by Stahl RJ


Eastern equine encephalitis (EEE) is an infection spread by a mosquito bite. EEE is rare. It can be serious and sometimes fatal.

Effect on Encephalitis on the Brain
Swollen brain
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EEE is caused by a virus. It is passed to humans from an infected mosquito.

Risk Factors

Things that raise the risk of EEE are:

  • Being in an area where EEE is present, and
  • Exposure to mosquitoes
  • Being near freshwater hardwood swamps or marshes
  • A weak immune system
  • Lab workers exposed to EEE

EEE is more common in those less than 15 years old or more than 50 years old.


Most people with EEE do not have symptoms. Those that do may have:

  • Headache
  • Neck stiffness
  • Fever
  • Chills
  • Tiredness
  • Joint and muscle pain
  • Vomiting

EEE can lead to swelling of the brain called encephalitis. This is more serious and life-threatening. It can cause change in behavior and thinking, seizures, and coma.


The doctor will ask about symptoms and past health. A physical exam will be done. A sample of blood and fluid around the spine will be tested. This will confirm EEE.

Images of the brain may also be needed. This may be done with:


The body will need time to get rid of the virus. Care may be needed for brain swelling. Treatment will help to support the body and decrease problems. Hospital care may be needed for severe illness. Treatment may include:

  • IV fluids
  • Medicine to:
  • Control seizures
  • Decrease brain swelling
  • Machines to help with breathing


If there is a risk of EEE in the area:

  • Stay inside at dawn and at dusk. This is when mosquitoes are most active.
  • Take steps to stop mosquitoes from getting into the house. Repair screens on windows and doors.
  • When outside:
    • Use mosquito netting at night. Look for netting treated with insecticide.
    • Wear insect repellent. Choose long pants and long-sleeved shirts to limit bites.
  • Clear out possible insect breeding areas. Empty areas of standing water, like pet water bowls, rain barrels, and other containers.

In some places, mosquitoes are controlled by widespread spraying.

A vaccine is available to lab workers at risk for EEE.


Centers for Disease Control and Prevention 

National Institute of Neurological Disorders and Stroke 


Alberta Health 

Health Canada 


Eastern equine encephalitis. Centers for Disease Control and Prevention website. Available at: Accessed April 28, 2022.

Eastern equine encephalitis. EBSCO DynaMed website. Available at: . Accessed April 28, 2022.

Encephalitis: an overview. EBSCO Nursing Reference Center website. Available at:  . Accessed April 28, 2022.

Lindsey NP, Staples JE, et al. Eastern equine encephalitis virus in the United States, 2003-2016. Am J Trop Med Hyg. 2018;98(5):1472-1477.

Mosquito avoidance. EBSCO DynaMed website. Available at: . Accessed April 28, 2022.

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