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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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.
A virus spread by infected mosquitos causes eastern equine encephalitis.
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.
EEE can result in many complications, including:
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:
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:
In recent years, cases have also been on the rise in Arkansas, Connecticut, Maine, North Carolina, Tennessee, and Vermont.
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:
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.
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.
By UPMC Editorial Staff. Last reviewed by Spencer Schrank, DO on 2025-01-16.
