying squirrels may also serve as a reservoir in some regions.

Transmission occurs when infected lice defecate while feeding. Scratching contaminates the bite site with infected louse feces.

⸻

Murine Typhus

Organism: Rickettsia typhi

Vector:

→ Fleas

Traditional reservoirs include:

Rats
Other rodents

In some regions, transmission cycles involving:

Cats
Opossums
Their fleas

also contribute.

⸻

Scrub Typhus

Organism: Orientia tsutsugamushi

Vector:

→ Larval trombiculid mites, also called chiggers

Reservoir:

→ Rodents and mites

Unlike flea- and louse-associated typhus, the mite directly inoculates the organism during feeding.

⸻

Epidemiology

Typhus historically caused devastating epidemics during periods of:

War
Famine
Population displacement
Overcrowding
Poor sanitation

Epidemic typhus was especially important during major conflicts in Europe during the twentieth century.

Improved hygiene, delousing, and public-health measures have dramatically reduced its incidence in many developed countries.

⸻

Geographic Distribution

Epidemic Typhus

Persists mainly in regions with poverty, crowding, and body-louse infestation, including parts of:

Africa
South America
Asia

⸻

Murine Typhus

Has a broad worldwide distribution.

It is particularly associated with warm regions and remains endemic in selected areas of the:

Southern United States
Gulf Coast
Mediterranean region
Tropical and subtropical areas

⸻

Scrub Typhus

Traditionally occurs within the so-called tsutsugamushi triangle, encompassing much of:

South Asia
Southeast Asia
East Asia
Western Pacific
Northern Australia

However, scrub-typhus-like infections have increasingly been recognized outside the traditional geographic range.

⸻

Brill-Zinsser Disease

Brill-Zinsser disease is a recrudescence of previous epidemic typhus caused by latent R. prowazekii infection.

It may occur:

Years or even decades after the original illness

The recurrent illness is usually milder than primary epidemic typhus.

Patients with Brill-Zinsser disease can become a source of infection for body lice and theoretically contribute to renewed outbreaks in crowded populations.

⸻

Risk Factors

Important risk factors include:

Poor sanitation
Overcrowding
Homelessness
War
Famine
Refugee or displaced-person settings
Prison populations
Body-louse infestation
Flea exposure
Rodent exposure
Exposure to scrub vegetation in mite-endemic regions

A careful travel and environmental exposure history is extremely important.

⸻

General Prevention

Prevention depends largely on controlling the relevant vector and reservoir.

Important measures include:

Improved personal hygiene
Adequate sanitation
Delousing
Washing or heat-treating contaminated clothing and bedding
Flea control
Rodent control
Avoidance of mite-infested vegetation
Protective clothing
Appropriate insect repellents

Routine vaccines are not generally available for modern civilian use.

Antibiotic chemoprophylaxis is generally not routinely recommended for ordinary travelers.

⸻

Pathophysiology

After inoculation, rickettsiae multiply locally and then disseminate hematogenously.

The primary target is the:

Vascular endothelial cell

Infection and destruction of endothelial cells produce widespread:

Vasculitis
Increased vascular permeability
Tissue edema
Microvascular thrombosis
Reduced organ perfusion

This explains many of the systemic manifestations, including:

Rash
Hypotension
Neurologic dysfunction
Pulmonary edema
Renal injury
Hepatic abnormalities

Severe disease may therefore resemble a systemic vasculitic or septic illness.

⸻

Incubation Period

Typical incubation periods are approximately:

Epidemic typhus

→ About 1–2 weeks

Murine typhus

→ Approximately 1–2 weeks

Scrub typhus

→ Approximately 6–21 days

Symptoms usually begin abruptly.

⸻

Clinical Presentation

Common manifestations across the typhus group include:

Sudden fever
Chills
Severe headache
Myalgias
Malaise
Nausea
Vomiting
Anorexia
Dry cough
Altered mental status in severe disease

Some patients may develop:

Tinnitus
Transient hearing impairment
Delirium
Encephalopathy

The presence and pattern of rash vary among the individual diseases.

⸻

Epidemic Typhus

Epidemic typhus is generally the most severe form.

