Reovirus - Classification, Morphology, Pathogenesis, Replication, Lab diagnosis, Medically important pathogens

Classification of Reovirus

The classification of Reovirus is as follows:

Realm: Riboviria

Kingdom: Orthornavirae

Phylum: Duplornaviricota

Class: Resentoviricetes

Order: Reovirales

Family: Reoviridae

The family Reoviridae is divided into two subfamilies Sedoreovirinae, and Spinareovirinae. Each sub families consists of several genera.

Sedoreovirinae

• Cardoreovirus

• Mimoreovirus

• Orbivirus

• Phytoreovirus

• Rotavirus

• Seadornavirus

Spinareovirinae

• Aquareovirus

• Coltivirus

• Cypovirus

• Dinovernavirus

• Fijivirus

• Idnoreovirus

• Mycoreovirus

• Orthoreovirus

• Oryzavirus

Medically important pathogens of Reovirus

Family Reoviridae contains 4 genera that cause human infections:

• Orthoreovirus- reovirus serotypes 1, 2 and 3

• Orbivirus and Colitivirus – various serotypes

• Rotavirus – 7 species present serogroups (A to G)

  Rotavirus A to Rotavirus C detects in humans

Morphology of Reovirus

Morphologically, Reoviridae has icosahedral symmetry, non-enveloped, with a double-shelled capsid surrounding the core, measuring 70-75nm in diameter. The genomic structure is double-stranded RNA which consists of 10-12 segments with a total genome size of 16-27 kbp.

Reovirus inner capsid layer shows well-defined subunits, whereas the outer layer of some viruses (e.g. rotavirus and orbiviruses) lack these structures. The virus core contains many enzymes essential for the transcription and capping of viral RNA.

They are ubiquitous with a very wide host range. The virus is usually resistant to heat, has a wide pH (3.0-9.0), and has lipid solvents but is sensitive to 95% ethanol, phenol, and chloride.

The 3 serotypes of orthoreovirus/reoviruses share a common complement fixation antigen but can be distinguished by Hemagglutination inhibition and Neutralization technique. Reovirus contains a hemagglutinin for human O or bovine erythrocytes.

Pathogenesis of Reovirus

Reovirus infections often occur in humans but are mild or subclinical. It also occurs in a wide variety of animals such as mice, chimpanzees, dogs, cats, sheep, swine, horses, and monkeys. Their role in human disease is uncertain.

The virus is detected efficiently in feces. It is also recovered from nasal or pharyngeal secretion, urine, blood, CSF, and organ autopsy. Reovirus infection has been observed in patients with various conditions such as:

• fever

• exanthema

• URT and LRT illness

• GI tract illness

• Hepatitis

• pneumonitis

• meningitis

• encephalitis

• keratoconjunctivitis

• Neonatal cholestasis

• Myocarditis

• Burkitt’s lymphoma

Although they readily infect humans, they are not important agents of human disease.

They are, however, potential oncolytic viruses. The transformed cell is susceptible to reovirus replication while non-transformed cells were resistant to the virus. It causes oncolysis (apoptosis) in a variety of cancer cells and tumors.

The possible role of reovirus in the treatment of brain and leptomeningeal metastasis from brain cancer is seen. The beneficial role of reovirus in reducing the sequential spiral and leptomeningeal metastasis from medulloblastoma has been suggested.

Replication of Reovirus

Reovirus replicates in the cytoplasm of infected cells. Attachment via a specific protein component of the outer capsid. i.e. σ 1 to cellular receptor i.e. sialic acid and junction adhesion molecule A.

The viral protein-cellular receptor interaction leads to a conformational change in the viral capsid. This enables viruses to enter cells by receptor-mediated endocytosis. The outer capsid is removed, but the viral particle is never completely uncoated.

The Reovirus genome RNA remains in the core of the sub-viral particle (double-layered particle). RNS-dependent RNA polymerase transcribes RNA to give mRNA. The mRNA molecules which are 5’ capped by not polyadenylated leave the subviral particle through channels present in outer and inner capsids.

The mRNA is translated to generate various viral proteins. The mRNA also acts as a template for RNS replication. RNA polymerase aids the replication process. Viral genome RNA is packed within new core structures.

Double-layered virion particles bond to intracellular viral receptors (NSP4) and buds from ER. During budding through ER, double-layered virion particles transiently acquire an envelope.

At the same time, outer capsid proteins, VP7 and VP4 are incorporated into new virions which become mature. They lose the envelope (transiently acquired from ER) and are passed through the Golgi apparatus. They are finally released from enterocytes.

Lab diagnosis of Reovirus

The laboratory diagnosis of Reovirus begins with the collection of samples.

Sample

• faces

• throat swab

• nasopharyngeal secretion/swab

Culture/isolation

Isolation of viruses and detection of viral antigen (Ag) and RNA genome are done.

Serological test

Serological test for Reovirus is done mostly for epidemiological studies than for laboratory diagnosis. Some tests used are:

• Haemagglutination inhibition (HAI)

• CFT

• Virus neutralization to demonstrate antibody (Ab)

Treatment of Reovirus

There is no treatment for Reovirus.