The typical form of eosinophilic meningitis was prevalent and widely distributed in Thailand, especially in the northeastern and central parts of the country. The disease occurred seasonally in some areas (e.g., Bangkok) but not in others (e.g., Korat). All age groups were affected, but 71% of cases occurred in persons 20 to 39 years old. Males were affected more than twice as often as females. Most patients gave a history of having consumed raw or rare Pila snails within 30 days before onset of symptoms. A small percentage of patients had eaten other raw or rare animal food, but not Pila, and a few had not eaten any raw or rare animal food. If it is assumed that persons who ate only a single type of raw or rare animal food within 30 days of the onset of symptoms acquired their disease from that source, half the patients had incubation periods of 6 to 15 days. The mean incubation period for all patients was 16 days. Twenty percent of 257 Pila snails, collected from the same areas as those that served as a source of the Pila consumed by patients, were infected with third-stage larvae of Angiostrongylus cantonensis. However, the number of larvae per infected snail was low compared with that in other species of mollusks. A relatively low rate of infection with A. cantonensis was noted among 1,736 rats examined from various parts of Thailand. The data support the conclusion that the typical form of eosinophilic meningitis in Thailand is caused by A. cantonensis and that thousands of cases occur in the country each year.
Division of Gastroenterology and Tropical Medicine, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand.
Department of Experimental Pathology, SEATO Medical Research Laboratory, Bangkok, Thailand.
Department of Tropical Medicine, Pra Mongkutklao Hospital, Bangkok, Thailand.
Pacific Research Section, National Institute of Allergy and Infectious Diseases, Honolulu, Hawaii 96806.