THE DEVELOPMENT OF FASCIOLA-HEPATICA PARTHENITAE IN LYMNAEA-TRUNCATULA BY MODIFICATION OF MUELLERIUS-CAPILLARIS INFECTION

Adult and juvenile Lymnaea truncatula (height 4 and 1 mm, respectively ) were subjected to a dual infection with either Fasciola hepatica and Muellerius capillaris, or with M. capillaris and F. hepatica at 4-h, 7-, 14- and 30-day intervals between the two exposures. The results we re compared with those of snails which had been infected with a single parasite species. In dually infected snails, there was a high mortali ty at the second exposure to both parasite species, and it was strongl y increased by each reinfection. The interexposure time had a signific ant influence on these mortality rates. Histological examination demon strated a decreased number of rediae (50% or greater) in dually infect ed snails beginning with the 4-h interval in adults and the 7-day inte rval in juveniles. The exposure order and the time interval between ex posures had a significant influence on the number of rediae: the numbe r of parasites per snail decreased as the time interval lengthened. De layed maturity occurred in live free rediae in snails infected by F. h epatica and M. capillaris at the 14- and 30-day intervals. In those in fected by M. capillaris and F. hepatica, time to reach maturity was no t modified compared to that in snails infected with a single species. Protostrongylid larvae were clearly less numerous in dually infected a dult snails than in corresponding mono-infected snails. Third-stage la rvae were found in the 14- and 30-day groups, regardless of exposure o rder and were absent in mono-infected snails.