Effects of aestivation on survival of Bithynia siamensis goniomphalos snails and the infection of Opisthorchis viverrini in the irrigation area of wet- and dry-season rice paddy.

The snail Bithynia siamensis goniomphalos acts as the first intermediate host of the human liver fluke, Opisthorchis viverrini, a major cause of cholangiocarcinoma in Northeast Thailand. In this study, we investigated host-parasite interactions in wet- and dry-season rice paddy plantation. The snails that aestivated through 4-month-dried period after rice harvest had average mortality rate of 36.45% and monthly increasing from 17.76% to 54.57%. Surprisingly, at depths greater than 5 cm experienced a higher mortality rate than upper level. Average mortality rate at the depth more than 5 cm, was 42.97%. In the initial month of aestivation, mortality rate of 0-5 and 5-10 cm depth was 9.13% and 26.39% then increase to 57.58% and 51.97%, respectively in the last 4th month. The average prevalence O. viverrini infection in snails during the study period was 0.44%. The highest prevalence of O. viverrini infection was found in the cool dry and wet season. The odds of O. viverrini infection in female snails and large snails were higher relative to male snails and medium-sized snails. The physicochemical factors involved in increased prevalence of O. viverrini infection in snail hosts were mean daily air temperature and average monthly rainfall. Short aestivation period made lower mortality in irrigation area than the previous report of non-irrigation area, that is, the aestivation is one of snail population control.