Hydropower reservoirs - their potential association with transmission of trematodes in Vietnam.

The effect of reservoir construction on medically important parasites is well known worldwide but lacks information in Vietnam. With 385 active hydropower plants and numerous water reservoirs, Vietnam provides an ideal setting for studying this issue. This study investigated trematode infection in snail first intermediate hosts from three hydropower reservoirs: Hoa Binh, Son La, and Thac Ba. In total, 25,299 snails representing 16 species were examined, with 959 individuals (8 species) shedding identifiable cercariae. Infection prevalence was highest in thiarid snails (5.4%-15.4%), followed by bithynid snails (2.9%-5.8%). Other snail species showed infection prevalence ranging from 0.3% to 2.9%. Infection prevalence varied significantly across regions, with the highest prevalence in Son La, followed by Hoa Binh and Thac Ba reservoirs. However, no significant differences were observed between snails collected from reservoirs versus canals and paddy fields. Morphological identification resulted in nine cercarial morphotypes, with pleurolophocercaria, xiphidiocercariae, and echinostome being the most common types, accounting for 89.2% of all cercarial infections. Echinostome cercariae were found in seven snail species, while the other cercarial morphotypes were shed by two to five species. Gabbia fuchsiana, Parafossarulus manchouricus, and Melanoides tuberculata were the most common hosts, each harboring five cercarial morphotypes, while Radix auricularia only released echinostome type. In conclusion, our findings highlight the endemic presence of trematodes in hydropower reservoirs and emphasize the need to consider the human-environment interaction around these reservoirs for a better understanding of disease transmission risks.