| Risk Factors
Western equine encephalitis (WEE) is a virus spread by a bite from an infected mosquito. While WEE is rare, an infection can be serious or fatal.
WEE is caused by a virus. The virus is passed through the bite of an infected mosquito.
Factors that may increase your chance 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
coma. 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:
- Blood tests
Cerebrospinal fluid tests
to evaluate the fluid that surrounds the brain and spinal cord
Imaging tests to evaluate the brain 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
- Antiseizure medications
- Medications to decrease brain swelling
Breathing support—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.
- Use proper mosquito netting at night. Look for netting treated with insecticide.
- Remove standing water (such as birdbaths, clogged gutters) to prevent mosquito breeding.
Fact sheet: Western equine encephalitis. Centers for Disease Control and Prevention website. Available at:
http://www.cdc.gov/ncezid/dvbd. Updated November 7, 2005. Accessed January 4, 2013.
Meningitis and encephalitis fact sheet. National Institutes of Neurological Disorders and Stroke website. Available at:
http://www.ninds.nih.gov/disorders/encephalitis_meningitis/detail_encephalitis_meningitis.htm. 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:
http://www.health.state.mn.us/divs/idepc/diseases/weencephalitis/wee.html. Accessed January 4, 2013.
10/1/2013 DynaMed Plus Systematic Literature Surveillance
http://www.dynamed.com/topics/dmp~AN~T208130/Encephalitis: Reimer LJ, Thomsen EK, Tisch DJ, et al. Insecticidal bed nets and filariasis transmission in Papua New Guinea. N Eng J Med. 2013;369(8):745-753.
Last reviewed November 2015 by David L. Horn, MD
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