Bovine leukemia, also known as bovine lymphosarcoma or leucosis, is a lymphoproliferative neoplastic disease of bovines. The virus belongs to genus Deltaretrovirus in the family Retroviridae. Oncogenesis depends on the integration of bovine proviral v-onc gene into cellular DNA. Transmission of Bovine leukemia virus occurs primarily by the transfer of lymphocytes between animals. The virus can be transmitted to the fetus but usually less than 40% calves born to infected dams are infected at birth.
Clinical signs: The symptoms of this disease are persistent lymphocytosis, leukemia and or lymphosarcoma in cattle. The lymphoid tumors are seen in lymph nodes, abomasums, heart, spleen, kidneys, uterus, spinal meninges, and brain.
Diagnosis: Antibodies to bovine leukemia virus antigens are demonstrated by immunodiffusion, radioimmunoassay, enzyme immunoassay, syncytium-inhibtion assay and complement-fixation test. The diagnosis is aided by the hematologic observations including lymphocytosis and the presence of immature lymphocytes. Electron microscopy, infectivity assay in cell-culture systems and sero-epidemiological observations provide a confirmatory diagnosis.
Prevention and control: Identification of the affected animals by serological testing followed by culling is the only available method of controlling this disease.