Potential impact of climate change on Opisthorchis viverrini and Opisthorchis felineus transmission in Eurasia

Human liver flukes of the family Opisthorchiidae, particularly Opisthorchis viverrini and Opisthorchis felineus, are major foodborne trematode parasites endemic to the Lower Mekong River Basin (Southeast Asia) and the Ob-Irtysh Basins (southern Western Siberia, Russian Federation), respectively. Together, these parasites infect over 14 million people, with an estimated 300 million at risk. Their transmission cycles involve Bithynia snails and Cyprinidae fish as first and second intermediate hosts, respectively, with humans and other fish-eating mammals serving as definitive hosts. The geographical distribution of these flukes is shaped by specific Bithynia species: B. siamensis, B. s. goniomphalos, and B. funiculata for O. viverrini, and B. troschelii, B. leachi, and B. inflata for O. felineus. Climate change directly influences liver fluke transmission by affecting parasite survival, host biology, and environmental conditions. Bithynia snails are highly temperature-sensitive, and O. viverrini transmission is notably temperature-dependent, with a 1 °C increase raising infection odds by 5.4 %. Temperatures exceeding 30 °C reduce cercarial survival and infectivity. In Western Siberia, favorable water temperatures for O. felineus transmission start at +15 °C, with higher temperatures leading to an increased infection rate in snails while permafrost regions lack Bithynia snails entirely. Projections from the Intergovernmental Panel on Climate Change (IPCC) indicate that warming will exceed the global average in northern Asia (affecting O. felineus) and approach the global average in Southeast Asia (impacting O. viverrini). These trends suggest that climate change may have a more pronounced impact on O. felineus transmission in Siberia than on O. viverrini transmission in Southeast Asia. This review provides an in-depth discussion of Bithynia biology and the effects of temperature on snail growth, cercarial release, survival, infection, and aestivation, emphasizing how global warming could influence the transmission dynamics of these liver flukes.