Typical features include:

Abrupt high fever
Severe frontal headache
Marked myalgias
Profound malaise
Delirium or altered consciousness in severe cases
Rash developing several days after fever begins

⸻

Rash in Epidemic Typhus

The rash classically begins around the:

Upper trunk
Axillary regions

It then spreads centrifugally to the extremities.

Initially it may be:

Macular
Blanching

and later may become:

Petechial
Confluent

Classically, the rash tends to spare the face, palms, and soles.

There is usually no eschar.

⸻

Murine Typhus

Murine typhus is usually milder than epidemic typhus.

Symptoms include:

Fever
Headache
Myalgias
Malaise
Nausea
Cough
Abdominal symptoms

A rash occurs in only a proportion of patients.

⸻

Rash in Murine Typhus

The rash often appears several days after fever begins.

It is usually:

Macular
Maculopapular

and commonly involves:

Trunk
Extremities

Petechiae are less common than in severe epidemic typhus.

There is usually no eschar.

⸻

Scrub Typhus

Scrub typhus frequently causes:

Fever
Severe headache
Myalgias
Lymphadenopathy
Rash
Respiratory symptoms

A particularly important clue is the presence of an:

Eschar

⸻

Eschar in Scrub Typhus

At the mite inoculation site, a lesion may evolve from:

Papule
Vesicle
Ulcer

into a characteristic:

Black necrotic eschar

The eschar may be painless and can occur in hidden areas such as:

Axilla
Groin
Inframammary region
Genital region

Therefore, a careful skin examination is important.

An eschar is highly suggestive of scrub typhus when present, but its absence does not exclude the diagnosis.

⸻

Other Findings in Scrub Typhus

Possible findings include:

Regional lymphadenopathy
Generalized lymphadenopathy
Splenomegaly
Conjunctival injection
Maculopapular rash

Severe cases can progress to:

Shock
Encephalitis
Acute respiratory distress syndrome
Renal failure
Multiorgan dysfunction

⸻

Brill-Zinsser Disease

Brill-Zinsser disease generally resembles a mild episode of epidemic typhus.

Manifestations may include:

Fever
Headache
Myalgias
Mild rash
Malaise

The illness is usually substantially less severe than the original infection.

⸻

Diagnosis

Typhus should be suspected in a patient with:

Acute fever + severe headache ± rash + relevant vector or geographic exposure

Important exposure questions include:

Body lice?
Fleas?
Rodents?
Homelessness or crowded living?
Refugee camp exposure?
Scrub vegetation?
Travel to endemic regions?

Treatment should not be delayed while awaiting confirmatory testing if clinical suspicion is high.

⸻

Routine Laboratory Findings

Common abnormalities include:

Mild thrombocytopenia
Normal or mildly reduced leukocyte count
Anemia in some patients
Elevated liver enzymes
Hyponatremia
Hypoalbuminemia

More severe disease may cause:

Azotemia
Coagulopathy
Renal impairment
Marked electrolyte abnormalities

These findings are supportive but nonspecific.

⸻

Serologic Testing

Serology is commonly used for laboratory confirmation.

The most useful modern method is typically:

Indirect immunofluorescence assay (IFA)

A diagnosis is best supported by:

A fourfold rise in antibody titer between acute and convalescent specimens

An important limitation is that antibodies may not become detectable until several days or even more than a week after illness begins.

Therefore:

Early negative serology does not exclude typhus.

⸻

Weil-Felix Test

The Weil-Felix test is an old serologic test based on cross-reacting antibodies to certain Proteus antigens.

It has historically been used in settings where better testing is unavailable.

However, it has poor:

Sensitivity
Specificity

Therefore, it should not be relied upon when modern molecular or serologic diagnostics are available.

⸻

PCR

PCR-based testing can detect rickettsial DNA.

It may be useful early in the disease, particularly before antibodies develop.

Samples may include:

Blood
Eschar material
Tissue

For scrub typhus, PCR of an eschar can be particularly useful.

⸻

Imaging

Imaging is dictated by the organ system involved.

Possible studies include:

Chest radiograph

May reveal:

Interstitial infiltrates
Pneumonitis
Pulmonary edema

Echocardiography

May be indicated when myocarditis or endocarditis is suspected.

Neuroimaging

May be needed for severe encephalopathy, seizures, or focal neurologic signs.

