Orthoreoviruses

Orthoreoviruses

Orthoreoviruses are nonenveloped viruses, measuring 80 nm in diameter. It is composed of an inner protein shell, i.e., core and an outer protein shell known as outer capsid. The inner core is com-posed of three major lipids, g1, g2, and s2, and many minor pro-teins. The core consists of a 10-segmented double-stranded RNA. The reoviruses have three serotypes, namely, type 1, 2, and 3, based on neutralization and hemagglutination inhibition test. All these serotypes share a common complement fixation antigen.

The reoviruses are very stable. They are stable to heat, to a wide range of pH, and are also stable in aerosols. Reoviruses can be cultured in monkey kidney cells, HeLa cells, and mouse L-cell fibroblast.

Human volunteers’ studies have failed to establish a clear cause-and-effect relationship between reoviruses and human ill-ness. So far, reoviruses have been linked with upper respiratory infection, fever, enteritis, and febrile exanthema in children. All three serotypes of the virus have been recovered from healthy children and from children with minor febrile illness, diarrhea, or enteritis. The exact method of transmission of reoviruses is not known. Since viruses are isolated most frequently from the feces, the infection appears to be transmitted by the fecal–oral route.

Recent studies have shown the potential of reovirus as an oncolytic virus and have shown the susceptibility of trans-formed cell to reovirus replication. It has been demonstrated that normal nontransformed cells were resistant to the virus. Reovirus causes oncolysis (apoptotic cell death) in a wide variety of cancer cells and tumors.

Results of many studies have shown a possible role of reovirus in the treatment of brain and leptomeningeal metastasis from breast cancer. The beneficial role of reovirus in reducing the sequential spinal and leptomeningeal metastasis from medul-loblastoma has also been suggested. The laboratory diagnosis of the human orthoreovirus infection can be made by:

The isolation of the virus and detection of the viral anti-gen and RNA genome in various clinical specimens, such as feces, throat swabs, and nasopharyngeal specimens.

The serological tests, such as hemagglutination inhibition, complement fixation, or virus neutralization to demon-strate antibodies. These serological tests are used primarily for epidemiological studies.

No specific treatment is available for orthoreovirus infection. No preventive measures have been suggested due to the lack of definitive association of orthoreovirus with human disease.