A clinical case of enzootic bovine leukosis in a 13-month-old Holstein heifer

A 13-month-old Holstein heifer presented with emaciation and enlarged superficial lymph nodes. Hematological examination showed remarkable lymphocytosis with atypical lymphocytes. Increased activities of serum total lactate dehydrogenase and thymidine kinase were detected. Fine needle aspiration cytology of the subiliac lymph node revealed large lymphoblasts undergoing mitosis. Nested PCR for bovine leukemia virus (BLV) and antibody against BLV were both positive. BLV proviral load was relatively high. Pathological examination confirmed that the case was diffuse large B-cell lymphoma. B-cell monoclonality was also confirmed by PCR for V-D-J junctional variability. Monoclonal integration of BLV provirus in the bovine genome was demonstrated with the inverse PCR method. The heifer was definitively diagnosed with enzootic bovine leukosis based on these findings.