Fasciola hepatica: the characteristics of experimental infections in Lymnaea truncatula subjected to miracidia differing in their mammalian origin

Experimental infections of Lymnaea truncatula. using two susceptible snail populations (Berneuil, or Migne, central France) and four isolates of Fasci ola hepatica miracidia differing in their mammalian host of origin (cattle, nutrias, rabbits, or sheep). were performed under laboratory conditions to determine whether the host of origin had an effect on the daily production of cercariae. Snails were each subjected to bimiracidial exposures and wer e then reared under semi-natural conditions (a constant temperature of 20 d egreesC and natural photoperiod). Significantly lower values were noted in the rabbit groups for survival rates at day 30 post-exposure, as well as fo r prevalences of infection, snail growth, duration of shedding period, and the total numbers of cercariae these snails shed. The total number of cerca riae shed by both nutria groups was significantly higher than those recorde d in the six other infected groups. In the cattle, rabbit, and sheep (Berne uil only) groups, the peaks in the daily distribution of cercariae occurred between day 2 and day 4 after the first shedding. and the number of cercar ia-shedding snails decreased with increasing number of shedding waves. In c ontrast, in the three other groups, the peaks were only observed between da ys 20 and 45. Snails shedding their cercariae during nine or more waves wer e numerous in these last groups. No inf-radian-type rhythm in the daily dis tribution of cercarial numbers over the shedding period was noted for any s nail group. The highest production of F. hepatica cercariae in both nutria groups would be a consequence of a higher success rate of miracidia when th ey infected an allopatric population of snails. The absence of an inf-radia n-type rhythm in the distribution of daily cercarial numbers in the eight g roups suggests that this rhythm, if it occurs, would only be influenced by temperature and thus be limited to periods with optimal conditions for cerc arial shedding.