⸻

Pathology

The characteristic pathologic process is:

Small-vessel vasculitis caused by endothelial infection

This may lead to:

Endothelial swelling
Perivascular inflammation
Thrombosis
Leakage of blood and plasma into tissues

These changes account for the characteristic rash and multiorgan complications.

⸻

Differential Diagnosis

Important differential diagnoses include:

Rocky Mountain spotted fever
Ehrlichiosis
Anaplasmosis
Meningococcemia
Bacterial meningitis
Typhoid fever
Leptospirosis
Dengue
Malaria
Secondary syphilis
Measles
Rubella
Infectious mononucleosis
Other viral febrile illnesses

In scrub typhus, additional considerations include other causes of:

Fever + eschar

such as:

Anthrax
Tularemia
Spotted-fever rickettsioses

⸻

Treatment

The most important principle is:

Start treatment promptly when typhus is clinically suspected.

Waiting for serologic confirmation can increase the risk of complications.

⸻

First-Line Therapy

Doxycycline

Doxycycline is the drug of choice for most typhus-group infections.

A typical adult regimen is:

Doxycycline 100 mg orally or intravenously every 12 hours

Treatment is generally continued until:

The patient has been afebrile for at least 48 hours

and usually for a minimum total course appropriate to the clinical syndrome.

Clinical improvement is often rapid.

⸻

Response to Therapy

One of the characteristic features of rickettsial infections is rapid defervescence after appropriate doxycycline treatment.

Most patients improve within approximately:

24–72 hours

Failure to improve should prompt reconsideration of:

Diagnosis
Drug absorption
Resistance, especially in selected scrub-typhus regions
Complications

⸻

Chloramphenicol

Chloramphenicol has historically been an alternative treatment.

However, its role is now limited because of:

Bone marrow toxicity
Aplastic anemia risk
Availability of safer alternatives

It may still be considered in selected circumstances when doxycycline cannot be used.

⸻

Azithromycin

Azithromycin is an important alternative for scrub typhus, particularly in:

Pregnancy
Patients unable to take doxycycline
Areas where reduced doxycycline responsiveness is suspected

⸻

Fluoroquinolones

Fluoroquinolones have been studied in rickettsial infections, but they are generally not preferred over doxycycline.

They should not be considered universal first-line therapy for typhus.

⸻

Pregnancy

The choice of antibiotic in pregnancy should be individualized.

For scrub typhus, azithromycin is commonly used.

Management should account for:

Disease severity
Organ involvement
Local recommendations
Maternal and fetal risks

⸻

Supportive Treatment

Patients with severe disease may require:

Intravenous fluids
Electrolyte correction
Oxygen
Mechanical ventilation
Vasopressors
Renal replacement therapy
Nutritional support

Care must be taken because widespread endothelial injury can result in both:

Intravascular volume depletion
Tissue edema

⸻

Vector Control in Epidemic Typhus

For patients with suspected louse-borne typhus, treatment must include delousing.

Measures include:

Bathing
Changing clothing
Heat treatment or laundering of clothes and bedding
Appropriate pediculicides when indicated

Without vector control, transmission can continue.

⸻

Admission Criteria

Hospitalization should be considered for:

Severe systemic illness
Hypotension
Altered mental status
Seizures
Respiratory compromise
Renal failure
Significant hepatic dysfunction
Inability to tolerate oral therapy

Severe epidemic or scrub typhus may require ICU-level care.

⸻

Prognosis

The prognosis depends strongly on:

Type of typhus
Age
Comorbidities
Delay before treatment
Presence of organ failure

Prompt doxycycline therapy dramatically improves outcomes.

⸻

Epidemic Typhus Prognosis

Epidemic typhus is the most dangerous form.

Untreated disease can have substantial mortality, particularly among:

Older adults
Malnourished patients
Severely ill patients

With appropriate antimicrobial treatment, mortality decreases markedly.

⸻

Murine Typhus Prognosis

Murine typhus is generally a milder disease.

Most patients recover completely with treatment.

Severe complications can occur but are much less common.

⸻

Scrub Typhus Prognosis

Severity varies considerably.

Untreated scrub typhus may lead to:

ARDS
Encephalitis
Shock
Renal failure
Myocarditis
Multiorgan failure

Early therapy greatly reduces mortality.

