RHABDOVIRIDAE FAMILY

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Rhabdoviridae family is comprised of viruses generally known as rhabdoviruses. Rhabdoviruses have a ss(-)RNA genome and they measure between 45-100 nm in diameter. They are enveloped viruses. Rhabdoviruses replicate in the cytoplasm of their host cell. They are released from their host cell by a budding process through the cytoplasmic membrane of the infected host cell. Rhabdoviruses have a helical nucleocapsid. Viruses in the Rhabdoviridae family infect humans, animals, fish, insects and even plants. There are six genera of viruses that make up the Rhabdoviridae family. These viral genera are: Vesiculovirus, Lyssavirus, Ephemerovirus, Novirhabdovirus, Cytorhabdovirus and Nucleorhabdovirus.

Only the Vesiculovirus and Lyssavirus contain important human viruses. Vesicular stomatitis virus (VSV) and rabies virus which are found in the Vesiculovirus and Lyssavirus genera respectively are of importance to humans because they cause significant human disease. VSV causes an asymptomatic herpes-like disease in humans especially those in close contact with animals such as horses, pigs and cattle that are naturally infected by the viral agent. VSV is mostly endemic in South American countries. Rabies is an acute and fatal, zoonotic viral infection of the central nervous system (CNS) of humans. It is caused by rabies virus in the genera Lyssavirus. Rabies is globally distributed, and the disease occurs in both animals and humans.

Human infection with rabies virus occurs following the bite of a rabid dog or other animals such as wolves, foxes, jackals, bats and monkeys harbouring the virus. The virus is present in the saliva of rabid animals and it is passed on or transmitted to humans by the bite of the animal and even when they lick an open wound on the body of the human host. Rabies virus is destroyed by UV radiation, heat, ether treatment and trypsin treatment. Rabies virus multiplies in the connective tissues or muscle cells at the site of bite. The virus is transported to peripheral nerves of the CNS from where neurological dysfunction occurs. Sore throat, headache, lack of appetite, malaise and fever are other mild clinical symptoms of rabies virus infection in humans.

The incubation period of the disease is 1-3 days after exposure but it can last for weeks and even months and years depending on the intensity and site of bite as well as the virulence of the infecting virus strain. Localized paralysis, jerky movements, increased muscle tone and hydrophobia (the fear of water) are the most significant clinical syndromes of the rabies disease. Infected patients may develop these clinical symptoms even within weeks after infection especially when appropriate medical intervention is delayed. Human-to-human transmission of rabies virus infection is not possible, but animal-to-human infection of the virus is very possible. No treatment exists for rabies virus infection once the virus has invaded the body and symptoms starts to appear. However, supportive therapy is administered to infected individuals in order to save their lives. And rabies vaccine exists as a prophylactic measure in susceptible human population.     

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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