The stress of Lymnaea truncatula just before miracidial exposure with Fasciola hepatica increased the prevalence of infection

Single-miracidium infections of Lymnaea truncatula with Fasciola hepatica w ere carried out under laboratory conditions to determine whether the stress of snails just before miracidial exposure had any influence on the prevale nce of Fasciola infection, redial burden, and cercarial shedding. Three met hods, i.e., the fasting of L. truncatula for 3 days in water filtered throu gh a Millipore membrane, the effect of 6-8 degreesC water for 15 min, or th e immersion of L. truncatula in a detergent solution at low concentration f or 15 min, were used to stress snails. Enhanced susceptibility of snails to F. hepatica infection was noted in stressed groups (93-96% vs 48-50% in co ntrols). The number of free rediae. did not show any variation in controls as well as in stressed groups, except for fasted snails in which free redia e were significantly fewer. No differences in cercarial production between controls and the cold group were noted. Fasting, cold shock, or detergent e xposure prior to exposure to F. hepatica miracidia might have weakened the snails so that they were not as efficient in avoiding miracidial penetratio n, thus leading to higher infection rates. (C) 2001 Academic Press.