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Fact Sheet: West Nile Virus Infection
(West Nile Encephalitis, West Nile Fever)

What is a West Nile virus infection?

It is an infection caused by West Nile virus, which is spread to people by the bite of a mosquito infected with West Nile virus. Viruses that are spread to people by mosquitoes are called arboviruses. In temperate climates, West Nile virus infections generally occur during warm weather months when mosquitoes are active.

Is West Nile fever a new disease?

No. This virus was first identified in 1937 in Uganda, Africa. Prior to 1999, the virus had only been identified in Africa, Europe, the Middle East, and Asia. West Nile virus was first detected in the United States in 1999, when at least 62 cases and seven deaths from West Nile virus were reported in the New York City area.

Who gets West Nile virus?

Anyone can get infected with West Nile virus. More severe infections are seen in the elderly and those with a weakened immune system.

What are the symptoms of a West Nile virus infection?

Most people infected with West Nile virus do not become ill. People with a mild infection may present with fever, headache, eye pain, muscle aches, joint pain, a rash on the trunk and swollen lymph nodes. In severe cases symptoms include extreme muscle weakness, inflammation of the brain (encephalitis), paralysis, and coma. In rare cases the infection may be fatal, particularly in the elderly and people with other medical conditions.

How is West Nile virus spread?

This virus is spread by the bite of a West Nile virus infected mosquito. Mosquitoes get infected with West Nile virus by feeding on infected birds. There is no evidence that a person can acquire the virus from handling live or dead birds or other infected animals. The virus can not be spread from one person to another.

How soon after being bitten by a West Nile virus infected mosquito do symptoms occur?

Symptoms usually occur 5 to 15 days after a West Nile virus infected mosquito bites a person.

Does past infection with this virus make a person immune?

Yes. Prior infection with West Nile virus can provide lifelong immunity to the virus.

What is the treatment for West Nile virus infection?

There is no specific treatment for West Nile virus infection. A physician may prescribe medications to relieve the symptoms of the illness. In severe cases hospitalization may be required.

What can be done to prevent an infection with West Nile virus?

Preventing mosquito bites will prevent West Nile virus infection. Personal protective measures such as limiting the time spent outdoors at dawn and dusk or other times mosquitoes are active, wearing long sleeve shirts and long pants when outdoors, using insect repellents when outdoors, and screening your home to prevent mosquito entry can serve to reduce or prevent mosquito bites.

Reducing mosquito populations will also reduce mosquito bites. In some communities, public funded surveillance and control programs reduce mosquito populations by eliminating mosquito breeding habitat, mosquito larvae or adults. You can also take measures in your own yard or on your property to eliminate standing water where mosquitoes breed. Sources of standing water include old tires, metal cans, ceramic pots, clogged rain gutters, wading pools, pool covers, or birdbaths.