Influence of Water Irrigation Schemes and Seasonality on Transmission Dynamics of in the Snail Intermediate Host, in Rice Paddy Fields in Northeast Thailand.

is a fish-borne zoonotic trematode that causes significant public health problems in Southeast Asia. Its life cycle requires snails as the first intermediate hosts, fish, and human and/or carnivore hosts. This study assessed impacts of land use practice for rice cultivation and seasonality on the transmission dynamics of in in rice paddy field habitats. The transmission of cercariae in was monitored at monthly intervals over a 4-year period from January 2010 to December 2013. From a total of 59,727 snails examined by standard cercarial shedding, the prevalence of was 0.7% (range, 0.0-4.1%). The prevalence of infection in varied with the amount of rainfall, with peaks of infection occurring in the cool-dry season, that is, after each rainy season. A shift of peak prevalence from cool-dry to hot-dry season observed in 2013 was associated with the increase in preceding water irrigation to support the production of second annual rice crop. Significant positive correlations were found between the prevalence and intensity of cercarial infection and the size of snails. Our results revealed substantial variation between years so that to have a clear understanding of the population dynamics of this complex system, studies should be conducted over an extended period (> 1 year). Results from this study highlight that water irrigation schemes in rice paddy cultivation and seasonality have a significant effect on the prevalence of in .