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. During that outbreak, 61 people, including 46 residents of New
York City, became ill. Seven people died of West Nile virus-related infections
during this initial outbreak. While we are uncertain how West Nile virus 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.
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.