Reoviridae

• TRANSMISSION ROUTE: Direct contact, ingestion, inhalation

Definition

The Reoviridae is a ubiquitous and diverse family of viruses. Family members infect plants, insects, humans, and other animals. The Reoviridae family comprises the only viruses known to have double-stranded RNA (ribonucleic acid) genomes. Reovirus infections in humans affect the gastrointestinal and respiratory tracts. Illnesses caused by reoviruses are common but generally mild.

Natural Habitat and Features

The reovirus family is represented worldwide, with many species isolated to particular geographic areas. Five genera of reoviruses cause disease in humans. Three of these five genera, Coltivirus, Seadornavirus, and Orbivirus, are composed entirely of arboviruses. Arboviruses infect insects, which then transmit the virus to humans as vectors.

All reovirus family members have a symmetrical structure composed of two concentric icosahedral capsids. Virions measure 60 to 80 nanometers (nm) in diameter and have no outer envelope. The double-stranded RNA genome, located in the viral core, is segmented into ten to twelve separate molecules. The total genome is 16 to 27 kilobase pairs in size, and individual RNA molecules range in size from 680 to 3900 base pairs. Viral replication takes place only in the host cell cytoplasm; the virion core thus carries all the enzymes required for RNA transcription.

Pathogenicity and Clinical Significance

Rotavirus is the most significant reovirus because of the number of people it infects and because of the severity of the resulting illness. Rotavirus is the leading cause of acute vomiting and severe diarrhea among infants and young children worldwide. Rotavirus accounts for 50 to 80 percent of all cases of viral gastroenteritis. It is more frequent in winter, during cold and dry conditions. Most cases resolve on their own within three to eight days of the start of symptoms.

Rotavirus infections are most severe in infants eleven months of age and younger. Dehydration is a serious complication of rotavirus, leading to high mortality rates in developing countries. Worldwide, one-half million children age five years and younger die each year from rotavirus infection. Before the introduction of a rotavirus vaccine in 2006, nearly all children in the United States, for example, had been infected with rotavirus by their fifth birthday.

Orthoreovirus infection is generally benign in humans, causing no disease symptoms. In rare cases, respiratory or gastrointestinal symptoms may be present. Coltiviruses, orbiviruses, and seadornaviruses are all spread by insects and cause infections only rarely in humans. Symptoms of infection are similar for all viruses in these genera and include fever, muscle aches, and headache. Neurological complications, such as meningitis or encephalitis, may occur but are very rare.

Colorado tick fever (CTF) is caused by a coltivirus found only in the western United States and Canada. Transmitted by the Dermacentor andersoni wood tick, CTF is the most serious of the insect-borne reoviruses. Several hundred cases are reported each year in the United States. CTF can be serious in children, with hospitalization required in 20 percent of cases. The illness lasts five to ten days, and fatalities are very rare. A similar human coltivirus is Eyach virus, found in central Europe. As with CTF, Eyach virus is spread by ticks.

Human diseases caused by orbiviruses are extremely rare, with about fifty cases reported worldwide. Orungo virus and Lebombo virus are both transmitted by mosquitoes in Africa, and they have been isolated from humans. Kemovoro, Lipovnik, and Tribec viruses are tickborne and are associated with encephalitis in central Europe and Russia. Meningitis and possibly the autoimmune disorder Guillain-Barré syndrome have been attributed to Lipovnik virus in the area of the Czech Republic.

In South America, serum antibodies against Changuinola virus are common, indicating frequent infection. This virus is transmitted by Phlebotomous flies. However, only one case of human disease due to this virus, in Panama, has been reported.

Seadornaviruses are spread by mosquitoes and are endemic to China and Indonesia. The only seadornavirus known to infect humans is Banna virus. The prevalence of Banna virus is unknown because it may be confused with Japanese encephalitis, which is common in Banna virus-endemic areas. Symptoms of Banna virus infection are similar to other arboviruses in the reovirus family and include muscle aches, headache, and, in some cases, encephalitis.

Drug Susceptibility

No drugs exist for the treatment of reovirus infection. One possible exception is the drug ribavirin, which has shown promising results against CTF in studies. A vaccine against rotavirus is available.

Bibliography

"About Rotavirus." Centers for Disease Control, 22 Apr. 2024, www.cdc.gov/rotavirus/about/index.html. Accessed 4 Feb. 2025.

Attoui, Houssam, et al. “Coltiviruses and Seadornaviruses in North America, Europe, and Asia.” Emerging Infectious Diseases 11, no. 11 (2005): 1673-1679.

Crum-Cianflone, Nancy F. “Orbivirus.” 12 Nov. 2021, emedicine.medscape.com/article/224420-overview. Accessed 4 Feb. 2025.

Madigan, Michael T., and John M. Martinko. Brock Biology of Microorganisms. 12th ed. Upper Saddle River, N.J.: Pearson/Prentice Hall, 2010.

Rasouli, Gholamreza, and John W. King. “Reoviruses.” 13 Nov. 2023, emedicine.medscape.com/article/227348-overview. Accessed 4 Feb. 2025.