A clinical case of enzootic bovine leukosis diagnosed by using clonal analysis of peripheral B lymphocytes in a Japanese Black cow

A 7-year-old Japanese Black cow with anorexia was presented at a local veterinarian. As rectal palpation revealed an enlarged induration of the uterus, lymphoma was suspected, and the patient was introduced to the Veterinary Teaching Hospital of Obihiro University of Agriculture and Veterinary Medicine. Although lymphadenopathy and lymphocytosis were not found, a high proviral load of bovine leukemia virus (BLV) with 464 copies/10 ng DNA was recorded, and lymphocytes with constricted or flower-like nuclei were found occasionally in the peripheral blood; accordingly, enzootic bovine leukosis (EBL) was suspected. According to PCR for clonality analysis of B cells based on immunoglobulin heavy chain (IGH) gene rearrangement, monoclonal proliferation of peripheral blood B cells was evident, suggesting the presence of tumorigenic B cells in the peripheral blood and onset of EBL. Pathological examination including necropsy and histopathological examination confirmed the diagnosis of EBL. Clonality analysis for B cells in the peripheral blood is thought to be useful for diagnosing B-cell tumors such as EBL, especially in cases lacking lymphadenopathy and lymphocytosis. This is the first clinical case of EBL diagnosed by demonstrating monoclonal proliferation of peripheral blood B cells using IGH gene rearrangement-based PCR.