Infectious Disease and Microbiology - Bacteroides Species

Basics

Bacteroides species are anaerobic Gram-negative bacilli that form an important component of the normal human microbiota, particularly within the gastrointestinal tract. Although they normally exist as harmless commensals, they can become important opportunistic pathogens when mucosal barriers are disrupted.

The Bacteroides fragilis group is particularly important clinically and is frequently involved in polymicrobial infections containing both aerobic and anaerobic organisms.

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Important Species

Clinically recognized Bacteroides species include:

• Bacteroides fragilis

• B. thetaiotaomicron

• B. ovatus

• B. vulgatus

• B. uniformis

• B. caccae

• B. eggerthii

• B. stercoris

• B. distasonis

• B. merdae

• B. capillosus

• B. putredinis

• B. tectum

• B. ureolyticus

• Other related species

Taxonomy within this group has changed over time, so some organisms historically classified as Bacteroides have subsequently been reassigned to other genera.

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Microbiologic Characteristics

Bacteroides species are:

• Gram-negative bacilli

• Obligate anaerobes

• Non-spore-forming organisms

Many species are normal inhabitants of the colon.

Despite representing only part of the normal intestinal microbiota, members of the B. fragilis group are disproportionately important causes of clinically significant anaerobic infections.

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Epidemiology

Bacteroides infections occur worldwide.

Because these organisms normally colonize the gastrointestinal tract, most infections are endogenous. Disease typically develops when disruption of a mucosal barrier allows organisms to enter normally sterile tissues.

Common predisposing events include:

• Gastrointestinal perforation

• Abdominal surgery

• Trauma

• Bowel ischemia

• Appendicitis

• Diverticulitis

• Pelvic infection

• Malignancy involving the gastrointestinal tract

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Polymicrobial Infection

A major characteristic of Bacteroides infection is its association with mixed aerobic-anaerobic infections.

Rather than occurring alone, Bacteroides may be isolated together with organisms such as enteric Gram-negative bacilli and other components of the normal gastrointestinal flora.

Therefore:

Disruption of bowel integrity + abscess formation + polymicrobial infection

→ strongly suggests involvement of anaerobic organisms such as Bacteroides.

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Infections

Intra-Abdominal Infection

Intra-abdominal disease is among the most important manifestations of Bacteroides infection.

Clinical syndromes include:

• Intra-abdominal abscess

• Peritonitis

• Appendiceal infection

• Diverticular infection

• Postoperative abdominal infection

• Infection following gastrointestinal perforation

B. fragilis is particularly important in intra-abdominal abscess formation.

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Pelvic Infection

Bacteroides species may participate in polymicrobial pelvic infections, including infections involving the female reproductive tract.

Possible manifestations include:

• Pelvic abscess

• Postoperative pelvic infection

• Other mixed anaerobic pelvic infections

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Pleuropulmonary Infection

Anaerobic pulmonary infection may occur following aspiration of organisms from the upper aerodigestive tract.

Possible manifestations include:

• Aspiration pneumonia

• Lung abscess

• Necrotizing pulmonary infection

• Empyema

These infections are frequently polymicrobial.

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Cervicofacial Infection

Bacteroides species may contribute to mixed anaerobic infections involving the oral cavity, head, and neck.

Possible sites include:

• Dental infections

• Deep neck infections

• Cervicofacial abscesses

These infections often contain several anaerobic and aerobic organisms simultaneously.

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Brain Abscess

Anaerobic bacteria, including Bacteroides, can occasionally contribute to brain abscesses.

Potential sources include:

• Dental infection

• Chronic sinusitis

• Otogenic infection

• Hematogenous dissemination

Brain abscess requires antimicrobial therapy with adequate CNS penetration together with drainage when appropriate.

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Bacteremia and Sepsis

Disruption of gastrointestinal or pelvic barriers may allow Bacteroides organisms to enter the bloodstream.

Patients may develop:

• Bacteremia

• Sepsis

• Septic shock in severe cases

Detection of Bacteroides bacteremia should prompt investigation for an underlying abdominal, pelvic, or gastrointestinal source.

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Skin and Soft-Tissue Infection

Bacteroides species can participate in polymicrobial infections involving:

• Surgical wounds

• Traumatic wounds

• Deep soft tissues

• Abscesses

• Necrotic tissue

Anaerobic infection should be considered particularly when there is tissue necrosis, abscess formation, or infection near gastrointestinal or genitourinary structures.

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Diagnosis

Anaerobic Culture

Diagnosis is established primarily through:

Anaerobic culture

Appropriate specimen collection is essential because exposure to oxygen may reduce recovery of anaerobic organisms.

High-quality specimens include:

• Abscess aspirates

• Deep tissue specimens

• Blood cultures

• Normally sterile body fluids

Superficial swabs are generally less useful because they may contain colonizing organisms and may not accurately represent the organisms causing deep infection.

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Treatment

Metronidazole

Metronidazole has traditionally been one of the most reliable agents against clinically important Bacteroides, particularly the B. fragilis group.

It provides strong anaerobic activity and is commonly incorporated into treatment regimens for intra-abdominal and pelvic infections.

However, antimicrobial susceptibility can vary, and resistance should be considered in refractory or severe infections.

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Carbapenems

Carbapenems provide broad coverage against anaerobic and aerobic organisms.

Options include:

• Imipenem

• Meropenem

• Ertapenem

These agents are particularly useful for complicated polymicrobial intra-abdominal infections when broad-spectrum treatment is required.

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Beta-Lactam/Beta-Lactamase Inhibitor Combinations

Important options include:

• Piperacillin-tazobactam

• Ampicillin-sulbactam

Historically, ticarcillin-clavulanate has also been used.

These combinations provide activity against many anaerobic organisms while simultaneously covering several aerobic pathogens involved in polymicrobial infections.

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Cephamycins

Agents with anaerobic activity include:

• Cefoxitin

• Cefotetan

However, resistance among Bacteroides species limits their reliability in some settings.

They should therefore not automatically be assumed to provide adequate treatment for every serious Bacteroides infection.

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Tigecycline

Tigecycline has activity against many anaerobic organisms, including members of the B. fragilis group.

Its use depends on the site and severity of infection as well as susceptibility patterns and patient-specific considerations.

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Antimicrobial Resistance

Antimicrobial resistance is increasingly important among Bacteroides species.

The B. fragilis group commonly produces beta-lactamases, making many unprotected beta-lactam antibiotics unreliable.

Resistance has also been reported to:

• Clindamycin

• Cephamycins

• Metronidazole, although resistance remains comparatively uncommon in many settings

Because susceptibility patterns vary geographically and over time, serious infections should be managed according to contemporary local susceptibility data whenever available.

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Clindamycin Resistance

Clindamycin was historically used extensively for anaerobic infections, but resistance among Bacteroides has become sufficiently common that it is no longer reliably active empirically in many settings.

Therefore:

Do not automatically assume that clindamycin covers the B. fragilis group.

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Source Control

Antibiotics alone may be insufficient for many Bacteroides infections.

Effective management frequently requires source control.

Examples include:

• Drainage of an intra-abdominal abscess

• Drainage of a pelvic abscess

• Removal of infected or necrotic tissue

• Surgical repair of gastrointestinal perforation

• Management of bowel ischemia

• Removal of infected foreign material when appropriate

This principle is particularly important in intra-abdominal infection.

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Prevention

Because many Bacteroides infections originate from the patient’s own intestinal flora, prevention focuses on reducing opportunities for organisms to enter sterile tissues.

Important measures include:

• Appropriate surgical technique

• Timely management of bowel perforation

• Prevention and treatment of intra-abdominal contamination

• Appropriate perioperative antimicrobial prophylaxis when indicated

• Proper wound care

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High-Yield Clinical Pattern

Bowel perforation

Polymicrobial intra-abdominal infection

Abscess formation

→ Think Bacteroides fragilis and other anaerobic organisms.

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High-Yield Treatment Pattern

Serious Bacteroides infection

→ Ensure anaerobic antimicrobial coverage

Common options:

→ Metronidazole

→ Piperacillin-tazobactam

→ Carbapenem

PLUS

→ Drain the abscess or otherwise control the source when necessary

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Exam Essentials

Organism:

→ Bacteroides species

Microbiology:

→ Anaerobic Gram-negative bacilli

Most clinically important group:

→ Bacteroides fragilis group

Normal habitat:

→ Gastrointestinal tract

Typical infections:

→ Intra-abdominal and pelvic infections

Characteristic infection pattern:

→ Polymicrobial infection with abscess formation

Other infections:

→ Pleuropulmonary infection, cervicofacial infection, brain abscess, bacteremia/sepsis, and skin or surgical-wound infection

Diagnosis:

→ Anaerobic culture

Classic antimicrobial:

→ Metronidazole

Broad-spectrum alternatives:

→ Carbapenems or beta-lactam/beta-lactamase inhibitor combinations

Important resistance issue:

→ Increasing resistance, particularly to clindamycin and some cephamycins

Critical management principle:

→ Source control

Key clinical pearl: When gastrointestinal contents escape into normally sterile tissue, particularly after bowel perforation or abdominal surgery, Bacteroides fragilis is one of the most important anaerobic pathogens to consider.

Infectious Disease and Microbiology - Bacillus Species

Basics

Bacillus is a genus of aerobic, Gram-positive bacilli that includes several environmental organisms capable of causing human disease. Important species include Bacillus cereus, B. subtilis, B. pumilus, B. circulans, B. alvei, and B. anthracis. B. anthracis is the cause of anthrax and is usually discussed separately because of its distinct clinical importance.

Among the non-anthrax species, B. cereus is the most clinically important. It is well known for causing food poisoning but can also produce severe invasive infections.

Microbiologic Characteristics

Bacillus species are large Gram-positive bacilli that grow aerobically.

