Nematodes of rats of the genus Angiostrongylus cause two distinct syndromes in humans. Angiostrongylus cantonensis, the rat lungworm, causes eosinophilic meningoencephalitis, primarily in Southeast Asia and some Pacific islands, but with multiple recent reports also from the Americas, Hawaii (82 reported cases in 2007–17), and Australia. In one study, A cantonensis was responsible for 67% of evaluable cases of eosinophilic meningitis in Vietnam. Angiostrongylus costaricensis causes gastrointestinal inflammation. In both diseases, human infection follows ingestion of larvae within slugs or snails (and also crabs, prawns, or centipedes for A cantonensis) or on material, such as salads, contaminated by these organisms. Since the parasites are not in their natural hosts, they cannot complete their life cycles, but they can cause disease after migrating to the brain or gastrointestinal tract. A cantonensis can also migrate from the brain to the pulmonary arteries.
A. A cantonensis Infection
The disease is caused primarily by worm larvae migrating through the CNS and an inflammatory response to dying worms. After an incubation period of 1 day to 2 weeks, presenting symptoms and signs include headache, stiff neck, nausea, vomiting, cranial nerve abnormalities, and paresthesias. Most cases resolve spontaneously after 2–8 weeks, but serious sequelae and death have been reported. The diagnosis is strongly suggested by the finding of eosinophilic CSF pleocytosis (over 10% eosinophils) in a patient with a history of travel to an endemic area. Peripheral eosinophilia may not be present. Definitive diagnosis is made by recovery of A cantonensis larvae from the CSF and the eyes, although this is uncommon.
B. A costaricensis Infection
Parasites penetrate ileocecal vasculature and develop into adults, which lay eggs, but do not complete their life cycle. Disease is due to an inflammatory response to dying worms in the intestinal tract, with an eosinophilic granulomatous response, at times including vasculitis and ischemic necrosis. Common findings are abdominal pain, vomiting, and fever. Pain is most commonly localized to the right lower quadrant, and a mass may be appreciated, all mimicking appendicitis. Symptoms may recur over months. Uncommon findings are intestinal perforation or obstruction, or disease due to migration of worms to other sites. Many cases are managed surgically, usually for suspected appendicitis. Biopsy of inflamed intestinal tissue may show worms localized to mesenteric arteries and eosinophilic granulomas.
Antihelminthic therapy may be harmful for A cantonensis infection, since responses to dying worms may worsen with therapy. If antihelminthic treatment is to be used, albendazole is probably the best choice, and therapy should be early in the disease course (within 3 weeks of exposure). Corticosteroids have commonly been used, and these are probably appropriate if antihelminthics are provided. Ocular infection is treated surgically. It is not known if antihelminthic therapy is helpful for A costaricensis infection.
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