Infectious Disease and Microbiology – Dipylidium caninum

Overview

Dipylidium caninum is a cestode (tapeworm) helminth that primarily infects dogs and cats. Human infection is uncommon and occurs most frequently in young children, particularly toddlers, who accidentally acquire the parasite.

Most human infections are asymptomatic. A characteristic clue is the appearance of small, seed-like or rice-like proglottids in the stool or around the anus.

Microbiologic Characteristics

Dipylidium caninum is a cestode (tapeworm).

The adult tapeworm normally inhabits the intestinal tract of dogs and cats.

Humans are accidental hosts.

Epidemiology

Adult D. caninum worms occur in dogs and cats worldwide.

Human infection is rare but is reported most often in young children because of their close contact with household pets and greater likelihood of accidental ingestion of infected fleas.

Transmission

Human infection occurs through the accidental ingestion of an infected flea.

The flea serves as an intermediate host for the parasite.

Dogs and cats acquire infection in the same way when they ingest infected fleas during grooming.

Life Cycle

The simplified life cycle is:

Dog or cat → proglottids/eggs released into environment → flea larvae ingest eggs → cysticercoid develops in flea → infected flea swallowed → adult tapeworm develops in intestine

Humans, particularly toddlers, can accidentally enter this cycle by swallowing an infected flea.

Clinical Infection

Most infected humans are asymptomatic.

The most noticeable finding is often the passage of motile tapeworm segments rather than gastrointestinal illness.

Proglottids

Patients or parents may notice seed-like or rice-like proglottids:

• In the stool

• On the surface of freshly passed stool

• Around the anus

• Occasionally on clothing or bedding

Recognition of these characteristic segments is an important diagnostic clue.

Gastrointestinal Manifestations

In heavier infections, D. caninum may occasionally cause gastrointestinal symptoms.

These can include:

• Abdominal discomfort

• Abdominal pain

• Other nonspecific gastrointestinal complaints

Clinically significant symptoms are uncommon.

Diagnosis

Diagnosis is made through stool examination.

The characteristic findings are:

• Proglottids

• Parasite eggs or characteristic egg packets

Direct examination of the visible proglottids may be particularly helpful.

Treatment

The preferred treatment described in the source is:

Praziquantel 10–20 mg/kg orally as a single dose

Treatment is usually highly effective.

Alternative Treatment

An alternative treatment is:

Niclosamide 2 g orally as a single dose

Prevention

Because infection is acquired by swallowing an infected flea, prevention requires flea control in dogs and cats.

Important preventive measures include:

• Treating infected household pets

• Effective flea control

• Preventing recurrent flea infestation

• Appropriate hand hygiene after handling pets

• Preventing young children from close contact with fleas

Treating the human infection without controlling fleas and pet infection may allow reinfection.

High-Yield Clinical Pattern

Toddler with close dog or cat exposure

• ●

Rice-like or seed-like segments around the anus or in stool

• ●

Flea exposure

→ Think Dipylidium caninum

Dipylidium vs. Diphyllobothrium

Dipylidium caninum

→ Dogs and cats

→ Ingestion of infected flea

→ Commonly recognized by rice-like proglottids

Diphyllobothrium species

→ Raw or undercooked fish

→ Fish tapeworm

→ Classically associated with vitamin B12 deficiency

Exam Essentials

Organism: Dipylidium caninum

Type: Cestode (tapeworm)

Definitive hosts: Dogs and cats

Intermediate host: Flea

Human infection: Accidental

Typical patient: Young child/toddler

Transmission: Accidental ingestion of an infected flea

Usual course: Asymptomatic

Classic finding: Seed-like/rice-like proglottids in stool or around the anus

Possible symptom: Abdominal discomfort with heavy infection

Diagnosis: Stool examination for proglottids or eggs

Treatment: Single-dose praziquantel

Alternative: Niclosamide

Prevention: Pet treatment and flea control

Key clinical pearl: The classic association is young child + dog or cat + accidental ingestion of an infected flea + rice-like proglottids in the stool = Dipylidium caninum.

Infectious Disease and Microbiology – Diphyllobothrium Species

Overview

Diphyllobothrium species are cestode helminths (tapeworms) acquired through consumption of raw or inadequately cooked infected fish. Infection is commonly called diphyllobothriasis and is usually asymptomatic.

Important species include D. dalliae, D. dendriticum, D. latum, D. pacificum, and D. ursi. D. latum is classically known as the broad fish tapeworm.

Microbiologic Characteristics

Diphyllobothrium species are cestodes, or segmented tapeworms.

Adult worms inhabit the human small intestine and consist of numerous segments called proglottids.

Eggs produced by the adult parasite are subsequently passed in the stool.

Incubation Period

Approximately 3–6 weeks may pass between ingestion of infected fish and the appearance of parasite eggs in the stool.

However, clinical manifestations may not develop until months or even years later, particularly when the infection persists.

Epidemiology

Diphyllobothriasis is strongly associated with regions where raw or inadequately cooked fish is traditionally consumed.

Historically, infection has been especially associated with lake regions and populations with dietary practices that increase exposure to infected fish.

Transmission

Humans acquire infection by eating raw or undercooked fish containing infective larvae.

The infection is not transmitted directly from one person to another because the parasite requires intermediate hosts to complete its life cycle.

Life Cycle

The life cycle requires two intermediate hosts.

Human/fish-eating mammal → eggs passed in feces → freshwater → copepod → freshwater fish → human

The first intermediate host is a freshwater copepod, historically described from genera such as Cyclops and Diaptomus.

Second Intermediate Host

Freshwater fish become the second intermediate host after consuming infected copepods.

Fish associated with transmission include:

• Salmon

• Perch

• Pike

• Other susceptible fish species

Humans and other fish-eating mammals become infected when they consume infected fish without adequate cooking.

Clinical Infection

Most Diphyllobothrium infections are asymptomatic.

The adult tapeworm can persist within the intestine for prolonged periods without causing significant disease.

Gastrointestinal Manifestations

Heavy infections may occasionally produce:

• Abdominal discomfort

• Diarrhea

• Nausea or other nonspecific gastrointestinal symptoms

These manifestations are generally more likely when the intestinal worm burden is substantial.

Intestinal and Biliary Obstruction

Rarely, a large worm burden may result in mechanical complications such as:

• Intestinal obstruction

• Biliary obstruction

These are unusual manifestations.

Vitamin B12 Deficiency

One of the most important associations is vitamin B12 deficiency, classically associated with D. latum.

The parasite can compete with the human host for vitamin B12 within the intestine.

Only a minority of infected individuals develop clinically significant deficiency.

Megaloblastic Anemia

Significant vitamin B12 depletion may eventually cause megaloblastic anemia.

Possible findings include:

• Macrocytosis

• Fatigue

• Weakness

• Pallor

• Low serum vitamin B12

Severe or prolonged deficiency can potentially produce neurologic manifestations associated with vitamin B12 deficiency.

Diagnosis

Diagnosis is primarily based on stool examination.

Macroscopic stool examination may reveal characteristic proglottids.

Microscopic examination of concentrated stool specimens can demonstrate parasite eggs.

Treatment

The preferred treatment described in the source is:

Praziquantel 10–20 mg/kg orally as a single dose

Treatment is generally highly effective.

Alternative Treatment

An alternative is:

Niclosamide 2 g orally as a single dose

Niclosamide tablets should be thoroughly chewed before swallowing.

