The acquirement of growth ability for third-stage larvae of Strongyloides ratti during the head-passage in the rat.

The role of larval passage through the head in the course of the migration of Strongyloides ratti in rats was investigated. Third-stage larvae (L3) recovered from various portions of donor rats were re-injected into the skin, cranial cavity and small intestine of recipient rats to check their ability for further growth. Cultured L3 (L3c) and the L3 recovered from the skin of donor rats (L3s) did not survive in the small intestine after intestinal inoculation. However, intestinal inoculation of L3 recovered from the head of donor rats (L3h) revealed growth to the adult stage. Cultured L3 injected into the cranial cavity of rats also became adult worms in the small intestine. L3 incubated in the cranial cavity for more than 24 h could grow in the small intestine of the recipient rats. These experiments suggest that S. ratti L3 acquire their ability to mature in the small intestine during their migration through the head of rats.