Paramphistomum daubneyi and Fasciola hepatica:: the prevalence of natural or experimental infections in four species of freshwater snails in eastern France

Parasitological investigations were performed in July and September-October 1997 in six farms located in the department of Saone et Loire (eastern France) to determine the prevalence of natural infections with Paramphistomum daubneyi and Fasciola hepatica in four species of freshwater snails. Cercaria-containing rediae of P. daubneyi and/or F. hepatica were found in Lymnaea palustris (one snail only) and Lymnaea truncatula. Some living sporocysts and immature rediae were noted in Lymnaea ovata (P. daubneyi or F. hepatica) and in Physa acuta (P. daubneyi only). The prevalence of each trematode infection was often less than 10%. Experimental infections of juvenile and preadult snails (1 and 4 mm in height, respectively) were also performed to test the susceptibility of these four snail species to P. daubneyi, either singly or in combination with F. hepatica. Both 1 and 4 mm high L. truncatula could sustain the full development of P. daubneyi, whether in single or double infections. Ln L. palustris dually exposed to both trematodes, cercaria-containing rediae of P. daubneyi were found in one juvenile and one preadult snails, while immature infections were noted in ten juvenile and two preadult snails. The overall prevalence of P, daubneyi infection in L. palustris was 11.1% in juvenile snails and 2.1% in preadults. Larval forms of P. daubneyi and F. hepatica were only noted in dually-exposed juvenile L. ovata and P. acuta. Ln L. ovata, mature and immature rediae of F. hepatica were detected in 17.6% of snails, while immature rediae of P. daubneyi were noted in 4.4% of snails. In P. acuta, only immature infections were detected (5.1% of snails with P. daubneyi, and 1.2% with F. hepatica). These results demonstrated that Lymnaea species other than L. truncatula could sustain the full development of P. daubneyi and that immature larvae of this trematode might be found in naturally- or experimentally-infected L. ovata and P. acuta.