Many species form spores, allowing them to persist in the environment and survive adverse conditions. They are widely distributed in soil, dust, food products, and environmental surfaces.

Because environmental contamination is common, isolation of a Bacillus species from a clinical specimen does not always indicate true infection. However, recovery from blood in a patient with compatible symptoms, particularly with an intravascular catheter or intravenous drug use, may represent genuine bacteremia.

Important Species

Clinically recognized species include:

• Bacillus cereus

• B. subtilis

• B. pumilus

• B. circulans

• B. alvei

• B. laterosporus

• B. sphaericus

• B. pseudoanthracis

• B. anthracis

B. cereus is the classic cause of Bacillus-associated gastroenteritis.

Bacillus cereus Food Poisoning

B. cereus produces two major forms of food poisoning:

Emetic syndrome

and

Diarrheal syndrome

These syndromes differ in incubation period, food association, and predominant symptoms.

Emetic Syndrome

The emetic form is caused by ingestion of preformed toxin in contaminated food.

The incubation period is short:

1–6 hours

Symptoms are dominated by:

• Nausea

• Vomiting

• Abdominal discomfort

Diarrhea may occur but is usually less prominent.

Classic Food Association

The classic food associated with the emetic syndrome is:

Cooked rice

This is particularly associated with rice that is cooked, left at room temperature, and later reheated.

The spores may survive cooking and subsequently germinate, allowing toxin production.

High-Yield Pattern

Reheated rice

• ●

Vomiting within a few hours

→ Think Bacillus cereus emetic food poisoning.

Diarrheal Syndrome

The diarrheal form results from toxin production in the intestine after contaminated food is consumed.

The incubation period is longer:

6–24 hours

Typical manifestations include:

• Watery diarrhea

• Abdominal cramps

• Nausea

Vomiting is less prominent than in the emetic form.

Food Association

The diarrheal syndrome is commonly associated with:

• Meat

• Vegetables

• Sauces

• Soups

• Other prepared foods

Thus, the food association differs from the classic reheated-rice pattern of the emetic form.

Comparison of the Two Syndromes

Emetic form

Incubation:

→ 1–6 hours

Main symptom:

→ Vomiting

Classic food:

→ Rice

Diarrheal form

Incubation:

→ 6–24 hours

Main symptom:

→ Watery diarrhea and cramps

Classic foods:

→ Meat and vegetables

This distinction is highly useful for examinations.

Invasive Bacillus Infections

Although gastroenteritis is the best-known manifestation, Bacillus species can occasionally cause serious systemic infections.

Risk is greater in patients with:

• Intravascular catheters

• Intravenous drug use

• Immunosuppression

• Severe underlying disease

• Traumatic wounds

Bacteremia

Bacteremia can occur particularly in:

• Intravenous drug users

• Patients with central venous catheters

• Hospitalized or immunocompromised patients

Because Bacillus organisms may contaminate blood cultures, the clinical context is essential.

Repeated positive blood cultures or persistent bacteremia strongly suggest true infection rather than contamination.

Catheter-Associated Infection

Intravascular lines can become colonized or infected with Bacillus species.

Patients may develop:

• Fever

• Chills

• Persistent positive blood cultures

• Sepsis

Removal of the infected catheter may be necessary in addition to antimicrobial therapy.

Endocarditis

Bacillus species can rarely cause infective endocarditis.

The risk is particularly recognized in intravenous drug users and patients with persistent bacteremia.

Possible manifestations include:

• Prolonged fever

• Cardiac murmur

• Embolic phenomena

• Persistent bloodstream infection

Echocardiography may be necessary when endocarditis is suspected.

Central Nervous System Infection

Serious CNS infections can include:

• Meningitis

• Brain abscess

These infections are uncommon but potentially severe.

They occur more often in patients with significant underlying disease, invasive procedures, or bloodstream infection.

Pneumonia

Bacillus species can rarely cause severe pneumonia.

Although most pulmonary Bacillus infections are unusual, rapidly progressive disease can occur in selected patients.

Blood cultures and respiratory cultures are useful when invasive disease is suspected.

Soft-Tissue Infection

Bacillus organisms can occasionally cause:

• Cellulitis

• Wound infection

• Deep soft-tissue infection

Trauma and environmental contamination may provide the portal of entry.

Ocular Infections

Bacillus cereus is particularly important in severe eye infections.

Possible manifestations include:

• Conjunctivitis

• Keratitis

• Corneal ulcers

• Endophthalmitis

• Panophthalmitis

Post-traumatic ocular infection can progress rapidly and threaten vision.

Prompt ophthalmologic evaluation and aggressive treatment are essential.

High-Yield Eye Association

Penetrating eye trauma

• ●

Rapid severe ocular inflammation

→ Consider Bacillus cereus.

Diagnosis

Diagnosis is primarily based on:

Culture

Depending on the clinical syndrome, specimens may include:

• Stool or food samples in outbreak investigations

• Blood

• Cerebrospinal fluid

• Wound material

• Respiratory secretions

• Ocular specimens

For bloodstream infection, repeated isolation from separate blood cultures strengthens evidence for true infection.

Treatment of Gastroenteritis

Specific antimicrobial therapy is usually not required for uncomplicated B. cereus gastroenteritis.

The illness is generally self-limited.

Management includes:

• Oral fluid replacement

• Electrolyte replacement

• Antiemetics when necessary

• Intravenous fluids for severe dehydration

Antibiotics do not meaningfully shorten uncomplicated toxin-mediated food poisoning.

Treatment of Invasive Disease

For serious systemic infection, vancomycin is commonly active and may be used empirically.

The source regimen emphasizes:

Vancomycin ± an aminoglycoside

Combination therapy may be considered in severe infections such as endocarditis or persistent bacteremia.

Definitive therapy should be guided by culture and antimicrobial susceptibility testing.

Additional Antimicrobial Options

Depending on susceptibility, potentially active agents include:

• Imipenem

• Ciprofloxacin

• Tetracyclines

• Clindamycin

• Macrolides

Therapy should be individualized according to the site and severity of infection.

Beta-Lactam Resistance

An important microbiologic feature of B. cereus is resistance to many beta-lactam antibiotics.

This occurs because the organism produces beta-lactamases.

Therefore, drugs such as penicillin and many cephalosporins should not be assumed to be effective against invasive B. cereus infection.

Source Control

In device-associated disease, antibiotics alone may not be sufficient.

Management may require:

• Removal of an infected catheter

• Drainage of abscesses

• Surgical debridement

• Ophthalmologic surgery for severe ocular infection

Source control is especially important in persistent bacteremia.

Prevention

Food poisoning can be reduced by proper food handling.

Important measures include:

• Refrigerate cooked foods promptly

• Avoid leaving cooked rice at room temperature for prolonged periods

• Reheat food thoroughly

• Store meat and vegetables safely

• Maintain proper food-preparation hygiene

Because Bacillus spores can survive cooking, preventing post-cooking bacterial growth is especially important.

High-Yield Food Poisoning Pattern

Emetic form

Reheated rice

• ●

Vomiting

• ●

1–6 hour incubation

→ Bacillus cereus

Diarrheal form

Meat or vegetables

• ●

Watery diarrhea and abdominal cramps

• ●

6–24 hour incubation

→ Bacillus cereus

Exam Essentials

Genus:

→ Bacillus

Microbiology:

→ Aerobic Gram-positive bacillus

Important non-anthrax species:

→ B. cereus

Classic food poisoning organism:

→ B. cereus

Emetic incubation:

→ 1–6 hours

Emetic classic food:

→ Rice

Diarrheal incubation:

→ 6–24 hours

Diarrheal foods:

→ Meat and vegetables

Treatment of uncomplicated gastroenteritis:

→ Supportive care only

Major invasive infections:

→ Bacteremia, endocarditis, meningitis, brain abscess, pneumonia, soft-tissue and ocular infection

Important bacteremia risk:

→ IV drug use or intravascular catheter

Diagnosis:

→ Culture

Empiric treatment of serious infection:

→ Vancomycin, sometimes with an aminoglycoside

Other possible agents:

→ Imipenem, ciprofloxacin, tetracycline, clindamycin, macrolides

Important resistance:

→ B. cereus is resistant to many beta-lactam antibiotics

Major preventive measure:

→ Proper food handling and refrigeration

Key distinction:

B. cereus + rice + rapid vomiting → emetic syndrome

B. cereus + meat/vegetables + later watery diarrhea → diarrheal syndrome

Infectious Disease and Microbiology - Aureobasidium Species

Basics

Aureobasidium is a genus of uncommon environmental fungi that can occasionally cause opportunistic infection in humans. The principal species associated with disease are Aureobasidium pullulans and Aureobasidium mansoni.

These organisms are especially important in immunocompromised patients and in individuals undergoing peritoneal dialysis.

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Microbiologic Characteristics

Aureobasidium species are dematiaceous filamentous fungi, meaning that they contain dark melanin pigment within their cell walls.

In human tissue they may appear in several different forms, including:

• Yeast-like cells

• Pseudohyphae

• Pigmented septate hyphae

In culture, particularly around 30°C, the organism grows predominantly in a hyphal form.

This variable morphology can make recognition more difficult unless a fungal infection is specifically considered.

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Epidemiology

Aureobasidium has a worldwide distribution, but human infection is rare.

The organisms are environmental molds and are generally considered opportunistic pathogens rather than common causes of disease.

Clinically significant infection is more likely in patients with:

• Immunosuppression

• Chronic debilitating illness

• Indwelling medical devices

• Peritoneal dialysis catheters

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Phaeohyphomycosis

Aureobasidium can cause phaeohyphomycosis, a broad category of infection produced by darkly pigmented fungi.

Disease occurs particularly in immunocompromised individuals.

Possible manifestations include:

• Cutaneous lesions

• Subcutaneous nodules

• Localized soft-tissue infection

• Occasionally deeper or disseminated disease

The appearance of pigmented fungal elements in tissue supports the diagnosis of a dematiaceous fungal infection.

