Changes in the Populations of Two Lymnaeidae and Their Infection by and/or over the Past 30 Years in Central France.

Field investigations were carried out during three periods (from 1976 to 1997, in 2013-2014, and in 2020-2021) on 39 cattle-raising farms on acidic soils to track changes in the populations of two Lymnaeidae ( and ) and their infection with and/or . Compared to the survey between 1976 and 1997 on these farms, there was a significant decrease in the number of the two lymnaeid populations and the size of the populations in both 2013-2014 and 2020-2021. This decline was significantly faster in the last nine years than it was before 2013. The area of habitats colonized by showed no significant variation over the years, while that of habitats with significantly decreased in the period covered by the three surveys. The prevalence of infection in snails significantly decreased over the years, while infection increased over time in both lymnaeid species. These changes are due to the use of triclabendazole to treat fasciolosis in ruminants since the 1990s, and are probably a consequence of the successive heatwaves that have occurred since 2018 in the region.