Orbiviruses

The family Reoviridae contains 15 genera with the genus Orbivirus being the largest of the currently classified ones. It contains Bluetongue virus (the Orbivirus type species), 27 virus species with bluetongue virus as type species and (at least) 8 currently unclassified ‘orbiviruses’. With a few exceptions, the orbiviruses infect, replicate in and are transmitted by ticks, mosquitoes, Culicoides or other blood-sucking insect vectors like phlebotomine flies. Collectively, they infect a varied vertebrate host species, including humans, domesticated and wild ruminants, felines, canines, equines, marsupials, sloths, bats and birds. Bluetongue virus (BTV), epizootic haemorrhagic disease virus (EHDV) and African horse sickness virus (AHSV) are the most economically important orbiviruses, based on their global impact on ruminant-based livestock industries (BTV and EHDV), and on horses primarily in Africa (AHSV). Complete genome sequences are currently accessible for 27 formally recognised species of Orbivirus, a complete reference database and comprehensive phylogenetic analysis for the entire genus Orbivirus, to further appreciate the taxonomic relationships, epidemiology, replication mechanisms and evolutionary process of these viruses. The phylogenetic trees show branching patterns of orbiviruses as per their vector grouping, supporting the assumption that they have evolved with their vectors through ‘co-speciation’. These analyses helped identification of novel Orbivirus species and grouped the previously unclassified viruses into existing species. The bioinformatic analyses suggest that the evolution of orbiviruses has occurred at a slower rate than other RNA arboviruses and non-vector-borne reoviruses.