Eimeria vermiformis: host strains and the developmental cycle.

After confirmatory studies of the endogenous development of Eimeria vermiformis in hybrid mice, a comparison, both qualitative and quantitative, was made of the developmental cycle of the parasite in two strains of host of contrasting susceptibility. No differences were apparent between the resistant, BALB/c, and susceptible, C57BL/6, during the first 5 days of the cycle. Thereafter, more parasites were seen in the C57BL/6, they were more widely distributed along the intestine, and they persisted in the tissues for a considerably greater time. Schizogony continued for longer in the C57BL/6 mice, concurrently with gametogony, and there were probably up to four additional generations of schizonts, which resembled those of the accepted third generation. The kinetics of oocyst production, measured in the feces, reflected events in the intestinal epithelium. The findings are discussed in relation to eimerian life cycles and the immune response.