Field studies on the transmission of the human liver fluke, Opisthorchis viverrini, in northeast thailand: population changes of the snail intermediate host

Abstract

Field studies on the transmission of the human liver fluke, Opisthorchis viverrini, in northeast Thailand: population changes of the snail intermediate host. International Journal for Parasitology 16: 545-552. A natural population of Bithynia siamensis goniomphalos, snail vector of the human liver fluke Opisthorchis viverrini was sampled for 3 years in a shallow reservoir in Khon Kaen Province, northeast Thailand. During the study period, the habitat experienced a 17-month drought followed by a surging flood. Snails suffered over 90% mortality during drying of the reservoir but died at an average rate of only 5% per month during aestivation. When water returned they migrated to new edge habitats, apparently on floating debris, and reproduced. Peaks in reproduction occurred following spring rains and after the fall monsoon flooding subsided. Normally, two generations are produced per year in seasonal habitats. The prevalence of O. viverrini infection averaged 0.11 % in adult snails over 8 mm in length; smaller snails were not infected. Control of opisthorchiasis through snail control does not appear practical because of the widespread distribution of the snails, their ability to survive in very unstable habitats, and for other reasons concerned with the existence of the fish host between snail and human hosts. © 1986.