Western Equine EncephalitisEn Español (Spanish Version)
Western equine encephalitis (WEE) is a virus spread by a bite from an infected mosquito. While WEE is rare, an infected person can become seriously ill and even die from the virus.
WEE is caused by being bitten by a mosquito that is infected with the virus.
Factors that may increase your risk of WEE include:
- Living in or visiting the plains regions of western and central United States
- Doing activities outdoors and not using insect repellent
Most people with WEE do not have any symptoms.
If symptoms do occur, they appear within 5-10 days after infection and include:
- Neck stiffness
- Joint and muscle pain
WEE can lead to more serious, life-threatening symptoms like inflammation of the brain (encephalitis), seizures, and
. These serious symptoms are more common in infants and older adults.
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In addition to taking your medical history and doing a physical exam, your doctor will ask you:
- What kind of symptoms you are experiencing
- Where you have been living or traveling
- Whether you have been exposed to mosquitoes
Your doctor may need to test your bodily fluids. This can be done with:
Your doctor may need pictures of structures inside your head. This can be done with:
Because the infection is viral, there is no specific treatment for WEE. Treatment will focus on managing your symptoms and related complications through:
- IV fluids
- Medicine to control seizures
- Medicine to decrease brain swelling
- Mechanical ventilation
There is no vaccine for humans. There is a vaccine for horses. Prevention of WEE focuses on controlling mosquitoes and avoiding mosquito bites. Steps you can take to avoid mosquito bites include:
- Stay inside between dusk and dark, when mosquitoes are most active.
- Wear long pants and long-sleeved shirts when outside.
- Use an insect repellent with DEET.
- Repair screens to prevent mosquitoes from entering the house.
- Remove standing water (eg, bird baths, clogged gutters) to prevent mosquito breeding.
Centers for Disease Control and Prevention
National Institute of Allergy and Infectious Diseases
About Western equine encephalitis. Minnesota Department of Public Health website. Available at:
. Accessed January 4, 2013.
Eastern equine encephalitis. EBSCO DynaMed website. Available at:
. Updated July 13, 2012. Accessed January 4, 2013.
Fact sheet: Western equine encephalitis. Centers for Disease Control and Prevention website. Available at:
. Updated November 7, 2005. Accessed January 4, 2013.
Meningitis and encephalitis fact sheet. National Institutes of Neurological Disorders and Stroke website. Available at:
. Updated February 16, 2011. Accessed January 4, 2013.
Reimann CA, Hayes EB, DiGuiseppi C, et al. Epidemiology of neuroinvasive arboviral disease in the United States, 1999-2007.
Am J Trop Med Hyg.
Western equine encephalitis fact sheet. Minnesota Department of Public Health website. Available at:
. Accessed January 4, 2013.
Last Reviewed November 2012