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Introduction to Reoviridae
The first human orthoreovirus was isolated in 1953 from a rectal swab collected from a healthy child. Later 3 serotypes were identified which were designated as reovirus and categorized under the Reoviridae family. Later it was discovered that the 3 serotypes share a common group antigen as detected by complement fixation. The name reovirus was proposed originally by Sabin in 1959 to reflect the fact that viruses of this group had been isolated from the respiratory and enteric tracts and were orphan (reo) viruses without known associated disease.


Viral Characteristics

Reoviridae enters the cell through endocytosis. Early transcription of the dsRNA genome by the viral polymerase occurs inside the subviral particle. The 10-12 segments of the genome are transcribed and translated at different frequencies. RNA is transcribed conservatively with only (-)sense strands being used as a template to synthesize the (+)sense strands which are capped inside the viral core and are not polyadenylated. The mRNAs leave the core and are translated in the cytoplasm. Secondary transcription takes place in the cytoplasm leading to uncapped (+)sense strands which serve as templates for (-)strand synthesis.


Reoviridae family has a virion of 60-80 nm in diameter and has a genomic size of 16-27 kilobase pairs. The genome consists of double-stranded RNA in 10-12 discrete segments. Reo viruses are not enveloped and has an icosahedral nucleocapsid and outer capsid. The inner capsids of all genera display sharply defined subunits; the outer capsids of rotaviruses and orbiviruses lack well-defined subunit structures. The virion core contains several enzymes needed for transcription and capping of viral RNA.

The pathonegicity of reoviruses with human diseases has not been clear. Mostly reoviruses are known to be associated with childhood diarrhea. Reoviruses cause many inapparent infections because most people have serum antibodies by early adulthood. Antibodies also are present in other species. All 3 types have been recovered from healthy children, from young children during outbreaks of minor febrile illness, and from children with diarrhea or enteritis. Human volunteer studies have failed to demonstrate a clear cause-and-effect relationship between reoviruses and human illness.



Gholamreza Rasouli, MD John W King, MD. Reoviruses. July 6, 2005.


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