Occurrence of brachylaimid trematodes, alive and shell-trapped, in sympatric species of terrestrial gastropods in France.

Following the detection of Brachylaima spp., which are potentially pathogenic for domestic animals and humans, in Cornu aspersum and Cepaea nemoralis at a rural site in France, we investigated trematode distribution among sympatric gastropod species to assess their role in the parasite life cycle. Eight species were investigated (Cepaea nemoralis, Cernuella neglecta, Clausilia bidentata, Cochlicella acuta, Cornu aspersum, Lauria cylindracea, Pomatias elegans, and Theba pisana). Four species were parasitised by trematodes: C. aspersum (prevalence 56%), C. nemoralis (10%), and T. pisana (2%) as second intermediate hosts of Brachylaima spp., and C. neglecta (6%) as new first intermediate host of Pseudoleucochloridium sp. Moreover, we observed for the first time shell-encapsulation of trematodes in a non-helicid species (C. neglecta) and nematodes in a non-stylommatophoran species (P. elegans), suggesting more general anti-parasite defence than previously thought among land snails. Our current and previous results, including molecular data (28S rDNA, COI mtDNA), suggest the occurrence of four Brachylaima species at the site: Brachylaima mesostoma and three unidentified species. Cornu aspersum is the only identified first intermediate host for B. mesostoma and one of the unidentified trematode species also found at a metacercarial stage in C. aspersum and C. nemoralis. Another unidentified species recorded in C. aspersum and C. nemoralis, characterised by small orange metacercariae, may be a new species. The sole metacercaria found in T. pisana may also belong to an undescribed species.