Land snails and periods at high risk for protostrongylid infection on a sheep-grazed pasture of northeast Tunisia

The population density and level of infection of terrestrial molluscs, and the output by sheep of first stage protostrongylid larvae, were assessed monthly during a 1-year study. Muellerius capillaris was the predominant protostrongylid (approximately 80% of the larval output); Neostrongylus was also found. Eobania vermiculata, Cernuella virgata and Trochoidea elegans were the most common molluscs. Juveniles were less infected than adults. Banded E. vermiculata had a lower intensity of infection than unbanded ones. Nearly 75% of protostrongylid larvae harboured by molluscs on the studied pasture were found in E. vermiculata. The infectivity of pasture was at its lowest in the dry and hot period (June-September). Infection of snails was primarily related to temperature and the importance and frequency of rains, and secondarily to larval excretion in sheep faeces.