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Eastern Equine Encephalitis

Eastern Equine Encephalitis, Placeholder Image

What is Eastern Equine Encephalitis?

  • Eastern Equine Encephalitis (EEE) virus is spread to people by the bite of an infected mosquito.
  • Human cases of EEE disease are rare but can cause serious illness.
  • About 30% of people ill from EEE die and many who survive the infection are left with permanent neurologic damage.
  • There are no vaccines to prevent EEE infection in people and no specific treatments for EEE disease.
  • People can reduce their risk for EEE infection by preventing mosquito bites.

    2022 Weekly Arbovirus Surveillance Report thumbnail
    • Winter has brought an end to the 2023 mosquito season. In 2023, one horse from Mecosta County, one deer from Livingston County, and four mosquito pools from Barry, Bay, and Saginaw counties have tested positive for EEE. Preparations for the 2024 mosquito season are underway.
    • If EEE is suspected in a horse, it should be reported to the Michigan Department of Agriculture and Rural Development at 800-292-3939 (support may be available to pay for testing).
    • If EEE is suspected in a person, it should be reported to MDHHS at 517-335-8165

  • Who is at risk of Eastern Equine Encephalitis (EEE) illness?

    • EEE virus has been reported from the Atlantic to the Gulf Coast states and the Great Lakes region, including Michigan.
    • Anyone in an area where the virus is present can get infected with EEE virus from a mosquito bite.
    • People who engage in outdoor work and recreational activities in endemic areas are at increased risk of infection.
    • Persons over age 50 and under age 15 seem to be at greatest risk for developing severe disease when infected with EEE.
    • EEE infection is thought to confer life-long immunity against re-infection to survivors.

    Where is EEE a risk in Michigan?

    • EEE has been reported in animals and people throughout the state.  
    • EEE is most commonly found in swamp and bog habitats.
    • All residents of and visitors to areas where EEE activity has been identified are at risk of infection.


  • What are the symptoms of Eastern Equine Encephalitis (EEE) infection?

    • No symptoms in many people. Most people who become infected with EEE do not develop any symptoms.
    • Febrile illness in some people. Some people who are infected will develop chills, fever, weakness, muscle and joint pain. The illness may last up to two weeks.  Most people with this type of EEE disease recover completely, but fatigue and weakness can last for weeks or months.
    • Severe symptoms in a few people. Less than 1% of people who are infected will develop a serious neurologic illness such as encephalitis or meningitis (inflammation of the brain or surrounding tissues).
    • The symptoms of neurologic illness can include high fever, headache, irritability, restlessness, drowsiness, anorexia, vomiting, diarrhea, bluish discoloration of the skin, convulsions, and coma.
    • Serious illness can occur in people of any age. However, children and people over 60 years of age are at the greatest risk for severe disease. People with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and people who have received organ transplants, are also at greater risk for serious illness.
    • Recovery from severe disease may take several weeks or months. Of those who recover, many are left with disabling and progressive mental and physical sequelae, which include can range from minimal brain dysfunction to severe intellectual impairment, personality disorders, seizures, paralysis, and cranial nerve dysfunction. Many patients with severe sequelae die within a few years.
    • About 30 percent of people who develop neurologic infection due to Eastern Equine Encephalitis will die.


  •  What should I do if I think a family member might have Eastern Equine Encephalitis? 
    Consult a healthcare provider for evaluation and diagnosis.

    How is Eastern Equine Encephalitis diagnosed?
    Diagnosis is based on a combination of clinical signs and symptoms and specialized laboratory tests of blood or spinal fluid. These tests typically detect antibodies that the immune system makes against the viral infection.

    Important Links

    MDHHS BOL Mosquito-Borne and Tick-Borne Disease Testing

    • Case Reporting

      The Michigan Public Health Code requires physicians, clinical laboratories, schools, childcare centers, and camps to report certain diseases, conditions or infections, including Arboviruses.

    • Specimen Collection and Submission

      Instructions on submitting samples for Arbovirus testing to the Michigan Department of Health and Human Services

    • Laboratory Testing
  • How is Eastern Equine Encephalitis (EEE) treated?

    No human vaccine against EEE infection or specific antiviral treatment for clinical EEEV infections is available. Patients with suspected EEE should be immediately evaluated by a healthcare provider, appropriate serologic and other diagnostic tests ordered, and supportive treatment provided.

  • How do I protect myself and my family from Eastern Equine Encephalitis (EEE)?

    There is no vaccine against EEE virus for humans. Reducing exposure to mosquitoes is the best defense against infection with EEE and other mosquito-borne viruses. There are several approaches you and your family can use to prevent and control mosquito-borne diseases.

    • Use repellent: When outdoors, use insect repellent containing DEET, picaridin, IR3535 or oil of lemon eucalyptus on exposed skin and/or clothing. The repellent/insecticide permethrin can be used on clothing to protect through several washes. Always follow the directions on the package.
    • Wear protective clothing: Wear long sleeves and pants when weather permits.
    • Install and repair screens: Have secure, intact screens on windows and doors to keep mosquitoes out.
    • Keep mosquitoes from laying eggs near you: Mosquitoes can lay eggs even in small amounts of standing water. Get rid of mosquito breeding sites by emptying standing water from flower pots, buckets, barrels, and tires. Change the water in pet dishes and replace the water in bird baths weekly. Drill holes in tire swings so water drains out. Empty children's wading pools and store on their side after use.

    How do I protect my horse(s) from Eastern Equine Encephalitis (EEE)??

    Vaccines are available for horses that will protect them from EEE and West Nile virus.  Contact your veterinarian for information regarding vaccinations.