Unveiling a cryptic snail host of major trematodes in Europe: The susceptibility of Galba schirazensis (Lymnaeidae) to Calicophoron daubneyi (Paramphistomatidae) facilitates Fasciola hepatica (Fasciolidae).

Species of Lymnaeidae (Mollusca: Gastropoda) are important intermediate hosts of major parasites some of which are responsible for zoonosis worldwide. Particularly liver and rumen flukes impact livestock production with increasing costs due to flukicide treatments. In Europe, a single snail species, Galba trunctaula, is considered as responsible for the transmission of Fasciola hepatica and Calicophoron daubneyi, two trematode species with almost identical transmission cycles. However, the occurrence of a second cryptic and largely overlooked Galba species in Europe raises questions about the possibility of a different player in the transmission of these parasites. The sibling snail Galba schirazensis, a species with a controversial role in F. hepatica transmission but found to be infected in the field in South America, seems to be present in the field in Europe, but its role in rumen and liver fluke transmission remains unknown. After a series of experimental infections, we present two main results: (1) for the first time, the ability of G. schirazensis to become infected (100 % infection rate) and produce viable cercariae that encysted into metacercariae of the rumen fluke C. daubneyi after crush-dissection. We found significant higher parasite intensity in terms of rediae and metacercariae production in G. schirazensis compared to G. truncatula (used here as control). (2) While there was no F. hepatica development after performing mono infections in G. schirazensis, the latter became infected with the liver fluke when previously exposed to C. daubneyi (subsequent exposure). We obtained metacercariae for both trematodes after crush-dissection (23 % overall coinfection prevalence). Our results shed light on the potential role of the lymnaeid species G. schirazensis in major trematode life cycles that could mark a shift in our general understanding of the field transmission of rumen and liver flukes.