⸻

Complications

Potential complications across the typhus group include:

Cardiovascular collapse
Myocarditis
Endocarditis
Acute kidney injury
Hepatitis
Hepatic failure
Pneumonitis
Pulmonary edema
Acute respiratory distress syndrome
Gastrointestinal bleeding
Encephalitis
Seizures
Delirium
Coma
Secondary bacterial infections

Severe endothelial injury may result in widespread multiorgan dysfunction.

⸻

High-Yield Comparison

Epidemic typhus

→ Rickettsia prowazekii

→ Body louse

→ Humans

→ Severe disease

→ Rash starts on trunk and spreads outward

→ Usually spares face, palms, and soles

→ No eschar

Murine typhus

→ Rickettsia typhi

→ Fleas

→ Rodents/opossums and other mammalian hosts

→ Generally milder

→ Rash may be absent

→ No eschar

Scrub typhus

→ Orientia tsutsugamushi

→ Chigger/larval mite

→ Rodents and mites

→ Asia-Pacific predominance

→ Characteristic eschar may occur

→ Generalized lymphadenopathy may occur

Brill-Zinsser disease

→ Reactivation of R. prowazekii

→ Years after epidemic typhus

→ Usually milder than primary disease

⸻

High-Yield Clinical Approach

Fever + headache + rash + body lice

→ Think epidemic typhus

Fever + flea/rodent exposure + mild maculopapular rash

→ Think murine typhus

Fever + travel in Asia + black eschar

→ Think scrub typhus

Previous epidemic typhus years ago + recurrent febrile illness

→ Think Brill-Zinsser disease

Early serology negative but clinical suspicion strong

→ Do not exclude typhus

Suspected typhus

→ Start doxycycline promptly

Rapid improvement after doxycycline

→ Supports a rickettsial diagnosis

⸻

Exam Essentials

Typhus organisms:

→ Obligate intracellular bacteria

Main pathologic target:

→ Vascular endothelial cells

Major mechanism of injury:

→ Systemic vasculitis and increased vascular permeability

Epidemic typhus organism:

→ Rickettsia prowazekii

Epidemic typhus vector:

→ Body louse

Murine typhus organism:

→ Rickettsia typhi

Murine typhus vector:

→ Flea

Scrub typhus organism:

→ Orientia tsutsugamushi

Scrub typhus vector:

→ Chigger/larval mite

Classic scrub-typhus clue:

→ Black eschar

Brill-Zinsser disease:

→ Reactivation of previous epidemic typhus

Preferred diagnostic serology:

→ Indirect immunofluorescence assay

Best confirmation:

→ Fourfold rise in paired antibody titers

Old, poorly specific test:

→ Weil-Felix reaction

Drug of choice:

→ Doxycycline

Expected response to therapy:

→ Defervescence usually within 1–3 days

Most severe form:

→ Epidemic typhus

Major complications:

→ Encephalitis, ARDS, renal failure, shock, myocarditis, multiorgan dysfunction

Published on: August 25, 2026

Infectious Disease and Microbiology - Typhoid Fever

Infectious Disease and Microbiology - Typhoid Fever

Basics

Description

Typhoid fever is a systemic bacterial infection caused by Salmonella enterica serovar Typhi, commonly called Salmonella Typhi.

Unlike most nontyphoidal Salmonella infections, which usually remain confined to the gastrointestinal tract, typhoid fever is characterized by invasion of the intestinal mucosa, bacteremia, and dissemination to the reticuloendothelial system and other organs.

The illness may range from an uncomplicated febrile disease to severe infection with:

Encephalopathy
Gastrointestinal hemorrhage
Intestinal perforation
Septic complications
Multiorgan involvement

⸻

Epidemiology

Typhoid fever remains an important global infection, particularly in regions with inadequate sanitation and limited access to safe drinking water.

The greatest burden occurs in:

South Asia
Southeast Asia
Parts of Africa
Areas of Latin America
Other regions with poor sanitation infrastructure

In countries with low endemicity, most cases are associated with:

International travel
Recent residence in endemic areas
Household exposure to infected individuals or chronic carriers

Humans are the only important reservoir of S. Typhi.

