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Press Release

For Immediate Release: September 30, 1999
Contact: CDC Media Relations (404) 639-3286

West Nile-like Virus in the United States

CDC has now made the link between the West Nile-like virus found in birds in New York City and the ongoing human encephalitis outbreak in the area. Late Friday, CDC identified a West Nile-like virus in tissue sample from a New York City resident who recently died from encephalitis. Last week, CDC identified West Nile-like virus from birds that died in New York City and were submitted for testing by the Bronx Zoo.

In addition, CDC confirmed that birds and mosquitoes in Connecticut also have been infected with West Nile-like virus. CDC, in collaboration with the New York State, New York City and Connecticut health departments, continues to investigate this outbreak.

West Nile virus is an arbovirus closely related to St. Louis encephalitis virus, but generally causes a milder disease in humans. Both viruses are transmitted through the bite of a mosquito that becomes infected with the virus by feeding on an infected bird. Like St. Louis encephalitis, West Nile virus is not transmitted from person to person or from birds to persons. West Nile virus never before has been recognized in the United States or any other area of the Western Hemisphere.

Since late August, New York City has been experiencing an outbreak of arboviral (mosquito-borne) encephalitis. Previously, diagnostic tests on serum from human cases in this outbreak were reported as consistent with St. Louis encephalitis virus infection. Because St. Louis encephalitis and West Nile are genetically similar, cross reactivity occurs in the diagnostic tests for these infections. CDC performed further serologic testing on diagnostic specimens from suspected encephalitis cases using West Nile reagents: results were compatible with West Nile infection. To support this ongoing investigation, CDC has provided six medical or technical assistants to work in the New York area and is continuing laboratory tests for West Nile-like virus infection in humans, birds and mosquitoes.

CDC and city and state health departments emphasize that current mosquito control efforts by individuals and communities are appropriate because the same mosquito species transmit both viruses.

Individuals should continue to do the following to reduce their contact with mosquitoes:

  • When outdoors, wear clothing that covers the skin such as long sleeve shirts and pants; spray clothing and exposed skin with insect repellant.
  • Curb outside activity at dawn, dusk and during the evening.

Communities should continue to do the following:

  • Raise public awareness about the outbreak, control measures, and personal protection.
  • Continue current efforts for mosquito control.

For more information:


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