Management of Vitamin B12 Deficiency

Patients with documented vitamin B12 deficiency should receive appropriate vitamin B12 replacement in addition to treatment of the parasitic infection.

Correction of the underlying infection prevents continued parasite-associated depletion.

Prevention

The primary preventive measure is:

Avoid eating raw or inadequately cooked fish.

Adequate preparation of fish prevents ingestion of viable infective larvae.

High-Yield Clinical Pattern

History of eating raw or undercooked fish

• ●

Tapeworm eggs or proglottids in stool

• ●

Vitamin B12 deficiency or megaloblastic anemia

→ Think Diphyllobothrium infection

Exam Essentials

Genus: Diphyllobothrium

Type: Cestode (tapeworm)

Classic species: D. latum

Common name: Broad fish tapeworm

Transmission: Raw or undercooked infected fish

First intermediate host: Copepod

Second intermediate host: Fish

Direct person-to-person transmission: No

Usual clinical course: Asymptomatic

Possible symptoms: Abdominal discomfort and diarrhea

Rare complications: Intestinal or biliary obstruction

Classic nutritional complication: Vitamin B12 deficiency → megaloblastic anemia

Diagnosis: Proglottids or eggs in stool

Treatment: Single-dose praziquantel

Alternative: Niclosamide

Prevention: Properly cook fish

Key clinical pearl: The classic association is raw freshwater fish → Diphyllobothrium tapeworm infection → vitamin B12 deficiency → megaloblastic anemia.

Infectious Disease and Microbiology – Dientamoeba fragilis

Overview

Dientamoeba fragilis is an intestinal protozoan found worldwide. Infection is frequently asymptomatic, although some infected individuals develop gastrointestinal symptoms, particularly abdominal pain and diarrhea.

Despite its name and intestinal location, D. fragilis should not be confused with Entamoeba histolytica, the invasive protozoan responsible for amebiasis.

Microbiologic Characteristics

Dientamoeba fragilis is a protozoan parasite that inhabits the human gastrointestinal tract.

Important characteristics include:

• Intestinal protozoan

• Usually identified in its trophozoite form

• Does not cause the invasive amebiasis associated with E. histolytica

Epidemiology

D. fragilis has a worldwide distribution.

The organism can be detected in both symptomatic and asymptomatic individuals, which can make determining its clinical significance challenging in some patients.

Clinical Infection

Most infections are asymptomatic.

When symptomatic disease occurs, gastrointestinal manifestations predominate.

Abdominal Pain

Abdominal discomfort or pain is one of the principal symptoms associated with D. fragilis infection.

The severity and duration can vary considerably among affected individuals.

Diarrhea

Some patients develop diarrhea, which may occur alone or together with abdominal pain.

Other nonspecific gastrointestinal complaints may accompany symptomatic infection.

Distinction from Entamoeba histolytica

An important microbiologic distinction is:

Dientamoeba fragilis ≠ Entamoeba histolytica

E. histolytica causes amebiasis, which can produce invasive colitis and extraintestinal disease such as liver abscess.

D. fragilis, in contrast, is generally associated with asymptomatic intestinal colonization or relatively mild gastrointestinal symptoms.

Diagnosis

Traditional diagnosis is based on microscopic examination of stool specimens.

Diagnostic techniques include:

• Direct stool examination

• Ferrous hematoxylin staining

Because trophozoites can be difficult to recognize, appropriately collected and processed stool specimens are important.

Molecular Diagnosis

Where available, PCR-based stool testing can provide sensitive detection of D. fragilis and may be incorporated into multiplex gastrointestinal parasite testing.

However, a positive result should be interpreted together with the patient’s symptoms because asymptomatic carriage occurs.

Treatment

Treatment is generally considered for patients with compatible gastrointestinal symptoms when D. fragilis is believed to be responsible.

One regimen described in the source is:

Paromomycin 500 mg orally every 8 hours for 7 days

Iodoquinol

Another treatment regimen is:

Iodoquinol 650 mg orally every 8 hours for 20 days

Additional Treatment Options

Other agents historically used include:

Tetracycline for approximately 7–10 days

or

Metronidazole for approximately 7 days

Treatment selection depends on patient factors, availability, tolerance, and the clinical significance of the detected organism.

Asymptomatic Infection

Because D. fragilis frequently occurs without symptoms, detection of the organism does not necessarily establish it as the cause of gastrointestinal complaints.

The decision to treat should therefore consider:

• Presence and severity of symptoms

• Alternative causes of diarrhea or abdominal pain

• Persistence of symptoms

• Other organisms detected in stool

High-Yield Clinical Pattern

Abdominal pain and/or diarrhea

• ●

Intestinal protozoan detected in stool

• ●

No evidence of invasive amebiasis

→ Consider Dientamoeba fragilis

Exam Essentials

Organism: Dientamoeba fragilis

Type: Protozoan parasite

Distribution: Worldwide

Most common course: Asymptomatic infection

Possible symptoms: Abdominal pain and diarrhea

Important distinction: Not Entamoeba histolytica

Traditional diagnosis: Direct stool examination + ferrous hematoxylin stain

Modern diagnostic option: Stool PCR

Treatment options: Paromomycin or iodoquinol

Additional historical therapies: Tetracycline or metronidazole

Key clinical pearl: Dientamoeba fragilis is a worldwide intestinal protozoan that is often asymptomatic but may cause abdominal pain and diarrhea; it should not be confused with the invasive amebiasis caused by Entamoeba histolytica.

Microbiologic Characteristics Dientamoeba fragilis is a protozoan parasite that inhabits the human gastrointestinal tract. Important characteristics include: • Intestinal protozoan

• Usually identified in its trophozoite form

• Does not cause the invasive amebiasis associated with E. histolytica

Epidemiology D. fragilis has a worldwide distribution. The organism can be detected in both symptomatic and asymptomatic individuals, which can make determining its clinical significance challenging in some patients.

Clinical Infection Most infections are asymptomatic. When symptomatic disease occurs, gastrointestinal manifestations predominate.

Abdominal Pain Abdominal discomfort or pain is one of the principal symptoms associated with D. fragilis infection. The severity and duration can vary considerably among affected individuals.

Diarrhea Some patients develop diarrhea, which may occur alone or together with abdominal pain. Other nonspecific gastrointestinal complaints may accompany symptomatic infection.

Distinction from Entamoeba histolytica An important microbiologic distinction is: Dientamoeba fragilis ≠ Entamoeba histolytica E. histolytica causes amebiasis, which can produce invasive colitis and extraintestinal disease such as liver abscess. D. fragilis, in contrast, is generally associated with asymptomatic intestinal colonization or relatively mild gastrointestinal symptoms.

Diagnosis Traditional diagnosis is based on microscopic examination of stool specimens. Diagnostic techniques include: • Direct stool examination

• Ferrous hematoxylin staining Because trophozoites can be difficult to recognize, appropriately collected and processed stool specimens are important.

Molecular Diagnosis Where available, PCR-based stool testing can provide sensitive detection of D. fragilis and may be incorporated into multiplex gastrointestinal parasite testing. However, a positive result should be interpreted together with the patient’s symptoms because asymptomatic carriage occurs.

