West Nile Virus


  • West Nile virus (WNV) is a mosquito-borne flavivirus infection. RNA virus is part of the Japanese encephalitis antigenic complex of viruses.
  • Humans mainly acquire through the bite of an infected mosquito in tropical and temperate regions; the virus is mainly found in birds and dogs, cats, horses, bats, chipmunks, and other rodents (see transmission cycle).
    • Culex spp. is a leading vector of WNV infection, but other mosquito species may participate.
    • Birds, especially crows and jays, sicken and die when infected. Some locales offer evaluation of dead birds to assess the presence of WNV in the environment.
  • Cause of epidemic encephalitis, now endemic in the U.S.

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Last updated: March 18, 2023