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Western Equine Encephalitis
En Español (Spanish Version)

Definition
Western equine encephalitis (WEE) is a virus spread by a bite from an infected mosquito. While WEE is rare, an infected person can become seriously ill and even die from the virus.

Causes
WEE is caused by being bitten by a mosquito that is infected with the virus.

Risk Factors
Factors that may increase your risk of WEE include:

  • Living in or visiting the plains regions of western and central United States
  • 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
  • Neck stiffness
  • Chills
  • Fatigue
  • Joint and muscle pain
  • Vomiting
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:

Your doctor may need pictures of structures inside your head. This 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:

  • IV fluids
  • Medicine to control seizures
  • Medicine to decrease brain swelling
  • Mechanical ventilation (breathing support)
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 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.
  • Remove standing water (eg, bird baths, clogged gutters) to prevent mosquito breeding.


RESOURCES:
Centers for Disease Control and Prevention

National Institute of Allergy and Infectious Diseases

CANADIAN RESOURCES:


References:
About Western equine encephalitis. Minnesota Department of Public Health website. Available at: http://www.health.state.mn.us/divs/idepc/diseases/weencephalitis/basics.html . Accessed January 4, 2013.

Eastern equine encephalitis. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed/ . Updated July 13, 2012. Accessed January 4, 2013.

Fact sheet: Western equine encephalitis. Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/ncidod/dvbid/arbor/weefact.htm . 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. 2008;79(6):974-979.

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.

Last Reviewed November 2012