Treatment Treatment is generally considered for patients with compatible gastrointestinal symptoms when D. fragilis is believed to be responsible. One regimen described in the source is: Paromomycin 500 mg orally every 8 hours for 7 days

Iodoquinol Another treatment regimen is: Iodoquinol 650 mg orally every 8 hours for 20 days

Additional Treatment Options Other agents historically used include: Tetracycline for approximately 7–10 days or Metronidazole for approximately 7 days Treatment selection depends on patient factors, availability, tolerance, and the clinical significance of the detected organism.

Asymptomatic Infection Because D. fragilis frequently occurs without symptoms, detection of the organism does not necessarily establish it as the cause of gastrointestinal complaints. The decision to treat should therefore consider: • Presence and severity of symptoms

• Alternative causes of diarrhea or abdominal pain

• Persistence of symptoms

• Other organisms detected in stool

High-Yield Clinical Pattern Abdominal pain and/or diarrhea  ●  Intestinal protozoan detected in stool  ●  No evidence of invasive amebiasis → Consider Dientamoeba fragilis

Exam Essentials Organism: Dientamoeba fragilis

Type: Protozoan parasite

Distribution: Worldwide

Most common course: Asymptomatic infection

Possible symptoms: Abdominal pain and diarrhea

Important distinction: Not Entamoeba histolytica

Traditional diagnosis: Direct stool examination + ferrous hematoxylin stain

Modern diagnostic option: Stool PCR

Treatment options: Paromomycin or iodoquinol

Additional historical therapies: Tetracycline or metronidazole

Key clinical pearl: Dientamoeba fragilis is a worldwide intestinal protozoan that is often asymptomatic but may cause abdominal pain and diarrhea; it should not be confused with the invasive amebiasis caused by Entamoeba histolytica.

Medicine – Papilloedema Papilloedema is optic-disc swelling caused specifically by raised intracranial pressure (ICP). It is usually bilateral and represents transmission of increased intracranial pressure along the optic nerve sheath, producing impaired axoplasmic flow and swelling of the optic nerve head. An important terminology point is that not every swollen optic disc is papilloedema. Optic-disc swelling from hypertension, optic neuritis, retinal vein occlusion, or other local ocular disease is better described as optic-disc oedema unless raised intracranial pressure is responsible. 

1. Mechanism of Papilloedema The optic nerve is surrounded by meninges and a continuation of the intracranial subarachnoid space. When intracranial pressure rises, this increased pressure is transmitted along the optic nerve sheath toward the back of the eye. The resulting pressure disrupts normal axoplasmic transport within optic nerve fibres and produces swelling of the optic nerve head. The basic sequence is: Raised intracranial pressure → increased pressure around optic nerve → impaired axoplasmic flow → optic-disc swelling → papilloedema. 

2. Space-Occupying Intracranial Lesions An intracranial space-occupying lesion is an important cause of raised intracranial pressure and therefore papilloedema. Examples include: Brain tumour. Intracranial haematoma. Brain abscess. These lesions can increase ICP through their mass effect, surrounding cerebral oedema, obstruction of cerebrospinal fluid circulation, or a combination of these mechanisms. 

3. Brain Tumours Both primary and metastatic intracranial tumours can produce raised intracranial pressure. Associated symptoms may include progressive headache, vomiting, seizures, focal neurological deficits, personality or cognitive changes, depending on the tumour’s location. Papilloedema in this setting indicates raised ICP rather than direct tumour involvement of the eye. 

4. Intracranial Haematoma An intracranial haemorrhage or expanding haematoma can increase intracranial volume and produce raised ICP. Depending on the cause and speed of bleeding, the patient may present acutely with headache, altered consciousness, focal neurological signs, or signs of intracranial hypertension. 

5. Brain Abscess A brain abscess can behave as a space-occupying lesion. The abscess itself and surrounding cerebral oedema can increase intracranial pressure. Patients may have headache, fever, seizures, altered mental status, or focal neurological abnormalities, although the complete classic picture is not always present. 

6. Meningitis and Encephalitis Meningitis and encephalitis can increase intracranial pressure through inflammation, cerebral oedema, impaired cerebrospinal fluid absorption, or other complications. Papilloedema may therefore occur in severe cases. Its presence is clinically important because it suggests raised ICP and influences the safety and timing of investigations such as lumbar puncture. 

7. Subarachnoid Haemorrhage Subarachnoid haemorrhage (SAH) can produce a sudden increase in intracranial pressure. The classic presentation is a sudden severe “thunderclap” headache, often reaching maximal intensity rapidly. Vomiting, neck stiffness, photophobia, reduced consciousness, and neurological abnormalities may also occur. Papilloedema is not necessarily present immediately, but significant or sustained raised ICP can cause optic-disc swelling. 

8. Cerebral Oedema Cerebral oedema increases the volume of brain tissue within the fixed cranial cavity and can therefore raise intracranial pressure. It may occur following conditions such as severe brain injury, stroke, infection, hypoxic-ischaemic injury, or metabolic disturbances. Severe cerebral oedema can ultimately lead to brain herniation and is therefore potentially life-threatening. 

9. Idiopathic Intracranial Hypertension The older term benign intracranial hypertension is now generally replaced by idiopathic intracranial hypertension (IIH). The term “benign” is misleading because prolonged papilloedema can produce permanent visual-field loss and blindness. IIH is characterised by raised intracranial pressure without an intracranial mass lesion, hydrocephalus, or another clear structural explanation after appropriate investigation. 

10. Typical IIH Patient IIH occurs particularly commonly in women of reproductive age with obesity, although it can occur outside this group. Patients may present with: Headache. Transient visual obscurations. Pulsatile tinnitus. Diplopia, sometimes from a sixth cranial nerve palsy. Papilloedema. Visual-field monitoring is particularly important because persistent papilloedema can damage the optic nerves. 

11. Hypertensive Retinopathy The original notes list hypertensive retinopathy as a cause of papilloedema. This requires an important distinction. Severe hypertension, particularly a hypertensive emergency, can produce bilateral optic-disc swelling as part of severe hypertensive retinopathy. However, this is not necessarily papilloedema in the strict modern definition unless the disc swelling is caused by raised intracranial pressure. Other retinal findings may include flame haemorrhages, cotton-wool spots, hard exudates, and vascular abnormalities. 

12. Carbon Dioxide Retention Severe hypercapnia, or CO₂ retention, can increase cerebral blood flow because carbon dioxide causes cerebral vasodilatation. Marked hypercapnia may therefore increase intracranial pressure, particularly in susceptible patients. The relationship can be remembered as: ↑ PaCO₂ → cerebral vasodilatation → ↑ cerebral blood volume → ↑ ICP. Therefore, severe chronic or acute hypercapnia can occasionally contribute to papilloedema. 

13. Vitamin A Toxicity Excessive vitamin A exposure can produce a syndrome resembling idiopathic intracranial hypertension. Raised intracranial pressure can subsequently cause papilloedema. This association is especially relevant to excessive vitamin A intake and medications related to vitamin A. 

14. Vitamin A Analogues Retinoid medications, which are vitamin A derivatives, can cause intracranial hypertension in susceptible individuals. An important example is isotretinoin. Patients taking retinoids who develop persistent headache and visual symptoms require assessment for raised intracranial pressure. 

15. Tetracyclines Tetracycline-class antibiotics are another recognised medication association with intracranial hypertension. Examples include tetracycline, doxycycline, and minocycline. The clinical sequence is: Tetracycline exposure → intracranial hypertension → papilloedema. 

16. Retinoids and Tetracyclines The combination of tetracyclines and systemic retinoids is particularly important because both have associations with intracranial hypertension. Therefore, concurrent use is generally avoided. 

