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Eastern Equine Encephalitis

  • Definition

    Eastern equine encephalitis (EEE) is an infection spread by a bite from an infected mosquito. While EEE is rare, it can be serious and in some cases, fatal.
    Effect on Encephalitis on the Brain
    Swollen brain
    Copyright © Nucleus Medical Media, Inc.
  • Causes

    EEE is caused by a virus.
  • Risk Factors

    The greatest risk factors for EEE are spending time in areas where mosquitoes are present, such as wetlands and swamps. Another risk factors is failing to use insect repellent.
    Risk factors for developing serious symptoms from EEE include:
    • Being over 50 years old or younger than 15 years old
    • Having a condition that affects your immune system
  • Symptoms

    Most people with EEE do not have any symptoms.
    If symptoms do occur, they may appear in 4-10 days and include:
    • Headache
    • Neck stiffness
    • Fever
    • Chills
    • Fatigue
    • Joint and muscle pain
    • Vomiting
    EEE can lead to more serious, life-threatening symptoms of inflammation of the brain, like altered mental status, weakness, numbness, paralysis, seizures, and coma.
  • Diagnosis

    Your doctor will ask about your symptoms and medical history. A physical exam will be done. Questions may include:
    • Where you have been living or traveling
    • Whether you have been exposed to mosquitoes
    A blood test or a test of your spinal fluid is commonly used to confirm the diagnosis of EEE.
    Imaging tests may include:
  • Treatment

    Treatment for EEE focuses on supportive care. Severe symptoms require hospitalization, which may include:
  • Prevention

    To help reduce your chance of EEE:
    • Stay inside when mosquitoes are most active (at dawn and at dusk).
    • Repair screens on your windows and doors to prevent mosquitoes from getting into your house.
    • Use proper mosquito netting at night. Look for netting treated with insecticide.
    • When outside, wear insect repellent, long pants and long-sleeved shirts to limit exposure to bites.
    • Eliminate insect breeding areas. These may include areas of standing water, like pet water bowls, rain barrels, and other containers.

    Centers for Disease Control and Prevention

    National Institute of Neurological Disorders and Stroke


    Health Canada

    Healthy Alberta


    Eastern equine encephalitis. Centers for Disease Control and Prevention website. Available at: Updated August 16, 2010. Accessed January 4, 2013.

    Eastern equine encephalitis. EBSCO DynaMed website. Available at: Updated July 13, 2012. Accessed January 4, 2013.

    Encephalitis: an overview. EBSCO Nursing Reference Center website. Available at: Updated March 9, 2012. Accessed January 4, 2013.

    10/1/2013 DynaMed Systematic Literature Surveillance Reimer LJ, Thomsen EK, Tisch DJ, et al. Insecticidal bed nets and filariasis transmission in Papua New Guinea. N Eng J Med. 2013;369(8):745-53.

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