Western equine encephalitis (WEE) is an infection from a mosquito. WEE is rare. It can range from mild to severe or fatal.
WEE is caused by a virus. It is spread to humans from the bite of an infected mosquito. The virus is not spread from person to person.
Things that may raise the risk of WEE are:
Most people with WEE do not have any symptoms.
If symptoms do happen, they may be:
WEE can lead to more serious, life-threatening symptoms. These may include inflammation of the brain (encephalitis), seizures, and coma. Serious symptoms are more common in infants and older adults.
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The doctor will ask about your symptoms, travel, and health history. A physical exam will be done.
Tests may be done to diagnose the infection. They may be:
Imaging tests may be done to check the brain. They may include:
There is no specific treatment for WEE. Treatment depends on how severe the disease is. The goal is to manage symptoms and problems. In severe cases, hospital care is needed.
Depending on the symptoms, options may be:
WEE can be prevented by avoiding mosquito bites. Things that may help are:
Centers for Disease Control and Prevention
National Institute of Allergy and Infectious Diseases
Alberta Ministry of Health
About Western equine encephalitis. Minnesota Department of Health website. Available at: https://www.health.state.mn.us/diseases/weencephalitis/wee.html Accessed April 7, 2021.
Alpern JD, Dunlop SJ, et al. Personal protection measures against mosquitoes, ticks, and other arthropods. Med Clin North Am. 2016;100(2):303-16.
Meningitis and encephalitis information page. National Institutes of Neurological Disorders and Stroke website. Available at: https://www.ninds.nih.gov/Disorders/All-Disorders/Meningitis-and-Encephalitis-Information-Page. Accessed April 5, 2021.
Mosquito avoidance. EBSCO DynaMed website. Available at: https://www.dynamed.com/prevention/mosquito-avoidance. Accessed April 5, 2021.
Last reviewed December 2020 by
EBSCO Medical Review Board
David L. Horn, MD, FACP
Last Updated: 4/5/2021