Distribution and Fasciola infection rates of Lymnaea snails and cattle in high-salinity areas of Mekong Delta, Vietnam.

Fasciola-induced fascioliasis is a zoonotic disease with significant health and economic impacts on humans and livestock. Freshwater Lymnaea snails serve as intermediate hosts, contributing to the increasing prevalence of fascioliasis in cattle in coastal areas. The salinity tolerance of Lymnaea snails was investigated along with their distribution and Fasciola infection rates in both snails and grazing cattle in Ben Tre, Tra Vinh, and Soc Trang provinces in Mekong Delta, Vietnam, where seawater reversely enters into the paddy field during the dry season. Lymnaea snails were collected from 53 communes across the three provinces and analyzed for Fasciola larval infections. Additionally, cattle fecal samples were examined for the presence of Fasciola eggs. The salinity levels in the study areas ranged from 0.03% to 1.90%. In total, 1,152 Lymnaea snails including L. viridis and L. rubiginosa were collected. The maximum salinity levels of L. viridis and L. rubiginosa habitats were 0.64% and 0.74%, respectively. The Fasciola infection rates of L. viridis were 2.0% in low-salinity areas and 3.7% in high-salinity areas, whereas no L. rubiginosa infections were detected in either salinity area. The prevalence of cattle fascioliasis in high-salinity areas (35.7%) was similar to low-salinity areas (32.9%). This study is the first to demonstrate that L. viridis can thrive and sustain Fasciola transmission under high-salinity conditions, suggesting the salinity tolerance of these intermediate host snails as a key factor contributing to the expansion of fascioliasis in high-salinity coastal areas.