Reoviridae

Overview
Reoviridae is a family of viruses that can affect the gastrointestinal system (such as Rotavirus) and respiratory tract. Viruses in the family Reoviridae have genomes consisting of segmented, double-stranded RNA (dsRNA). The name "Reoviridae" is derived from respiratory enteric orphan viruses. The term "orphan virus" means that a virus that is not associated with any known disease. Even though viruses in the Reoviridae family have more recently been identified with various diseases, the original name is still used.

Reovirus infection occurs often in humans, but most cases are mild or subclinical. The virus can be readily detected in feces, and may also be recovered from pharyngeal or nasal secretions, urine, cerebrospinal fluid, and blood. Despite the ease of finding Reovirus in clinical specimens, their role in human disease or treatment is still uncertain.

Reoviruses are non-enveloped and have an iscohedral capsid (T-13) composed of an outer and inner protein shell.

The genomes of viruses in Reoviridae contain 10-12 segments which are grouped into three categories corresponding to their size: L (large), M (medium) and S (small). Segments range from ~ 3.9 kbp – 1kbp and each segment encodes 1-3 proteins. Reoviridae proteins are denoted by the Greek character corresponding to the segment it was translated from (the L segment encodes for λ proteins, the M segment encodes for μ proteins and the S segment encodes for σ proteins).

Since these viruses have dsRNA genomes, replication occurs exclusively in the cytoplasm and the virus encodes several proteins which are needed for replication and conversion of the dsRNA genome into (+)-RNAs. The virus can enter the host cell via a receptor on the cell surface. The receptor is not known but is thought to inlcude sialic acid and junctional adhesion molecules (JAMs). The virus is partially uncoated by proteases in the endolysosome, where the capsid is partially digested to allow further cell entry. The core particle then enters the cytoplasm by a yet unknown process where the genome is transcribed conservatively causing an excess of (+) sense strands, which are used as mRNA templates to synthesize (-) sense strands. Viral particles begin to assemble in the cytoplasm 6-7 hours after infection.

Work is also being done using the reovirus in approaches for combative cancer research. Oncolytics Biotech Inc in Canada has various Type I & II trials going forward using their compounded REOLYSIN® designed to focused on the development of oncolytic viruses as potential cancer therapeutics. Oncolytics’ clinical program includes a variety of Phase I and Phase I/II human trials.

Genera and type species

 * Genus Orthoreovirus: type species Mammalian orthoreovirus
 * Genus Orbivirus: type species Bluetongue virus
 * Genus Rotavirus: type species Rotavirus A - a common cause of diarrhea
 * Genus Coltivirus: type species Colorado tick fever virus (CTFV)
 * Genus Aquareovirus: type species Aquareovirus A
 * Genus Cypovirus: type species Cypovirus 1 (CPV 1)
 * Genus Fijivirus: type species Fiji disease virus
 * Genus Phytoreovirus: type species Rice dwarf virus
 * Genus Oryzavirus: type species Rice ragged stunt virus
 * Genus Idnoreovirus: type species Idnoreovirus 1
 * Genus Mycoreovirus: type species Mycoreovirus 1