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Peritoneal Dialysis-Associated Peritonitis

One of the more important clinical associations is peritonitis in patients receiving peritoneal dialysis.

Patients may develop:

• Abdominal pain

• Fever

• Cloudy dialysis fluid

• Nausea

• Peritoneal irritation

Fungal peritonitis should always be regarded as a serious complication because persistent infection can occur if the dialysis catheter remains in place.

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Diagnosis

Diagnosis is based primarily on:

• Fungal culture

• Histopathologic examination of tissue

In suspected peritonitis, peritoneal dialysis fluid should be submitted for fungal culture.

In localized tissue disease, biopsy may reveal pigmented fungal forms.

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Histopathology

Tissue specimens may show:

• Pigmented septate hyphae

• Pseudohyphae

• Yeast-like fungal elements

Special fungal stains can improve visualization.

Because Aureobasidium is an environmental organism, isolation from a nonsterile specimen must be interpreted carefully. Demonstration of fungal invasion in tissue or recovery from a normally sterile site strongly supports true infection.

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Differential Diagnosis

The differential diagnosis includes other dematiaceous fungi capable of producing phaeohyphomycosis, such as:

• Alternaria

• Cladophialophora

• Exophiala

• Curvularia

• Other pigmented molds

In peritoneal dialysis-associated peritonitis, other fungal pathogens such as Candida must also be considered.

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Treatment

Amphotericin B

There are limited clinical data defining the optimal treatment of Aureobasidium infection.

Amphotericin B has historically been considered a potentially effective therapy, particularly for invasive or serious disease.

Treatment should be individualized according to:

• Site of infection

• Severity

• Host immune status

• Culture and susceptibility results when available

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Peritoneal Dialysis Catheter Removal

For Aureobasidium peritonitis related to peritoneal dialysis, removal of the infected dialysis catheter is an important part of management.

Catheter removal helps eliminate the persistent source of fungal infection and generally improves the likelihood of successful treatment.

Antifungal therapy without source control may be inadequate.

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Azoles

Older data do not clearly establish the clinical effectiveness of azole antifungals against Aureobasidium.

Therefore, azoles should not automatically be assumed to be effective solely on the basis of the organism’s fungal classification.

If an azole is being considered, susceptibility testing and expert guidance are helpful.

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Source Control

When infection is associated with a foreign body or catheter, management should include evaluation for removal whenever feasible.

Potential source-control measures include:

• Removal of a peritoneal dialysis catheter

• Drainage of localized collections

• Debridement of infected tissue

• Reduction of immunosuppression when medically possible

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Prognosis

Localized disease may respond well when recognized early and managed with appropriate antifungal therapy and source control.

Prognosis is less favorable when infection is:

• Disseminated

• Deeply invasive

• Associated with severe immunosuppression

• Persistent because an infected device remains in place

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High-Yield Clinical Pattern

Immunocompromised patient

Pigmented fungal elements in tissue

Cutaneous or subcutaneous infection

→ Consider phaeohyphomycosis due to a dematiaceous fungus such as Aureobasidium.

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High-Yield Dialysis Pattern

Peritoneal dialysis patient

Abdominal pain

Cloudy dialysis fluid

Dematiaceous fungus in culture

→ Think fungal peritonitis, with Aureobasidium as a rare possibility.

Management often requires:

Antifungal therapy + dialysis catheter removal

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Exam Essentials

Genus:

→ Aureobasidium

Important species:

→ A. pullulans and A. mansoni

Organism type:

→ Dematiaceous filamentous fungus

Forms seen in tissue:

→ Yeasts, pseudohyphae, and pigmented septate hyphae

Distribution:

→ Worldwide

Frequency:

→ Rare human pathogen

Major infection:

→ Phaeohyphomycosis

Important risk group:

→ Immunocompromised patients

Important healthcare-associated infection:

→ Peritoneal dialysis-associated peritonitis

Diagnosis:

→ Culture and tissue biopsy

Historically useful antifungal:

→ Amphotericin B

Critical management step in dialysis-associated peritonitis:

→ Removal of the peritoneal dialysis catheter

Azoles:

→ Clinical efficacy not well established

Key clinical pearl: In fungal peritonitis related to peritoneal dialysis, source control is essential; removing the infected catheter can be as important as the antifungal therapy itself.

Infectious Disease and Microbiology - Ascaris lumbricoides

Basics

Ascaris lumbricoides is a large intestinal nematode, or roundworm, that causes ascariasis. Adult worms are among the largest intestinal helminths infecting humans and usually measure about 15–35 cm in length.

Ascariasis is one of the most common helminthic infections worldwide and is especially prevalent in tropical and developing regions where sanitation is inadequate.

Microbiologic Characteristics

Ascaris lumbricoides is a nematode helminth.

Its life cycle involves ingestion of embryonated eggs, larval migration through the lungs, and eventual maturation of adult worms within the small intestine.

Adult worms may survive for a prolonged period in the gastrointestinal tract.

Life Cycle and Incubation

The life cycle takes approximately 4–8 weeks.

After embryonated eggs are swallowed, larvae hatch in the intestine and penetrate the intestinal wall. They then enter the bloodstream and migrate through the liver to the lungs.

From the pulmonary circulation, the larvae enter the alveoli, ascend the bronchial tree, are swallowed, and return to the small intestine, where they mature into adult worms.

Eggs usually become detectable in feces approximately 2 months after ingestion of infective eggs.

Transmission

Transmission occurs by the fecal–oral route.

Humans become infected by ingesting embryonated eggs from:

• Contaminated soil

• Contaminated food

• Unwashed vegetables

• Dirty hands

• Fecally contaminated environments

Hand-to-mouth transmission is particularly important in children.

Epidemiology

Ascariasis is extremely common worldwide.

Approximately 1 billion people have historically been estimated to be infected.

The highest prevalence occurs in:

• Tropical regions

• Subtropical areas

• Developing countries

• Communities with poor sanitation

• Areas where human feces contaminate soil

Children are especially vulnerable because of frequent contact with contaminated soil and poorer hand hygiene.

Clinical Manifestations

Many infections are asymptomatic, particularly when the worm burden is low.

Disease manifestations depend on the stage of infection and number of worms present.

The two major clinical phases are:

Larval pulmonary migration

and

Adult intestinal infection

Pulmonary Phase

During larval migration through the lungs, patients may develop a transient eosinophilic pneumonitis known as Löffler syndrome.

Symptoms may include:

• Dry cough

• Wheezing

• Shortness of breath

• Fever

• Chest discomfort

• Occasionally hemoptysis

Pulmonary Findings

Imaging may reveal transient or migrating pulmonary infiltrates.

Laboratory testing frequently demonstrates:

Peripheral eosinophilia

This is most prominent during the tissue-migration phase.

High-Yield Pulmonary Pattern

Recent helminth exposure

• ●

Cough or wheezing

• ●

Transient pulmonary infiltrates

• ●

Eosinophilia

→ Think larval migration from Ascaris or another tissue-migrating helminth.

Intestinal Ascariasis

Once the worms mature in the small intestine, patients may develop gastrointestinal symptoms.

Possible manifestations include:

• Abdominal discomfort

• Cramping

• Nausea

• Poor appetite

• Intermittent diarrhea

• Abdominal distention

Many patients remain asymptomatic despite harboring adult worms.

Intestinal Obstruction

Heavy worm burdens can form a large mass within the intestine and cause mechanical obstruction.

This is particularly important in children.

Clinical features may include:

• Severe colicky abdominal pain

• Vomiting

• Abdominal distention

• Failure to pass stool or flatus

• Signs of complete or partial intestinal obstruction

In severe cases, surgical evaluation may be required.

Biliary Tract Disease

Adult worms can migrate from the intestine into the biliary system.

Possible complications include:

• Biliary obstruction

• Biliary colic

• Cholangitis

• Cholecystitis

• Pancreatitis

Migration into the biliary tree is an important complication of adult ascariasis.

Nutritional Effects

Heavy chronic infection can interfere with nutrition.

Possible consequences include:

• Reduced nutrient absorption

• Poor weight gain

• Growth impairment in children

• Protein-calorie malnutrition in severe cases

The impact is greatest in patients who already have limited nutritional reserves.

Eosinophilia

Peripheral eosinophilia is most prominent during larval tissue migration.

Once adult worms are confined to the intestinal lumen, eosinophilia may decrease or disappear.

Therefore:

Pulmonary phase → eosinophilia more likely

Chronic intestinal phase → eosinophilia may be minimal or absent

Diagnosis

Stool Examination

The standard diagnosis of intestinal ascariasis is made by detecting characteristic eggs on stool microscopy.

A concentrated stool examination improves sensitivity.

Eggs may be:

• Fertilized

• Unfertilized

The presence of characteristic Ascaris eggs confirms intestinal infection.

Important Timing Point

Stool microscopy may be negative early in infection because adult female worms have not yet matured and begun producing eggs.

Eggs typically appear in feces about:

2 months after infection

Therefore, early pulmonary ascariasis may occur before stool microscopy becomes positive.

Imaging

Imaging may be useful when complications are suspected.

Possible studies include:

• Abdominal x-ray for obstruction

• Ultrasound for biliary ascariasis

• CT when complications are unclear

• Chest x-ray during the pulmonary migration phase

Ultrasound may sometimes directly demonstrate worms within the biliary tract.

Differential Diagnosis

Pulmonary manifestations may resemble:

• Strongyloidiasis

• Hookworm migration

• Tropical pulmonary eosinophilia

• Asthma

• Bacterial or viral pneumonia

Intestinal disease may resemble:

• Other helminthic infections

• Mechanical bowel obstruction

• Appendicitis

• Gastroenteritis

• Biliary tract disease

Treatment

Albendazole

A standard regimen is:

Albendazole 400 mg orally as a single dose

This is widely used because of its simplicity and high efficacy.

