Eastern Equine Encephalitis (EEE)

What is eastern equine encephalitis (EEE)?

Eastern equine encephalitis (EEE) is a virus that spreads to people through bites from an infected mosquito. It causes brain inflammation (encephalitis). The virus can affect how your brain and nerves function. About 30% of people bitten by an EEE-infected mosquito develop encephalitis and die from the infection.

Research suggests EEE is more common during late spring through early fall. Infections usually peak in summer months, and are most common around bodies of fresh water and swamps and near coasts.

EEE got its name because researchers first discovered the virus in horses (equines) in the 1830s.

Where do mosquitoes that carry EEE live?

EEE infections occur in North, South and Central America and the Caribbean islands. In the United States, most EEE cases happen near:

• The Gulf Coast (near the Gulf of Mexico).
• The Atlantic Ocean coastline.
• States bordering the Great Lakes.

Is EEE contagious?

No. The virus can only spread to humans through an infected mosquito bite. It can’t spread from human to human or from horses (or other animals) to humans.

How common is EEE?

The U.S. Centers for Disease Control and Prevention (CDC) reported five cases of EEE in the United States in 2021. In 2019, the highest annual case report in the last 10 years occurred with 38 infections.

What are the symptoms of EEE?

Most people don’t have any symptoms of EEE. If you do experience symptoms, they could include:

• Chills.
• Fever.
• Joint pain.
• Muscle pain (myalgia).

Symptoms usually appear four to 10 days after a bite from an infected mosquito (incubation period).

Symptoms of a severe infection that causes brain inflammation (encephalitis) may include:

• Confusion.
• Diarrhea.
• Drowsiness.
• Headache.
• High fever (higher than 104 degrees Fahrenheit or 38 degrees Celsius.
• Loss of appetite.
• Vomiting.

Severe EEE symptoms can look and feel the same as the flu. Visit a healthcare provider if you have flu-like symptoms after being bitten by a mosquito or if you have a weakened immune system.

What causes EEE?

An arbovirus causes EEE. This virus spreads to humans after an infected mosquito bites your skin. The virus attacks your immune system and leads to inflammation in your brain.

How do mosquitoes get EEE?

Certain types of mosquitoes get the EEE virus by biting and feeding on birds that have the EEE virus. These mosquitoes then bite humans and animals. Infected birds originally get the infection after being bitten by another infected mosquito.

What are the risk factors for EEE?

You may be more at risk of getting an EEE infection if you:

• Live or work in areas where mosquitos live and breed (wetlands, swamps or wooded areas).
• Spend a lot of time outdoors, especially at dawn or dusk when mosquitos are most active.

Age groups most affected by EEE include:

• Adolescents (children younger than 15).
• Adults older than 50.

In addition, a weakened immune system may lead to severe symptoms. This can be the result of:

• Cancer treatment.
• Organ transplantation.
• Diabetes.
• High blood pressure.
• Kidney disease.

What are the complications of EEE?

EEE can be life-threatening and cause permanent brain damage. Complications of EEE may include:

• Behavioral changes.
• Issues with how your brain develops or functions (intellectual impairment).
• Seizures.
• Paralysis.
• Coma.

How is EEE diagnosed?

A healthcare provider will diagnose EEE after a physical exam to learn more about your symptoms. Your provider will take a complete medical history and ask you questions about recent insect bites, including when they happened and when you started noticing symptoms.

There isn’t a specific EEE test available. Blood tests can help your healthcare provider rule out conditions with similar symptoms. Your provider may test your cerebrospinal fluid to look for antibodies your body makes while trying to defend itself from a virus.

How is EEE treated?

There isn’t a cure for EEE. Your provider will suggest a combination of treatments to relieve mild symptoms. This may include:

• Getting plenty of rest.
• Drinking fluids to prevent dehydration.
• Taking over-the-counter pain relievers as directed.

If you have severe symptoms, you may need to stay in the hospital so a healthcare provider can monitor how your body reacts to the virus around the clock. If brain inflammation causes a buildup of pressure against your skull, you may need a type of brain surgery called a craniotomy to relieve the pressure.

Medications like antibiotics don’t treat EEE. A healthcare provider may recommend immunoglobulin therapy (an antibody treatment given through a needle in a vein in your arm) for severe cases.

Is there a vaccine for EEE?

There aren’t any vaccines available to prevent EEE in humans. The only EEE vaccine that exists is to prevent infections in horses. The vaccine for horses isn’t safe for humans to take.

How soon after treatment will I feel better?

A mild EEE infection can last for one to two weeks. However, you may feel tired or weak for several weeks to months. It could take a few months to recover completely from a severe infection.

Can EEE be prevented?

There isn’t a vaccine available to prevent EEE. You can protect yourself from mosquito bites by:

• Using insect repellent when outdoors.
• Wearing clothing that covers your arms and legs.
• Emptying all standing water that collects outside your home — from birdbaths, buckets/pots, sprinkling cans, trash containers, flower pots, etc. Standing water is a breeding ground for mosquitos.
• Using screens on doors and windows.
• Avoiding being outdoors at dawn and dusk if possible. These are the times when mosquitos are most active.

What’s the prognosis for EEE?

Most people who have a bite from an EEE-infected mosquito don’t have any symptoms or only have mild symptoms like a fever and muscle aches. But it can be life-threatening and lead to permanent brain damage. A healthcare provider can tell you what to expect. You may need to be admitted and treated in a hospital if you have severe symptoms or if you have a compromised immune system to prevent life-threatening outcomes.

Is EEE deadly?

Yes, EEE can be deadly, but it isn’t life-threatening for everyone. Life-threatening complications may happen two to 10 days after symptoms begin. If you notice symptoms of EEE after a mosquito bite, contact a healthcare provider.

When should I see a healthcare provider?

Call a healthcare provider right away if you or your loved one suddenly develops symptoms of EEE. Your provider will evaluate your symptoms, order tests (if necessary) and suggest any treatments you’ll need.

What questions should I ask my doctor?

• What type of treatment do you recommend?
• How did the virus affect my brain?
• What type of over-the-counter medications can I take at home?
• What over-the-counter medications are safe for my child to take?
• Do I need to go to the emergency room or stay in the hospital?

A note from Cleveland Clinic

Eastern equine encephalitis (EEE) is a virus that spreads to people through bites from an infected mosquito. It can be challenging to detect on your own, as symptoms may resemble the flu. Let your healthcare provider know if you were recently bitten by a mosquito and experienced symptoms of EEE. As there isn’t a human vaccine available for EEE, you can protect yourself from mosquito bites by applying an EPA-approved mosquito repplent and wearing long pants or long-sleeve shirts when you go outdoors.