The family Reoviridae is divided into 9 genera, 4 of which—Orthoreovirus, Coltivirus, Rotavirus, and Orbivirus —can infect humans and animals. Four other genera infect only plants and insects, and one infects fish. Although almost 100 orbivirus serotypes are known, only 3 serotypes of orthoreovirus and 2 of coltivirus have been identified. The genus Rotavirus contains 3 groups, A, B, and C, with group A causing most outbreaks of disease. Both orthoreoviruses and orbiviruses contain 10 segments of double-stranded RNA. Rotaviruses contain 11 genome segments, and coltiviruses have 12 segments.
Reovirus is now used as a therapeutic agent in the treatment of various types of malignancy. Reolysin, a strain of reovirus, has been studied extensively as an anticancer agent in the treatment of head and neck cancers, metastatic melanoma, and other solid-organ tumors.