Mebendazole

The source regimens include:

Mebendazole 100 mg orally every 12 hours for 3 days

or

Mebendazole 500 mg orally as a single dose

Both are effective against uncomplicated intestinal ascariasis.

Pyrantel Pamoate

Another option is:

Pyrantel pamoate 11 mg/kg orally as a single dose

Maximum dose:

1 g

Ivermectin

Ivermectin may also be effective.

The source regimen is:

150–200 μg/kg orally as a single dose

Nitazoxanide

An additional option described in the source is:

Nitazoxanide 500 mg orally every 12 hours for 3 days

Its role is generally less prominent than albendazole or mebendazole.

Management of Intestinal Obstruction

Anthelmintic treatment alone may not be sufficient in patients with complete obstruction.

Management may include:

• Intravenous fluids

• Nasogastric decompression

• Electrolyte correction

• Bowel rest

• Surgical consultation

Surgery may be required if obstruction does not resolve or if ischemia, perforation, or another complication develops.

Management of Biliary Ascariasis

Biliary disease may require:

• Supportive care

• Anthelmintic therapy

• Endoscopic intervention

• Surgical management in selected cases

Endoscopic removal may be necessary if a worm causes persistent biliary obstruction or pancreatitis.

Prevention

Prevention depends on interrupting fecal contamination of soil and food.

Important measures include:

• Hand washing after defecation and before eating

• Proper disposal of human feces

• Improved sanitation

• Washing fruits and vegetables thoroughly

• Avoiding ingestion of contaminated soil

• Community deworming programs in highly endemic areas

Prognosis

Most uncomplicated infections respond well to treatment.

The prognosis is generally excellent when complications are absent.

Heavy infections may become serious because of:

• Intestinal obstruction

• Biliary obstruction

• Pancreatitis

• Malnutrition

• Rare perforation or other mechanical complications

High-Yield Life Cycle

Embryonated egg ingested

→ Larva hatches in intestine

→ Penetrates bowel wall

→ Bloodstream migration

→ Liver

→ Lungs

→ Alveoli

→ Ascends bronchial tree

→ Swallowed

→ Returns to small intestine

→ Adult worm

→ Eggs passed in stool

High-Yield Clinical Pattern

Child from an endemic area

• ●

Abdominal pain

• ●

Possible bowel obstruction

• ●

Large roundworms

→ Think ascariasis

High-Yield Pulmonary Pattern

Eosinophilia

• ●

Transient pulmonary infiltrates

• ●

Cough/wheezing

→ Think Löffler syndrome from Ascaris larval migration

High-Yield Biliary Pattern

Patient with known or likely ascariasis

• ●

Biliary colic, cholangitis, or pancreatitis

→ Consider migration of an adult Ascaris worm into the biliary tree.

Exam Essentials

Organism:

→ Ascaris lumbricoides

Type:

→ Nematode helminth

Adult worm length:

→ Approximately 15–35 cm

Transmission:

→ Fecal–oral ingestion of embryonated eggs

Major geographic association:

→ Tropical and developing regions

Life cycle duration:

→ Approximately 4–8 weeks

Eggs detectable in stool:

→ Approximately 2 months after infection

Pulmonary syndrome:

→ Löffler syndrome

Key laboratory finding during migration:

→ Eosinophilia

Major intestinal complication:

→ Bowel obstruction

Important extraintestinal complication:

→ Biliary tract obstruction

Diagnosis:

→ Stool microscopy after concentration

First-line therapy:

→ Albendazole 400 mg single dose or mebendazole

Other options:

→ Pyrantel pamoate, ivermectin, nitazoxanide

Key distinction:

Larval phase → lungs + eosinophilia

Adult phase → intestine + obstruction/biliary disease

Infectious Disease and Microbiology - South American Arenavirus Group

Basics

The South American arenavirus group consists of several closely related viruses responsible for severe viral hemorrhagic fever syndromes in South America. These viruses belong to the Tacaribe complex of arenaviruses and are related to the viruses responsible for Lassa fever and lymphocytic choriomeningitis.

Important viruses include:

• Junín virus — Argentine hemorrhagic fever

• Machupo virus — Bolivian hemorrhagic fever

• Guanarito virus — Venezuelan hemorrhagic fever

• Sabiá virus — Brazilian hemorrhagic fever

⸻

Microbiologic Characteristics

These pathogens are members of the arenavirus group and belong to the South American or Tacaribe complex.

Arenaviruses are enveloped RNA viruses maintained primarily in rodent reservoirs. Human infection usually occurs after exposure to infected rodents or material contaminated by their secretions or excreta.

They are related to:

• Lassa virus

• Lymphocytic choriomeningitis virus

⸻

Incubation Period

The usual incubation period is approximately:

7–16 days

Symptoms subsequently develop as an acute systemic febrile illness.

⸻

Epidemiology

South American arenavirus infections occur primarily in specific endemic regions of South America, where sporadic cases and occasional outbreaks have been reported.

Each virus is geographically associated with the hemorrhagic fever syndrome reflected in its name:

• Junín virus → Argentina

• Machupo virus → Bolivia

• Guanarito virus → Venezuela

• Sabiá virus → Brazil

Rodents serve as the principal natural reservoirs.

⸻

Transmission

The major route of human infection is exposure to infected rodent excreta or secretions.

Transmission commonly occurs through inhalation of small aerosolized particles contaminated with:

• Rodent urine

• Feces

• Saliva

Direct person-to-person transmission can occur with some arenaviruses but is considerably less common than rodent-associated transmission.

⸻

Clinical Presentation

South American arenavirus infections typically begin as an acute systemic febrile illness.

Common early manifestations include:

• Fever

• Severe headache

• Retro-orbital pain

• Profuse sweating

• Conjunctival injection

• Myalgias

• Malaise

• Marked weakness and prostration

The early illness may initially resemble several other systemic viral infections.

⸻

Severe Disease

Progressive infection can produce a potentially fatal hemorrhagic fever syndrome.

Severe manifestations may include:

• Hemorrhage

• Central nervous system dysfunction

• Bradycardia

• Hypotension

• Circulatory instability

Neurologic manifestations may become particularly prominent in severe disease.

⸻

Hemorrhagic Manifestations

Bleeding abnormalities may develop as the illness progresses.

Possible manifestations include:

• Petechiae

• Ecchymoses

• Mucosal bleeding

• Gastrointestinal bleeding

• Other manifestations of systemic hemorrhage

Hemorrhagic manifestations indicate severe systemic disease and require intensive supportive management.

⸻

Central Nervous System Involvement

Severe South American arenavirus infections can involve the CNS.

Patients may develop:

• Altered mental status

• Tremor

• Neurologic dysfunction

• Seizures or other severe neurologic manifestations

The combination of hemorrhage, neurologic abnormalities, and cardiovascular instability suggests advanced disease.

⸻

Diagnosis

Because these infections are uncommon and potentially dangerous, diagnosis requires specialized laboratory testing and appropriate biosafety precautions.

Viral Detection

Diagnosis may be established through:

• Detection of viral nucleic acid by molecular methods such as RT-PCR

• Detection of viral antigen in blood or affected tissues

• Virus isolation in appropriately equipped specialized laboratories

Routine clinical laboratories generally should not attempt viral culture when a highly pathogenic arenavirus is suspected.

⸻

Serology

Serologic testing can demonstrate antibodies directed against the causative arenavirus.

Testing may include detection of:

• Virus-specific IgM

• Rising virus-specific antibody titers

Serology can therefore support the diagnosis when interpreted in conjunction with the clinical presentation and epidemiologic exposure.

⸻

Differential Diagnosis

South American arenavirus hemorrhagic fever should be distinguished from other causes of acute febrile or hemorrhagic illness, including:

• Dengue

• Yellow fever

• Lassa fever

• Other viral hemorrhagic fevers

• Severe malaria

• Leptospirosis

• Typhoid fever

• Meningococcemia

• Severe bacterial sepsis

The combination of appropriate South American exposure + rodent contact + acute fever + hemorrhagic or neurologic manifestations should raise suspicion for an arenavirus infection.

⸻

Treatment

Supportive Care

Management primarily requires careful supportive treatment.

Depending on severity, patients may require:

• Intravenous fluid and electrolyte management

• Hemodynamic support

• Management of bleeding

• Respiratory support

• Treatment of shock

• Intensive monitoring for neurologic and cardiovascular complications

⸻

Ribavirin

Historically, ribavirin has been used for South American arenavirus hemorrhagic fevers, although the quality and extent of clinical evidence vary substantially by virus.

Because these are rare, severe infections, antiviral treatment should be directed with expert infectious-disease and public-health consultation rather than assuming that the same regimen is established for all four viruses.

⸻

Argentine Hemorrhagic Fever

For Junín virus infection, early administration of immune plasma containing neutralizing antibodies has historically demonstrated substantial benefit.

Treatment is most effective when administered early in the course of illness, particularly within approximately the first 8 days after symptom onset.

This is a distinctive therapeutic feature of Argentine hemorrhagic fever.

⸻

Prevention

Rodent Control

Prevention centers on minimizing human exposure to infected rodents and their excreta.

Important measures include:

• Controlling rodent populations

• Preventing rodents from entering homes and workplaces

• Protecting stored food from rodent contamination

• Avoiding direct contact with rodent urine, feces, and saliva

• Safely cleaning rodent-contaminated environments

Because aerosolization can transmit infection, contaminated rodent material should not be swept or handled in a way that generates airborne particles.

⸻

Infection-Control Precautions

Patients with suspected South American arenavirus hemorrhagic fever require prompt isolation and rigorous infection-control precautions, particularly when hemorrhage or exposure to body fluids is possible.

Public-health and infectious-disease authorities should be involved promptly when a case is suspected.

