Extraintestinal stages of Eimeria bovis in calves and attempts to induce relapse of clinical disease

Monoclonal antibodies to all life cycle stages of Eimeria bovis were used in an avidin-biotin immunoperoxidase test to examine extraintestinal tissues from experimentally infected calves for developmental stages of the parasite. First-generation meronts of Eimeria bovis were found in the mesenteric lymph nodes (MLNs) of three of four calves examined during the first 18 days of primary experimental infection. No extraintestinal stages were found in the MLNs of two calves examined 69 days after a primary infection or in five calves examined 6 months after a challenge infection. Tissue homogenates of liver, spleen, and MLNs from immune calves were not infectious for nonimmune recipient calves following oral or intraperitoneal inoculation indicating that infectious stages were not present in these extraintestinal tissues at the time of inoculations. Relapse of clinical coccidiosis and reoccurrence of oocyst shedding were not seen in E. bovis immune calves that were stressed by being put on a 16-week corticosteroid treatment program.