Orbiviruses andBluetongue Virus

AbstractBluetongue virus(BTV) is the type species of the genusOrbiviruswithin the familyReoviridae(the largest double‐strandedribonucleic acid(dsRNA) virus family). BTV is an arthropod‐borne pathogen that is transmitted by the bites of its vector, theCulicoidesmidges, which transmit the virus between its ruminant hosts. The virus can infect most species of domestic and wild ruminants. BT clinical signs are most common in sheep and some species of deer. In recent years, the distribution of BTV has changed considerably, particularly in Europe. New outbreaks have occurred each year from 1998 to 2006 in southern and central Europe, involving several strains from five different serotypes. In 2006, BTV serotype 8 caused an outbreak approximately 5° further north in Europe than ever before, infecting ruminants in a wide area across northern Europe and bringing the number of European serotypes to six. A new virus (Toggenburg virus) has been identified in goats from Switzerland in 2008 and designated as the twenty‐fifth serotype of BTV.Key concepts:GenusOrbivirusis the most diverse genus of familyReoviridaecontaining 22 virus species.Bluetongue disease affects mainly sheep causing severe clinical signs and high mortality.Bluetongue virusis transmitted by competent species ofCulicoidesmidges.Phylogenetic analysis identifies two major groups of orbiviruses, those with their subcore shell protein (T2 protein) being the VP2 and those with the T2 being VP3. Orbiviruses are nonturreted members of familyReoviridae, and the atomic structure of BTV core has been determined.