Nippostrongylus brasiliensis goes through both a tissue and a gut phase during its life cycle in the rat. It enters the body through the skin (experimentally, by subcutaneous injection) as a third stage larva. The larvae migrate rapidly to the lungs where they molt, about 30–40 h after entering the body, to the fourth larval stage. These larvae migrate up the trachea and down the esophagus to the small intestine, where they molt again (about 60–120 h after infection) to the final adult worm stage. The male and female worms do not penetrate into the mucosa but lie tightly coiled between the villi like snakes in the grass. They do not suck blood.
The rejection of Nippostrongylus brasiliensis from rats by the immune response is thought to involve several aspects of the host's immunological armory. In this report we consider the many immune responses detectable during an infection, and attempt to relate their occurrence with the fate of the parasite in primary and subsequent infections.
Present address: Department of Veterinary Medicine, University of Sydney, Sydney, New South Wales, Australia.