Molecular Characterization of Bovine Leukemia Virus Prevalent in Okayama Prefecture

Abstract

A survey was conducted of the bovine leukemia virus (BLV) prevalent in Okayama prefecture based on the 59 bovine leukosis cases found between 2009 and 2015. The presence of BLV proviral DNA in the tumor tissue samples for each case was detected using PCR and the BLV genotypes were determined using the RFLP method. All samples tested positive for BLV- and genotype 1 was the most predominant (45 samples), followed by genotype 3 (8 samples), genotype 5 (2 samples), and genotype 6 (2 samples). Cases of mixed infection were recognized in 2 samples. It is notable that this is the third case where genotype 6 has been identified in Japan. Genotypes 1 and 3 were distributed throughout the prefecture, while genotypes 5 and 6 were respectively distributed in the northern area and in limited areas. The detection rate of genotype 3 was significantly higher in Japanese Black cattle than Holstein cattle. Phylogenetic analysis of the nucleotide sequences of the genotype 6 strains isolated in this study demonstrated that the strains were classified as an independent cluster and were more closely related to the strains in genotypes 1 and 3 than the known genotype 6 strains.