• Western Equine Encephalitis



    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.


    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


    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.
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    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:


    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)


    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.


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

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


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

    Healthy U http://www.healthyalberta.com


    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%5Fmeningitis/detail%5Fencephalitis%5Fmeningitis.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.

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