⸻

Prognosis

These infections can be severe and potentially fatal.

Historically reported case-fatality rates for South American arenavirus hemorrhagic fevers have ranged approximately from:

10–30%

Mortality varies according to the specific virus, severity of disease, availability of supportive care, and access to effective early therapy.

⸻

High-Yield Clinical Pattern

South America + rodent exposure + acute fever + headache + retro-orbital pain + hemorrhage/CNS abnormalities

→ Think South American arenavirus hemorrhagic fever

Argentina

→ Junín virus

Bolivia

→ Machupo virus

Venezuela

→ Guanarito virus

Brazil

→ Sabiá virus

⸻

Exam Essentials

Virus group:

→ Arenaviruses

Complex:

→ Tacaribe complex

Major reservoir:

→ Rodents

Main transmission:

→ Inhalation or exposure to material contaminated by rodent excreta or secretions

Incubation period:

→ 7–16 days

Typical early illness:

→ Fever + headache + retro-orbital pain + myalgias + malaise

Severe manifestations:

→ Hemorrhage + CNS dysfunction + hypotension

Argentine hemorrhagic fever:

→ Junín virus

Bolivian hemorrhagic fever:

→ Machupo virus

Venezuelan hemorrhagic fever:

→ Guanarito virus

Brazilian hemorrhagic fever:

→ Sabiá virus

Important historical treatment for Junín virus:

→ Early immune plasma

Major preventive strategy:

→ Rodent control and avoidance of contaminated rodent excreta

Key clinical pearl: The combination of a compatible South American exposure, rodent contact, acute febrile illness, and subsequent hemorrhagic or neurologic manifestations should immediately raise concern for a South American arenavirus hemorrhagic fever.

Infectious Disease and Microbiology - Arcanobacterium Species

Basics

Arcanobacterium species are uncommon Gram-positive bacteria capable of causing human infections. The most clinically important species is Arcanobacterium haemolyticum, which is particularly associated with acute pharyngitis accompanied by a characteristic skin rash.

Important species include A. haemolyticum, A. pyogenes, and A. bernardiae.

Microbiologic Characteristics

Arcanobacterium species are aerobic, Gram-positive bacilli. They may be overlooked in routine cultures because infections are relatively uncommon and their clinical presentation can resemble more familiar bacterial illnesses.

Epidemiology

Arcanobacterium infections have been reported worldwide but remain relatively rare.

The incubation period is not clearly established.

Infections

Pharyngitis

Pharyngitis is the classic clinical manifestation of A. haemolyticum infection.

Patients may develop:

• Sore throat

• Pharyngeal erythema

• Fever

• Cervical lymphadenopathy

• General constitutional symptoms

An important distinguishing feature is the development of an erythematous rash in approximately half of affected patients.

The eruption may have a:

• Morbilliform appearance, resembling measles

or

• Scarlatiniform appearance, resembling the rash of scarlet fever

Because of this presentation, A. haemolyticum pharyngitis can easily be confused with group A streptococcal pharyngitis and scarlet fever.

Endocarditis

Although uncommon, A. haemolyticum can cause invasive infection, including infective endocarditis.

Possible manifestations include prolonged fever, constitutional symptoms, a new or changing cardiac murmur, and other complications associated with bloodstream infection.

Diagnosis

Diagnosis is established primarily by bacterial culture.

When Arcanobacterium infection is suspected, appropriate clinical specimens should be obtained depending on the presentation.

For pharyngitis:

→ Throat culture

For suspected invasive infection:

→ Blood cultures and other appropriate specimens

Because the organism may not initially be suspected, communication with the microbiology laboratory can be useful.

Differential Diagnosis

The differential diagnosis of A. haemolyticum pharyngitis includes:

• Group A streptococcal pharyngitis

• Scarlet fever

• Infectious mononucleosis

• Viral pharyngitis

• Diphtheria

• Other bacterial causes of pharyngitis

The combination of pharyngitis plus a morbilliform or scarlatiniform rash is an important diagnostic clue.

Treatment

Macrolides

Macrolide antibiotics are important treatment options.

Examples include:

• Erythromycin

• Azithromycin

These agents are particularly useful for A. haemolyticum pharyngitis when the organism is susceptible.

Additional Treatment

Other potentially active agents include:

• Clindamycin

• Tetracyclines

Treatment of serious invasive disease, such as endocarditis, should be guided by antimicrobial susceptibility testing and the site and severity of infection.

Prognosis

Most uncomplicated cases of pharyngitis respond well to appropriate antimicrobial therapy.

Invasive infections are uncommon but potentially serious and require more intensive evaluation and treatment.

High-Yield Clinical Pattern

Pharyngitis + erythematous morbilliform or scarlatiniform rash

→ Think of Arcanobacterium haemolyticum, particularly when the presentation resembles streptococcal scarlet fever.

High-Yield Microbiology

Arcanobacterium:

→ Gram-positive bacillus

→ Aerobic

→ Worldwide distribution

→ Uncommon human pathogen

→ A. haemolyticum is the major species associated with pharyngitis

Exam Essentials

Genus:

→ Arcanobacterium

Important species:

→ A. haemolyticum

→ A. pyogenes

→ A. bernardiae

Microbiology:

→ Aerobic Gram-positive bacillus

Classic infection:

→ Pharyngitis

Characteristic associated finding:

→ Morbilliform or scarlatiniform rash

Frequency of rash:

→ Approximately 50% of cases

Important invasive complication:

→ Endocarditis

Diagnosis:

→ Culture

Main treatment options:

→ Erythromycin or azithromycin

Alternatives:

→ Clindamycin or tetracycline

Key clinical pearl: A. haemolyticum should be considered in a patient with acute pharyngitis and a scarlet fever-like rash, especially when routine testing for more common causes does not explain the illness.

Infectious Disease and Microbiology - Apophysomyces elegans

Basics

Apophysomyces elegans is a rare environmental mold that can cause mucormycosis in humans. Unlike many other fungi responsible for mucormycosis, Apophysomyces is notable because severe infection can occur even in previously healthy, immunocompetent individuals.

The organism is especially associated with traumatic inoculation of soil-contaminated wounds, followed by rapidly progressive soft-tissue infection.

⸻

Microbiologic Characteristics

Apophysomyces elegans is a filamentous fungus belonging to the molds.

Characteristic features include:

• Broad hyphae

• Hyaline appearance

• Predominantly nonseptate or sparsely septate hyphae

• Branching filamentous morphology

These features are typical of fungi that cause mucormycosis.

⸻

Epidemiology

Human infection is rare but has been reported worldwide.

Unlike classic mucormycosis caused by organisms such as Rhizopus or Mucor, which frequently occurs in patients with diabetes, neutropenia, or severe immunosuppression, Apophysomyces infection may develop after traumatic exposure in otherwise healthy people.

A common epidemiologic clue is:

Trauma + soil contamination + rapidly progressive soft-tissue infection

⸻

Transmission

Infection generally occurs through direct inoculation of fungal spores into damaged tissue.

Important settings include:

• Traumatic wounds

• Soil-contaminated injuries

• Burns

• Motor vehicle or agricultural trauma

• Penetrating injuries

• Natural disasters with heavily contaminated wounds

After entering tissue, the fungus can invade blood vessels and spread rapidly through adjacent soft tissues.

⸻

Pathogenesis

Like other causes of mucormycosis, Apophysomyces has a strong tendency toward angioinvasion.

The fungus invades blood vessel walls, producing:

• Vascular thrombosis

• Tissue ischemia

• Infarction

• Necrosis

• Rapid progression of infection

This explains the characteristic black or necrotic appearance that may develop in severely infected tissue.

⸻

Cutaneous and Soft-Tissue Infection

The most characteristic manifestation is invasive infection of the skin and underlying soft tissues following trauma.

Early manifestations may include:

• Pain

• Swelling

• Erythema

• Local warmth

• Wound drainage

Disease may then progress rapidly to:

• Bullae

• Skin discoloration

• Necrosis

• Extensive tissue destruction

Because early disease can resemble ordinary bacterial cellulitis, diagnosis may be delayed.

⸻

Necrotizing Fasciitis

Apophysomyces elegans can cause fulminant necrotizing fasciitis.

Clinical warning signs include:

• Severe pain out of proportion to examination

• Rapidly spreading edema

• Dusky or violaceous skin

• Bullae

• Necrosis

• Fever and systemic toxicity

• Hypotension or shock in advanced disease

This is a surgical emergency.

⸻

Burn and Wound Infection

Burns and heavily contaminated wounds provide a portal of entry for the fungus.

The organism may invade deeply into:

• Subcutaneous tissue

• Fascia

• Muscle

• Blood vessels

Progression can occur despite antibacterial therapy because antibacterial drugs have no activity against the fungus.

⸻

Wound Infection With Secondary Spread

A localized traumatic infection may extend into surrounding tissues or disseminate.

Potential progression includes:

Skin

→ Subcutaneous tissue

→ Fascia

→ Muscle

→ Bone

→ Bloodstream and distant organs

Early source control is therefore essential.

⸻

Osteomyelitis

Bone involvement can occur by direct extension from a deep soft-tissue infection or contaminated traumatic wound.

Possible manifestations include:

• Persistent focal pain

• Swelling

• Chronic drainage

• Destructive bone changes on imaging

• Poor wound healing

Treatment generally requires prolonged antifungal therapy together with surgical debridement of infected bone.

⸻

Diagnosis

Diagnosis requires a high index of suspicion.

The main diagnostic methods are:

• Fungal culture

• Histopathologic examination of tissue

Deep tissue specimens are preferable to superficial swabs.

⸻

Histopathology

Tissue biopsy may demonstrate broad, ribbon-like, nonseptate or sparsely septate hyphae invading tissue.

A particularly important finding is:

Fungal invasion of blood vessels

This supports invasive mucormycosis and explains the associated tissue necrosis.

