Fasciola hepatica: the effect of food quality on the development of redial generations in Galba truncatula infected with allopatric miracidia.

Individual bimiracidial infections of French Galba truncatula with an allopatric (Moroccan) isolate of Fasciola hepatica were carried out under laboratory conditions to count free rediae and intraredial daughter rediae in snails just after their death, and to determine whether feeding the snails on lettuce only or lettuce plus Tetraphyll had an effect on the development of redial generations. Controls consisted of snails infected with sympatric (French) miracidia and reared with lettuce only. In the allopatric group, reared with lettuce only as food, a higher mortality rate of snails in the first 4 weeks of the experiment was noted, and most G. truncatula showed 1-sporocyst infections, with the usual development of redial generations. Compared to the sympatric group, the growth of the first mother redia (R1a redia) in each snail of the allopatric group was significantly slower during the first weeks of infection, whereas a significantly increased formation of intraredial daughter rediae in the other mother rediae (R1b rediae) was noted over the same period. In the allopatric group, reared with cos lettuce and commercial fish food, 1-sporocyst infections (45.5% of snails) and 2-sporocyst infections (53.9%), with the usual development of redial generations, were noted. Compared to the sympatric group, a significantly slower development of the first mother redia during the first weeks of the experiment was noted in the 1-sporocyst infections, whereas the values in the 2-sporocyst infections did not significantly differ from those noted in the sympatric group. Similar results were noted for the production of intraredial daughter rediae in the R1b rediae during the first weeks of the experiment. In all infections derived from the growth of a single sporocyst per snail, the differentiation of numerous daughter rediae inside R1b rediae would be induced by the slow growth of the R1a redia (from which the most important group of R2a rediae originated) during the first weeks of infection and might represent a mechanism to replace free rediae absent from the inside of the snail.