A retrospective study on the metacercarial production of Fasciola hepatica from experimentally infected Galba truncatula in central France.

A retrospective study of the experiments performed during the past 15 years on infections of Galba truncatula with Fasciola hepatica was carried out to determine what susceptible populations of snails might be used for the commercial production of metacercariae, and to examine this metacercarial production in relation to the characteristics of snail infections. Of the four groups of snail populations studied, the ablest snails to sustain a complete larval development of F. hepatica originated from populations living on siliceous soils at 600 m and more in altitude. In contrast, snail populations living along river banks on siliceous soils were inappropriate due to the poor characteristics of snail infections (high snail mortality, low prevalence of snail infections, and low number of cercariae produced). Except for these last populations, 86-87% of cercaria-shedding (CS) snails in the other populations shed less than 300 cercariae, even if a maximum of 1,772 cercariae were obtained from a single snail. The date of the first cercarial shedding at 20 degrees C began during week 7 or 8 PE for 80.1-83.5% of CS snails. Most metacercariae (82.0-85.9% of the total production) were recorded during the first 10 days of the patent period. In these conditions, the authors collected metacercarial production up to the beginning of week 10 PE (20 degrees C) and did not use snails that shed their cercariae during the following weeks due to too low numbers of parasites. This method allows to have a continuous production of metacercariae over time by using successive groups of infected snails, each being separated from the other by a fortnight's time.