Ecological Niche Model based on Maximum Entropy for mapping distribution of Bithynia siamensis goniomphalos, first intermediate host snail of Opisthorchis viverrini in Thailand.

The snail Bithynia siamensis goniomphalos acts as first intermediate host of the liver fluke, Opisthorchis viverrini, which causes opisthorchiasis in humans. In this study, we used a geographic information system (GIS), remote sensing (RS) and software using the maximum entropy (MaxEnt) algorithm to predict the distribution of B. s. goniomphalos in Thailand on the basis of environmental and climatic factors. The MaxEnt model for B. s. goniomphalos was excellent, with average test AUC values of 0.89. The predicted distribution of B. s. goniomphalos was affected by altitude, land cover, normalized difference vegetation index (NDVI), precipitation in the driest month (BIO 14), land surface temperature (LST) and soil pH. The areas suitable for B. s. goniomphalos were mostly in Northeast Thailand and some northern parts of the country. The presence of B. s. goniomphalos decreases with increasing altitude and increasing NDVI value. Bithynia s. goniomphalos is most likely to occur in paddy fields and cropland. Opisthorchiasis prevalence was directly proportional to the likelihood of snail occurrence as predicted by the model. This is the first time this ecological niche model has been used to predict Bithynia snail distribution and hence to provide a basis for future work of opisthorchiasis prevention in opisthorchiasis-endemic countries.