Orthoreovirus is part of the family Reoviridae. Its genome is composed of segmented double-stranded RNA (dsRNA), thus it is classified as a group III virus according to the Baltimore classification system of viruses. This family of viruses is taxonomically classified into 15 distinct genera. These genera are sorted out taking into account the number of dsRNA genomes. The Orthoreovirus genus has 10 segments that have been isolated from a large range of hosts including mammals, birds, and reptiles. These genera are further divided into two phenotypic groups: fusogenic and non-fusogenic. The way that they are determined to belong to a specific group is if the virus is able to cause multinucleated cells known as syncytial cells. According to this classification, mammalian orthoreoviruses (MRV) are known to be non-fusogenic, meaning it does not produce syncytia, while other members of this genus are fusogenic, such as avian orthoreoviruses (ARV), baboon orthoreoviruses (BRV), reptilian orhtoreoviruses (RRV).
