West Nile Virus

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What is West Nile virus?

West Nile virus is a virus that can infect humans, birds, horses and mosquitoes. Infection from this virus is most commonly found in Africa, West Asia and the Middle East. The virus spread to the United States in the summer of 1999, and has now been reported in 48 states.


What are the symptoms of West Nile virus infection?

Most people who are infected with West Nile virus have no symptoms. Others may have only mild symptoms, which is called West Nile fever. Symptoms include:

  • Skin rash
  • Fever
  • Headache
  • Nausea
  • Vomiting
  • Diarrhea
  • Loss of appetite
  • Swollen lymph nodes (lymph glands)
  • An achy feeling in the back and muscles

Symptoms usually occur 3 to 14 days after a person is bitten by an infected mosquito and last for 3 to 6 days. Symptoms of the more severe illness the West Nile virus include:

  • A sudden high fever (above 102°F)
  • Severe headache
  • Stiff neck
  • Feeling disorientated or confused
  • Tremors or muscle jerks
  • Seizures
  • Coma
  • Weakness or partial paralysis

These symptoms may last for several weeks. Contact your doctor if you have any of these symptoms and have recently been bitten by a mosquito.

Causes & Risk Factors

How is West Nile virus spread?

West Nile virus is most often spread by mosquitoes. Mosquitoes become infected by biting birds that carry the virus. People can get West Nile virus when an infected mosquito bites them. This happens most often in the warm-weather months of spring, summer and early fall. You cannot get West Nile virus from another person or from your pet.

During the 2002 West Nile virus epidemic in the United States, a few people got the virus through blood transfusions and organ transplants. However, the risk of getting the virus in these ways is very low.

A few cases were also reported of the West Nile virus being passed from a pregnant or breastfeeding woman to her baby. However, these cases are extremely rare.

Who is at risk for infection with West Nile virus?

People who live where West Nile virus has been found in humans, birds, horses or mosquitoes are at risk for infection. You are also at a greater risk if you spend lots of time outdoors during the warmer months or if you don’t protect your skin with an insect repellent that contains DEET. However, even in areas where the virus has been reported, it’s very unlikely that a person will get sick from a mosquito bite.

People 50 years of age and older and people who have weakened immune systems are at greatest risk of becoming severely ill from West Nile virus. Remember, less than 1% of the people who do get infected with West Nile become severely ill.

How many people with severe West Nile virus infection die?

Most people who are infected with West Nile either do not develop symptoms or only develop the mild symptoms of West Nile fever. Less than 1% of people infected with the virus will develop severe symptoms or complications, and almost all of those people fully recover. Of the small number of people who do get severely ill from West Nile virus, about 10% will die.


Is there a vaccine for West Nile virus?

There is no vaccine to prevent West Nile virus in humans yet.

How can West Nile virus infection be prevented?

The best way to avoid infection with West Nile virus is to reduce the number of mosquitoes around your home and neighborhood.

The following are a few things you can do:

  • Get rid of standing water in birdbaths, ponds, flowerpots, wading pools, old tires and other places where mosquitoes might breed. Garden supply stores carry products to keep mosquitoes from breeding in small ponds.
  • Repair any tears in window screens, and porch and patio screens to keep mosquitoes out of your home.
  • Stay indoors during dawn, dusk and early evening hours. Mosquitoes are most active during these times. If you go outdoors at these times, wear shoes and socks, long pants and a long-sleeved shirt. Loose-fitting, light-colored clothing is best.
  • If you go outdoors, use an insect repellent that contains 20% to 30% DEET. Apply it according to the directions on the label. Talk to your doctor before you use insect repellent on your child.


Is there a treatment for West Nile virus infection?

There is no specific treatment for West Nile virus infection. People who experience mild symptoms usually get better without any medicine after a few days. People who have severe illness may be hospitalized and given intravenous (IV) fluids. They may need to be on a machine called a ventilator to help them breathe. Their doctor also will try to keep them from getting other infections, such as pneumonia.


Can West Nile virus cause any other problems?

In rare cases, West Nile virus causes a disease such as a swelling of the brain called encephalitis (say: en-seff-uh-lie-tuss) or swelling of the membrane around the brain and spinal cord called meningitis (say men-in-ji-tuss). This can lead to permanent brain damage or death.


Questions to Ask Your Doctor

  • Is West Nile virus common in this area?
  • Am I at risk of contracting West Nile virus?
  • What can I do to protect myself from West Nile virus?
  • What treatment is best for me?
  • Will cold or flu medicines help?
  • Can my child get West Nile virus from me?
  • What kind of insect repellent should I use?
  • If I start feeling worse, when should I call my doctor?


  • West Nile Virus in the United States: An Update on an Emerging Infectious Disease by GD. Huhn, M.D., M.P.H.T.M., JJ Sejvar, M.D., SP Montgomery, D.V.M., M.P.H., and MS Dworkin, M.D., M.P.H.T.M.( 08/15/03, http://www.aafp.org/afp/20030815/653.html)