West Nile Virus

What is West Nile virus?

West Nile virus can be a serious, even fatal, illness. It can affect people, horses, birds, and other animals. In 1999, West Nile virus first appeared in the United States in New York City. Since that time, it has spread rapidly throughout the country. In Washington, the first cases of people becoming ill from West Nile virus were reported in 2006. To see data and statistics on human cases and environmental detections in Washington, see West Nile Virus surveillance maps and statistics.

How is West Nile virus spread?

West Nile virus is almost always spread to people by the bite of an infected mosquito. Mosquitoes become infected after feeding on birds that carry the virus. There is no evidence that West Nile virus can be spread by direct contact with infected people or animals.

Who is at risk?

The risk of getting West Nile virus is very low, but anyone can become infected. People with certain medical conditions, such as cancer, diabetes, hypertension and kidney disease are at greater risk of serious illness.

What are the symptoms of West Nile virus?

Most people who are infected with West Nile virus will not get sick. About 1 in 5 people infected will have mild symptoms such as fever, headache, and body aches. Even fewer, about 1 in 150 people infected, will have more severe symptoms. Severe symptoms may include headache, high fever, neck stiffness, stupor, disorientation, tremors, convulsions, muscle weakness, paralysis, and coma. If you have any of these symptoms, contact your healthcare provider.

How can I protect myself?

There is no human vaccine for West Nile virus. The best way to protect yourself and your family is to avoid mosquito bites and reduce the places mosquitoes live and breed around your home. Take these steps:

Avoid Mosquito Bites

Don't Give Mosquitoes a Home

What is an effective mosquito repellent?

The most effective mosquito repellents contain the active ingredient of DEET (N, N-diethyl-m-toluamide), picaridin, IR3535, oil of lemon eucalyptus, PMD the synthesized version of oil of lemon eucalyptus, or 2-undecanone. These active ingredients typically offer long-lasting protection against mosquito bites. Repellents come in lotions, creams, gels, sprays, and towelettes.

Mosquito repellents must be used properly. Read and follow instructions on the label. Don't over use repellents.

Do birds infected with West Nile virus die?

West Nile virus infects a variety of wild birds. Of those birds infected, crows, jays, ravens, magpies, and raptors, such as hawks and owls tend to become sick and die. Increasing numbers of dead birds may be an indication of West Nile virus in your community.

Are dead birds tested for West Nile virus?

Department of Health tests birds upon request by local health departments and tracks where tested birds are found. The agency, however, no longer tracks public reporting of dead birds. In recent years, monitoring of mosquitoes has proven to be a more reliable indication of current West Nile virus activity.

Dispose of the dead bird safely. Don't handle it with your bare hands. Use gloves or an inverted plastic bag to place the bird in a garbage bag, and dispose in your outdoor garbage can.

You can report dead birds to Department of Fish & Wildlife, Report Observations of Dead Wildlife. They investigate the cause of death involving large wild bird die-offs, including suspected diseases such as West Nile virus.

Can West Nile virus infect my pet?

West Nile virus can cause serious illness in horses, mules, and donkeys. Though most horses that become infected will not get sick, about 1 in 3 horses infected will die. To protect your horse, ask your veterinarian about the West Nile virus vaccine. West Nile virus can infect dogs and cats, but it is rare.

Find more surveillance data

The Washington Tracking Network presents 2006-2019 vector mosquito species, Culex pipiens and Cx. tarsalis, test data by county. It also shows bird and mammal test data. View data in a table, chart, and map format and export data for your own use.

See Washington Tracking Network - mosquito samples, birds, and mammals tested for West Nile virus.

More Information

Notifiable Conditions


Content Source: Zoonotic Disease Program, Communicable Disease Epidemiology