Distribution and superinfection of bovine leukemia virus genotypes in Japan

A study to investigate the types and distribution of bovine leukemia virus (BLV) was conducted on about eight hundred cattle drawn from 53 farms found in 16 prefectures in Japan. Agar gel immunodiffusion (AGID) tests of serum samples and nested-PCR to detect BLV provirus, in peripheral blood leukocytes were performed. To identify genotypes, restriction fragment length polymorphism (RFLP) was performed with a PCR-amplified 444 bp fragment of the env gene using endonucleases. Three genotypes (1, 3, and 5) were dominant in Japan, and were found in 48.3%, 32.7%, and 16.9% of PCR positive cattle, respectively. Of the cattle infected with genotype 1, 84.7% were strongly positive in the AGID test. Similarly, in cattle with genotype 3, 78.9% were strongly positive. However, only 59.1% of cattle with genotype 5 were strong positive. Three cattle showed unusual RFLP patterns and they were found to be infected with more than one genotype. These results suggest that some BLV infected cattle can not induce effective immune reactions and suffer from superinfection by BLV in the field.