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Transmission

The evidence shows that most people infected with West Nile virus got it from the bite of an infected mosquito. A mosquito becomes infected when it feeds on the blood of a bird that is infected with the virus. About two weeks later, the mosquito becomes capable of passing the virus to people and animals by biting them. There is some evidence that female mosquitoes may be able to transfer West Nile virus to their offspring, but researchers are still looking into this possibility.

In 2002, scientists discovered that people could be infected with West Nile virus in other ways, including blood transfusions and organ/tissue transplants. The risk of getting West Nile virus this way is considered to be quite low. There is also evidence that pregnant women can pass the virus to their unborn babies and that the virus may be passed through breast milk. In addition, laboratory workers who handle infected specimens can get West Nile virus through needle punctures or cuts.

There is no evidence to suggest that people can get West Nile virus by touching or kissing someone who is infected, or from being around a health care worker who has treated an infected person. Likewise, there is no evidence to date that the virus can pass from infected animals (horses, pets, etc.) to people.

Last Updated: 2003-06-17