| Abstract: | ABSTRACT: Isolates of Anaplasma marginale and of Babesia bigemina were obtained from naturally infected calves with mixed infections of A. marginale, B. bigemina and B. argentina. Babesia bigemina was separated from B. argentina and A. marginale by rapid serial passage through 5 splenectomized calves. Anaplasma marginale was separated from B. bigemina and B. argentina by administering a sterilizing dose of a babesiacidal drug. Following the separation procedures, the isolates of A. marginale and B. bigemina were frozen and stored at -79 C. Twenty-two, 7 month old, male, nonsplenectomized Holstein-Friesian calves were divided into 4 experimental groups. Group I and II consisted of 3 calves each and served as control groups to study anaplasmosis and babesiosis respectively. Groups III and IV consisted of 8 calves each and served to study a concurrent infection with B. bigemina in calves recovering from anaplasmosis and a concurrent infection with A. marginale in calves recovering from babesiosis respectively. The calves were infected by subcutaneous inoculation. Calves infected with A. marginale received approximately 9.5x10⁸ organisms. Calves infected with B. bigemina received approximately 10.5x10⁸ organisms. Clinical manifestations of disease were mild and consisted of slight fever, poor body condition, decreased weight gain and inactivity. Fever was routinely observed only in the calves infected with A. marginale. The clinical signs of disease observed in the concurrently infected calves were attributed predominately to infection with A. marginale. Associated with the appearance of parasitized erythrocytes were decreases in packed cell volume, hemoglobin, albumin:globulin ratio, and serum albumin, and slight increases in the levels of serum bilirubin, serum glutamic oxalacetic transaminase, and alpha and beta serum globulins. Decreases in PCV and hemoglobin concentration were more prolonged and severe in the concurrently infected calves and were considered to have resulted predominately from infection with A. marginale. Changes observed later in the experiment included the appearance of reticulocytes in the blood, a decrease in myeloid:erythroid ratio in the bone marrow, and an increase in the levels of total serum proteins, serum gamma globulins and serum sorbital dehydrogenase. A prolonged monocytosis occurred in each of the 4 groups of calves. Gross lesions observed in the concurrently infected calves included a moderately excessive quantity of yellow fluid in the peritoneal and pleural cavities, moderate lymph node enlargement, splenomegaly and hepatomegaly, moderate renal congestion, and occasional serous atrophy of depot fat. Hepatocellular degeneration and necrosis were observed in the centrolobular areas of the liver. Lymphoid hyperplasia was observed in the malpighian corpuscles of the spleen and in the lymphoid follicles of the lymph nodes. Hemosiderosis of the spleen, liver, kidney and lymph nodes was attributed to the increased removal of damaged erythrocytes from the circulation with the subsequent release of breakdown products of hemoglobin. Complement fixing antibodies for Anaplasma were first observed on days 17 to 26 postinoculation and corresponded to the increase in the alpha and beta globulins. Increases in complement fixing antibody titer corresponded to the increase in gamma globulin and persisted until the concentration of gamma globulin began to recede during the terminal days of the experiment. Complement fixing antibodies for Babesia were first observed on day 12 postinoculation, which corresponded to the increase in gamma globulin. The increase and decrease in antibody titer for babesiosis corresponded to the increase and decrease in gamma globulin. The biological relationship of A. marginale and B. bigemina during the concurrent infection appeared to be one of independency. Neither an inhibitory nor a synergistic relationship was apparent during the investigation. The clinical and pathological manifestations of concurrent infection were more severe than those observed during infection with either of the hemotrophic parasites alone, and were attributed to the concurrent infection being additive in nature. |
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