Special fungal stains may help highlight the organism.

⸻

Culture

Culture can identify Apophysomyces species, although recovery and sporulation may sometimes be difficult under routine laboratory conditions.

The microbiology laboratory should be informed when mucormycosis is suspected so specimens can be processed appropriately.

⸻

Differential Diagnosis

The clinical presentation may resemble:

• Bacterial necrotizing fasciitis

• Clostridial myonecrosis

• Severe cellulitis

• Aspergillus infection

• Other mucormycetes such as Rhizopus or Mucor

• Fusariosis

• Traumatic wound necrosis

Failure to improve with broad-spectrum antibacterial therapy should increase suspicion for an invasive fungal process.

⸻

Treatment

Amphotericin B

Amphotericin B is the major antifungal treatment for invasive Apophysomyces infection.

For severe mucormycosis, lipid formulations of amphotericin B are generally favored in current practice because they allow high-dose therapy with less nephrotoxicity than conventional amphotericin B deoxycholate.

Treatment is often prolonged and guided by:

• Clinical response

• Extent of disease

• Surgical source control

• Immune status

• Radiologic improvement

⸻

Surgical Debridement

Although the original source emphasizes amphotericin B, effective treatment of invasive soft-tissue mucormycosis usually requires aggressive surgery in addition to antifungal therapy.

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

Therefore, management often requires:

• Urgent exploration

• Wide excision of necrotic tissue

• Repeated debridement

• Removal of infected bone when necessary

In extensive disease, multiple operations may be required.

⸻

Azoles

Older data did not clearly establish the effectiveness of itraconazole or other azoles against Apophysomyces.

Itraconazole is not considered a reliable primary treatment for mucormycosis.

Newer agents with activity against many mucormycetes, particularly posaconazole and isavuconazole, may be considered in selected settings, often as step-down, salvage, or combination management depending on species susceptibility and clinical guidance.

⸻

Supportive Management

Severe infection may require:

• Intensive care

• Fluid resuscitation

• Vasopressor support

• Management of organ dysfunction

• Correction of metabolic abnormalities

• Treatment of concurrent bacterial infection when present

Prompt surgical and infectious-disease consultation is important.

⸻

Prognosis

Outcome depends strongly on how quickly the infection is recognized and treated.

Better outcomes are associated with:

• Early diagnosis

• Rapid initiation of effective antifungal therapy

• Aggressive surgical debridement

• Limited disease extent

Poor prognostic factors include delayed diagnosis, extensive tissue necrosis, vascular invasion, and dissemination.

⸻

Prevention

There is no vaccine.

Risk reduction includes:

• Immediate cleaning of soil-contaminated wounds

• Removal of foreign material

• Early debridement of devitalized tissue

• Careful monitoring of major traumatic wounds

• Prompt evaluation of rapidly worsening wounds despite antibacterial therapy

⸻

High-Yield Clinical Pattern

Previously healthy patient

Traumatic soil-contaminated wound

Rapidly progressive necrotizing soft-tissue infection

Broad nonseptate fungal hyphae

→ Think Apophysomyces mucormycosis.

⸻

High-Yield Microbiology

Apophysomyces elegans:

→ Filamentous mold

→ Hyaline

→ Broad, nonseptate or sparsely septate hyphae

→ Causes mucormycosis

⸻

High-Yield Distinction

Classic mucormycosis often occurs in:

→ Diabetic or severely immunocompromised patients

Apophysomyces mucormycosis can importantly occur in:

→ Immunocompetent patients after traumatic inoculation

⸻

Exam Essentials

Genus:

→ Apophysomyces

Important species:

→ A. elegans

Organism:

→ Filamentous fungus

Hyphae:

→ Broad, hyaline, nonseptate or sparsely septate

Major disease:

→ Mucormycosis

Classic exposure:

→ Soil-contaminated traumatic wound

Important host feature:

→ Can infect immunocompetent individuals

Major manifestations:

→ Wound infection, invasive soft-tissue disease, necrotizing fasciitis, osteomyelitis

Diagnosis:

→ Tissue biopsy and culture

First-line antifungal:

→ Amphotericin B, usually a lipid formulation for severe invasive disease

Critical additional management:

→ Aggressive surgical debridement

Older azole with uncertain efficacy:

→ Itraconazole

Key clinical pearl:

→ Rapid tissue necrosis after a contaminated wound should trigger urgent consideration of invasive mucormycosis, even in a healthy patient.

Infectious Disease and Microbiology - Anisakis Species

Basics

Anisakis is a genus of parasitic nematodes, or roundworms, that can infect humans after ingestion of raw or inadequately prepared marine seafood. Human infection is called anisakiasis.

Several Anisakis species can cause disease. Humans are accidental hosts, and the larvae do not usually mature into adult worms in the human gastrointestinal tract. Instead, disease results from larval penetration of the stomach or intestinal wall and the associated inflammatory response.

Microbiologic Characteristics

Anisakis species are nematode helminths.

The infective form for humans is the larval stage, which may be present in marine fish and cephalopods.

The larvae are usually several centimeters long and may be directly visualized during endoscopy.

Transmission

Humans acquire anisakiasis by eating:

• Raw saltwater fish

• Undercooked saltwater fish

• Raw squid

• Raw or inadequately treated octopus

• Smoked seafood that has not been adequately processed

• Marinated or salted seafood in which viable larvae remain

The important principle is that preservation methods such as salting, smoking, or marinating do not always reliably kill the larvae.

Epidemiology

Anisakiasis is particularly associated with regions where consumption of raw or lightly prepared seafood is common.

It has been reported frequently in:

• Japan

• Scandinavian countries

• The Netherlands

• Pacific coastal regions of Latin America

The number of recognized cases has also increased in the United States and Europe as raw seafood dishes have become more widely consumed.

Incubation Period

The timing of symptoms depends on the site of infection.

Gastric anisakiasis

Symptoms may begin within a few hours after ingestion of infected seafood.

Intestinal anisakiasis

Symptoms involving the small or large intestine may develop more slowly, usually over:

Several days to weeks

This difference in timing is clinically useful.

Gastric Anisakiasis

Clinical Presentation

Gastric anisakiasis occurs when an infective larva penetrates the gastric mucosa.

Typical symptoms include:

• Sudden or severe epigastric abdominal pain

• Nausea

• Vomiting

• Abdominal discomfort

Symptoms often begin relatively soon after eating raw or inadequately cooked seafood.

High-Yield Pattern

Raw seafood ingestion

• ●

Severe upper abdominal pain within hours

• ●

Nausea or vomiting

→ Think gastric anisakiasis.

Intestinal Anisakiasis

If the larva passes beyond the stomach and penetrates the intestinal wall, patients may develop intestinal disease.

Possible manifestations include:

• Lower abdominal pain

• Nausea

• Abdominal distention

• Localized tenderness

• Signs of bowel obstruction

• Inflammatory mass-like lesions

Because symptoms may develop days after the original meal, the connection to raw seafood exposure can easily be missed.

Intestinal Obstruction

Inflammation and edema around an embedded larva may narrow the intestinal lumen and produce partial or complete obstruction.

Clinical findings may include:

• Cramping abdominal pain

• Vomiting

• Abdominal distention

• Failure to pass stool or flatus

Severe cases may resemble appendicitis, Crohn disease, or other surgical abdominal disorders.

Oropharyngeal Disease

Occasionally, larvae may attach to the oropharynx shortly after contaminated seafood is eaten.

Patients may experience:

• Throat irritation

• Foreign-body sensation

• Cough

• Nausea

• Occasionally visible larval movement

Direct removal can be curative.

Allergic Manifestations

Anisakis can also provoke significant hypersensitivity reactions.

Some patients develop:

• Urticaria

• Angioedema

• Wheezing

• Anaphylaxis

These allergic manifestations may occur with or without obvious gastrointestinal invasion.

Therefore, sudden allergic symptoms after consumption of raw marine fish should raise consideration of Anisakis exposure.

Diagnosis

Diagnosis is based on a combination of:

• Recent ingestion of raw or inadequately treated marine seafood

• Compatible gastrointestinal symptoms

• Direct visualization of the larva

The most definitive finding is identification of an Anisakis larva attached to or penetrating gastrointestinal tissue.

Endoscopy

Upper gastrointestinal endoscopy is particularly valuable in gastric anisakiasis.

The larva may be seen:

• Attached to the gastric mucosa

• Partially penetrating the gastric wall

• Moving within the stomach

Direct visualization often establishes the diagnosis immediately.

Parasite Appearance

The larva is typically approximately a few centimeters in length.

The original description notes a larva of about 2 cm invading the oropharynx or stomach.

When visible, the organism can often be removed directly during endoscopy.

Laboratory Findings

Routine laboratory abnormalities are not always present.

Possible findings include:

• Peripheral eosinophilia

• Mild leukocytosis

• Elevated inflammatory markers

Eosinophilia may be absent early and therefore should not be required for diagnosis.

Imaging

In intestinal disease, CT imaging may show:

• Bowel-wall thickening

• Localized edema

• Inflammatory changes

• Ascites

• Evidence of obstruction

These findings are nonspecific but may support the diagnosis in a patient with appropriate dietary exposure.

Differential Diagnosis

Gastric anisakiasis may resemble:

• Peptic ulcer disease

• Gastritis

• Pancreatitis

• Gallbladder disease

• Food poisoning

Intestinal anisakiasis may resemble:

• Appendicitis

• Small-bowel obstruction

• Crohn disease

• Diverticulitis

• Intestinal tumor

• Other parasitic infections

A careful dietary history is therefore crucial.

Treatment

Endoscopic Removal

For gastric anisakiasis, the preferred treatment is:

Endoscopic removal of the larva

Removal usually produces rapid symptomatic improvement because the main cause of inflammation is eliminated.

