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Eastern Equine Encephalitis

Eastern equine encephalitis (EEE) is a rare but serious disease caused by the bite of an infected mosquito. It can lead to severe illness, neurological damage, and even death.

The best way to protect yourself against EEE is to prevent mosquito bites.


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On this page:

  • What Is Eastern Equine Encephalitis?
  • What Are the Symptoms of Eastern Equine Encephalitis?
  • How Do You Diagnose Eastern Equine Encephalitis?
  • How Do You Treat Eastern Equine Encephalitis?

What Is Eastern Equine Encephalitis?

Eastern equine encephalitis — sometimes called EEE or Triple E — is a rare but serious disease caused by a virus that spreads to people and some animals, like horses, through the bite of an infected mosquito. The virus attacks the body’s immune system, potentially leading to brain inflammation and severe neurological damage.

People and horses are considered dead-end hosts to the virus, meaning they can't spread it to others.

Just because you contract the EEE virus doesn't mean that you'll definitely develop the disease. Only 4% to 5% of EEE infections result in the development of eastern equine encephalitis.

While rare, EEE can be very serious — about 30% of people who develop a severe case of EEE die. About 50% of survivors have long-term neurological issues.

There is no vaccine to prevent EEE or medicine to treat the disease. It's believed that being infected by the EEE virus causes immunity from being infected by EEE again. If you think you may have been bitten by an infected mosquito and/or contracted EEE, you should talk to your doctor right away.

What causes eastern equine encephalitis?

A virus spread by infected mosquitos causes eastern equine encephalitis.

Eastern equine encephalitis risk factors and complications

Eastern equine encephalitis risk factors

You may be at a higher risk of EEE infection if you live, work, visit, or participate in outdoor activities in endemic areas. These include the Caribbean and states along the Atlantic Coast, Gulf Coast, and Great Lakes.

Children younger than 5 and adults older than 60 seem to have a higher risk of developing severe cases of EEE.

Complications of eastern equine encephalitis

EEE can result in many complications, including:

  • Autonomic nervous system failure.
  • Cognitive, motor, or sensory deficits.
  • Complications that may require long-term care — Including intellectual impairment, personality disorders, seizures, paralysis, behavioral changes, and cranial nerve dysfunction.
  • Death — About a third of people who develop severe EEE will die within two to 10 days after symptoms start.
  • Febrile illness — Fever, chills, body aches, and joint pain lasting one to two weeks.
  • Neurologic diseases — Including meningitis (inflammation of the membranes that protect the brain and spinal cord) and encephalitis (inflammation of the brain). These conditions tend to occur sooner after infection in infants than in older children and adults.
  • Organ failure.
  • Shortened lifespan — People with severe EEE and ongoing disabilities may die within a few years as a result of their complications.

How can I prevent eastern equine encephalitis?

There is no vaccine to prevent EEE, so the best way to protect yourself is to prevent mosquito bites. 

You can prevent mosquito bites by:

  • Covering strollers, baby carriers, tents, and sleeping bags with mosquito netting.
  • Limiting outdoor activities during peak hours and times of year. Mosquitoes are out during both the day and night but tend to be most active at dawn and dusk. A majority of U.S. EEE cases occur between May and October.
  • Planting mosquito-repelling plants, such as citronella, marigolds, and lavender.
  • Regularly emptying and cleaning out items that hold standing water in and around your home, such as buckets, plant saucers, birdbaths, and containers.
  • Treating your clothing and gear with permethrin insecticide.
  • Using fans in outdoor and indoor settings. Mosquitoes are weak flyers, so fans can help keep them away.
  • Using insect repellent on your skin/body. Choose insect repellents registered with the Environmental Protection Agency (EPA). If you're using sunscreen and insect repellent at the same time, you should apply the sunscreen first and then the insect repellent.
  • Using screens on open windows and doors or air conditioning to keep mosquitoes from entering your home.
  • Wearing loose-fitted, long-sleeved shirts, pants, socks, and close-toed shoes. Mosquitoes can also be attracted to dark clothing, so wear light clothing when possible.

How common is eastern equine encephalitis? 

The Centers for Disease Control and Prevention (CDC) reports an average of 11 cases of EEE in the United States every year. Most cases occur in and around freshwater hardwood swamps in the Caribbean and North America, especially along the Atlantic Coast, Gulf Coast, or Great Lakes.

The states with the highest rate of EEE incidence are:

  • Florida
  • Georgia
  • Maryland
  • New Jersey
  • Wisconsin

In recent years, cases have also been on the rise in Arkansas, Connecticut, Maine, North Carolina, Tennessee, and Vermont. 

What Are the Signs and Symptoms of Eastern Equine Encephalitis? 

The majority of people (96%) who are infected with EEE don't develop any symptoms. In others, symptoms may appear four to 10 days after the virus is transmitted.

Symptoms may include:

  • Behavioral changes, such as psychosis.
  • Body aches.
  • Chills.
  • Coma.
  • Diarrhea.
  • Drowsiness.
  • Fever.
  • Headache.
  • Joint pain or stiffness.
  • Limb weakness.
  • Seizures.
  • Tingling, burning, or itching of the skin.
  • Vomiting.
  • Weakness.

How Do You Diagnose Eastern Equine Encephalitis?

To diagnose EEE, your doctor will evaluate your symptoms and ask if you live or have traveled to areas where EEE is commonly found. To confirm an EEE diagnosis, your doctor may take a sample of your blood or cerebrospinal fluid (CSF) to test for the presence of the virus.

How Do You Treat Eastern Equine Encephalitis?

There are no medicines to treat EEE, but your doctor may recommend a combination of rest, fluids, and over-the-counter (OTC) pain relievers.

Most people experiencing severe symptoms of EEE need to be hospitalized to monitor symptoms and receive supportive treatments, such as IV fluids, respiratory support, pain medicine, and nursing care. Doctors may also recommend an antibody treatment for people with severe EEE or brain surgery for those with severe neurological difficulties.

Additional resources

  • Eastern Equine Encephalitis: What to Know About EEE

By UPMC Editorial Staff. Last reviewed on 2025-01-16 by Spencer Schrank, DO.

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