Experimental Infection of Lymnaea glabra and L. truncatula by Fasciola hepatica

Abstract

Epidemiological studies on human fascioliasis recorded the role of Lymnaea glabra as an accidental intermediate host in the life-cycle of the parasite in the region of Limousin, France (Rondelaud, 1980, Ann. Parasit. Hum. Comp. 55:393405). Only snails averaging 0.5 to 1 mm in length at miracidial exposure (between 1 hr and 8 days of life) supported the development of fasciolid parthenitae and produced viable cercariae (BouixBusson et al., 1983, Ann. Parasit. Hum. Comp. 58: 347-352). Our studies were undertaken in order to investigate the susceptibility of L. glabra to infection with Fasciola hepatica and to compare it with that of L. truncatula, a common snail host of the parasite in western Europe. Four groups of snails were exposed to miracidia of F. hepatica. Group 1 consisted of 2,550 L. glabra measuring 0.5 mm in length at the beginning of the experiment; batches of 200 survivors each were randomly collected in breeding containers and killed respectively at days 4, 7, 14, 21, 28, 35, 42 and 49 after exposure. Group 2 was composed of 500 L. truncatula measuring 0.5 mm in length at miracidial exposure; all survivors were killed at day 28 postexposure. Groups 3 and 4 consisted of 300 L. glabra and 500 L. truncatula adults respectively measuring 4 ? 0.1 mm at miracidial exposure; all survivors were killed at day 28 postexposure. At the beginning of the experiment, every snail was exposed for 4 hr to a single miracidium of F. hepatica and then bred at 23 C in standard containers with 50 snails per container for L. glabra, 35 snails for L. truncatula. Methods for breeding the snails and exposing them to miracidia were described in a previous note (Busson et al., 1982, Ann. Parasit. Hum. Comp. 57: 555563). Snails were killed by dipping them in Bouin's fluid and breaking their shells immediately. Five Atm serial sections were stained in Harris' hematoxylin-modified Gabe's trichrome. Three categories of snails could be recognized among survivors of the 4 groups. Snails with an evolutive infection (1st category) contained living parthenitae (sporocysts, rediae, cercariae) and their organs showed distinctive cell lesions, i.e., necrosis of epithelial cells followed by a reconstitution with cell hyperplasia (Rondelaud and Barthe, 1983, Ann. Parasit. Hum. Comp. 58:109116); they also showed numerous tunnel-shaped cavities averaging 30-40 tum in diameter in either the foot or mantle or both. Snails with an abortive infection (second category) sometimes showed degenerating sporocysts; variable tissue lesions similar to those of snails with an evolutive infection occurred and cavities were frequently noted in the foot and mantle. Snails devoid of fasciolid larvae, lesions and cavities (category 3) have been designated uninfected snails. The results obtained with L. glabra of group