Angiostrongyliasis

Infection with the parasitic nematode (roundworm) Angiostrongylus. It belongs to the order Strongyloidea subfamily metastrongyloidea (lungworms).

• The normal life cycle of the lungworm angiostrongylus involves rats (definitive host) and snails or slugs (intermediate hosts), but also paratenic (transport) hosts such as crabs, freshwater shrimps, fish, reptiles and amphibians who feed on them.
• Rats ingest snails or slugs that are infected by larvae. The larvae develop into adult worms and the females lay eggs, which pass into the faeces of the rat.
• The first stage larvae then infect snails and slugs and so the cycle continues.
• Humans are incidental hosts and acquire the infection by eating raw or undercooked infected snails,¹ crabs, or shrimps, or by eating raw vegetables contaminated by a small snail or slug, or parts.
• There is also a question of whether the larva can exit the infected mollusc in slime, which may become infective to humans as on food produce.
• Humans do not transmit either eggs or larvae.

Infection leads to two different clinical presentations depending on the infecting species:

• Eosinophilic meningitis
• Abdominal angiostrongyliasis

• Due to infection with Angiostrongylus cantonensis, the rat lungworm (mainly the cotton rat), which was identified in 1944, when it was thought to be a parasite only of rodents.
• It is the most common cause of human eosinophilic meningitis. Other causes include Gnathostomiasis, Cysticercosis, and non-infectious causes e.g. haematological malignancies and antibiotics (e.g. ciprofloxacin).

Prevalence

Most cases have been reported from Southeast Asia and the Pacific Basin, although the infection is spreading to many other areas of the world, including Africa and the Caribbean.

Presentation

• Symptoms are caused by the presence of larvae and local host reactions in the brain. Eye involvement can occur but ocular angiostrongyliasis is very rare.²
• Symptoms include severe headaches, nausea, vomiting, neck stiffness, seizures and paraesthesiae.

Investigations

• Full blood count - eosinophilia.
• The CSF is abnormal with elevated pressure, proteins, and eosinophilia. On rare occasions, larvae have been found in the CSF.
• Tests for parasite specific IgG antibodies are reliable.³

Management

• There is no effective curative treatment.⁴ Treatment is supportive, including adequate analgesia, therapeutic CSF aspiration and the use of corticosteroids.
• Repeated CSF drainage may give symptomatic relief.
• Steroid treatment appears to be beneficial with reported regimens of 40-60 mg per day of prednisolone for up to 2 weeks.
• Avoidance of anthelmintic agents has been recommended because of their potential for harm from the inflammatory response provoked by antigen release after the death of the parasite.⁵

Prognosis

• Meningitis is usually mild and resolves spontaneously over six weeks.
• Occasionally cases are severe and may lead to long-term neurological complications.

• Caused by Angiostrongylus costaricensis.
• Acute abdominal disease may develop with severe abdominal pain due to inflammatory and thrombotic lesions in the intestines.
• Infection usually involves the terminal ileum, appendix or ascending colon.

Prevalence

Cases have been reported from Central and South America, and occurs most commonly in young children.

Presentation

Prolonged fever, anorexia and acute abdominal pain in the right-lower quadrant.

Differential diagnosis

Acute appendicitis, hydatid disease, cysticercosis, strongylodiasis, and visceral larva migrans.

Investigations

• Full blood count - eosinophilia.
• Tests for parasite specific IgG antibodies are reliable.⁶
• Eggs and larvae can be identified in the tissues removed at surgery.

Management

There is no effective treatment.⁴

Prognosis

Usually benign but it may cause intestinal obstruction or perforation requiring surgery.⁷

• Theoretically control of rodents and molluscs should limit disease.
• Scrupulous attention to personal hygiene and handwashing after outdoor work.
• Washing vegetables thoroughly.
• Avoiding raw or undercooked molluscs, crustaceans, and fish etc.
• Provision of clean drinking water.