An adult angus bull was presented to a veterinarian for lethargy and weakness. The bull died shortly after blood collection. Blood and tissue samples were submitted to the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL). The complete blood count revealed a marked leukocytosis characterized by a lymphocytosis at 43,000 lymphocytes/µL (reference interval 1,800 – 9,000 lymphocytes/µL) and a marked anemia with a PCV of 10 % (reference interval 24-46%). Blood smear examination confirmed the marked lymphocytosis and revealed numerous organisms consistent with Anaplasma marginale. Confirmatory testing included BLV PCR and Anaplasmosis ELISA.
Bovine leukemia virus (BLV) is a retrovirus spread by contact with bodily fluids through biting flies, breeding, colostrum/milk, and certain management practices. Infections can results in asymptomatic carriers or severe clinical disease. Approximately 40% of infected cattle will develop persistent lymphocytosis, as seen in this case. Although numbers vary between studies, approximately 5% of infected animals will develop lymphoid neoplasms.
Anaplasmosis in cattle is most commonly caused by Anaplasma marginale, intraerythrocytic bacteria spread primarily by ticks. Although carrier states are also seen with Anaplasma sp. infections, severe disease, marked anemia, and death can occur. Evaluation of a blood smear can be highly specific for these infections; however, a negative blood smear does not rule out anaplasmosis or BLV infections.
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