The susceptibility of Lymnaea fuscus to experimental infection with Fasciola hepatica

Three experiments on the infection of Lymnaea fuscus with Fasciola hepatica were carried out to determine if successful infections and maturation of t he parasite were dependent on the size of snails at miracidial exposure. Th e first experiment was performed using 1-4-mm-high snails from 2 population s of L. fuscus and 1 population of lymnaea palustris. In these snails each subjected to a single bimiracidial exposure, the prevalence of F. hepatica infection at day 35 postexposure ranged from 20.3% to 46.2% in snails measu ring 1 mm in height at exposure: it was lower in the 2-mm snails and was 0 in higher size classes. The second experiment was performed by subjecting 1 and 4-mm L. fuscus to 1, 2, and 3 bimiracidial exposures. The prevalence o f F. hepatica infection at day 35 postexposure was maximum in the l-mm snai ls exposed once to miracidia and decreased with increasing number of exposu res. The results were negative in 4-mm snails. Cercarial shedding of F. hep atica was studied in the third experiment using 1- and 2-mm L. fuscus each subjected to a single bimiracidial exposure. The total number of cercariae released from these snails was less than 50. From these results, it can be concluded that L. fuscus showed a partial resistance to F. hepatica infecti on due to snail age.