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