The Life Cycle of Schistosoma mansoni under Germ Free Conditions

Abstract

The complete life cycle of Schistosoma mansoni under germ free (GF) or axenic conditions was achieved. The study of a parasitic disease under axenic conditions may be of great help in understanding the host-parasite relationship, since any interference of the associated microflora is excluded. The snail Biomphalaria glabrata, reared under axenic conditions (Vieira, 1967, American Journal of Tropical Medicine and Hygiene 16: 792796), was infected with S. mansoni miracidia (LE strain) derived from conventional (CV) hamster liver, according to the technique described by Chernin (1960, Proceedings of the Society for Experimental Biology and Medicine 105: 292296). The emergent axenic cercariae, collected in water, were put in ampoules. These were sealed and passed into an isolator containing GF LOB (CFW) mice which are free of all demonstrable microbes except for a leukemogenic virus acquired prenatally which remains latent unless activated by radiation (Pollard, 1965, National Cancer Institute Monograph 20: 167-172). The transcutaneous infection of mice was performed by putting the cercarial suspension (50 ml of water containing 30 cercariae) in a bottle into which a mouse was forced and kept for 1 hr. Each mouse was exposed twice. CV control mice were treated similarly, using the same batch of cercariae. Four mice were used; 2 CV and 2 GF. Eggs in the feces were determined, starting on day 40 after infection, by Kato's method modified by Martin and Beaver (1968, American Journal of Tropical Medicine and Hygiene 17: 382-391). Eggs appeared in the feces on day 49 and 53 in CV mice and on day 56 and 62 in GF mice. Sixty-one and 84 days after infection, 1 GF and 1 CV mouse from each group was sacrificed for worm recovery and egg count (Pellegrino and Siqueira, 1956, Revista Brasileira de Malariologia e Doencas Tropicais 8: 589-597; Pellegrino and Faria, 1965, American Journal of Tropical Medicine and Hygiene 14: 363-369). The GF status of the isolators was maintained throughout the experiment, as determined by the method of Wagner (1959, Annals of the New York Academy of Science 78: 89-101). Table I shows the adult worm and egg recovery from livers and intestines of GF and CV mice after 61 and 84 days of infection. GF mice produced more eggs than their CV counterparts. Since a small sample was used, the differences in parasitological findings may be due to individual variation in the strain of mice. On the other hand, it is well known that the GF status interferes with the immune system of the host animal, thereby changing the host-parasite relationship, especially for metazoan parasites