⸻

Risk Factors

Important risk factors include:

Travel to an endemic region
Household contact with a recent case
Consumption of contaminated food or water
Eating food from street vendors in high-risk areas
Inadequate hand hygiene
Lack of proper toilet facilities
Use of contaminated ice
Reduced gastric acidity

Conditions that reduce gastric acidity may lower the infectious dose required for disease.

These include:

Achlorhydria
Previous gastrectomy
Proton-pump inhibitor use
Histamine-2 receptor blocker use

⸻

General Prevention

Prevention depends on interrupting fecal-oral transmission.

Important measures include:

Frequent handwashing with soap and safe water
Safe drinking water
Proper sewage disposal
Adequate sanitation
Safe preparation and storage of food
Identification and management of chronic carriers
Appropriate vaccination before travel to endemic areas

Travelers should avoid:

Untreated water
Ice made from unsafe water
Raw or undercooked foods
Unpeeled fruits and vegetables
Food from vendors with questionable hygiene

⸻

Vaccination

Vaccination is recommended for selected travelers to areas where typhoid fever is endemic.

Available vaccine strategies include oral live-attenuated and injectable Vi-based vaccines.

Vaccination reduces risk but does not provide complete protection, so food and water precautions remain essential.

⸻

Transmission and Pathophysiology

Transmission occurs predominantly through the:

Fecal-oral route

The organism is acquired by ingesting food or water contaminated by feces from:

An acutely infected patient
A recovering patient
A chronic carrier

After ingestion, the bacteria must survive gastric acidity and reach the small intestine.

They then:

Attach to and invade the intestinal mucosa.
Penetrate particularly through lymphoid tissue in the Peyer patches.
Enter lymphatic tissue.
Spread to macrophages in the reticuloendothelial system.
Disseminate through the bloodstream.

Important sites of dissemination include:

Liver
Spleen
Bone marrow
Gallbladder
Terminal ileum

Biliary excretion can reintroduce organisms into the intestine, contributing to intestinal inflammation and shedding in stool.

⸻

Incubation Period

The incubation period is usually approximately:

7–14 days

but may vary depending on:

Infectious dose
Host immunity
Gastric acidity

⸻

Etiology

Salmonella enterica serovar Typhi is a:

Gram-negative rod
Facultative anaerobe
Member of the Enterobacterales
Intracellular pathogen capable of surviving within macrophages

Typhoid fever should be distinguished from infection caused by:

Salmonella Paratyphi
Nontyphoidal Salmonella

⸻

Clinical Course

Traditionally, untreated typhoid fever has been described as progressing through several clinical stages.

First Week

Bacteremia becomes established.

Common features include:

Progressive fever
Headache
Malaise
Cough
Myalgias
Abdominal discomfort

⸻

Second Week

Systemic illness becomes more obvious.

Patients may develop:

Persistent high fever
Abdominal pain
Hepatomegaly
Splenomegaly
Diarrhea or constipation
Rose spots

⸻

Third Week

Without effective treatment, the patient may become markedly toxic.

Serious complications are more likely to develop, particularly:

Intestinal hemorrhage
Intestinal perforation
Encephalopathy
Severe systemic illness

Modern antibiotic treatment often alters this classic progression.

⸻

Clinical Presentation

Fever is the most consistent feature and occurs in nearly all patients.

Other manifestations include:

Headache
Malaise
Fatigue
Abdominal pain
Nausea
Diarrhea
Constipation
Cough
Myalgias
Arthralgias

Children may be more likely to develop diarrhea.

Adults may more commonly report constipation.

Neurologic symptoms can include:

Confusion
Delirium
Encephalopathy
Seizures, particularly in young children with severe disease

⸻

Physical Examination

Fever

The fever may initially be low grade and progressively rise.

By the second week, temperatures may approach:

39–40°C

⸻

Relative Bradycardia

Some patients demonstrate relative bradycardia, meaning the heart rate is lower than expected for the degree of fever.

This is sometimes called Faget sign, although it is neither sensitive nor specific.

⸻

Abdominal Findings

Possible findings include:

Diffuse abdominal tenderness
Abdominal distention
Hepatomegaly
Splenomegaly

Marked abdominal tenderness, rigidity, or sudden deterioration should raise concern for intestinal perforation.

⸻

Rose Spots

Rose spots are a classic but uncommon physical finding.