Surgical Treatment

Surgical intervention may be necessary when patients develop:

• Intestinal obstruction

• Perforation

• Severe inflammatory mass

• Persistent disease not amenable to endoscopic treatment

Surgery allows both removal of the affected tissue and definitive diagnosis.

Albendazole

Albendazole has been used in some cases when endoscopic or surgical removal is not possible.

There may be clinical benefit, but the evidence is less robust than for mechanical removal.

Therefore, treatment should be individualized according to the location and severity of disease.

Supportive Care

Supportive treatment may include:

• Analgesics

• Antiemetics

• Intravenous or oral fluids

• Bowel rest in selected intestinal cases

• Management of obstruction if present

If an allergic reaction occurs, treatment should follow standard management for urticaria, angioedema, or anaphylaxis.

Prevention

Prevention depends on killing larvae before seafood is eaten.

Important measures include:

• Thorough cooking of marine fish and squid

• Proper commercial freezing procedures

• Avoiding raw or inadequately frozen seafood

• Recognizing that marinating, salting, or smoking alone may not reliably eliminate viable larvae

Safe food preparation is the most effective preventive strategy.

High-Yield Gastric Pattern

Raw fish or squid

• ●

Severe epigastric pain within hours

• ●

Larva seen on endoscopy

→ Gastric anisakiasis

High-Yield Intestinal Pattern

Raw seafood exposure

• ●

Delayed lower abdominal pain

• ●

Inflammatory bowel thickening or obstruction

→ Intestinal anisakiasis

High-Yield Allergy Pattern

Raw marine seafood

• ●

Urticaria, angioedema, or anaphylaxis

± abdominal symptoms

→ Consider Anisakis-associated hypersensitivity.

Exam Essentials

Organism:

→ Nematode helminth

Genus:

→ Anisakis

Major source:

→ Raw or inadequately prepared saltwater fish, squid, or octopus

Important geographic associations:

→ Japan, Scandinavia, the Netherlands, and Pacific Latin America

Gastric incubation:

→ A few hours

Intestinal symptoms:

→ Days to weeks

Gastric disease:

→ Epigastric pain, nausea, vomiting

Intestinal disease:

→ Lower abdominal pain and possible obstruction

Classic diagnosis:

→ Direct visualization of larva

Best treatment for gastric disease:

→ Endoscopic removal

Complicated intestinal disease:

→ Surgical treatment may be required

Possible medical therapy:

→ Albendazole

Important extra manifestation:

→ Allergic reactions, including anaphylaxis

Key distinction

Rapid upper abdominal symptoms after raw seafood → gastric anisakiasis

Delayed lower abdominal symptoms or obstruction → intestinal anisakiasis

Infectious Disease and Microbiology - Angiostrongylus Species

Basics

Angiostrongylus is a genus of parasitic nematodes, or roundworms, capable of causing important zoonotic infections in humans. The two major species associated with human disease are Angiostrongylus cantonensis and Angiostrongylus costaricensis.

The clinical syndromes are quite different:

A. cantonensis → neurologic disease, especially eosinophilic meningitis

A. costaricensis → abdominal and intestinal disease

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Microbiologic Characteristics

Angiostrongylus species are multicellular nematode helminths.

Humans are accidental hosts. Infection usually occurs after ingestion of infective larvae carried by intermediate or paratenic hosts.

Because the parasites generally cannot complete their normal life cycle in humans, disease results largely from larval migration and the accompanying inflammatory response.

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Angiostrongylus cantonensis

Epidemiology

A. cantonensis, commonly called the rat lungworm, has historically been associated particularly with:

• Southeast Asia

• Pacific islands

• South Pacific regions

However, its geographic distribution has expanded, and infections have been recognized outside these traditional endemic areas.

Rats serve as the definitive hosts, while snails and slugs are important intermediate hosts.

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Transmission

Humans usually acquire A. cantonensis by ingesting infective larvae.

Important exposures include:

• Raw or undercooked snails

• Slugs

• Contaminated raw vegetables

• Foods contaminated by small snails or slugs

• Certain raw or undercooked paratenic hosts

After ingestion, larvae migrate through tissues and may reach the central nervous system.

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Eosinophilic Meningitis

The classic manifestation of A. cantonensis infection is:

Eosinophilic meningitis or meningoencephalitis

The inflammatory response to migrating larvae within the central nervous system produces the characteristic clinical syndrome.

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Clinical Presentation

Patients may develop:

• Severe headache

• Neck stiffness

• Nausea and vomiting

• Paresthesias

• Hyperesthesia

• Cranial nerve abnormalities

• Weakness

• Fever, although it may be mild or absent

More severe infection can produce meningoencephalitis with significant neurologic dysfunction.

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High-Yield Feature

The most important diagnostic clue is:

Meningitis + eosinophilia + relevant food/travel exposure

This combination should strongly suggest A. cantonensis.

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Ocular Disease

Occasionally, larvae migrate into ocular structures.

Possible manifestations include:

• Keratitis

• Iritis

• Visual disturbances

• Ocular inflammation

• Blepharospasm

Direct visualization of a larva within the eye can occasionally establish the diagnosis.

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Diagnosis of A. cantonensis

Cerebrospinal Fluid

Lumbar puncture is important when eosinophilic meningitis is suspected.

CSF may demonstrate:

• Elevated opening pressure

• Pleocytosis

• Increased eosinophils

• Elevated protein

• Normal or reduced glucose

The defining clue is CSF eosinophilia in an appropriate clinical setting.

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Peripheral Blood

Peripheral eosinophilia may also occur and further supports the diagnosis.

However, neither peripheral nor CSF eosinophilia is completely specific for angiostrongyliasis.

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Serology

Serologic testing may support the diagnosis when available.

Molecular testing may also be available through specialized or reference laboratories.

Direct recovery of larvae from CSF is uncommon.

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Differential Diagnosis of Eosinophilic Meningitis

Other causes should be considered, including:

• Gnathostoma infection

• Neurocysticercosis

• Toxocariasis

• Certain fungal infections

• Drug reactions

• Malignancy

• Other parasitic infections involving the CNS

Exposure history is therefore extremely important.

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Treatment of A. cantonensis

Treatment is directed primarily at controlling the inflammatory response and relieving symptoms.

Corticosteroids

Corticosteroids can reduce headache and inflammation associated with eosinophilic meningitis.

The original source describes approximately:

14 days of corticosteroid therapy

The exact regimen should be individualized according to disease severity.

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Management of Increased Intracranial Pressure

Severe headache frequently results from elevated intracranial pressure.

Therapeutic lumbar punctures may provide substantial symptomatic relief when increased CSF pressure is present.

Supportive management also includes:

• Analgesia

• Hydration

• Antiemetics

• Neurologic monitoring

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Anthelmintic Therapy

Albendazole is sometimes used, generally together with corticosteroids.

Historically, the role of anthelmintic therapy was controversial because killing larvae within the CNS could theoretically intensify inflammation. Contemporary management may include albendazole in selected patients, particularly with concurrent corticosteroid therapy.

The benefit and optimal regimen depend on the clinical setting and available guidance.

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Angiostrongylus costaricensis

Epidemiology

A. costaricensis primarily causes disease in:

• Central America

• South America

It produces a syndrome known as abdominal angiostrongyliasis.

Rodents are important definitive hosts, while mollusks such as slugs and snails participate in transmission.

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Pathogenesis

After humans ingest infective larvae, the parasites migrate toward the intestinal and mesenteric vasculature.

The resulting inflammatory reaction can produce:

• Eosinophilic infiltration

• Granulomatous inflammation

• Vascular injury

• Bowel-wall thickening

• Intestinal masses

The ileocecal region is commonly affected.

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Abdominal Angiostrongyliasis

Clinical disease varies considerably.

Some infections may be asymptomatic or mild, whereas others produce substantial intestinal inflammation.

Patients may develop:

• Persistent abdominal pain

• Fever

• Nausea

• Vomiting

• Anorexia

• Abdominal tenderness

• Palpable abdominal mass

• Peripheral eosinophilia

Severe inflammation can mimic a surgical abdomen.

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Abdominal Masses

One of the characteristic manifestations of A. costaricensis infection is development of an inflammatory abdominal mass.

This may clinically resemble:

• Appendicitis

• Crohn disease

• Intestinal malignancy

• Intra-abdominal abscess

• Other inflammatory bowel disorders

Consequently, the diagnosis may not become apparent until surgical exploration or histopathologic examination.

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Diagnosis

Diagnosis can be challenging.

Depending on the clinical presentation, evaluation may include:

• Complete blood count demonstrating eosinophilia

• Serologic testing where available

• Abdominal imaging

• Histopathologic examination of surgically obtained tissue

Unlike ordinary intestinal helminths, routine stool microscopy is generally not useful because humans do not typically pass diagnostic eggs or larvae in stool.

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Treatment of A. costaricensis

Management depends on disease severity.

Surgical Management

Surgery may be necessary when patients develop:

• Large inflammatory masses

• Intestinal obstruction

• Bowel ischemia

• Perforation

• Severe localized disease mimicking an acute surgical abdomen

Resection can be both diagnostic and therapeutic.

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Anthelmintic Therapy

The older source describes thiabendazole therapy.

However, the benefit of anthelmintic treatment for abdominal angiostrongyliasis is uncertain, and antiparasitic treatment is not as clearly established as it is for many other intestinal nematode infections.

Management should therefore be individualized, particularly when significant intestinal inflammation or surgical complications are present.

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Prevention

Prevention primarily involves avoiding ingestion of infective larvae.

Important measures include:

• Avoid eating raw or undercooked snails and slugs.

• Wash raw vegetables thoroughly.

• Carefully inspect leafy vegetables for small snails or slugs.

• Wash hands after handling mollusks.

• Prevent contamination of food by snails and slugs.

• Use appropriate food hygiene in endemic regions.

Control of rat populations and environmental sanitation can also reduce transmission.

