Suppressed Rejection of \u3ci\u3eTrichinella spiralis\u3c/i\u3e in Immunized Rats Concurrently Infected with \u3ci\u3eEimeria nieschulzi\u3c/i\u3e

This study deals with the effect of Eimeria nieschulzi infection on the host immune response to Trichinella spiralis. Six male Sprague-Dawley rats were inoculated with 104 and six with 106; sporulated E. nieschulzi oocysts. On days 2, 8, and 16 post-inoculation (PI), two rats from each infected group, and their paired uninfected controls, were killed and mucosal scrapings from their small intestines were assayed for peroxidase activity. Peroxidase levels were higher than corresponding control values on days 2 and 16 PI and significantly lower than the controls on day 8 PI. These data led us to initiate the present study because infection by T. spiralis in rats is known to cause an elevated gut peroxidase level which, in turn, is thought to contribute to worm expulsion. Twenty-eight male rats were then immunized by administration of 7.5 × 103 freshly isolated T. spiralis larvae. Thirty-two days after immunization 16 rats were inoculated with 5 × 105 sporulated oocysts of E. nieschulzi. The other 12 rats were retained as immlune controls. Each of the 28 rats was challenged with 7.5 × 103 T. spiralis larvae between 2 and 10 days postinoculation with E. nieschulzi. Two or three coccidia-infected rats and two immune controls were killed at 2 and 5 days post-challenge with T. spiralis, and the worms in each third of the small intestine were recovered and counted. In every instance, rats that had concurrent coccidia infections harbored at least 4 times more T. spiralis than did immune, coccidia-free controls. Distribution of T. spiralis through the small bowel was not altered by infection with E. nieschulzi, despite the fact that the coccidian significantly suppressed worm rejection