They are:

Faint
Blanching
Pink or erythematous
Maculopapular
Usually approximately a few millimeters in diameter

They most often appear on:

Abdomen
Chest

and less commonly on:

Back
Arms
Legs

They may be transient and therefore easily missed.

⸻

Other Physical Findings

Depending on severity, patients may demonstrate:

Cervical lymphadenopathy
Pulmonary crackles or rhonchi
Meningismus
New cardiac murmur
Altered mental status
Joint swelling
Bone tenderness

Severe disease may give the patient an apathetic or toxic appearance.

⸻

Diagnosis

The diagnosis should be suspected in a patient with:

Prolonged fever + compatible systemic symptoms + epidemiologic exposure

Important exposure clues include:

Recent travel to an endemic region
Consumption of unsafe food or water
Household contact with a case
Exposure to a chronic carrier

Microbiologic confirmation should be pursued whenever possible.

⸻

Laboratory Findings

Routine laboratory abnormalities are variable.

Possible findings include:

Leukopenia
Leukocytosis, particularly in infants
Anemia
Thrombocytopenia
Elevated transaminases
Elevated bilirubin

None of these findings is sufficiently specific to establish the diagnosis.

⸻

Blood Culture

Blood culture is one of the most important diagnostic tests.

It is most likely to be positive early in disease.

Sensitivity is imperfect and can be reduced by:

Previous antibiotic therapy
Low bacterial burden
Delayed specimen collection

Multiple cultures may improve yield.

⸻

Bone Marrow Culture

Bone marrow culture has historically been the most sensitive conventional culture technique for typhoid fever.

It may remain positive even after antibiotic exposure.

However, because it is invasive, it is generally reserved for selected difficult diagnostic situations.

⸻

Stool Culture

Stool cultures may become positive later in the course.

They can be useful for:

Diagnosis
Assessing fecal shedding
Evaluating possible carrier states

A negative stool culture does not exclude acute disease.

⸻

Other Culture Sites

S. Typhi may occasionally be recovered from:

Urine
Bile
Rose-spot biopsy specimens
Duodenal samples

These are not usually required for routine diagnosis.

⸻

Widal Test

The Widal test detects antibodies against Salmonella O and H antigens.

Its usefulness is limited because it can produce:

False-positive results
False-negative results
Cross-reactions with other organisms
Difficulty distinguishing previous exposure from acute infection

Therefore, it should not be relied upon as the sole diagnostic test when better microbiologic methods are available.

⸻

Molecular Testing

PCR-based and other molecular assays can detect S. Typhi DNA.

Advantages include rapid results.

However, availability and standardized performance vary considerably, and culture remains important because it permits:

Confirmation
Antimicrobial susceptibility testing

⸻

Imaging

Imaging is not routinely required in uncomplicated typhoid fever.

It becomes important when complications are suspected.

Possible studies include:

Chest imaging

May show pulmonary infiltrates if pneumonia develops.

Abdominal CT or ultrasound

May demonstrate:

Bowel-wall inflammation
Colitis
Hepatosplenomegaly
Abscesses
Free air or other evidence of perforation

⸻

Pathology

Histologic examination may demonstrate infiltration by macrophages sometimes called typhoid cells.

These macrophages may contain:

Bacteria
Cellular debris
Erythrocytes

The terminal ileum and Peyer patches are particularly important sites of intestinal pathology.

Necrosis and ulceration in this region contribute to the risk of:

Hemorrhage
Perforation

⸻

Differential Diagnosis

Important differential diagnoses include:

Paratyphoid fever
Nontyphoidal salmonellosis
Malaria
Dengue
Leptospirosis
Brucellosis
Tuberculosis
Viral hepatitis
Rickettsial infections
Bacterial endocarditis
Intra-abdominal abscess
Yersiniosis
Campylobacter infection

The differential is particularly broad in returning travelers with prolonged fever.

⸻

Treatment

Antimicrobial treatment should be guided by:

Disease severity
Region of acquisition
Local resistance patterns
Culture and susceptibility results
Patient age
Pregnancy
Ability to tolerate oral medications

The historical reliance on fluoroquinolones has declined because of widespread resistance.

⸻

Contemporary Resistance Considerations

Antimicrobial resistance is one of the most important issues in typhoid fever.

