Genetic heterogeneity among bovine leukemia viruses in Japan and their relationship to leukemogenicity.

Bovine leukemia virus (BLV) infection in cattle causes persistent lymphocytosis, and a few percent of infected animals develop lymphoid tumors, namely enzootic bovine leukosis (EBL). In this study, a 440-bp fragment of the env gene was amplified from 204 tumor samples collected from different regions of Japan and analyzed by restriction fragment length polymorphism (RFLP) to determine the association of BLV with EBL. Of the seven RFLP types defined, types I, II, and III were dominant and found in 12.