Sequence analysis of the S10 gene of six Bluetongue Virus isolates from India

Full-Genome Sequencing as a Basis for Molecular Epidemiology Studies of Bluetongue Virus in India

Since 1998 there have been significant changes in the global distribution of bluetongue virus (BTV). Ten previously exotic BTV serotypes have been detected in Europe, causing severe disease outbreaks in naïve ruminant populations. Previously exotic BTV serotypes were also identified in the USA, Israel, Australia and India. BTV is transmitted by biting midges (Culicoides spp.) and changes in the distribution of vector species, climate change, increased international travel and trade are thought to have contributed to these events. Thirteen BTV serotypes have been isolated in India since first reports of the disease in the country during 1964. Efficient methods for preparation of viral dsRNA and cDNA synthesis, have facilitated full-genome sequencing of BTV strains from the region. These studies introduce a new approach for BTV characterization, based on full-genome sequencing and phylogenetic analyses, facilitating the identification of BTV serotype, topotype and reassortant strains. Phylogenetic analyses show that most of the equivalent genome-segments of Indian BTV strains are closely related, clustering within a major eastern BTV 'topotype'. However, genome-segment 5 (Seg-5) encoding NS1, from multiple post 1982 Indian isolates, originated from a western BTV topotype. All ten genome-segments of BTV-2 isolates (IND2003/01, IND2003/02 and IND2003/03) are closely related (>99% identity) to a South African BTV-2 vaccine-strain (western topotype). Similarly BTV-10 isolates (IND2003/06; IND2005/04) show >99% identity in all genome segments, to the prototype BTV-10 (CA-8) strain from the USA. These data suggest repeated introductions of western BTV field and/or vaccine-strains into India, potentially linked to animal or vector-insect movements, or unauthorised use of 'live' South African or American BTV-vaccines in the country. The data presented will help improve nucleic acid based diagnostics for Indian serotypes/topotypes, as part of control strategies.

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.