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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 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.
  • 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
http://www.cdc.gov

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

CANADIAN RESOURCES:

Health Canada
http://www.hc-sc.gc.ca

Healthy U
http://www.healthyalberta.com

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: https://dynamed.ebscohost.com/about/about-us. 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, 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.

10/1/2013 DynaMed Systematic Literature Surveillance https://dynamed.ebscohost.com/about/about-us: Reimer LJ, Thomsen EK, Tisch DJ, et al. Insecticidal bed nets and filariasis transmission in Papua New Guinea. N Eng J Med. 2013 Aug 22; 369(8):745-753.



Last reviewed December 2013 by David L Horn, MD, FACP

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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