17. Lead Poisoning Severe lead poisoning has historically been associated with encephalopathy, cerebral oedema, raised intracranial pressure, and optic-disc swelling. This is now a relatively uncommon cause in many clinical settings but remains a recognised toxic association. Other features of significant lead toxicity can include abdominal symptoms, neurological abnormalities, anaemia, and cognitive or behavioural changes. 

18. Central Retinal Vein Occlusion The original notes list central retinal vein thrombosis, more commonly termed central retinal vein occlusion (CRVO). CRVO can cause optic-disc swelling, but it is not a true cause of papilloedema unless raised intracranial pressure is independently present. CRVO occurs because obstruction of retinal venous drainage produces retinal venous congestion. Fundoscopy classically demonstrates widespread retinal haemorrhages, dilated tortuous retinal veins, cotton-wool spots and optic-disc oedema—the classic “blood and thunder” appearance. Therefore: CRVO → optic-disc oedema, not usually true papilloedema. 

19. Cerebral Venous Sinus Thrombosis An important modern addition to the differential diagnosis is cerebral venous sinus thrombosis (CVST). CVST can impair cerebral venous drainage and cerebrospinal fluid absorption, producing raised intracranial pressure and true papilloedema. This is especially important because the presentation can sometimes resemble idiopathic intracranial hypertension. 

20. Clinical Features of Papilloedema Early papilloedema may produce relatively little reduction in central visual acuity. Patients may instead experience transient visual obscurations, in which vision temporarily dims or blacks out for several seconds. Other symptoms arise primarily from the underlying raised intracranial pressure. 

21. Symptoms of Raised Intracranial Pressure Important symptoms include: Headache. Nausea and vomiting. Transient visual obscurations. Pulsatile tinnitus. Diplopia, particularly from sixth nerve palsy. More severe intracranial disease may produce reduced consciousness or focal neurological abnormalities. 

22. Fundoscopic Appearance Typical features of established papilloedema include blurred optic-disc margins, elevation of the optic disc, hyperaemia, venous congestion, obscuration of vessels as they cross the disc margin, and sometimes peripapillary haemorrhages. The physiological optic cup may become progressively obscured as swelling increases. Papilloedema is generally bilateral, although the degree of swelling may be asymmetric. 

23. Vision in Early Papilloedema A useful examination point is that visual acuity can remain relatively normal during early papilloedema. This differs from many primary optic neuropathies, such as optic neuritis, where visual acuity and colour vision may deteriorate early. The blind spot may become enlarged because of swelling around the optic disc. 

24. Chronic Papilloedema If raised intracranial pressure persists, chronic papilloedema can progressively damage optic nerve fibres. Eventually the swollen optic discs may become pale as axons are lost. The sequence is: Raised ICP → papilloedema → chronic axonal injury → secondary optic atrophy → permanent visual loss. 

25. Papilloedema – Causes in Note Form Space-occupying lesions: brain tumour, intracranial haematoma and brain abscess can raise ICP. 

Meningitis/encephalitis: inflammation and cerebral oedema can increase intracranial pressure. 

Subarachnoid haemorrhage: acute intracranial bleeding can markedly increase ICP. 

Cerebral oedema: increased brain volume produces intracranial hypertension. 

Idiopathic intracranial hypertension: formerly called benign intracranial hypertension; an important cause of bilateral papilloedema. 

Cerebral venous sinus thrombosis: important secondary cause of intracranial hypertension and papilloedema. 

CO₂ retention: severe hypercapnia causes cerebral vasodilatation and can increase intracranial pressure. 

Vitamin A toxicity: can produce intracranial hypertension. 

Tetracyclines: recognised medication association with intracranial hypertension. 

Vitamin A analogues/retinoids: drugs such as isotretinoin can cause intracranial hypertension. 

Lead poisoning: severe toxicity can cause encephalopathy, cerebral oedema and raised ICP. 

Severe hypertensive retinopathy: can cause optic-disc oedema, but this should not automatically be called papilloedema. 

Central retinal vein occlusion: causes optic-disc oedema with widespread retinal venous congestion and haemorrhage, rather than true papilloedema in the strict sense. 

Key Clinical Pattern The most important definition to remember is: Papilloedema = optic-disc swelling specifically due to raised intracranial pressure. Therefore: Raised ICP → usually bilateral swollen optic discs → papilloedema. Important causes include: Intracranial mass + cerebral oedema + CNS infection + haemorrhage + IIH + cerebral venous sinus thrombosis + certain drugs/toxins. A particularly useful distinction is: Papilloedema → raised intracranial pressure. Optic neuritis → optic nerve inflammation, usually visual loss + pain on eye movement. CRVO → retinal venous obstruction + “blood and thunder” retina + optic-disc oedema. Chronic papilloedema → optic atrophy → irreversible visual loss.

Medicine – Optic Atrophy

Optic atrophy refers to degeneration and loss of retinal ganglion cell axons within the optic nerve, usually occurring as the final consequence of previous or ongoing damage to the visual pathway. It is therefore a clinical sign of optic nerve damage rather than a single disease.

The optic disc typically becomes pale, and patients may develop reduced visual acuity, impaired colour vision, visual-field defects, and a relative afferent pupillary defect when involvement is unilateral or asymmetric.

1. Congenital and Hereditary Optic Atrophy

Several inherited disorders can produce optic neuropathy followed by optic atrophy.

Important examples include Leber hereditary optic neuropathy (LHON) and optic nerve involvement associated with Friedreich ataxia.

Another important inherited disorder is dominant optic atrophy, commonly associated with pathogenic variants in the OPA1 gene.

2. Leber Hereditary Optic Neuropathy

Leber hereditary optic neuropathy (LHON) is a mitochondrial disorder that particularly affects retinal ganglion cells and the optic nerve.

Because mitochondrial DNA is transmitted through the mother, LHON demonstrates maternal inheritance, although not every individual carrying a pathogenic mitochondrial variant develops visual loss.

It classically affects young adults, particularly males.

Clinical Pattern of LHON

Patients typically develop painless central visual loss in one eye, followed by involvement of the other eye within weeks or months.

Central or centrocaecal scotomas and impaired colour vision are characteristic.

Progressive retinal ganglion cell loss eventually results in optic atrophy.

3. Friedreich Ataxia

Friedreich ataxia is an inherited neurodegenerative disorder that can be associated with optic nerve degeneration.

The neurological picture is usually dominated by progressive ataxia, loss of proprioception and vibration sensation, absent lower-limb reflexes, and other neurological abnormalities.

Optic atrophy may occur as part of this multisystem disease.

4. Multiple Sclerosis

Multiple sclerosis (MS) can eventually cause optic atrophy following episodes of demyelinating optic neuritis.

Repeated or severe optic nerve inflammation causes axonal injury and subsequent loss of optic nerve fibres.

The sequence can therefore be remembered as:

MS → optic neuritis → axonal loss → optic atrophy.

5. Previous Optic Neuritis

After an episode of optic neuritis, the optic disc may initially appear normal or swollen.

Several weeks later, loss of optic nerve fibres may become visible as optic-disc pallor.

Therefore, optic atrophy may represent the residual structural evidence of previous optic neuritis even after substantial recovery of visual acuity.

6. Compression of the Optic Nerve

Chronic compression of the optic nerve can progressively damage optic nerve axons and eventually produce optic atrophy.

