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The family Reoviridae is composed of eight genera: Orthoreovirus, Orbivirus, Coltivirus, Rotavirus, Aquareovirus, Cypovirus, Phytoreovirus, and Fijivirus. Certain Orthoreovirus, Orbivirus, Coltivirus, and Rotavirus species infect humans; Phytoreovirus and Fijivirus species infect plants and insects; the cypoviruses (the cytoplasmic polyhidrosis viruses) infect insects, and aquareoviruses infect fish. This chapter concerns only the members of the Reoviridae known to infect humans.
Although the orthoreoviruses (referred to commonly as reoviruses), orbiviruses,coltiviruses, and rotaviruses are similar in morphology, diameter (about 70 nm), and possession of a segmented, double-stranded RNA genome, they differ in epidemiology, association with disease, and ability to be cultured. In addition, the four groups are distinct antigenically.
Rotaviruses are major agents of severe diarrhea in infants and young children in developed and developing countries. Such diarrhea can lead to dehydration that may be fatal if rehydration fluids are not available. Reovirus infections are quite common in humans, although they tend to be mild or subclinical. The extent of their role as agents of illness in humans is unclear. Four human orbiviruses or coltiviruses have been associated with human disease. The most serious of these diseases is Colorado tick fever, characterized by diphasic fever, headache, muscle pain, anorexia, leukopenia, and weakness; some cases are complicated by encephalitis, hemorrhage, thrombocytopenia, or pericarditis; death is rare.
