MEDICAL IMPORTANCE OF VIRUSES IN THE POLYOMAVIRIDAE FAMILY

Polyomaviridae family contains DNA tumour viruses like the Papillomaviridae family. Polyomavirus is the only viral genera or genus in the Polyomaviridae family. They are so named because the polyomaviruses causes tumour in various organs of the body including the kidneys, ureter, bladder, brain and bones. However, there are various genotypes of viruses in this family that infect humans and other vertebrates/mammals such as monkey, cattle, mice, rabbits and birds. Mammals and birds are primarily the natural host of viruses in the Polyomaviridae family. The polyomavirus SV40 (which infects rhesus monkeys) and the BK polyomavirus and JC polyomavirus which are both human polyomaviruses are the typical examples of viruses in this family of viruses known as Polyomaviridae. The SV in ‘polyomavirus SV40’ stands for “simian vacuolating” virus.

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The initials BK and JC represent the initials of the names of the individuals from whom the virus (i.e., BK polyomavirus and JC polyomavirus) was initially isolated from in the early 1970s. Viruses in the Polyomaviridae family have a circular dsDNA genome that is devoid of envelope. They are icosahedral in shape, and measure about 45 nm in diameter. Polyomaviruses are also resistant to ether but sensitive to UV light and formalin. The replication site of viruses in the Polyomaviridae family is the nucleus of their infected host cell; and they are usually released from the host cells they infect through the process of cell lysis. BK polyomavirus causes cystitis and nephropathy while JC polyomavirus causes a fetal brain disease (known as progressive multifocal leukoencephalopathy) in immunocompromised individuals. Progressive multifocal leukoencephalopathy (PML) is a rare but fatal viral disease that occurs mainly in AIDS patients. Humans are the natural host of the BK and JC polyomavirus while rhesus monkeys and macaques are the natural host of polyomavirus SV40 virus. BK and JC polyomaviruses can both cause disease in children and adults especially in the immunocompromised adult hosts – whose immune system have been weakened and comprised.

Polyomavirus SV40 is known to infect only rhesus monkeys but it was discovered that the virus may also occur in individuals who received early jabs of killed and live poliovirus vaccine that had been cultivated in monkey cells which were unknowingly infected with SV40. This contamination may occur during the production of the vaccine. And thus, the SV40 is currently being considered as a pathogenic viral agent in human population due to its detection in human samples including blood and urine. Whether the presence of SV40 in human population was due to the use of contaminated poliovirus vaccine or from other sources is still a subject of discussion in the medical community, but the truth remains that the virus occur in human population as well as in the population of other mammals and birds as well. Highly active antiretroviral therapy (HAART) and other antiviral therapy are available for the treatment of infections caused by polyomaviruses. Rhesus monkeys happen to be the only known natural host of the polyomaviruses.

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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