Fasciola hepatica: Characteristics of infection in Lymnaea truncatula in relation to the number of miracidia at exposure

Experimental infections of Lymnaea truncatula by Fasciola hepatica were car ried our in three snail populations to determine whether the number of mira cidia used for each snail at exposure (1,2, 5, 10, or 20 per snail) had any influence on the characteristics of Fasciola infection and metacercarial p roduction. The number of miracidia had a significant influence on snail sur vival at day 30 postexposure and the frequency of infected L. truncatula th at died without shedding (NCS snails). The frequency of NCS snails, the gro wth of cercaria-shedding snails throughout the experiment, the time between exposure and the first cercarial shedding, the duration of shedding, and t he number of metacercariae were independent of the number of miracidia used for each snail. The highest metacercaria productivity for each miracidium was found in single-miracidium infections. Single-miracidium infections wer e the most effective, as the mean number of cercariae was the same as in ot her groups, whereas their survival rate was much higher. (C) 1999 Academic Press.