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What is it?

West Nile virus (WNV) was first discovered as a cause of an infectious disease in Uganda, Africa in 1937. It has since spread to the Middle East and Europe, Asia and, North and South America. In Australia, the Kunjin virus is a virus most closely related virus to WNV, and is endemic in the Northern Territory and Northern Western Australia.

WNV belongs to a group of disease-causing viruses known as flaviviruses. These lipid (fat)-enveloped viruses can be spread by insects, usually mosquitoes, to animals, including humans. Most human infections are mild, although in some cases serious illness such as encephalitis can result from infection. It is not contagious person-to-person. 

The most common route of transmission is through a mosquito bite. When a mosquito bites an infected bird, such as a crow (crows are highly susceptible to infection), it can then transmit the virus to another animal it bites. Transmission of the virus commonly peaks with wet weather during early spring when adult mosquitoes emerge and continues until Autumn. It is estimated that 1 in 200 mosquitoes in the US harbours the virus. The spread of exotic WNV is of concern to Australia as a number of mosquito species ( Culex sp) could possibly transmit the US strain of WNV.

As of October 30, 2018, there have been 2,204 reported confirmed human cases of WNV in the U.S. and of these 1,342 caused meningitis or encephalitis. For the most current numbers, visit the Centers for Disease Control and Prevention's West Nile Virus web site.

In Australia, the first laboratory-confirmed human case of WNV infection was reported in a returned traveller in 2009, but to date there have been no cases of WNV infection acquired from within Australia. Surveillance of mosquitoes and birds is being carried out, and blood plasma imported from the US is irradiated to kill viruses.

Last Review Date: December 30, 2018

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