Possible causes include intracranial or orbital tumours, aneurysms, orbital masses, and other space-occupying lesions.

The visual loss is often gradually progressive.

7. Compressive Optic Neuropathy

A compressive lesion may cause:

Progressive visual loss.

Reduced colour vision.

Visual-field abnormalities.

Relative afferent pupillary defect.

Eventual optic-disc pallor.

The precise visual-field defect depends on the location of the lesion.

For example, compression of the optic chiasm by a pituitary-region mass classically produces a bitemporal visual-field defect.

8. Glaucoma

Glaucoma causes progressive retinal ganglion cell and optic nerve damage and is therefore an important cause of optic nerve atrophy.

However, the appearance differs from many other optic neuropathies.

The characteristic optic-disc abnormality in glaucoma is progressive pathological cupping, with thinning and loss of the neuroretinal rim.

Therefore:

Glaucoma → optic nerve damage + increased optic-disc cupping.

9. Chronic Papilloedema

Papilloedema means optic-disc swelling caused by raised intracranial pressure.

Prolonged severe papilloedema can eventually damage optic nerve fibres.

As axons are lost, the previously swollen disc may become pale and atrophic, producing secondary optic atrophy.

10. Importance of Papilloedema

Papilloedema itself is not a diagnosis—it is a sign of raised intracranial pressure.

Potential causes include intracranial mass lesions, hydrocephalus, cerebral venous sinus thrombosis, and idiopathic intracranial hypertension.

Therefore, unexplained papilloedema requires investigation of the underlying cause of raised intracranial pressure.

11. Ischaemic Optic Atrophy

Loss of the blood supply to the optic nerve can produce ischaemic optic neuropathy, followed later by optic-disc pallor and atrophy.

A particularly important cause in older adults is giant cell arteritis (GCA), historically called temporal arteritis.

GCA can cause arteritic anterior ischaemic optic neuropathy, producing sudden and potentially profound visual loss.

12. Giant Cell Arteritis

Clinical clues include:

Age over 50 years.

New headache.

Scalp tenderness.

Jaw claudication.

Polymyalgia rheumatica symptoms.

Raised inflammatory markers.

Sudden visual disturbance.

Suspected GCA with visual symptoms is a medical emergency, because treatment is required urgently to reduce the risk of blindness in the other eye.

13. Retinal Artery Occlusion

The original notes include retinal artery occlusion under ischaemic causes of optic atrophy.

This needs some clarification.

Central retinal artery occlusion primarily causes retinal ischaemia, producing sudden profound painless monocular visual loss. Subsequent optic-disc pallor can develop, but the primary lesion is retinal rather than a classic ischaemic optic neuropathy.

For optic atrophy specifically, anterior or posterior ischaemic optic neuropathy is the more direct mechanism.

14. Nutritional Optic Neuropathy

Severe nutritional deficiencies can damage the optic nerve.

Deficiencies involving vitamin B12, folate, thiamine, or other nutrients may contribute depending on the clinical context.

Nutritional optic neuropathy is often bilateral and symmetrical.

15. Clinical Features of Nutritional Optic Neuropathy

Patients typically develop gradually progressive:

Bilateral visual impairment.

Reduced colour vision.

Central or centrocaecal scotomas.

The optic discs may initially appear relatively normal but can subsequently become pale as optic atrophy develops.

16. Methanol Toxicity

Methanol poisoning is a classic toxic cause of severe optic neuropathy.

Methanol is metabolised to toxic compounds, particularly formic acid/formate, which can cause metabolic acidosis and profound injury to the retina and optic nerve.

17. Methanol Presentation

Patients may develop:

Headache.

Nausea and vomiting.

Abdominal symptoms.

Visual blurring or visual loss.

Severe metabolic acidosis.

Visual disturbances are classically described as blurred or “snowfield” vision.

Severe poisoning can result in permanent blindness, neurological injury, or death.

Methanol poisoning is a medical emergency.

18. Retinitis Pigmentosa

Retinitis pigmentosa is primarily an inherited retinal photoreceptor degeneration rather than a primary optic nerve disease.

However, advanced RP characteristically produces a waxy pale appearance of the optic disc, along with attenuated retinal vessels and bone-spicule pigmentation.

Therefore, the association with optic-disc pallor is useful, but RP should fundamentally be remembered as a retinal dystrophy.

19. Ethambutol

Ethambutol is an important drug associated with toxic optic neuropathy.

It is used as part of multidrug treatment for tuberculosis.

Its most important ocular adverse effect is optic neuropathy, particularly with higher exposure and impaired renal clearance.

20. Ethambutol Optic Neuropathy

Patients may develop:

Reduced visual acuity.

Reduced colour discrimination.

Central or centrocaecal scotomas.

Bilateral visual impairment.

Red-green colour abnormalities are classically described.

Persistent or severe damage may ultimately result in optic atrophy.

21. Other Toxic Causes

Ethambutol and methanol are classic examination examples, but other toxic exposures and medications can also produce optic neuropathy.

The combination of bilateral symmetrical visual loss + impaired colour vision + central scotoma should raise suspicion of a toxic or nutritional optic neuropathy.

22. Clinical Features of Optic Atrophy

Regardless of the original cause, established optic atrophy commonly produces:

Optic-disc pallor.

Reduced visual acuity.

Reduced colour vision.

Reduced contrast sensitivity.

Visual-field defects.

Relative afferent pupillary defect when unilateral or asymmetric.

The pattern of visual-field loss can help identify the site and underlying mechanism of optic nerve damage.

23. Optic Atrophy – Causes in Note Form

Congenital/hereditary: Leber hereditary optic neuropathy, dominant optic atrophy, Friedreich ataxia and other inherited disorders.

Multiple sclerosis: previous demyelinating optic neuritis can cause axonal loss and subsequent optic atrophy.

Compression: optic nerve compression from tumour, aneurysm or orbital/intracranial mass can cause progressive optic neuropathy.

Glaucoma: progressive retinal ganglion cell loss causes characteristic optic-disc cupping and optic nerve damage.

Chronic papilloedema: prolonged raised intracranial pressure can eventually produce secondary optic atrophy.

Ischaemia: ischaemic optic neuropathy can cause subsequent optic atrophy; giant cell arteritis is an especially important emergency cause.

Retinal artery occlusion: causes retinal ischaemia and may subsequently produce optic-disc pallor, although it is primarily a retinal vascular disorder.

Nutritional deficiency: particularly consider vitamin B12 and other severe nutritional deficiencies.

Methanol: causes severe toxic optic neuropathy and may result in permanent blindness.

Retinitis pigmentosa: advanced disease produces characteristic waxy optic-disc pallor, although the primary pathology is retinal.

Ethambutol: important drug cause of toxic optic neuropathy with impaired colour vision and central/centrocaecal scotomas.

Key Clinical Pattern

Remember optic atrophy as:

Optic nerve axonal loss → pale optic disc + reduced vision + impaired colour vision + visual-field defect.

Important examination associations are:

MS → optic neuritis → optic atrophy.

Tumour/aneurysm → compressive optic neuropathy → optic atrophy.

Chronic papilloedema → secondary optic atrophy.

Giant cell arteritis → ischaemic optic neuropathy → optic atrophy.

Methanol → toxic optic neuropathy.

Ethambutol → bilateral toxic optic neuropathy + impaired colour vision.

Retinitis pigmentosa → waxy optic-disc pallor.

A particularly useful distinction is:

Optic atrophy → optic-disc pallor.

