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West Nile Virus


West Nile virus is transmitted only by mosquitoes during summer months and generally only appears between the months of May to October.

People who experience signs or symptoms of serious illness, and have been bitten by a mosquito in the geographic area where West Nile virus is known to appear, should see their doctor immediately.

Most people with mild symptoms of low-grade fever and muscle aches do not have West Nile virus and will not require specific diagnostic testing.

Anyone who has symptoms of severe illness such as mental status changes, high fever, neck stiffness, sensitivity to light, or confusion should go to the hospital's emergency department immediately. The West Nile encephalitis that occurred during the initial New York outbreak was especially notable for its severe muscle weakness. This is another important warning symptom.

Self-Care at Home

Home care for people who suspect they may have become infected with West Nile virus is fairly limited. There is no specific treatment.

Mild illness does not require therapy other than medications to reduce fever and pain. Avoid aspirin because it presents a risk for a fatal condition known as Reye syndrome, especially in children.



Anyone who has developed West Nile encephalitis should follow up with a doctor regularly to assure that recovery is taking place in an appropriate manner. The most severely affected people may take as long as 6 months to a year to recover. Some may have permanent nervous system problems.


The only way to reduce your risk of contracting West Nile virus is by avoiding contact with mosquitoes during the months of April to October. Mosquitoes are active in the early morning, from dawn until 10 am, and in the later afternoon and early evening. Limit your outdoor activities or protect yourself during those times. Take these precautions:

  • If outside during dawn and evening hours, when mosquitoes are most active, wear protective clothing such as long-sleeved shirts, long pants, and socks.
  • Consider using an insect repellent containing 10-30% DEET solution. Children should not use a DEET repellent stronger than 10% strength. Other precautions when using DEET include avoiding use on infants or  pregnant women, avoiding prolonged or excessive use, storing DEET out of the reach of children, and preventing children from applying it themselves. The manufacturer recommends applying DEET first to your own hands and then spreading it lightly on your children.
  • You can spray your clothing with repellents containing permethrin or DEET because mosquitoes may bite through thin clothing. Do not apply repellents containing permethrin directly to exposed skin. If you spray your clothing, there is no need to spray repellent containing DEET on the skin under your clothing. For more details on pesticides and their application, check the National Pesticide Information Center.
  • Citronella, which is frequently used in outdoor candles, is a good deterrent against mosquitoes; however, it does not provide long-term protection.
  • Limiting mosquito habitats and breeding grounds may also help limit human exposure. Mosquitoes lay their eggs in standing water, so dispose of all tin cans, plastic containers, rubber tires, or any other possible water-holding containers from your property. Drain water from pool covers. Make sure roof gutters drain properly. Clean your gutters regularly.
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    Make sure your doors and windows have tightly fitted screens without holes.

  • Birds who have died from West Nile virus pose no health risk. The disease is only transmitted by a mosquito bite. Mosquitoes become infected by biting birds that harbor the virus. Report dead birds (especially crows and blue jays) to local health officials so they can be tested and the virus tracked. Use gloves if you touch dead birds.
  • Development of a vaccine: Since the virus first appeared in New York, researchers began looking for a vaccine. According to the Proceedings of the National Academy of Sciences, US government scientists have now developed a vaccine that protects mice from the West Nile virus infection. Researchers were expected to begin testing the vaccine in monkeys in March 2002, with testing in humans likely to take place in late 2002.
  • The vaccine consists of a combination of genes from a virus called dengue and the West Nile Virus. Both the West Nile virus and dengue viruses are flaviviruses, a group of tick- and mosquito-borne organisms that cause diseases such as yellow fever and St. Louis encephalitis. Researchers from the National Institute of Allergy and Infectious Diseases (NIAID) and Walter Reed Army Institute of Research have shown that although the individual flaviviruses differ from one another, their parts can be intermixed with those of dengue virus to form a hybrid that can be used in a vaccine.
  • Because this new vaccine consists of a combination of 2 viruses, it offers 2 benefits. First, the vaccine consists mostly of the dengue virus, which does not target the central nervous system. This means that the vaccine will not infect the brain. Second, because the vaccine has West Nile parts, it will stimulate the body to produce strong antibodies to the virus, offering protection against future exposures.

The prognosis of West Nile virus is directly related to the severity of the illness and the age of the person with the infection.

Those with mild infection recover fully with no permanent disability.

Death occurs in 12% of people with West Nile encephalitis. The elderly are most at risk for death. Younger people recover much more quickly and are much less likely to show signs and symptoms of severe illness. In the New York outbreak, most cases occurred in people 50 years and older.


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