A clinical case of enzootic bovine leukosis in a Holstein cow with minor clonality of B-cell in the peripheral blood.

A 4-year 9-month-old Holstein-Friesian dairy cow presented with anorexia. On physical examination, swelling of superficial lymph nodes, pelvic masses, and prolonged urination posture after urinating a small amount were noted. Hematological examination revealed no lymphocytosis. The bovine leukemia virus proviral load was relatively high. At necropsy, enlarged lymph nodes, a large mass in the pelvic cavity, and mass lesions in several organs were observed. Histopathological examination revealed the proliferation of neoplastic lymphocytes, which were immune-positive for CD79α and negative for CD3. B-cell clonality test indicated the presence of monoclonality in the urine, masses, and lymph nodes and minor clonality in the peripheral blood. These findings led to a diagnosis of EBL with minor clonality of B-cell in the peripheral blood.