Glaucoma → pathological optic-disc cupping.

Papilloedema → swollen optic disc.

Infectious Disease and Microbiology – Dicrocoelium dendriticum

Overview

Dicrocoelium dendriticum is a trematode helminth, commonly referred to as the lancet liver fluke. Human infection is rare and is usually asymptomatic, although the parasite may occasionally involve the biliary tract and cause symptoms such as biliary colic.

Microbiologic Characteristics

D. dendriticum is a trematode (fluke) that primarily inhabits the biliary system of its usual mammalian hosts.

Human infection is unusual and generally occurs accidentally.

Epidemiology

Dicrocoelium dendriticum has a worldwide distribution, but true human infection is rare.

Its eggs may sometimes be identified in human stool specimens without indicating genuine infection.

Spurious Passage of Eggs

A particularly important point is that eggs of D. dendriticum may appear in stool after a person eats infected animal liver.

In this situation, the parasite has not established infection in the patient. The eggs are simply passing through the gastrointestinal tract.

Therefore, detection of D. dendriticum ova in stool does not always prove true human parasitism.

Clinical Infection

Most true infections are asymptomatic.

When symptoms occur, they are usually related to the biliary tract and may include:

• Right upper quadrant discomfort

• Intermittent biliary pain

• Biliary colic

Symptomatic disease is exceptional.

Diagnosis

Diagnosis is based on parasitologic examination of stool specimens for characteristic eggs.

Because false-positive or spurious egg passage can occur, stool findings should be interpreted together with the clinical picture and dietary history.

Repeated stool examinations may help distinguish true infection from transient passage after ingestion of infected animal liver.

Treatment

Treatment is generally unnecessary in asymptomatic patients.

For the rare patient with symptomatic infection in whom other causes of biliary symptoms have been excluded, the source recommends:

Praziquantel 25 mg/kg orally every 8 hours for 3 doses

High-Yield Clinical Pattern

Dicrocoelium eggs found in stool

• ●

No compatible symptoms

• ●

Recent ingestion of animal liver

→ Consider spurious passage rather than true infection

Exam Essentials

Organism: Dicrocoelium dendriticum

Type: Trematode helminth

Common name: Lancet liver fluke

Distribution: Worldwide

Human infection: Rare

Typical course: Usually asymptomatic

Possible manifestation: Biliary colic

Diagnosis: Stool parasitologic examination

Important pitfall: Eggs in stool may represent spurious passage after eating infected animal liver

Treatment for symptomatic true infection: Praziquantel

Key clinical pearl: Finding Dicrocoelium dendriticum eggs in stool does not automatically mean true infection; first consider spurious passage from recently consumed infected liver.

Infectious Disease and Microbiology – Cyclospora cayetanensis

Overview

Cyclospora cayetanensis is an intestinal protozoan parasite that causes cyclosporiasis, an enteric infection characterized primarily by prolonged, watery diarrhea. Infection is commonly associated with ingestion of contaminated food or water and may affect both immunocompetent and immunocompromised individuals.

⸻

Microbiologic Characteristics

Cyclospora cayetanensis is a coccidian protozoan parasite.

Important microbiologic features include:

• Protozoan organism

• Oocysts demonstrate variable acid-fast staining

• Previously described as a coccidian-like body

• Oocysts can demonstrate characteristic autofluorescence under ultraviolet fluorescence microscopy

⸻

Epidemiology

Cyclospora has a worldwide distribution, although the frequency of recognized infection varies considerably by geographic region.

Cases have historically been reported from areas including:

• Nepal

• Peru

• The Caribbean

• India

• Pakistan

• Sri Lanka

• Mexico

• Morocco

• Turkey

• Malaysia

• Australia

Cases also occur in travelers returning from endemic regions.

⸻

Infection Without Travel

Although travel history can provide an important clue, absence of international travel does not exclude cyclosporiasis.

Locally acquired infections and outbreaks can occur, including among otherwise healthy individuals.

In patients with prolonged diarrhea, immunocompromising conditions may influence the severity and duration of illness, but Cyclospora infection is certainly not restricted to immunocompromised patients.

⸻

Transmission

Humans acquire cyclosporiasis primarily by consuming food or water contaminated with sporulated oocysts.

Fresh produce has been an important vehicle in recognized outbreaks.

Unlike some other intestinal parasites, freshly excreted Cyclospora oocysts are not immediately infectious. They must mature in the environment before becoming capable of infecting another person.

Therefore, direct person-to-person transmission is relatively unlikely.

⸻

Clinical Infection

The characteristic manifestation is prolonged watery diarrhea.

Symptoms may include:

• Frequent watery stools

• Abdominal cramping

• Bloating

• Nausea

• Loss of appetite

• Fatigue

• Weight loss

• Malaise

Symptoms may persist for an extended period and can follow a relapsing pattern if infection is untreated.

⸻

Disease in Immunocompetent Patients

In immunocompetent individuals, cyclosporiasis may eventually be self-limited, although symptoms can persist for weeks.

The prolonged duration of watery diarrhea is an important diagnostic clue.

⸻

Disease in Immunocompromised Patients

Immunocompromised patients may experience more persistent or severe gastrointestinal disease.

Historically, prolonged infection has been particularly recognized in patients with advanced HIV infection.

⸻

Diagnosis

Diagnosis depends primarily on detecting Cyclospora oocysts in stool specimens.

Because oocysts may not be continuously shed, examination of multiple stool specimens may improve diagnostic sensitivity.

⸻

Concentrated Stool Examination

Concentration techniques can increase the likelihood of detecting the parasite.

A modified acid-fast stain, such as a modified Kinyoun technique, can demonstrate the oocysts.

Importantly, staining may be variable, so some oocysts may stain strongly while others stain only weakly or not at all.

⸻

Fluorescence Microscopy

Fresh stool specimens can also be examined using fluorescence microscopy.

Cyclospora oocysts demonstrate characteristic autofluorescence, which can help distinguish them from other intestinal organisms.

⸻

Molecular Diagnosis

Where available, molecular gastrointestinal panels or specific PCR-based assays can also detect Cyclospora cayetanensis.

⸻

Treatment

The preferred antimicrobial treatment is:

Trimethoprim-sulfamethoxazole (TMP-SMX)

The source describes a regimen of:

TMP-SMX 160/800 mg orally every 12 hours

Treatment duration may need to be longer in immunocompromised patients than in otherwise healthy individuals.

⸻

Alternative Treatment

For patients unable to receive TMP-SMX, alternative therapy may be considered.

The source lists:

Ciprofloxacin 500 mg orally every 12 hours

However, alternative agents may be less effective than TMP-SMX, making TMP-SMX the preferred therapy when it can be safely administered.

⸻

Recurrent Infection

Recurrence can occur, particularly in immunocompromised patients.

The source describes secondary prophylaxis with intermittent TMP-SMX following treatment in selected patients with recurrent disease.

The need for prolonged or suppressive therapy should be individualized according to immune status and recurrence risk.

⸻

Prevention

Prevention focuses on reducing exposure to contaminated food and water.

Important measures include:

• Safe drinking water

• Appropriate sanitation

• Careful handling of fresh produce

• Washing fruits and vegetables

• Avoiding potentially contaminated food or water during travel

Because oocysts require environmental maturation before becoming infectious, direct transmission from freshly passed stool is less efficient than with several other intestinal pathogens.

