Fasciola hepatica and Paramphistomum daubneyi: decrease in prevalence of natural infection in habitats colonized by Galba truncatula and Lymnaea glabra

SUMMARY Parasitological investigations in six snail communities formed by Galba truncatula and Lymnaea glabra on cristallophyllian or metamorphic soils were carried out during four successive years to determine prevalence of snail infection with Fasciola hepatica or Paramphistomum daubneyi. The dynamics of snail populations and snail growth throughout the year in other two snail communities was also studied during two years to specify their eventual relations with prevalence of snail infection. Control sites were constituted by habitats frequented by a single lymnaeid species. In sites colonized by a lymnaeid community, each population occupied a distinct zone (G. truncatula upstream and L. glabra downstream), even if there was always an overlapping area. Prevalence of infection with F. hepatica or P. daubneyi was significantly lower in the overlapping area of habitats with a snail community. In contrast, the differences in percentages noted in the upstream or downstream areas of habitats colonized by a lymnaeid community and in control sites were insignificant. The number of snails for each population was significantly lower in a lymnaeid community than in a monospecific population, while the shell height of overwintering snails in March did not show any significant difference. The greater density of snails in the overlapping areas of habitats colonized by a lymnaeid community and the role of L. glabra as an intermediate host of both digeneans (only susceptible in its first weeks of life) might be the cause of this decrease in prevalence of natural infection.