Resistance patterns include:

Fluoroquinolone nonsusceptibility
Multidrug-resistant strains
Extensively drug-resistant strains in some regions

This is particularly important in infections acquired in:

Pakistan
India
Bangladesh
Other parts of South Asia

Therefore, older recommendations that automatically use ciprofloxacin as universal first-line therapy should not be applied without considering susceptibility patterns.

⸻

Ceftriaxone

Ceftriaxone is widely used for:

Severe disease
Hospitalized patients
Suspected fluoroquinolone-resistant infection
Patients unable to tolerate oral therapy

It is administered intravenously.

The exact dose and duration depend on severity, susceptibility, and current guidelines.

⸻

Azithromycin

Azithromycin is an important oral option for uncomplicated typhoid fever when the isolate is susceptible.

It is particularly useful where fluoroquinolone resistance is common.

⸻

Fluoroquinolones

Fluoroquinolones such as ciprofloxacin were historically highly effective.

However, resistance and reduced susceptibility are now common in many endemic regions.

They should therefore be used only when susceptibility is known or strongly expected.

⸻

Extensively Drug-Resistant Typhoid

Some S. Typhi strains have acquired resistance to multiple traditional agents, including:

Ampicillin
Chloramphenicol
Trimethoprim-sulfamethoxazole
Fluoroquinolones
Certain third-generation cephalosporins

Severe suspected extensively drug-resistant disease may require agents such as a carbapenem, guided by susceptibility testing and infectious-disease expertise.

⸻

Older Antibiotics

Historically effective agents include:

Ampicillin
Amoxicillin
Trimethoprim-sulfamethoxazole
Chloramphenicol

Their use is now dependent on demonstrated susceptibility because resistance is common.

⸻

Pregnancy

Typhoid fever during pregnancy requires prompt treatment because maternal infection can be associated with:

Severe maternal illness
Miscarriage
Fetal complications

Agents with more established use during pregnancy, such as selected:

β-lactams
Cephalosporins
Macrolides

are generally preferred when active against the organism.

Treatment should be individualized according to susceptibility results and maternal disease severity.

⸻

Supportive Treatment

Supportive care is extremely important.

Measures include:

Oral or intravenous fluid replacement
Electrolyte correction
Antipyretics
Nutritional support
Monitoring for complications

Severely ill patients may require intensive care.

⸻

Severe Typhoid Fever

Severe disease may be characterized by:

Shock
Severe encephalopathy
Delirium
Major gastrointestinal bleeding
Intestinal perforation
Multiorgan dysfunction

These patients require:

Hospitalization
Intravenous antibiotics
Careful hemodynamic monitoring
Rapid evaluation for complications

⸻

Surgical Management

Surgery may be necessary for:

Intestinal perforation
Uncontrolled gastrointestinal hemorrhage
Peritonitis
Other serious intra-abdominal complications

Intestinal perforation is a surgical emergency.

⸻

Admission Criteria

Hospital admission should be strongly considered for:

Severe systemic illness
Hemodynamic instability
Significant dehydration
Persistent vomiting
Encephalopathy
Suspected intestinal bleeding
Suspected perforation
Very young or frail patients
Patients unable to reliably take oral therapy

⸻

Follow-up

Patients should be followed for:

Clinical improvement
Relapse
Persistent fecal shedding
Chronic carriage

Fever may take several days to resolve even after appropriate antibiotic therapy.

Failure to improve should prompt reassessment for:

Drug resistance
Incorrect diagnosis
Abscess
Intestinal complication
Inadequate antimicrobial exposure

⸻

Relapse

Relapse may occur after apparently successful treatment.

It usually develops within several weeks after clinical recovery.

Symptoms generally resemble the initial illness but may be milder.

Relapse should prompt:

Repeat cultures
Repeat susceptibility testing where possible
Appropriate retreatment

⸻

Chronic Carrier State

A small proportion of patients continue to excrete S. Typhi for prolonged periods after recovery.

Chronic carriage is especially associated with:

Older age
Female sex
Gallbladder disease
Cholelithiasis

The gallbladder is an important reservoir in chronic carriers.

Carriers may be completely asymptomatic yet remain capable of transmitting infection.

