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JAMA Patient Page
September 12, 2012

West Nile Virus

JAMA. 2012;308(10):1052. doi:10.1001/2012.jama.11678

West Nile virus is widely distributed throughout the world and first appeared in the United States in 1999. The virus is typically carried from infected birds (the host animal) to humans and other mammals through mosquito bites.


About 80% of people infected with the virus have no symptoms. Those who do usually start to feel sick 3 to 14 days after being bitten by an infected mosquito. Most people who get sick develop West Nile fever. Symptoms include fever, headache, fatigue, body aches, muscle pain, joint pain, and chills. More than half of sick people report a rash. Symptoms usually last for 3 to 6 days but some people have been sick for weeks. A few people (approximately 1 in 150 infected persons) develop severe disease with serious symptoms. The virus invades the nervous system, causing encephalitis (inflammation of the brain) or meningitis (inflammation of the tissues surrounding the brain and spinal cord). Symptoms of severe disease include headache, fever, stiff neck, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis. Severe disease may last for weeks and cause permanent injury or, in some cases, death.


Tests for West Nile virus may include blood work, computed tomography (CT) or magnetic resonance imaging (MRI) scans of the head, and lumbar puncture (spinal tap) for cerebrospinal fluid (the natural fluid that bathes the brain and spinal cord).


Spread of the disease is effectively managed by mosquito control. Very small amounts of pesticides are applied via ground and aerial spraying. These applications have been shown to result in negligible pesticide exposure and no adverse health effects to the public.


  • Use insect repellent.

  • Many mosquitoes are active between dusk and dawn. Use insect repellent and wear long sleeves and pants at these times or consider staying indoors during these hours.

  • Eliminate mosquito breeding areas—anywhere with standing water, such as flowerpots or buckets.

  • Make sure your windows have screens that are in good condition.

  • You cannot get West Nile virus by casual contact such as touching an infected person.


There is currently no specific treatment for West Nile virus infection. Since it is caused by a virus, not bacterium, antibiotics do not help. Most treatment is aimed at supporting the body's functions until the infection is cleared. You should see your doctor if you have symptoms. If your symptoms are severe, seek care in an emergency department.



To find this and previous JAMA Patient Pages, go to the Patient Page link on JAMA 's website at Many are available in English and Spanish.

Sources: National Institutes of Health, Centers for Disease Control and Prevention, Cornell University Department of Entomology

The JAMA Patient Page is a public service of JAMA. The information and recommendations appearing on this page are appropriate in most instances, but they are not a substitute for medical diagnosis. For specific information concerning your personal medical condition, JAMA suggests that you consult your physician. This page may be photocopied noncommercially by physicians and other health care professionals to share with patients. To purchase bulk reprints, call 312/464-0776.