PICORNAVIRIDAE FAMILY

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Picornaviridae family represents a large family of virus that causes infections in humans, primates and other mammals. Enteroviruses, polio virus, foot-and-mouth disease virus (the first animal virus to be discovered), hepatitis A virus (HAV) and rhinoviruses are some examples of viruses in the Picornaviridae family. With the exclusion of polio infection or poliomyelitis (caused by polio virus) which has been eradicated in some parts of the world (e.g., USA, Europe and parts of Asia and Africa), Picornaviruses have a worldwide distribution. There are nine genera of viruses in the Picornaviridae family; and these include Aphthovirus, Cardiovirus, Enterovirus, Erbovirus, Hepatovirus, Kobuvirus, Parechovirus, Rhinovirus, and Teschovirus.

Only five genera of Picornaviridae family including Enterovirus, Hepatovirus, Kobuvirus, Parechovirus and Rhinovirus contain Picornaviruses that cause infections in humans. Enteroviruses and polio virus are in the genus Enterovirus;foot-and-mouth disease virus (which causes foot-and-mouth disease in animals) is in the Aphthovirus genera; HAV is found in the Hepatovirus genera and rhinoviruses are found in the genera Rhinovirus. The human rhinovirus is the causative agent of the majority of common cold in humans; and the disease is characterized by inflammation of the nasal cavity. Rhinoviruses are transmitted through the respiratory route or respiratory tract of infected persons. HAV found in the Hepatovirus genera is the causative agent of infectious hepatitis in humans; and HAV is transmitted through the faecal-oral route.

Kobuvirus species which is transmitted through the faecal-oral route causes gastroenteritis in humans. Kobuvirus infection is common amongst people who eat raw sea foods such as oysters. Viruses in the Picornaviridae family are non-enveloped viruses that posses a ss(+)RNA genome. They measure between 28-30 nm in diameter and this makes members of viruses in this family one of the smallest viruses in terms of the size of their virion. Picornaviruses are resistant to ether. Enteroviruses which include polio virus, Coxsackie A, Coxsackie B and Echoviruses are the different serotypes that make up the Enterovirus genera. Enteroviruses are transient inhabitants of the gastrointestinal tract (GIT) of humans and they cause mild gastrointestinal disease in infected individuals. Poliomyelitis or polio caused by polio virus is one of the most serious diseases caused by Enteroviruses.

Poliomyelitis is clinically characterized by the deformity of the limbs of infected children, and it has been contained in most parts of the world due to massive immunization/vaccination programmes against the disease. Polio virus infects motor neurons of the spinal cord and other parts of the central nervous system (CNS), and this leads to flaccid paralysis in polio infected individuals. Enteroviruses are transmitted through the faecal-oral route in human population. There is vaccine for the prevention of polio infection in human population. The availability of vaccine for immunization of susceptible human population against the viral infection has helped in the drastic reduction of polio cases from around the world especially in most developing parts of the world like Africa where there are still some traces of polio infection.        

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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