orbiviruses

Orbivirus is a genus of viruses in the family Reoviridae, order Reovirales. They have a segmented double-stranded RNA genome consisting of ten segments and are non-enveloped, with an icosahedral capsid. The virion features an outer layer formed by VP2 and VP5 and a core shell composed of VP7 and VP3. Genome segments enable reassortment, contributing to serotype diversity. Replication occurs in the cytoplasm of infected cells and follows the dsRNA virus replication strategy typical of the family.

Most orbiviruses are transmitted by arthropod vectors, especially Culicoides midges; other species are tick- or mosquito-borne. The natural hosts are usually ruminants and other ungulates, with deer and horses among affected species in some diseases. Infections can range from subclinical to severe hemorrhagic disease.

Some orbiviruses are economically important. Bluetongue virus (BTV) causes bluetongue in sheep and other ruminants, Epizootic hemorrhagic disease virus (EHDV) affects deer and cattle, and African horse sickness virus (AHSV) causes severe disease in horses with high mortality. Outbreaks correlate with vector abundance and climate.

Diagnosis relies on molecular methods such as RT-qPCR, virus isolation, and serology (ELISA). Management includes vaccination (live-attenuated and inactivated vaccines exist for some serotypes), vector control, and movement restrictions to limit spread.

Orbiviruses illustrate the importance of segmented genomes, the role of vectors in transmission, and the potential for genetic reassortment to influence pathogenicity and host range.