RETROVIRIDAE FAMILY: RETROVIRUSES

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Retroviridae family is a unique family of viruses that contain reverse transcriptase (RT) enzyme which allows all viruses in this family to carryout reverse transcription of their genome. Viruses in this family are usually referred to as retroviruses because of their possession of RT enzyme which allows them to carryout reverse transcription. Retroviruses are distributed worldwide; and they cause infections in humans and non-human primates (NHPs). Reverse transcription is the genetic process of copying the genetic information found in the RNA genome of an organism into DNA. Viruses in the Retroviridae family cause various types of tumours, lymphomas or sarcomas in animals. And this implies that some retroviruses are oncogenic or cancer-causing in nature. Retroviruses also infect invertebrates as well as vertebrates.

Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) which causes acquired immunodeficiency syndrome (AIDS) and simian AIDS in humans and monkeys respectively are the most important viruses in the Retroviridae family. Viruses in the Retroviridae family have an icosahedral shape; and they measure between 80-110 nm in diameter. They possess a ss(+)RNA; and they replicate in the nucleus of their host cell. Retroviruses are enveloped viruses, and their envelope is rich in lipids and proteins. Retroviruses are released through the process of budding from the cytoplasmic membrane of their host cell. There are seven (7) genera of viruses in the Retroviridae family. These viral genera are Lentivirus, Spumavirus, Epsilonretrovirus, Betaretrovirus, Alpharetrovirus, Deltaretrovirus and Gammaretrovirus. HIV and SIV, which are one of the most significant viruses in this family, are found in the genus Lentivirus.

The human T-cell leukemia virus-1 (HTLV-1), a Deltaretrovirus is another important member of the Retroviridae family which causes lymphoma in humans. With the help of reverse transcriptase, the ss(+)RNA genome of retroviruses is transcribed by RT enzyme into a dsDNA molecule otherwise known as provirusor viral DNA. The provirus (which can also be called complementary DNA, cDNA) is finally integrated into the chromosomal DNA of the host cell; and the viral DNA surmounts or takes over the cellular machinery of their host cell to produce viral RNAs and protein molecules required for the formation of new virions. It is noteworthy that the provirus generally serves as the template for the biosynthesis of viral RNA and protein molecules that are required for the assembling of new viral progenies (i.e., new retroviruses).

Infections or diseases caused by retroviruses especially AIDS still have no permanent cure but the disease can be clinically managed or treated using some antiviral drugs and techniques such as zidovudine or azidothymidine (AZT) and highly active antiretroviral therapy (HAART). AZTs are nucleoside analogs that inhibit the activities of RT enzyme during the replication of retroviruses in vivo. There abound plethora of antiviral agents that are used for the clinical treatment and management of infections caused by pathogenic viruses. And for viral infections for which there are currently no antiviral drug or medication for its management or treatment, research is currently ongoing to find a potent treatment and vaccine for their proper control.           

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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