⸻

Public Health Importance of Carriers

Chronic carriers are particularly important if they work as:

Food handlers
Healthcare workers
Childcare workers

Public-health authorities may require microbiologic clearance before certain individuals return to high-risk occupations.

⸻

Prognosis

With timely diagnosis and appropriate antibiotics, the prognosis is generally good.

Mortality is now usually low with modern treatment.

Risk of poor outcome increases with:

Delayed therapy
Very young age
Older age
Encephalopathy
Shock
Intestinal perforation
Severe bleeding
Antimicrobial resistance

⸻

Complications

Gastrointestinal Hemorrhage

Bleeding may result from ulceration of intestinal lymphoid tissue.

It may range from occult blood loss to severe hemorrhage.

⸻

Intestinal Perforation

One of the most dangerous complications.

It most often involves the:

Terminal ileum

It classically occurs later in untreated disease.

Clinical clues include:

Sudden worsening abdominal pain
Rigidity
Peritoneal signs
Shock
Free intraperitoneal air

⸻

Hepatobiliary Complications

Possible complications include:

Hepatitis
Cholecystitis
Hepatic abscess

The gallbladder plays an important role in chronic carriage.

⸻

Neurologic Complications

These may include:

Encephalopathy
Delirium
Psychosis
Meningoencephalitis
Cerebral abscess
Seizures

⸻

Cardiovascular Complications

Rare complications include:

Myocarditis
Pericarditis
Endocarditis
Arteritis

⸻

Pulmonary Complications

Possible complications include:

Pneumonia
Empyema

⸻

Musculoskeletal Complications

Possible manifestations include:

Osteomyelitis
Septic arthritis
Psoas abscess

Patients with hemoglobinopathies may have particular susceptibility to Salmonella bone infections, although this association is especially recognized with nontyphoidal Salmonella.

⸻

High-Yield Clinical Approach

Traveler from South Asia + prolonged fever + abdominal symptoms

→ Think typhoid fever

Progressively increasing fever + headache + abdominal pain

→ Consider Salmonella Typhi

Fever + relative bradycardia + splenomegaly

→ Classic clue for typhoid fever

Faint blanching pink lesions on trunk

→ Rose spots

Early disease

→ Blood cultures have the highest routine diagnostic value

Most sensitive traditional culture

→ Bone marrow culture

Widal test

→ Limited reliability; do not depend on it alone

Third week + sudden severe abdominal pain

→ Suspect terminal ileal perforation

Persistent shedding after recovery

→ Think chronic carrier state

Chronic carrier reservoir

→ Gallbladder

Travel to South Asia

→ Always consider antimicrobial resistance

Fluoroquinolone use

→ Only when susceptibility is appropriate

Uncomplicated susceptible disease

→ Azithromycin or other susceptibility-directed therapy

Severe disease

→ IV therapy such as ceftriaxone, adjusted for resistance patterns

⸻

Exam Essentials

Causative organism:

→ Salmonella enterica serovar Typhi

Type of organism:

→ Gram-negative rod

Reservoir:

→ Humans

Transmission:

→ Fecal-oral

Incubation period:

→ Usually 7–14 days

Major intestinal site:

→ Peyer patches of the terminal ileum

Most common symptom:

→ Fever

Classic skin finding:

→ Rose spots

Classic pulse finding:

→ Relative bradycardia

Important organ enlargement:

→ Hepatosplenomegaly

Routine diagnostic cornerstone:

→ Blood culture

Most sensitive traditional culture:

→ Bone marrow culture

Widal test:

→ Poor specificity and variable sensitivity

Major late gastrointestinal complication:

→ Intestinal perforation

Typical site of perforation:

→ Terminal ileum

Major resistance concern:

→ Fluoroquinolone-resistant and multidrug/extensively drug-resistant S. Typhi

Important oral treatment option in susceptible uncomplicated disease:

→ Azithromycin

Common IV option for severe susceptible disease:

→ Ceftriaxone

Important site in chronic carriage:

→ Gallbladder

Relapse:

→ Can occur several weeks after apparent recovery

Most important prevention:

→ Safe food, safe water, sanitation, hand hygiene, and vaccination before high-risk travel

Kembara Xtra

Facts about medicine and its subtopic such as anatomy, physiology, biochemistry, pharmacology, medicine, pediatrics, psychiatry, obstetrics and gynecology and surgery.

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