Reoviridae

Reoviridae is a family of RNA viruses that infect animals, protists, fungi, and plants. The genome is double-stranded RNA and therefore they are included in Group III of the Baltimore Classification. The name of "Reoviridae" is derived from "orphan enteric respiratory virus", where the term "orphan virus" It refers to the ignorance of a disease that can be associated with the virus.

Features

Virions are not enveloped. Their capsids, made up of multiple proteins, have icosahedral (T-13) symmetry and are generally organized in two concentric layers, one outer and one inner. The genomes of these viruses consist of 10-12 double-stranded RNA segments that are grouped into three categories according to their size: L (large), M (medium), and S (small). The segments are between 3.9 and 1 kbp in length, and each segment encodes 1-3 proteins. Proteins are denoted by the Greek letter corresponding to the segment from which it was translated (proteins λ for segment L, μ for M, and σ for S).

Since these viruses have double-stranded RNA genomes, replication occurs exclusively in the cytoplasm. The virus encodes several proteins that are necessary for genome replication and conversion of double-stranded RNA to positive- or negative-sense single-stranded RNA. The virus can enter the host cell through a receptor on the cell surface. The receptor is unknown but is believed to include sialic acid and cell adhesion molecules (JAMs). The virus has part of the endolysosome uncoated by proteases, where the capsid is partially digested to allow entry into the cell. The virus core then enters the cytoplasm through a still unknown process, and there the genome is conservatively transcribed, producing an excess of positive-sense strands, which are used as templates to synthesize negative-sense mRNA. Viral particles begin to assemble in the cytoplasm 6-7 hours after infection.

A characteristic that distinguishes double-stranded RNA viruses, regardless of the family to which they belong, is their ability to carry out transcription of double-stranded RNA segments under the appropriate conditions within the capsid. In all of these viruses, the enzymes required for endogenous transcription are therefore part of the virion structure.

Viral particles begin to assemble in the cytoplasm 6 to 7 hours after infection. Translation occurs by leaky scanning, termination suppression, and ribosome skipping. The virus exits the host cell by non-tubule-guided monopartite viral movement, cell-to-cell movement, and existing in occlusion bodies after cell death and remaining infectious until encountering another host.

Infection in Animals

In animals, they affect the gastrointestinal system (like Rotaviruses) and the respiratory tract of the host. Although various diseases caused by viruses of the Reoviridae family have recently been identified, the original name is still used.

Infection often occurs in humans, but most cases are mild or subclinical. The virus can be easily detected in feces and also in nasal or pharyngeal secretions, urine, cerebrospinal fluid, and blood. Despite the ease with which it is detected, the role of the virus in disease or treatment is still uncertain. The use of these viruses in the fight against cancer is currently being investigated.

Taxonomy

The updated ICTV taxonomy (2021) classifies the family as follows:

• Sedoreovirinae
  • Cardoreovirus
  • Mimoreovirus
  • Orbivirus
  • Phytoreovirus
  • Rotavirus
  • Seadornavirus
• Spinareovirinae
  • Aquareovirus
  • Coltivirus
  • Cypovirus
  • Dinovernavirus
  • Mycoreovirus
  • Fijivirus
  • Orthoreovirus
  • Idnoreovirus
  • Oryzavirus