Studies with Eimeria acervulina and E. mivati: pathogenicity and cross-immunity.

Pathogenic effects caused by graded doses of recent isolates of Eimeria acervulina, E. Mivati and a new isolate, thought at first to be E. mitis, were compared. Cross-immunity studies were conducted with 3 strains of E. acervulina and 2 strains of E. mivati, together with the new isolate. The results showed marked similarities between E. mivati and the new isolate and clear distinctions between these and E. acervulina. E. mivati produced scattered petechiae but did not form discrete lesions in the intestine comparable to those seen with E. acervulina. Endogenous stages of E. mivati were most numerous in the lower small intestine and proximal caeca. The ratio of villus height to total mucosal thickness in the lower intestine was reduced. Similar changes caused by E. acervulina were seen in the anterior intestine only.