⸻

High-Yield Clinical Pattern

Traveler or foodborne exposure

Prolonged or relapsing watery diarrhea

Variably acid-fast oocysts with autofluorescence

→ Think Cyclospora cayetanensis

⸻

Exam Essentials

Organism: Cyclospora cayetanensis

Type: Protozoan parasite

Disease: Cyclosporiasis

Distribution: Worldwide

Transmission: Contaminated food or water

Major manifestation: Prolonged watery diarrhea

Stool finding: Oocysts with variable acid-fast staining

Special diagnostic clue: Autofluorescence under fluorescence microscopy

Diagnosis: Concentrated stool examination, modified acid-fast staining, fluorescence microscopy, or molecular testing

Preferred treatment: TMP-SMX

Important complication: Persistent or recurrent disease, particularly with immunosuppression

⸻

Key clinical pearl: The classic combination is prolonged watery diarrhea + variably acid-fast stool oocysts + autofluorescence = Cyclospora cayetanensis.

Infectious Disease and Microbiology – Curvularia Species

Overview

Curvularia species are dematiaceous (darkly pigmented), filamentous fungi that are uncommon causes of human infection. They most often produce keratitis or cutaneous and subcutaneous infections, although invasive disease involving the lungs, heart, bone, or other deep tissues can rarely occur.

Important species include C. boedijn, C. geniculata, C. lunata, C. pallescens, and C. senegalensis.

Microbiologic Characteristics

Curvularia species are dematiaceous filamentous fungi (molds).

In infected tissues, fungal elements may appear as:

• Yeast-like forms

• Pseudohyphae

• Septate, pigmented hyphae

The presence of melanin within the fungal cell wall produces the characteristic dark pigmentation associated with dematiaceous fungi.

Epidemiology

Human infection with Curvularia is rare.

These organisms are environmental molds, and human disease generally follows exposure or traumatic introduction of fungal material into tissues.

Keratitis

Fungal keratitis is an important manifestation of Curvularia infection.

Infection may follow corneal trauma, particularly when the eye has been exposed to environmental or plant material.

Clinical manifestations may include:

• Eye pain

• Redness

• Photophobia

• Excessive tearing

• Corneal ulceration

• Reduced visual acuity

Severe infection can threaten vision if not recognized and treated promptly.

Skin and Subcutaneous Tissue Infection

Curvularia may cause localized cutaneous or subcutaneous fungal infection, often following traumatic inoculation.

Patients may develop:

• Nodules

• Plaques

• Ulcerative lesions

• Cysts or abscess-like lesions

• Chronic localized inflammation

These infections fall within the broader spectrum of disease caused by dematiaceous fungi.

Deep-Tissue Infection

Deep invasive disease is uncommon but may occur, particularly in patients with impaired host defenses.

Reported manifestations include:

• Pneumonia

• Endocarditis

• Osteomyelitis

Other organs may occasionally become involved in disseminated disease.

Phaeohyphomycosis

Infections caused by dematiaceous fungi in which pigmented septate hyphae or yeast-like fungal elements are demonstrated in tissue are generally classified within the spectrum of phaeohyphomycosis.

Thus, Curvularia species are important potential causes of phaeohyphomycotic infection.

Diagnosis

Diagnosis is primarily established through:

• Tissue biopsy

• Fungal culture

Both methods are useful because histopathology demonstrates tissue invasion while culture helps identify the specific fungal organism.

Tissue Biopsy

Histopathologic examination may demonstrate pigmented, septate fungal hyphae, pseudohyphae, or yeast-like elements within infected tissue.

The pigmentation provides an important clue that the infection is caused by a dematiaceous fungus.

Culture

Fungal culture allows identification of Curvularia species and helps distinguish the organism from other pigmented molds.

Clinical specimens should be obtained directly from the involved tissue whenever possible.

Treatment

Historically, amphotericin B has been used for serious Curvularia infections.

Treatment depends on:

• Site of infection

• Severity

• Degree of tissue invasion

• Immune status

• Antifungal susceptibility

Additional Treatment

Azole antifungal agents have also been used for infections caused by dematiaceous fungi.

However, the source notes that clinical data regarding their effectiveness against Curvularia are limited.

Whenever possible, treatment of serious disease should be guided by fungal identification and antifungal susceptibility information.

Surgical Management

Localized infections may also benefit from surgical excision or debridement, particularly when there is extensive infected or necrotic tissue.

Keratitis requires prompt ophthalmologic management because progressive corneal disease can result in permanent visual impairment.

High-Yield Clinical Pattern

Environmental or plant-related trauma

• ●

Keratitis or chronic subcutaneous lesion

• ●

Pigmented, septate fungal hyphae in tissue

→ Think dematiaceous fungal infection such as Curvularia

Exam Essentials

Genus: Curvularia

Type: Dematiaceous filamentous fungus

Pigmentation: Darkly pigmented fungal elements

Tissue morphology: Yeasts, pseudohyphae, or septate pigmented hyphae

Frequency: Rare human pathogen

Common manifestations: Keratitis and skin/subcutaneous infection

Rare invasive infections: Pneumonia, endocarditis, osteomyelitis

Disease category: Phaeohyphomycosis

Diagnosis: Tissue biopsy + fungal culture

Traditional treatment: Amphotericin B

Other therapy: Azoles have been used, but supporting data are limited

Key clinical pearl: Curvularia is a dematiaceous mold that should be considered when pigmented septate hyphae are found in a patient with fungal keratitis or a chronic cutaneous/subcutaneous infection.

Infectious Disease and Microbiology – Cunninghamella bertholletiae

Overview

Cunninghamella bertholletiae is a rare filamentous fungal pathogen that can cause mucormycosis, particularly in severely immunocompromised patients. Infection can be rapidly progressive and invasive, with the potential for extensive tissue destruction and dissemination.

⸻

Microbiologic Characteristics

C. bertholletiae is a filamentous fungus (mold) traditionally classified among the organisms causing mucormycosis.

The organism characteristically produces:

• Broad, hyaline hyphae

• Nonseptate or sparsely septate hyphae

• Filamentous growth

Like other causes of mucormycosis, the fungus can invade blood vessels, resulting in vascular thrombosis, tissue ischemia, and necrosis.

⸻

Epidemiology

Cunninghamella bertholletiae is distributed worldwide, but human infection is rare.

Disease occurs predominantly in patients with impaired host defenses.

⸻

Major Risk Groups

Infection occurs more frequently in:

• Immunosuppressed patients

• Patients receiving intensive immunosuppressive therapy

• Patients with severe underlying disease

• Patients undergoing hemodialysis

Profound immunosuppression substantially increases the risk of invasive fungal disease.

⸻

Mucormycosis

The principal infection caused by C. bertholletiae is mucormycosis, historically referred to as zygomycosis.

Mucormycosis is an aggressive invasive fungal infection characterized by fungal invasion of tissues and blood vessels.

⸻

Angioinvasion and Tissue Necrosis

A major pathogenic feature is angioinvasion.

Fungal hyphae invade blood vessels, which can lead to:

Vascular invasion → thrombosis → impaired blood supply → tissue infarction and necrosis

This process helps explain the rapid progression and potentially high severity of invasive mucormycosis.

⸻

Clinical Manifestations

Depending on the site of infection and degree of immunosuppression, mucormycosis may involve:

• Lungs

• Sinuses and rhinocerebral structures

• Skin and soft tissues

• Gastrointestinal tract

• Multiple organs in disseminated infection

Pulmonary or disseminated disease is particularly concerning in severely immunocompromised patients.

