Angiostrongyliasis

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Angiostrongyliasis: FRCPath Revision Trainer

AngiostrongyliasisRat lungworm, eosinophilic meningitis and exam traps

microregistrar | Infection Institute
Revision aid, not clinical guidance. This page is built for FRCPath-style exam revision. Use local or specialist parasitology guidance for real patient management.

Why this organism is tested

The exam pattern is neurological presentation plus epidemiological clues.

Core pattern
Angiostrongyliasis is usually tested as a returning traveller with severe headache, meningism and eosinophilia. The key phrase is eosinophilic meningitis after raw snail, slug, contaminated salad, or paratenic host exposure.
Past question area
Angiostrongyliasis has featured through its neurological presentation and epidemiological clues: rat lungworm, tropical or subtropical travel, raw/undercooked snails or slugs, contaminated vegetables, and CSF eosinophilia.

Last-minute checklist

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Quick comparison table

Exam clueHigh-yield answer
Rat lungwormAngiostrongylus cantonensis
Parasite typeNematode; tissue helminth
Definitive hostRats
Intermediate hostsSnails and slugs
Infective stageThird-stage larvae, L3
Main syndromeEosinophilic meningitis
Main trapDo not confuse with migratory cutaneous tracks from hookworm, gnathostomiasis or Strongyloides

Condensed overview

Angiostrongyliasis is caused by nematodes. The main exam pathogen is Angiostrongylus cantonensis, the rat lungworm, which causes eosinophilic meningitis. Angiostrongylus costaricensis causes abdominal angiostrongyliasis but is less commonly tested.

Think angiostrongyliasis
Returning traveller, severe headache, meningism, peripheral eosinophilia, CSF eosinophilia, raised opening pressure, and exposure to snails, slugs, contaminated salad, freshwater prawns, crabs or frogs.
Do not be distracted
Migratory skin tracks after tropical exposure point away from angiostrongyliasis and toward cutaneous larva migrans, gnathostomiasis or larva currens from Strongyloides.

Geography and exposure clues

  • Endemic areas include Southeast Asia, China and Pacific Islands.
  • It is increasingly reported in the Caribbean, Central/South America and the southern USA.
  • Exam exposure clues include raw or undercooked snails or slugs, contaminated vegetables such as salad leaves, and paratenic hosts such as freshwater prawns, crabs and frogs.
  • Travel history is a key clue because the neurological syndrome is otherwise non-specific at first glance.

Past question areas

Past question area
Part 1 MCQ pattern: Angiostrongylus cantonensis causes eosinophilic meningitis after ingestion of raw or undercooked snails, slugs, or contaminated vegetables/water in endemic regions. Diagnosis is clinical and epidemiological plus CSF eosinophilia, with serology or PCR where available. Management is supportive; corticosteroids may be used and antihelminthics are cautious or controversial.
Past question area
Differential trap: Walking barefoot in the tropics plus migratory skin tracks points to cutaneous larva migrans, gnathostomiasis or larva currens, not angiostrongyliasis. Angiostrongyliasis is a CNS disease in the common exam stem.

Host roles

Host categoryRole
Definitive hostRats. Adult worms live in the rat pulmonary arteries in the classic rat lungworm cycle.
Intermediate hostsSnails and slugs. Larvae develop to the infective L3 stage.
Paratenic hostsCrustaceans and amphibians, especially freshwater prawns, crabs and frogs.
HumansAccidental dead-end hosts. The lifecycle is not completed in humans.

Life cycle in four exam steps

1

Rat shedding

Rats shed L1 larvae in faeces.

2

Snail or slug stage

Snails and slugs ingest larvae, which develop to L3.

3

Human ingestion

Humans ingest L3 via contaminated food, intermediate hosts or paratenic hosts.

4

CNS migration

In A. cantonensis infection, larvae migrate to the CNS and trigger eosinophilic inflammation.

Key sentence
The infective form for humans is the third-stage larva, L3, and humans are accidental dead-end hosts.

