Opisthorchis viverrini (Poirier), 1886) Stiles and Hassall, 1896

ETYMOLOGY:Opistho = posterior and orchis = testis along with viverrini = representing the host from which it was originally described Felis viverrus.

The adult Opisthorchis viverrini is morphologically very similar to and almost indistinguishable from Opisthorchis felineus; there are, however, morphological differences in the larval stages. This trematode is a common problem in Thailand, where in some villages infections in human populations may be as high as 94% (Upatham ES, Viyanant V, Kurathong S, Brockelman WY, Menaruchi A, Saowakontha S., Intarakhao C, Vajrasthira S, Warren KS. 1982. Morbidity in relation to intensity of infection in opisthorchiasis viverrini: study of a community in Khon Kaen, Thailand. Am J Trop Med Hyg 31:1156-1163.). The infection also occurs in Laos, Malaysia, and India. In Thailand, cats are found infected with this parasite even in areas where human infections are uncommon (Sadun EH. 1955. Studies on Opisthorchisviverrini in Thailand. Am J Hyg 62:81-115.); in 1965, 60% of cats sampled in the northeastern part of the country were infected. The second intermediate host is a fresh-water fish, and the infection is obtained by eating raw fish. Infections in humans have led to carcinoma of the bile ducts (Wykoff DE, Chittaysothorn K, WInn MM. 1966. Clinical manifestations of Opisthorchisviverrini infections in Thailand. Am J Trop Med Hyg 15:914-918.). Fecal examinations have shown that infected cats shed from 358 to 3,509 eggs per adult worm per day; sixteen naturally infected cats were found to harbor an average of 99 worms per cat (Wykoff DE, Ariyaprakai K. 1966. Opisthorchisviverrini in Thailand - Egg production in man and laboratory animals. J Parasitol 52:631).