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Can animals get sick from West Nile virus?

An infected mosquito can bite any animal, but not all animals will become sick. The disease most often affects birds but may occasionally cause disease in other animals. Wild birds serve as the main source of virus for mosquitoes. Infection has been reported in more than 225 bird species. Although many birds that are infected with WNV will not appear ill, WNV infection can cause serious illness and death in some birds. The most severe illnesses are seen among the corvid birds, which include crows, scrub jays, ravens and magpies. In Kern County, mockingbirds, scrub jays, crows, house finches and house sparrows have tested positive for WNV in previous years.

Like people, most horses bitten by infected mosquitoes will not become sick with WNV. However, of those that do, clinical signs may include stumbling, circling, hind leg weakness, inability to stand, muscle tremors and death. Vaccine is available to prevent West Nile virus in horses and horse-owners should consult with a veterinarian about WNV vaccine and other vaccines that protect against other mosquito-borne viruses, such as western equine encephalitis.

For more information on West Nile virus and horses, please visit the California Department of Food and Agriculture website at

Dogs and cats can be exposed to WNV in the same way as humans. However, these animals are very resistant to WNV and rarely become ill. Concerned pet owners should consult with a veterinarian.