The morphologic and immunologic alterations of bovine babesiosis were investigated in 2 experiments. In the first experiment, 10 Babesia bigemina infected calves were used to investigate the clinical signs, clinical pathological variations and gross, microscopic, and ultrastructural lesions in tissues collected sequentially from 36 hours to 10 days post-inoculation. In the second experiment, the clinical signs, clinical pathological variations, and the effects of B bigemina on in vitro lymphocyte blastogenesis and in vivo humoral responses were evaluated in 11 calves divided into 3 groups: non-stimulated calves (group A), stimulated calves (group B), and stimulated non-B bigemina infected calves (group C). Anorexia, anemia, jaundice, dyspnea, hemoglobinemia, and hemoglobinuria were observed during acute babesiosis. A decrease in the packed cell volumes (PCV) and total and differential leukocyte counts also occurred during acute babesiosis. Parasitemia became evident on day 7 PI and non-cell associated forms of B bigemina were found in tissue impression smears, although ultrastructurally macrophages in the renal lymph node and splenic pulp contained similar organisms. At the ultrastructural level, the plasmalemma of parasitized erythrocytes had radiating strands which may have contributed to the adhesiveness of such erythrocytes to leukocytes and endothelial cells. The gross lesions of acute babesiosis consisted of yellow discoloration of the fasciae, aponeuroses, and subcutaneous tissue. Subpleural petechial hemorrhages and slightly excessive pericardial, pleural, and peritoneal fluid occurred in the calves in the first experiment. The microscopic lesions observed in the first experiment were generalized vascular congestion and leukocyte margination transmigration, and infiltration in the parenchymatous tissues as well as edema, hemorrhagic foci, lymphoid, histiocytic, and reticular cell hyperplasia of visceral and peripheral lymph nodes. Marked congestion and leukocytic infiltration occurred in the spleen, heart, and kidneys of the calves necropsied during acute babesiosis. Increased bone marrow erythro- and myelopoilysis was observed during acute babesiosis...
