Detection of bovine leukemia virus by in situ polymerase chain reaction in tissues from a heifer diagnosed with sporadic thymic lymphosarcoma.

An 18-month-old bovine heifer was presented for clinical evaluation after a sudden onset of ventral edema. Clinical and pathological evaluations were consistent with thymic lymphosarcoma, a sporadic form of lymphosarcoma in cattle, which is not generally considered to be associated with bovine leukemia virus (BLV). This heifer was seropositive for BLV at 6 and 18 months of age. Tissues obtained at necropsy were evaluated using in situ polymerase chain reaction. The BLV proviral DNA was detected in lymphocytes of the thymus as well as in epithelial cells of the liver and kidney. This report presents evidence that thymic lymphosarcomas can be associated with BLV infection and that BLV may have a broader cellular tropism than was supposed previously.