Effect of cortisone on the resistance of the guinea pig to infection with the rat nematode, Nippostrongylus brasiliensis

Abstract

The guinea pig is a highly resistant host to infections of Nippostrongylus brasiliensis. Experiments were performed to compare the development of N. brasiliensis in normal and cortisone-treated guinea pigs. Several groups of guinea pigs were injected with different doses of cortisone, and control animals received saline. Treatment with cortisone rendered the guinea pigs less resistant and permitted nearly 11 times more larvae to complete the skin-lung migration as compared with the controls. A host-sex difference was observed in the lung-worm recoveries. Normal male guinea pigs harbored more larvae than normal females, and cortisone-treated males harbored more larvae than cortisone-treated females. Some of the larvae in cortisone-treated animals were successful in completing the migration from the lungs to the intestine where a few became established as mature adult worms. Skin sections of the larval inoculation sites showed that there was a delayed inflammatory response and nodular formation around the larvae in cortisone-treated animals which correlated with the increased numbers of larvae in their lungs. The suggested mechanism for the partial breakdown of the host's resistance is that the guinea pig offers a somewhat unfavorable environment to the penetrating nematode and as a consequence, the migration of the larvae is slowed down in the skin. Normally the larvae are trapped by the inflammatory response of the host, but cortisone suppresses this cellular response thus permitting many of the larvae to complete their migration to the lungs and some of them to become established as adults in the intestine.