Paramphistomum daubneyi and Fasciola hepatica: the effect of dual infection on prevalence and cercarial shedding in preadult Lymnaea glabra.

Preadult Lymnaea glabra measuring 4-6 mm in height were each exposed to 1 Paramphistomum daubneyi miracidium before being exposed to 1 miracidium of Fasciola hepatica. Total prevalence of infection in the snail groups from 3 different populations ranged from 33% to 39%. In each group, snails harboring larval forms of P. daubneyi, F. hepatica, or both, were noted. If the results from the 3 snail populations are pooled, the total prevalence of snail infection was 13.6% in snails harboring only F. hepatica larvae, 13% in those harboring only P. daubneyi larvae, and 10% in those with both trematodes. Cercarial shedding was obtained from snails harboring F. hepatica larval forms; in the case of snails infected with both trematodes, the mean number of metacercariae ranged from 13 to 21 for F. hepatica, and from 8 to 14 for P. daubneyi. No infected snails were found in snail groups exposed only to 1 trematode miracidia.