In Thailand eosinophilic meningoencephalitis is not an uncommon condition. In a period of one year, nine cases were recorded in one hospital in Bangkok. All of the patients gave a definite history of having eaten raw or pickled snails (Pila ampullacea), all complained of severe headache, and all had eosinophilia of the cerebrospinal fluid.
Adult Angiostrongylus cantonensis were recovered from the pulmonary arteries of two out of six laboratory-bred albino rats fed with Pila ampullacea from natural habitats while rats fed with other snails (Vivipara doliaris) and prawns (Caridina laevis) from the same area were negative. Pila was also proved experimentally as an intermediate host of A. cantonensis. Examination of 50 rats trapped from some areas of Bangkok and Dhonburi revealed no Angiostrongylus infections. It was concluded that A. cantonensis probably is a major cause of eosinophilic meningoencephalitis in Thailand, and Pila ampullacea is an important source of the infection in man.