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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 via an infected mosquito bite. The virus infects the body’s immune system, where it can replicate and further spread throughout the body.

This can include the brain and central nervous system, potentially leading to brain inflammation and severe neurological damage. Most people infected with the virus that causes EEE are asymptomatic. Fewer than 5% develop EEE.

The U.S. Centers for Disease Control and Prevention reported 17 cases of EEE in the United States so far in 2024. Though only a handful of cases are reported in the United States each year, roughly 30% of people who develop severe EEE die from complications of the infection. However, those who survive often develop irreversible neurological problems.

Virus transmission is most common in and around freshwater hardwood swamps in the Atlantic, Gulf Coast, and Great Lakes regions.

No vaccines can prevent the virus at this time. No specific medicines can treat it.

Here’s what you need to know about preventing eastern equine encephalitis and recognizing the symptoms of this potentially deadly condition.

What Is Eastern Equine Encephalitis?

Eastern equine encephalitis is caused by a virus found in North America and the Caribbean that circulates between mosquitoes and birds in freshwater hardwood swamps. That’s according to the CDC.

These waters are in the Atlantic, Gulf Coast, and Great Lakes states. States that have reported EEE cases include Massachusetts, Michigan, Florida, Georgia, and New York.

A bite from an infected mosquito transmits the virus to people and certain animals, such as horses. People and horses are “dead-end” hosts. This means they don’t spread the virus to others.

Symptoms of Eastern Equine Encephalitis

Symptoms of eastern equine encephalitis begin four to 10 days after a mosquito bite. For those who develop symptoms, most will have mild infections, while others may develop severe EEE. EEE can cause a severe fever and brain disease, including encephalitis and meningitis.

Symptoms of eastern equine encephalitis, according to the CDC, may include:

• Behavioral changes.
• Body aches and joint pain.
• Chills.
• Diarrhea.
• Drowsiness.
• Fever.
• Headache.
• Paralysis.
• Seizures.
• Vomiting.

EEE Risk Factors and Treatment

You may run a higher risk of getting an EEE infection if you live or work in areas where mosquitos breed. These can include wetlands or swamps. You may also run a higher risk of getting it if you spend a lot of time outdoors.

The virus appears to affect children younger than 15 and adults older than 50 most, according to the CDC. Those with a weakened immune system may experience more severe symptoms, too.

For people experiencing mild EEE symptoms, doctors may recommend a combination of treatments. These treatments can include rest, fluids, and over-the-counter pain relievers.

Those experiencing severe EEE symptoms may have to go to the hospital so providers can monitor their neurological status.

No specific treatments are available for EEE.

Talk with your health care provider immediately if you think you or a loved one might have eastern equine encephalitis.

Preventing EEE

The best way to prevent eastern equine encephalitis is to protect yourself from mosquito bites.

You can prevent mosquito bites through a combination of personal protection and environmental management.

Here are some effective strategies:

1. Avoid peak hours — Mosquitoes are most active at dawn and dusk. If possible, limit outdoor activities during these times.
2. Install screens — Use window and door screens to keep mosquitoes out of your home. Repair any holes or tears in screens to keep insects out.
3. Plant mosquito-repelling plants — Certain plants, like citronella, marigold, and lavender, can help deter mosquitoes.
4. Remove standing water — Eliminate any sources of standing water around your home, such as birdbaths, clogged gutters, and plant saucers. These are breeding grounds for mosquitoes. Once a week, empty and scrub, turn over, cover, or throw out items that hold water, such as buckets, toys, pools, or trash cans.
5. Use fans — Mosquitoes are weak flyers, so setting up fans in outdoor areas can help keep them away.
6. Use indoor insecticides — Consider using indoor insecticides or mosquito traps if you have a significant mosquito problem inside your home.
7. Use insect repellent — Apply an Environmental Protection Agency (EPA)-registered insect repellent on exposed skin when outdoors as directed. EPA-registered insect repellents include those with DEET, picaridin, IR3535, and oil of lemon eucalyptus.
8. Treat clothing and gear — Spray permethrin, an insecticide that kills or repels mosquitoes, as directed.
9. Use mosquito nets — If you’re sleeping outdoors or in areas with high mosquito activity, use bed nets treated with insect repellent.
10. Wear protective clothing — Opt for long sleeves, long pants, socks, and closed-toe shoes. Wearing light-colored clothing can also help because dark colors attract mosquitoes.