A study of the dynamics of the invasion of immunized birds by Eimeria sporozoites.

The invasion of the intestinal epithelium of immunized and unimmunized turkeys and chickens by four species of Eimeria was quantitated. In unimmunized birds, E. adenoeides, E. acervulina, and E. tenella invaded primarily the areas in which first-generation schizonts subsequently developed. Eimeria meleagrimitis invaded a larger area of the intestine. Between 1 and 4 hr postinoculation, the numbers of intracellular sporozoites increased, but their location within the intestine was little changed. When birds were immunized with either of two lower intestinal species, E. adenoeides or E. tenella, and then challenged with the immunizing species, invasion was reduced by 36% to 55%. In contrast, immunizing and then challenging birds with either of two upper intestinal species, E. meleagrimitis or E. acervulina, did not reduce invasion: there were 44% more intracellular sporozoites in E. meleagrimitis-immunized turkeys and 11% more in E. acervulina-immunized chickens than in their unimmunized counterparts.