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West Nile virus is an infection that is spread to humans through mosquitoes that have bitten infected birds. Some cases of West Nile virus are mild, but some are severe or even fatal. The infection has been on the rise since it first appeared in the United States in the summer of 1999. (1) Since then, the incidence rates of West Nile virus have ebbed and flowed, peaking in 2003 and then declining again. However, a nationwide resurgence of the infection since and a resulting epidemic in Dallas County, Texas has resulted in a new focus on West Nile virus—and efforts for prevention.(2)

The Facts About West Nile Virus

West Nile virus is a disease that infects birds and is then spread by mosquitoes to humans. The virus cannot be transmitted through human-to-human or human-to-animal contact; however, it can be spread through the blood—meaning people can be infected through blood transfusions and organ transplants. As such, all donated blood in the United States is screened to determine whether the virus is present.

The risk of contracting West Nile virus is highest from late summer through fall. A person who is bitten by an infected mosquito may show symptoms 3 to 15 days after the bite.

Symptoms of West Nile Virus

Most people (about 80 percent) with West Nile virus will have no symptoms of the infection. Others (about 20 percent) will have very mild symptoms of West Nile fever. These symptoms may include fever, headache, fatigue, body aches, joint pain, skin rash, diarrhea, vomiting, and swollen lymph glands. These symptoms usually resolve completely, although some people experience fatigue and weakness for weeks or even months.(3)

Less than 1 percent of people who are infected with West Nile virus will develop a serious neurologic illness, such as encephalitis (swelling of the brain) or meningitis, as a result of the infection. Symptoms of neurologic illness may include severe headache, high fever, neck pain, disorientation, coma, tremors, seizures, or paralysis. Recovery can takes weeks or months and some people experience permanent neurologic damage. Approximately 10 percent of those who do develop neurologic illness will die from the condition.(4) Some people are at a higher risk of developing severe neurologic illness, including people over age 50 and those with serious medical conditions like cancer, diabetes, kidney disease, and high blood pressure.

Treating West Nile Virus

There is no treatment for West Nile virus. In most mild cases, symptoms will go away on their own. Individuals with more severe cases of the infection may require hospitalization to receive supportive treatment such as intravenous fluids, pain management, and ventilator support to help with breathing.

Individuals who show signs of encephalitis may need to undergo a spinal tap and/or an MRI and will require hospitalization.

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Protecting Yourself from West Nile Virus

There is no vaccine to prevent West Nile virus, but there are some preventive strategies you can take. The best way to prevent West Nile virus is to prevent mosquito bites.

  • If possible, avoid the peak mosquito biting hours—dawn, dusk, and early evening.
  • Use insect repellent that contains an active ingredient such as DEET, picaridin, IR3535, or oil of lemon eucalyptus.
  • When possible, wear long sleeves, long pants, and socks. However, remember that mosquitoes can bite through thin clothing, so it’s always wise to spray clothing with repellent.
  • Eliminate any standing pools of water near your home, as mosquitoes breed in standing water. This includes puddles, flower pots, bird baths, buckets, pool covers, pet bowls, and more.
  • Install or repair window screens to prevent mosquitoes from entering your home.
  • Use a mosquito net to protect infants.

On a larger scale, many communities are making efforts to keep mosquito populations at bay. To help, you can:

  • Support local mosquito control efforts. Many communities have implemented aerial spraying programs to prevent outbreaks of West Nile virus.
  • Report dead birds to the authorities, as this can be a sign that West Nile virus is present.

Don’t Panic

Epidemics of West Nile virus—especially those that result in cases of encephalitis—can cause alarm, but it’s important to remember that the number of cases is actually relatively small. In fact, you are more likely to be struck by lightening than West Nile virus. Use common sense to protect yourself from mosquito bites and your chances of contracting the infection are quite small.

Researchers are working to develop a vaccine that prevents West Nile virus in humans.


  1. Nash D, Mostashari F, Fine A, et al. 1999 West Nile outbreak response working group: The outbreak of West Nile virus infection in the New York City area in 1999. New England Journal of Medicine. 2001; 344(24): 1807-1814.
  2. Chung WM, Buseman CM, Joyner SN, et al. The 2012 West Nile encephalitis epidemic in Dallas, Texas. JAMA. 2013; 310(3): 297-307.
  3. Centers for Disease Control and Prevention.
  4. Petersen LR, Brault AC, Nasci RS. West Nile virus: Review of the literature. JAMA. 2013; 310(3): 308-315.