Properties of Reoviridae 522
Coitiviruses and Orbiviruses 528
The name reovirus is an acronym, short for respiratory enteric orphan because the first members of this family to be discovered, now classified as the genus Orthorcovirus of the family Reoviridae, were found to inhabit both the respiratory and the enteric tract of humans and animals, but to be "orphans" in the sense that they are not associated with disease. The discovery of the human rotaviruses in 1973 changed all that, for members of the genus Rota-viru? are recognized to be the most important cause of infantile gastroenteritis throughout the world. In addition, dozens of arboviruses, at least one of them causing disease in humans, have been allocated to the genera Orhivirus and Coltivirus. Yet other genera contain pathogens that infect both plants and insects, raising the question of whether these fascinating viruses that cross kingdoms so readily might have evolved in insects.
Furthermore, reoviruses have attracted much attention from molecular biologists because of the unique nature of the genome. Composed of double-stranded RNA, the genome is segmented into 10-12 separate molecules, each representing a different, generally monocistronic, gene. For several reoviruses, each gene has been cloned and sequenced and its protein product characterized. Moreover, the facility with which these viruses undergo genetic reassortment has been exploited to exchange genes from temperature-sensitive (ts) mutants and thus determine the role of individual genes in pathogenesis and virulence.
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