Influence of Water Irrigation Schemes and Seasonality on Transmission Dynamics of Opisthorchis viverrini in the Snail Intermediate Host, Bithynia siamensis goniomphalos in Rice Paddy Fields in Northeast Thailand

Abstract

Opisthorchis viverrini is a fish-borne zoonotic trematode that causes significant public health problems in Southeast Asia. Its life cycle requires Bithynia 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 O. viverrini in Bithynia siamensis goniomphalos in rice paddy field habitats. The transmission of O. viverrini cercariae in B. s. goniomphalos 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 O. viverrini was 0.7% (range, 0.0-4.1%). The prevalence of O. viverrini infection in B. s. goniomphalos 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 O. viverrini in B. s. goniomphalos.

Population dynamics and diversity of trematode infections inBithynia siamensis goniomphalosin an irrigated area in northeast Thailand

“…The patterns of rainfall were consistent between years while the duration of irrigation and amount of irrigated water varied during the study period as previously reported (Kopolrat et al ., 2020) (Fig. 1).…”

“…The study area was a rice paddy-field habitat of B. s. goniomphalos in Sakon Nakhon Province, northeast Thailand, the same area as discussed in our previous report where detailed ecology and land-use practices in paddy rice cultivation were described (Kopolrat et al ., 2020). The area has a tropical monsoon climate with the year being divided into three seasons.…”

“…In endemic areas of O. viverrini , B. s. goniomphalos have varying trematode prevalence levels that are associated with seasonal and host factors (Kiatsopit et al ., 2012; Namsanor et al ., 2015). We recently reported the influence of water irrigation schemes and seasonality on transmission dynamics of O. viverrini in B. s. goniomphalos in the rice paddy fields in northeast Thailand (Kopolrat et al ., 2020). In addition to O. viverrini , this study also reported several other trematode cercariae found in B. s. goniomphalos , but how the environmental conditions, i.e.…”

“…Long-term studies to capture yearly variation, the effect of seasonality and human land use have not been reported. We hypothesize that seasonality and land use for agriculture have a profound impact on transmission dynamics of trematode cercariae in B. s. goniomphalos similar to that observed in the case of O. viverrini cercariae previously reported (Kopolrat et al ., 2020).…”

Towards Evidence-based Control of Opisthorchis viverrini

“…Furthermore, the informal nature of fish-distribution networks makes it challenging to impose food safety controls [7]. Controlling snail populations is also considered unfeasible as Bithynia snails inhabit many water sources, including rice paddies, and are resilient to cycles of drought and flooding [8,9]. Defecation into water sources occurs as fishermen and rice farmers work far from their homes for long periods of time [10].…”