Molecular genetic species definition of Opisthorchiidae-like cercariae from Bithyniidae snails of Chany Lake (South-Western Siberia, Russia)

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.

Idiopyrgus souleyetianus (Gastropoda: Tomichiidae) as an intermediate host of the liver fluke Amphimerus sp. (Trematoda: Opisthorchiidae) in Brazil

Despite the importance of fish-borne trematodes of the family Opisthorchiidae as causative agents of human liver fluke disease, studies on these parasites outside Asia are relativally scarce. In South America, human focus of amphimerosis is known in Ecuador since the mid-20th century, and Amphimerus spp. have also been reported in wild and domestic mammals. Nevertheless, the knowledge on the snails that act as the first intermediate host of these potentially zoonotic parasites are scarce. Herein, a new cercaria of the pleurolophocercous morphotype found in the freshwater snail Idiopyrgus souleyetianus from Brazil was subjected to morphological and molecular studies. Multigene phylogenetic analyses based on 28S, 5.8S-ITS-2 and Cox-1 sequences enabled the identification of Amphimerus sp., a species distinct from that reported in humans from Ecuador. This cercariae was morphologically compared with other opisthorchiid cercariae known. The possible occurrence of human amphimerosis in Brazil is discussed.