⸻

Diagnosis

Diagnosis requires rapid recognition because invasive mucormycosis can progress quickly.

The principal diagnostic methods are:

• Identification of fungal hyphae in tissue biopsy

• Fungal culture

⸻

Tissue Biopsy

Histopathologic examination may demonstrate characteristic broad, hyaline, sparsely septate or nonseptate hyphae invading tissue.

Evidence of vascular invasion, thrombosis, infarction, and necrosis supports the diagnosis of invasive mucormycosis.

⸻

Culture

Fungal culture can help identify Cunninghamella and distinguish it from other molds responsible for invasive fungal disease.

Whenever possible, both histopathology and culture should be obtained.

⸻

Treatment

The traditional treatment for severe C. bertholletiae infection is:

Intravenous amphotericin B

Because mucormycosis is potentially life-threatening, antifungal treatment should be initiated promptly when invasive disease is strongly suspected.

⸻

Additional Antifungal Therapy

Older literature contains limited information regarding the effectiveness of azole antifungals against Cunninghamella.

Itraconazole has historically been evaluated, but evidence for its effectiveness is limited.

Selection of antifungal therapy should take into account the organism, disease severity, infection site, susceptibility information, and patient characteristics.

⸻

Surgical Management

When anatomically feasible, surgical removal of infected or necrotic tissue can be an important component of mucormycosis treatment.

Management may therefore require:

Systemic antifungal therapy + aggressive surgical debridement + correction of underlying risk factors

⸻

High-Yield Clinical Pattern

Severely immunocompromised or hemodialysis patient

Rapidly progressive invasive fungal infection

Broad, nonseptate/sparsely septate hyaline hyphae in tissue

→ Consider mucormycosis, including Cunninghamella bertholletiae

⸻

Exam Essentials

Organism: Cunninghamella bertholletiae

Type: Filamentous fungus (mold)

Hyphae: Broad, hyaline, nonseptate or sparsely septate

Distribution: Worldwide

Frequency: Rare

Major risk factor: Immunosuppression

Additional association: Hemodialysis

Major disease: Mucormycosis

Important pathogenic feature: Angioinvasion with thrombosis and tissue necrosis

Diagnosis: Tissue biopsy + fungal culture

Traditional treatment: IV amphotericin B

Older alternative studied: Itraconazole, with limited supporting data

⸻

Key clinical pearl: Cunninghamella bertholletiae should be considered in a severely immunocompromised patient with rapidly invasive mucormycosis and broad, sparsely septate or nonseptate hyphae on tissue biopsy.

Infectious Disease and Microbiology – Crimean–Congo Hemorrhagic Fever Virus

Overview

Crimean–Congo hemorrhagic fever virus (CCHFV) is a tick-borne enveloped RNA virus that causes a potentially severe viral hemorrhagic fever. It is found across parts of Eastern Europe, Central Asia, the Balkans, the Middle East, and Africa.

Severe disease can involve hepatitis, jaundice, thrombocytopenia, disseminated intravascular coagulation, and major bleeding.

Microbiologic Characteristics

Crimean–Congo hemorrhagic fever virus belongs to the Nairovirus genus.

It is an:

• Enveloped virus

• Single-stranded RNA virus

• Segmented RNA virus

• Virus with helical symmetry

The genome contains three RNA segments.

Epidemiology

CCHFV is transmitted primarily through the bite of infected ticks.

The virus is endemic in several geographic regions, including:

• Eastern Europe

• Central Asia

• The Balkans

• The Middle East

• Africa

People with occupational or environmental exposure to ticks or infected animals are at increased risk.

Transmission

The major route of transmission is:

Tick bite → human infection

Person-to-person spread may also occur through direct exposure to infected blood or body fluids, which is particularly important in healthcare settings.

Clinical Manifestations

Crimean–Congo hemorrhagic fever can range from a nonspecific febrile illness to a severe hemorrhagic syndrome.

Early symptoms may include:

• Fever

• Headache

• Myalgia

• Malaise

• Nausea and vomiting

• Abdominal discomfort

Severe cases may progress rapidly.

Hemorrhagic Fever

The characteristic severe syndrome includes:

• Acute hepatitis

• Jaundice

• Thrombocytopenia

• Disseminated intravascular coagulation

• Petechiae or ecchymoses

• Mucosal bleeding

• Gastrointestinal or other internal bleeding

• Shock

The combination of thrombocytopenia and coagulation abnormalities contributes substantially to the bleeding tendency.

Hepatic Involvement

Acute hepatitis can be prominent.

Patients may develop:

• Markedly elevated liver enzymes

• Jaundice

• Hepatic dysfunction

• Coagulopathy

Severe hepatic injury is associated with a worse prognosis.

Mortality

Severe Crimean–Congo hemorrhagic fever has historically been associated with a high case-fatality rate, often cited around 30–40% in severe cases.

Outcome depends on disease severity, supportive care, and host factors.

Diagnosis

Laboratory diagnosis can include:

• PCR

• Viral antigen detection

• Serologic testing

• Viral culture in specialized laboratories

PCR is especially useful during the acute phase because it directly detects viral nucleic acid.

Infection Control

Patients with suspected or confirmed disease require strict infection-control precautions because transmission can occur through blood and body fluids.

Healthcare workers should use appropriate barrier protection, including gloves, gowns, eye protection, and respiratory protection when indicated by the procedure.

Treatment

Management is primarily supportive.

Treatment may include:

• Fluid and electrolyte management

• Hemodynamic support

• Blood-product replacement when indicated

• Management of coagulopathy

• Organ support in critically ill patients

Antiviral Therapy

There is no universally established specific antiviral treatment with consistently proven benefit.

Supportive care therefore remains the central component of management.

Prevention

Prevention focuses on reducing tick exposure and preventing contact with infected blood or tissues.

Important measures include:

• Tick-bite prevention

• Protective clothing

• Appropriate use of repellents

• Safe handling of animals and animal tissues

• Strict hospital infection-control precautions

• Isolation of affected patients when clinically indicated

Related Bunyavirus Syndromes

Other historically grouped bunyavirus-associated diseases include:

• California encephalitis

• Rift Valley fever

• Hemorrhagic fever with renal syndrome

• Hantavirus pulmonary syndrome

These diseases differ substantially in vectors, reservoirs, geography, and clinical presentation.

High-Yield Clinical Pattern

Tick exposure in an endemic region

• ●

Acute fever

• ●

Thrombocytopenia + hepatitis + bleeding/DIC

→ Think Crimean–Congo hemorrhagic fever

Exam Essentials

Virus: Crimean–Congo hemorrhagic fever virus

Genus: Nairovirus

Genome: Segmented single-stranded RNA

Segments: 3

Envelope: Present

Symmetry: Helical

Vector: Tick

Geography: Eastern Europe, Central Asia, Balkans, Middle East, Africa

Major syndrome: Viral hemorrhagic fever

Key findings: Hepatitis, jaundice, thrombocytopenia, DIC, bleeding

Diagnosis: PCR, antigen detection, serology

Treatment: Primarily supportive

Severe-case mortality: High

Prevention: Tick avoidance and strict infection-control precautions

Key clinical pearl: Tick exposure + hemorrhagic fever + thrombocytopenia + hepatitis + DIC is the classic pattern for Crimean–Congo hemorrhagic fever.