Tap to reveal the organism pair

Angiostrongylus cantonensis high yield›
  • Known as rat lungworm.
  • Main exam syndrome is eosinophilic meningitis.
  • Exposure is classically raw or undercooked snails/slugs or contaminated vegetables in endemic areas.
Angiostrongylus costaricensis lower yield›
  • Associated with abdominal angiostrongyliasis.
  • Less commonly tested than A. cantonensis in the supplied exam themes.
  • Useful mainly as a contrast if an MCQ asks for the CNS species.

Typical exam stem

Think: returning traveller plus headache plus eosinophilia.

  • Severe headache is often the dominant symptom.
  • Neck stiffness, photophobia, nausea and vomiting support meningitis.
  • Paraesthesiae or cranial nerve involvement may be included as neurological clues.
  • Peripheral eosinophilia is a major clue but the decisive laboratory discriminator is CSF eosinophilia.

CSF and diagnosis

FindingExam meaning
CSF eosinophilic pleocytosisKey diagnostic clue for eosinophilic meningitis.
Raised opening pressureExplains severe headache and may guide repeated therapeutic lumbar punctures.
SerologySupportive where available; not always routine everywhere.
PCRSpecialist laboratory support where available.
Clinical plus epidemiological diagnosisOften the main practical exam answer: exposure history plus eosinophilic meningitis.

Worked stem

A traveller returns from Southeast Asia with severe headache, photophobia and vomiting. They ate raw salad and a local snail dish. Blood eosinophils are raised, and CSF shows eosinophilic pleocytosis with raised opening pressure.

Reveal answer and reasoning›

The best answer is Angiostrongylus cantonensis. The syndrome is eosinophilic meningitis, and the epidemiology points to rat lungworm exposure through snails/slugs or contaminated vegetables. Raised opening pressure explains the severe headache and supports supportive management with repeated lumbar punctures if needed.

Treatment sequence

1

Supportive care

Analgesia and symptom control are the foundation.

2

Raised pressure

Repeated lumbar punctures may be used for raised intracranial pressure.

3

Corticosteroids

Used to reduce inflammatory response in many teaching summaries.

4

Antihelminthics

Albendazole is controversial because larval death may worsen inflammation.

Exam-safe phrasing
Management is mainly supportive. Corticosteroids may reduce inflammation. Antihelminthics such as albendazole are controversial and should be used cautiously or avoided depending on guidance and specialist advice.

Differential trap: skin tracks versus CNS disease

Skin migratory tracks
Cutaneous larva migrans, gnathostomiasis, or larva currens from Strongyloides. Walking barefoot and serpiginous tracks are not the classic angiostrongyliasis answer.
Angiostrongyliasis
Neurological presentation: eosinophilic meningitis, severe headache, meningism and CSF eosinophilia after relevant food or travel exposure.
Common wrong turn
Do not choose angiostrongyliasis for a stem that is mainly about migratory cutaneous tracks. The supplied exam trap explicitly separates angiostrongyliasis from those skin-track diagnoses.

Yes / No quick check

Does angiostrongyliasis usually cause migratory cutaneous tracks?›

No. In the common exam presentation, angiostrongyliasis causes CNS disease, especially eosinophilic meningitis. Migratory tracks point to other helminth differentials.

Is CSF eosinophilia a key discriminator?›

Yes. CSF eosinophilia is the high-yield laboratory clue that turns a non-specific meningitis stem into an eosinophilic meningitis stem.

Are humans definitive hosts?›

No. Humans are accidental dead-end hosts. Rats are the definitive host.

Flashcard deck

WordPress-safe version: each card contains its own text in the HTML. No JavaScript is needed.

MCQ collection

Static reveal format so answers still work when WordPress blocks JavaScript.

Q1. A returning traveller from Southeast Asia has severe headache, photophobia and CSF eosinophilia after eating raw snails. What is the most likely parasite?
  1. Strongyloides stercoralis
  2. Angiostrongylus cantonensis
  3. Toxocara canis
  4. Echinococcus granulosus
  5. Schistosoma mansoni
Show answer and explanation

Answer: B. Angiostrongylus cantonensis. A. cantonensis is rat lungworm and causes eosinophilic meningitis after ingestion of L3 larvae via snails, slugs, contaminated vegetables or paratenic hosts.

