Western Equine Encephalitis
by Rebecca J. Stahl, MA
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:
Most people with WEE do not have any symptoms.
If symptoms do occur, they appear within 5-10 days after infection and include:
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.
In addition to taking your medical history and doing a physical exam, your doctor will ask you:
Your doctor may need to test your bodily fluids. This can be done with:
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:
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:
Centers for Disease Control and Prevention
National Institute of Allergy and Infectious Diseases
About Western equine encephalitis. Minnesota Department of Health website. Available at:
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Accessed December 7, 2017.
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 December 7, 2017.
Mosquito avoidance. EBSCO DynaMed Plus website. Available at: http://www.dynamed.com/topics/dmp~AN~T115142/Mosquito-avoidance . Updated November 21, 2016. Accessed December 7, 2017.
Last reviewed November 2018 by EBSCO Medical Review Board David L. Horn, MD, FACP
Last Updated: 12/20/2014
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