Zoonotic Disease Program
West Nile Virus Facts

History

West Nile Virus is a mosquito-borne virus that can cause encephalitis (inflammation of the brain) or meningitis (inflammation of the lining of the brain and spinal cord). Outbreaks of the West Nile Virus have occurred before in Egypt, Asia, Israel, South Africa, and in some parts of Europe. West Nile Virus was first found in the United States in New York City in the fall of 1999. In 2001, Ohio had birds and mosquitos that tested positive for West Nile Virus. In 2002, Ohio had its first human case of West Nile Virus and eventually had a total of 441 human cases of West Nile Virus. This dropped to just 23 human cases of West Nile Virus in Ohio by 2007. While we are uncertain how West Nile Virus first arrived in the USA, the most likely explanation is that the virus was introduced by an infected bird that was imported or an infected human returning from a country where the virus is common, or a mosquito hitchhiking on an airplane.

Transmission Cycle

West Nile Virus is spread to humans by the bite of an infected mosquito. When a mosquito bites a bird that carries the virus, the mosquito becomes infected. It is believed that people cannot get West Nile Virus directly from another person, or animal, that has the disease. It is believed that this disease is only transmitted by mosquitoes.

Being bitten by an infected mosquito will not necessarily make you sick, since most people who are infected with West Nile Virus either have no symptoms or experience mild illness. If illness were to occur, it would occur within 5 to 15 days of being bitten by an infected mosquito.

Last Updated: 6/12/08

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