Carl R. Darnall Army Medical Center - Health Library

Western Equine Encephalitis

(WEE)

Definition

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.

Causes ^

WEE is caused by a virus. The virus is passed through the bite of an infected mosquito.

Risk Factors ^

Factors that may increase your chance of WEE include:

  • Living in or visiting the plains regions of western and central US
  • Doing activities outdoors and not using insect repellent

Symptoms ^

Most people with WEE do not have any symptoms.

If symptoms do occur, they appear within 5-10 days after infection and include:

  • Headache
  • Fever
  • Nausea and vomiting
  • Neck stiffness
  • Chills
  • Fatigue
  • 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.

Encephalitis
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Diagnosis ^

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
  • Lumbar puncture to evaluate the fluid that surrounds the brain and spinal cord

Imaging tests to evaluate the brain can be done with:

Treatment ^

Because the infection is viral, there is no specific treatment for WEE. Treatment will focus on managing your symptoms and related complications through:

Prevention ^

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:

  • 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.
RESOURCES:

Centers for Disease Control and Prevention
https://www.cdc.gov

National Institute of Allergy and Infectious Diseases
https://www.niaid.nih.gov

CANADIAN RESOURCES:

Alberta Health
http://www.health.alberta.ca

Health Canada
https://www.canada.ca

REFERENCES:

About Western equine encephalitis. Minnesota Department of Health website. Available at: http://www.health.state.mn.us/divs/idepc/diseases/weencephalitis/basics.html. 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 December 2017 by EBSCO Medical Review Board David L. Horn, MD, FACP  Last Updated: 12/20/2014