REOVIRIDAE FAMILY

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Reoviridae family is a unique family of RNA-containing viruses because it is among the family of RNA viruses that contain viruses which posses a double-stranded RNA (dsRNA) genome. Viruses in the Reoviridae family cause infection in humans and other mammals. Other families of RNA viruses with dsRNA genome include Birnaviridae, Chrysoviridae, Cystoviridae, Hypoviridae, Partitiviridae, and Totiviridae. Only the Birnaviridae and Reoviridae families contain viruses that infect vertebrates. The other five families (including Chrysoviridae, Cystoviridae, Hypoviridae, Partitiviridae, and Totiviridae) contain viruses that infect other forms of life including fungi, birds, plants, protozoa, insects and bacteria.

All RNA viruses with the exclusion of reoviruses have single-stranded RNA (ssRNA) genome. Reoviruses are non-enveloped viruses with dsRNA genome and they measure between 60-80 nm in diameter. They have an icosahedral nucleocapsid. Reoviruses are resistant to ether. However, reoviruses are sensitive to UV light, formalin and chlorine compounds. Reoviruses replicate in the cytoplasm of their host cell, and they exit their host cell through cell lysis. During their replication in the cytoplasm of their host cell, the RNA-dependent RNA polymerase which is contained in the virion is used for the transcription of the organism’s dsRNA into an mRNA since the dsRNA genome is entirely inactive to act as mRNA template in the synthesis of viral proteins.

There are twelve (12) genera of viruses in the Reoviridae family; and these include Orthoreovirus, Orbivirus, Coltivirus, Rotavirus, Seadornavirus, Aquareovirus, Cypovirus, Idnoreovirus, Fijivirus, Phytoreovirus, Oryzavirus and Mycoreovirus. Only members of the generaOrthoreovirus, Rotavirus, Orbivirus, Coltivirus and Seadornavirus infect humans and other vertebrates. The other genera of Reoviridae family contain viruses that cause infection in non-vertebrates, some vertebrates and microorganisms such as fungi, protozoa and bacteria. Rotaviruses in the genus Rotavirus are the most importanthuman pathogen of the Reoviridae family; and this is because they cause diarrhea in young children including infants. The elderly, transplant patients and the immunocompromised host are also not left out as rotaviruses cause diarrhea in these individuals because of the weak nature of their immune system. Rotaviruses are distributed worldwide; and they are the most frequent cause of severe diarrheal disease or gastroenteritis in newborns/infants and young children.

Different serotypes of rotaviruses exist including rotavirus A, B, C, D, and E. Rotaviruses are usually transmitted through the faecal-oral route and respiratory route. Rotaviruses invade the microvilli or villi of the small intestines where they attach to the mucosa of the intestinal wall to cause several diarrheal illnesses. The incubation period of the disease is between 1-2 days; and clinical symptoms of gastroenteritis due to rotavirus infection include vomiting, diarrhea (characterized by profuse passing of watery stool) and abdominal cramp. No antiviral treatment exists for infections caused by rotaviruses. And the management of the diseases is usually based on the administration of O.R.T (oral rehydration therapy) to affected patients on time.

The disease can be fatal if medical care is not administered on time to individuals especially infants and young children who ingest the virus through contaminated hands, water or food. Severe diarrheal disease caused by rotaviruses is responsible for a significant amount of infant and child morbidity and mortality across the globe. And the mortality rate of the disease is high in developing countries where environmental sanitation and personal hygiene in young children is averagely poor. Children who have been previously exposed to rotavirus infection usually develop passive immunity against the infectious agent. Due to the worldwide morbidity and mortality caused by rotaviruses in infants and young children, there have been steps to develop vaccines against the infection and some of such potent vaccines (usually administered orally) are currently in use in some developed economies.

Frequent and proper hand washing as well as proper personal and environmental sanitation is vital to the prevention of rotavirus infection especially in hospitals and other healthcare facilities where outbreaks due to rotaviruses are possible. The best form of therapy for rotavirus infection in humans is by the replenishment of lost fluid from the body, especially the use of ORT and other forms of supportive therapy to replenish lost electrolytes from the body.                

Further reading

Acheson N.H (2011). Fundamentals of Molecular Virology. Second edition. John Wiley and Sons Limited, West Sussex, United Kingdom.

Brian W.J Mahy (2001). A Dictionary of Virology. Third edition. Academic Press, California, USA.

Cann A.J (2011). Principles of Molecular Virology. Fifth edition. Academic Press, San Diego, United States.

Carter J and Saunders V (2013). Virology: Principles and Applications. Second edition. Wiley-Blackwell, New Jersey, United States.

Dimmock N (2015). Introduction to Modern Virology. Seventh edition. Wiley-Blackwell, New Jersey, United States.

Kudesia G and Wreghitt T (2009). Clinical and Diagnostic Virology. Cambridge University Press, New York, USA. 

Marty A.M, Jahrling P.B and Geisbert T.W (2006). Viral hemorrhagic fevers. Clin Lab Med, 26(2):345–386.

Strauss J.H and Straus E.G (2008). Viruses and Human Diseases. 2nd edition. Elsevier Academic Press Publications, Oxford, UK.

Zuckerman A.J, Banatvala J.E, Schoub B.D, Grifiths P.D and Mortimer P (2009). Principles and Practice of Clinical Virology. Sixth edition. John Wiley and Sons Ltd Publication, UK.

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