REOVIRIDAE FAMILY

Reoviridae family is a unique family of RNA-containing viruses in that it is the only family of RNA viruses that contain viruses which posses a double-stranded DNA (dsRNA) genome; and one which 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, and reoviruses are resistant to ether. However, reoviruses are sensitive to UV light, formalin and chlorine compounds. Reoviruses replicate in the cytoplasm and they exit their host cell via 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 genera Orthoreovirus, 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 important human 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. 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; and rotaviruses are usually transmitted via the feacal-oral route and respiratory route. Rotaviruses invade the microvilli or villi of the small intestines where they attach to the mucosa of the intestine to cause several diarrheal illnesses. The incubation period of the disease is between 1-2 days; and clinical symptoms of diarrhea due to rotaviruses 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 to affected patients on time. The disease can be fatal if care is not administered on time to individuals especially infants and young children who ingests the virus via contaminated hands, water or food. Severe diarrheal disease caused by rotaviruses is responsible for a significant amount of infant and child morality 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 is vital to the prevention of rotavirus infection especially in hospitals and other healthcare facilities where outbreaks due to rotaviruses are possible.           

SELECTED REFERENCES

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

Ahmad K (2002). Norwalk-like virus attacks troops in Afghanistan. Lancet Infect Dis, 2:391.

Alan J. Cann (2005). Principles of Molecular Virology. 4th edition. Elsevier Academic Press,   Burlington, MA, USA.

Alba R, Bosch A and Chillon M (2005). Gutless adenovirus: last-generation adenovirus for gene therapy. Gene Ther, Suppl 12:S18-S27.

Alberts B, Bray D, Johnson A, Lewis J, Raff M, Roberts K and Walter P (1998). Essential Cell Biology: An Introduction to the Molecular Biology of the Cell. Third edition. Garland Publishing Inc., New York.

Balows A, Hausler W, Herrmann K.L, Isenberg H.D and Shadomy H.J (1991). Manual of clinical microbiology. 5th ed. American Society of Microbiology Press, USA.

Barrett   J.T (1998).  Microbiology and Immunology Concepts.  Philadelphia,   PA: Lippincott-Raven Publishers. USA.

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