Genetic and phylogenetic characterization of genome segments 2 and 6 of bluetongue virus isolates in Japan from 1985 to 2008

This study conducted genetic and phylogenetic analyses of genome segments 2 and 6 (Seg-2 and Seg-6), which encode serotype-specific structural proteins of the outer capsid, of bluetongue virus (BTV) isolated in Japan from 1985 to 2008. The Japanese strains of BTV were clearly sorted into six groups by several genetic characteristics of Seg-2, including segment length, ORF length and 5'- and 3'-terminal sequences, and were identified as serotypes 2, 3, 9, 12, 16 and 21 by phylogenetic comparisons with Seg-2 of reference and field strains of serotypes 1-24. In contrast, phylogenetic comparisons of Seg-6 also revealed some variations among the Japanese strains and partial correlations of the serotypes between the Japanese strains and the reference or field strains. Thus, the results revealed that at least six serotypes of BTV were isolated in Japan and that there were some variations in the genetic and phylogenetic characteristics of Seg-2 and Seg-6 among the Japanese strains, suggesting that BTV of several different origins has appeared sporadically in Japan. These data will be beneficial for understanding BTV epidemiology and taking better control measures against bluetongue in Japan and its neighbouring countries in the Asia-Pacific region.