Orbiviruses and Bluetongue Virus

Abstract Bluetongue virus (BTV) is the type species of the genus Orbivirus within the family Reoviridae (the largest double‐stranded ribonucleic acid (dsRNA) virus family). BTV is an arthropod‐borne pathogen that is transmitted by the bites of its vector, the Culicoides biting midges, 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 in southern and central Europe, involving several strains from 10 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. A new virus ( Toggenburg virus ) has been identified in goats from Switzerland in 2008 and designated as the twenty‐fifth serotype of BTV and another one isolated from goats in Corsica in France more recently and was designated as serotype 27. Additional serotypes have been detected/isolated, bringing now the number of serotypes to 29. Key Concepts Genus Orbivirus is the most diverse genus of family Reoviridae containing 32 virus species. Bluetongue disease affects mainly sheep causing severe clinical signs and high mortality. Bluetongue virus is transmitted by competent species of Culicoides midges. 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 family Reoviridae , and the atomic structure of BTV core has been determined.