Effect of Cortisone on the Establishment of Nippostrongylus brasiliensis in the Rabbit

Abstract

The present investigation has shown that neither the cortisonenor saline-treated rabbit is a satisfactory host for the maintenance of Nippostrongylus brasiliensis. In the saline-treated rabbit, this is due primarily to an inflammatory reaction that occurs in the skin and leads to subsequent nodulation of the infective larvae. Cortisone did suppress the rabbit's inflammatory skin response and a greater number of larvae were able to complete the skin-lung and lung-intestine migrations and become established as adults. However, the majority of larvae recovered from the lungs had failed to undergo the third molt and there was an extension of the worm prepatent period. In addition, other factors (undetermined) appear to prevent the larvae from undergoing normal development in the skin and lungs. There was no stunting of adult worms in the intestine of the rabbit and eggs recovered from feces were viable. Male worms were more numerous than females over a 10-day period postinfection. Thorson (1953) reported that the rabbit is a highly refractory abnormal host to Nippostrongylus brasiliensis (Travassos, 1914). Further experimental evidence concerning this host-parasite relationship could not be found in the literature. In our laboratory, previous experiments established that in young rabbits (8 weeks of age) an effective resistance develops, or exists, against the successful migration of inoculated N. brasiliensis larvae. Only 0.03% of these larvae completed migration from skin to intestine as compared to an average of 90% (Haley, 1962b) in the rat (the normal host). Skin sections from rabbits 40 hr postinfection (PI) showed low-grade inflammation beginning to localize around the larvae, with defensive cells (mononuclear and polymorphonuclear) migrating toward the larvae. Skin sections from rabbits 3 days PI revealed that the larvae were coiled and surrounded by an intense inflammatory response preceding encapsulation. In skin sections from rabbits 6 days PI, completely formed nodules around larvae were evident and the larvae were in early stages of degeneration. The results obtained are similar to those reported by Parker (1961) for the guinea pig. During recent years there have been several reports on the effect of cortisone on N. braReceived for publication 6 June 1969. * Based in part on a thesis submitted to the Graduate School, Kent State University, in partial fulfillment of the requirements for the Master of Arts degree. siliensis in the rat (Weinstein, 1953, 1955; Ogilvie, 1965). Reports on the effect of cortisone on N. brasiliensis in certain abnormal hosts, ground squirrel and guinea pig, have also been published (Cross, 1960, 1964; Parker, 1961). These authors concluded that cortisone had a suppressive effect on the host's cellular response. The work herein reported deals with the treatment of rabbits with cortisone to determine if it would suppress the cellular response and, as a result, permit a greater number of worms to reach maturity in the intestine. MATERIALS AND METHODS