Characteristics of Fasciola hepatica infections in Galba truncatula originating from riverbank populations.

Four geographical strains of Galba truncatula living on riverbanks (the first on a sedimentary soil and the other three on an acid soil) were subjected to bimiracidial exposures with Fasciola hepatica to study their aptitude for cercarial shedding and to count metacercariae in snails dissected at day 42 post-exposure. All snails were reared in 14-cm Petri dishes at 24 °C, with the same spring water (60-73 mg/l of Ca²+) and the same diet (grass and lettuce leaves). Metacercariae of F. hepatica were noted in the four populations after a cercarial shedding or after snail dissection. However, in spite of the breeding method used, the characteristics of snail infections varied with the origin of each geographical strain. For example, the shell heights of infected snails at day 42 were close to those found for the corresponding adults in the field (6.8-8.0 mm for the population living on the sedimentary soil, but only 4.6-5.5 mm for another strain originating from the acid soil). This variability may be explained by assuming that the diet of these riverbank G. truncatula would be different from that of snails living in swampy meadows. However, another hypothesis based on the influence of snail habitat on the characteristics of snail life cannot be excluded.