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.

  • Causes

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

  • 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.

  • 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
    • Cerebrospinal fluid analysis

    Your doctor may need pictures of structures inside your head. This can be done with:

    • MRI scan
    • CT scan

  • 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.

  • 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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  • 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)