Q2. What type of parasite is Angiostrongylus?
  1. Cestode
  2. Trematode
  3. Nematode tissue helminth
  4. Protozoan flagellate
  5. Microsporidian
Show answer and explanation

Answer: C. Nematode tissue helminth. Angiostrongylus is a nematode tissue helminth.

Q3. Which host is the definitive host for A. cantonensis?
  1. Human
  2. Rat
  3. Snail
  4. Slug
  5. Freshwater prawn
Show answer and explanation

Answer: B. Rat. Rats are the definitive host. Snails and slugs are intermediate hosts, and humans are accidental dead-end hosts.

Q4. Which is the infective stage for humans?
  1. Egg
  2. L1 larva
  3. L2 larva
  4. L3 larva
  5. Adult worm
Show answer and explanation

Answer: D. L3 larva. Humans ingest third-stage larvae, L3, through contaminated food or intermediate/paratenic hosts.

Q5. Which CSF finding is the key diagnostic clue in the classic A. cantonensis presentation?
  1. Low glucose only
  2. Neutrophilic pleocytosis only
  3. Eosinophilic pleocytosis
  4. Gram-positive diplococci
  5. Oligoclonal bands
Show answer and explanation

Answer: C. Eosinophilic pleocytosis. CSF eosinophilic pleocytosis is the key discriminator for eosinophilic meningitis.

Q6. Which exposure best fits angiostrongyliasis in an exam stem?
  1. Barefoot walking with serpiginous tracks
  2. Raw or undercooked snails/slugs or contaminated salad in an endemic area
  3. Dog bite followed by encephalitis
  4. Freshwater swimming followed by haematuria
  5. Mosquito bite followed by cyclical fever
Show answer and explanation

Answer: B. Raw or undercooked snails/slugs or contaminated salad in an endemic area. Raw/undercooked snails or slugs, contaminated vegetables and paratenic hosts such as freshwater prawns, crabs or frogs are classic exposure clues.

Q7. A traveller has migratory cutaneous tracks after walking barefoot on a tropical beach. Which statement is most exam-safe?
  1. This is typical angiostrongyliasis
  2. This points away from angiostrongyliasis and toward cutaneous larva migrans or related differentials
  3. This proves A. costaricensis infection
  4. This is diagnostic of eosinophilic meningitis
  5. This is the classic rat lungworm presentation
Show answer and explanation

Answer: B. This points away from angiostrongyliasis. Migratory cutaneous tracks favour cutaneous larva migrans, gnathostomiasis or larva currens. Angiostrongyliasis presents classically with CNS disease and eosinophilic meningitis.

Q8. What is the mainstay of management for eosinophilic meningitis due to A. cantonensis?
  1. Immediate praziquantel only
  2. Supportive care, analgesia, management of raised intracranial pressure, and consideration of corticosteroids
  3. No treatment or monitoring
  4. High-dose antibacterial therapy only
  5. Emergency surgery in all cases
Show answer and explanation

Answer: B. Supportive care. Management is mainly supportive. Repeated lumbar punctures may be needed for raised intracranial pressure. Corticosteroids may reduce inflammation.

Q9. Why are antihelminthics such as albendazole controversial in A. cantonensis infection?
  1. They have no activity against any nematode
  2. They may worsen inflammation because larval death can intensify the inflammatory response
  3. They cause immediate bacterial resistance
  4. They are contraindicated because rats are definitive hosts
  5. They convert infection into malaria
Show answer and explanation

Answer: B. They may worsen inflammation. Antihelminthics may worsen inflammation due to larval death, so they are used cautiously or avoided depending on specialist guidance.

Q10. Which Angiostrongylus species is associated with abdominal angiostrongyliasis rather than the classic rat lungworm meningitis stem?
  1. A. cantonensis
  2. A. costaricensis
  3. A. duodenale
  4. A. lumbricoides
  5. A. braziliense
Show answer and explanation

Answer: B. A. costaricensis. A. costaricensis causes abdominal angiostrongyliasis and is less commonly tested.

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