THE POPULATIONS OF LYMNAEA-TRUNCATULA LIV ING ALONG RIVERSIDES - EXPERIMENTAL STUDIES ON THEIR APTITUDE FOR FASCIOLA-HEPATICA INFECTION

Experimental infections of Lymnaea truncatula by Fasciola hepatica wer e performed on 4 snail populations living along riversides in order to determine their aptitude for Fasciola infection. No cercaria was shed from the L. truncatula of Saint-Martin-Terressus (department of Haute -Vienne). The snails from the 3 other colonies have shed cercariae and the frequency of shedding snails was 3-6 % in the Saint-Priest-Taurio n population (department of Haute-Vienne), 11-15 % in that of Limoges (department of Haute-Vienne), and 41 % in that of Saint-Gaultier (depa rtment of Indre). The duration of the prepatent period ranged from 39. 7 to 43.9 days, whereas that of the patent period ranged from 5.2 to 1 2.7 days. The total number of metacercariae varied according to the po pulation used for experiments : a mean of 51 per snail in the colony o f Saint-Gaultier, 43.4 in that of Limoges, and 19.7 in that of Saint-P riest-Taurion. The percentage of floating cysts was 13.9 % in the Sain t-Priest-Taurion population and 4.4 % in the 2 other colonies. The num ber of snails shedding their cercariae into a single wave was dominant in the 3 colonies (a total of 48.8 %). From these studies, it can be concluded that the L. truncatula living along riversides would be unus ual intermediate hosts in the cycle of F. hepatica because they were l ittle infected and had a limited cercaria production.