Note on Re-Infection under "Natural" Conditions with a Gut Nematode of the Rabbit

The occurrence in domestic sheep of self-cure and protection against the common stomach worm, Haemonchus contortus, under conditions of natural re-infection (Stoll, I929), led to tests of the same possibility with other worm-host systems. The rabbit appeared to offer the advantage of a useful small-sized host for such study, and wild rabbits of the region as well as some of the domestic stock in the laboratory carried low-grade infections with the small strongyloid Trichostrongylus calcaratus, which inhabits the jejunum. This nematode has the characteristic life history of worms of this group: males and females more or less localized during their adult life in a relatively small area of the food tract; no multiplication of the parasites in vivo but the extrusion of eggs into the lumen of the tract from whence they escape to the outer world in the feces; then the development in the dung of larval stages, which after an interval of a week or so at summer temperatures become infective, re-enter the host either through the food or skin, and assume final development to adult life within about two weeks in the gut area earlier parasitized by the adult worms which produced them. Such a cycle is characteristic of H. contortus, as it is of the hookworms and allied forms.