A duplex RT-PCR assay for detection of genome segment 7 (VP7 gene) from 24 BTV serotypes

Since 1998, six distinct serotypes of Bluetongue virus (BTV) have invaded Southern and Central Europe, persisting in some regions for up to 6 years and resulting in the deaths of >1.8 million sheep. Rapid and reliable methods of virus detection and identification play an essential part in our fight against bluetongue disease (BT). We have therefore developed and evaluated a duplex, one-step RT-PCR assay that detects genome segment 7 (encoding the major serogroup (virus-species) specific antigen and outer-core-protein VP7) from any of the 24 BTV serotypes. Although Seg-7 is highly conserved, there are sequence differences in the near terminal regions that identify two distinct phylogenetic groups. Two sets of primers (targeting Seg-7 terminal regions of viruses from these two groups) were included in a duplex RT-PCR assay system. Assay sensitivity was evaluated using tissue culture derived virus, infected vector insects and clinical samples (blood and other tissues). The assay reliably amplified Seg-7 from any of the BTV strains tested, including isolates of the 24 BTV serotypes and isolates from different geographic origins. No cross-reactions were detected with members of closely related Orbivirus species (African horse sickness virus (AHSV), Epizootic haemorrhagic disease virus (EHDV), Equine encephalosis virus (EEV) and Palyam virus (PALV)).