Angiostrongylus cantonensis: proof of direct transmission with its epidemiological implications.

Infective larvae of the rat lungworm Angiostrongylus cantonensis, presumed cause of human eosinophilic meningoencephalitis, are shed in mucus exuded by naturally infected Malayan slugs (Microparmarion malayanus). Larvae passed by slug hosts were recovered from lettuce and produced normal infection in white rats. Lettuce sold in the local public market also yielded small numbers of infective larvae. Experimental evidence from rats suggests that the local human population, exposed to repeated low-level infections, may become immunized against the rare massive exposure and against clinical disease that might otherwise result after ingestion of heavily infected raw mollusks.