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Western Equine Encephalitis

  • Amy Scholten, MPH
Publication Type:


Western Equine Encephalitis



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.

Risk Factors

Things that may raise the risk of WEE are:

  • Living in or visiting the plains region of western and central US
  • Being outdoors
  • Not using bug spray


Most people with WEE do not have any symptoms.

If symptoms do happen, they may be:

  • Headache
  • Fever and chills
  • Nausea and vomiting
  • Neck stiffness
  • Feeling tired
  • Joint and muscle pain

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:

  • Blood tests
  • Lumbar puncture—some fluid around the brain and spinal cord is taken and tested

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:

  • Covering up the skin
  • Using bug sprays, netting, and screens
  • Staying indoors between dusk and dark




  • 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.


  • David L. Horn, MD, FACP
Last Updated:

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.