Dynamics of erythrocyte indices in relation to anemia development in Theileria orientalis-infected cattle

摘要

Theileria orientalis often causes clinical anemia in cattle. In the present study, the red blood cell (RBC) indices of cattle, as measured in T. orientalis-endemic regions of Hokkaido, Japan, were analyzed. In comparison with the non-infected animals,the mean values for RBC counts, hematocrit, and hemoglobin concentration (HGB) were lower in T. orientalis-infected Holstein and Hereford cattle but not in Japanese Shorthorn and Angus, suggesting that the hemolysis induced by T. orientalis is not pronounced in the later. Anemic animals (HGB < 8 g/dl) were detected only in Holstein and Hereford, and the anemia rate was higher for Holstein than that for Hereford. The mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH) values in the T. orientalis-infected but non-anemic animals were significantly higher than those for the non-infected Hereford, but not for the Holstein, suggesting that the host response to hemolysis influenced anemia development. To clarify this phenomenon, three Holstein calves experimentally infected with T. orientalis were monitored for the parasitemia and RBC indices. Among the infected animals, a calf with low parasitemia had elevated MCV and MCH values, but lacked anemia. In contrast, despite elevated MCV and MCHvalues, HGB in the calf with high parasitemia dropped to a low value. These findings indicate that the cattle breed, parasitemia level, and host response may influence anemia development in T. orientalis-infected cattle.