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A. cantonensis vs A. costaricensis

A. cantonensis

Main geographic association:

→ Southeast Asia and Pacific regions

Common name:

→ Rat lungworm

Major disease:

→ Eosinophilic meningitis/meningoencephalitis

Important clue:

→ Severe headache with CSF eosinophilia

Other manifestation:

→ Ocular angiostrongyliasis

Diagnosis:

→ CSF examination + exposure history ± serologic/molecular testing

Main treatment:

→ Corticosteroids and supportive management; albendazole may be considered in selected cases

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A. costaricensis

Main geographic association:

→ Central and South America

Major disease:

→ Abdominal angiostrongyliasis

Important clue:

→ Abdominal pain/mass + eosinophilia

Major site:

→ Intestinal and mesenteric tissues

Diagnosis:

→ Clinical findings, imaging, serology when available, and often histopathology

Treatment:

→ Supportive care; surgery for significant intestinal complications

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Exam Essentials

Organism:

→ Nematode helminth

Two important species:

→ A. cantonensis and A. costaricensis

A. cantonensis:

→ Eosinophilic meningitis

Classic exposure:

→ Raw/undercooked snails, slugs, or contaminated produce

Definitive host of A. cantonensis:

→ Rat

Important intermediate hosts:

→ Snails and slugs

Key laboratory finding:

→ CSF eosinophilia

Important treatment:

→ Corticosteroids

Severe headache with increased CSF pressure:

→ Therapeutic lumbar puncture may provide relief

A. costaricensis:

→ Abdominal angiostrongyliasis

Classic presentation:

→ Abdominal pain or inflammatory mass + eosinophilia

Major complication:

→ Severe intestinal inflammation, obstruction, ischemia, or perforation

Important treatment for complicated abdominal disease:

→ Surgical management

Most important distinction

A. cantonensis → brain/CNS → eosinophilic meningitis

A. costaricensis → bowel/abdomen → eosinophilic inflammatory abdominal disease

Infectious Disease and Microbiology - Ancylostoma

Basics

Ancylostoma is a genus of parasitic nematodes, or roundworms, that includes important human and animal hookworms. Human disease ranges from a localized pruritic skin eruption caused by migrating animal hookworm larvae to true intestinal hookworm infection associated with chronic blood loss and iron-deficiency anemia.

Important species include:

• Ancylostoma braziliense — primarily a hookworm of dogs and cats

• Ancylostoma ceylanicum — a zoonotic hookworm capable of establishing intestinal infection in humans

• Ancylostoma duodenale — one of the major human hookworms

Microbiologic Characteristics

Ancylostoma species are multicellular helminths belonging to the nematodes.

They have an elongated, cylindrical, unsegmented body and undergo several developmental stages:

Egg → larva → adult worm

The clinical manifestations depend strongly on the species and whether the larvae remain confined to the skin or mature into adult intestinal hookworms.

Epidemiology

Ancylostoma braziliense

A. braziliense occurs predominantly in tropical and subtropical regions.

Dogs and cats are its major hosts. Humans are accidental hosts, usually becoming infected when exposed skin comes into contact with soil or sand contaminated by animal feces.

This organism is an important cause of cutaneous larva migrans.

Ancylostoma ceylanicum

A. ceylanicum occurs particularly in Asia and the Pacific region and is an important zoonotic hookworm of dogs and cats.

Unlike A. braziliense, it can mature into an adult intestinal hookworm in humans.

Ancylostoma duodenale

A. duodenale has historically been prevalent in areas including:

• Mediterranean regions

• North Africa

• South and East Asia

• China

• Southeast Asia

• Parts of South America

• Pacific regions

It is an important cause of human intestinal hookworm disease.

Transmission

Infective hookworm larvae develop in warm, moist soil contaminated by feces.

A. braziliense

Humans typically acquire infection when bare skin contacts contaminated soil or sand.

Common exposure settings include:

• Beaches

• Sandboxes

• Moist soil

• Areas contaminated with dog or cat feces

Because humans are not the normal definitive host, the larvae generally cannot complete their life cycle. Instead, they migrate superficially through the epidermis.

A. duodenale

Infective larvae can penetrate human skin and eventually migrate to the intestine, where they mature into adult worms.

Oral acquisition can also occur with A. duodenale.

Cutaneous Larva Migrans

Clinical Presentation

A. braziliense is a classic cause of cutaneous larva migrans, also called creeping eruption.

After penetrating the skin, the larvae migrate within the superficial epidermis.

The characteristic lesion is:

Intensely pruritic + erythematous + serpiginous + progressively migrating skin track

The feet, legs, buttocks, and other areas exposed to contaminated sand or soil are commonly affected.

Appearance

The eruption usually consists of:

• Raised erythematous tracks

• Curved or serpiginous lesions

• Progressive extension of the track

• Marked pruritus

• Local inflammatory reaction

Scratching may result in excoriations and secondary bacterial infection.

High-Yield Clinical Clue

Recent tropical beach exposure

• ●

Barefoot contact with sand

• ●

Extremely itchy serpiginous migrating lesion

→ Think cutaneous larva migrans due to animal hookworm, classically A. braziliense.

Intestinal Hookworm Disease

Ancylostoma duodenale

A. duodenale produces true intestinal hookworm infection.

Adult worms attach to the mucosa of the small intestine and consume blood. Continued intestinal blood loss can eventually produce clinically significant iron deficiency.

Clinical Manifestations

Light infections may be asymptomatic.

More substantial infections can cause:

• Abdominal discomfort

• Dyspepsia

• Diarrhea

• Fatigue

• Weakness

• Iron-deficiency anemia

• Protein loss in severe infection

Heavy chronic infection is particularly important in patients with poor nutritional reserves.

Anemia

The most important systemic consequence of intestinal hookworm infection is chronic blood loss.

This may produce:

Iron-deficiency microcytic anemia

Patients may consequently develop:

• Pallor

• Fatigue

• Exercise intolerance

• Weakness

• Dyspnea with severe anemia

The severity depends largely on the intensity and duration of infection and the patient’s underlying iron stores.

Diagnosis

Intestinal Hookworm

Diagnosis is primarily established by detecting hookworm eggs on microscopic examination of stool.

Concentration techniques can increase diagnostic sensitivity, particularly when the parasite burden is low.

Because the eggs of different hookworm species may look very similar, routine stool microscopy may identify hookworm infection without reliably establishing the exact species.

Diagnosis of Cutaneous Larva Migrans

Cutaneous larva migrans is generally a clinical diagnosis based on:

Characteristic serpiginous lesion

• ●

Compatible exposure history

Routine stool examination is generally not useful for A. braziliense cutaneous larva migrans because the larvae do not normally mature into egg-producing adult worms in humans.

Treatment

Cutaneous Larva Migrans

Systemic antiparasitic therapy rapidly improves most cases.

Commonly used agents include:

Ivermectin

Ivermectin is often given as a short oral regimen and is highly effective for uncomplicated cutaneous larva migrans.

Albendazole

Albendazole is another effective treatment, particularly when lesions are multiple or extensive.

The source regimen lists:

Albendazole 400 mg orally every 12 hours for 3 days.

Exact dosing and duration may vary according to contemporary guidelines and the clinical situation.

Treatment of

A. duodenale

Intestinal hookworm infection is treated with an anthelmintic agent.

The source regimen lists:

Mebendazole 100 mg orally every 12 hours for 3 days.

Albendazole is also widely used for intestinal hookworm infection.

Additional Treatment

Pyrantel pamoate represents another potential treatment for intestinal hookworm.

More importantly, patients with significant anemia require correction of the consequences of chronic blood loss.

Management may therefore include:

• Oral iron replacement

• Nutritional rehabilitation

• Treatment of severe anemia when clinically necessary

Successful eradication of the parasite without correction of substantial iron deficiency may leave the patient symptomatic for some time.

Prevention

Prevention centers on interrupting contact with infective larvae and reducing environmental fecal contamination.

Important measures include:

• Wear footwear in areas where hookworm contamination may occur.

• Avoid sitting or lying directly on potentially contaminated sand or soil.

• Properly dispose of dog and cat feces.

• Regular veterinary care and deworming of pets can reduce environmental contamination.

• Improve sanitation and prevent human fecal contamination of soil in endemic regions.

A. braziliense

vs

A. duodenale

A. braziliense

Animal reservoir:

→ Dogs and cats

Human role:

→ Accidental host

Major disease:

→ Cutaneous larva migrans

Characteristic finding:

→ Intensely pruritic serpiginous skin tracks

Diagnosis:

→ Usually clinical

Treatment:

→ Ivermectin or albendazole

A. duodenale

Major host:

→ Humans

Major disease:

→ Intestinal hookworm infection

Characteristic complication:

→ Chronic intestinal blood loss

Classic laboratory consequence:

→ Iron-deficiency anemia

Diagnosis:

→ Hookworm eggs in stool

Treatment:

→ Albendazole or mebendazole

Exam Essentials

Organism:

→ Nematode helminth

Classic animal hookworm:

→ A. braziliense

Reservoir of A. braziliense:

→ Dogs and cats

Classic disease caused by A. braziliense:

→ Cutaneous larva migrans

Typical lesion:

→ Intensely pruritic, serpiginous, migrating skin track

Classic exposure:

→ Barefoot walking on contaminated tropical beach or soil

Major human intestinal species:

→ A. duodenale

Major complication of intestinal hookworm:

→ Iron-deficiency anemia from chronic intestinal blood loss

Diagnosis of intestinal infection:

→ Stool microscopy for hookworm eggs

Diagnosis of cutaneous larva migrans:

→ Usually clinical

Treatment of cutaneous larva migrans:

→ Ivermectin or albendazole

Treatment of intestinal hookworm:

→ Albendazole or mebendazole

Key distinction:

A. braziliense → skin disease

A. duodenale → intestinal disease + anemia