4 Things to Know About Eastern Equine Encephalitis

Older adults face a greater risk of complications from the rare but serious mosquito-borne disease

Peter Urban,

AARP

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Published August 28, 2024

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Hearing news that a New Hampshire resident died after being infected with eastern equine encephalitis (EEE) virus may be worrisome, but there’s no need for panic. Although mosquito season is still going strong, this mosquito-borne disease is a rarity. Only a few cases are reported in the United States each year.

So far in 2024, the Centers for Disease Control and Prevention (CDC) has confirmed five cases total in New Jersey, Wisconsin, Massachusetts, Vermont and New Hampshire. Several communities in Massachusetts are taking extra precautions to limit the potential spread of the virus after discovering elevated levels of the virus in mosquitoes.

What is eastern equine encephalitis?

Eastern equine encephalitis is a rare but serious mosquito-borne disease. On average, fewer than 10 cases are reported annually in the U.S., mostly in eastern or Gulf Coast states. There is no approved vaccine or antiviral treatment available for infections, which can cause flu-like symptoms.

More severe cases include inflammation of brain tissue, known as encephalitis. About a third of people who develop encephalitis from the virus die from the infection; those who survive often have ongoing physical or neurological problems, according to the CDC.

Speaking to the Associated Press, Richard Ellison, M.D., an immunologist and infectious disease specialist at the University of Massachusetts Memorial Medical Center, explained that such an infection is “very, very severe.”

“Although it’s a very rare infection, we have no treatment for it,” he said. “Once someone gets it, it’s just — all we can do is provide supportive care, and it can kill people.”

There were seven cases nationally last year. The last major outbreak occurred in 2019 when 38 cases, including at least a dozen deaths, were reported.

Here are four things you should know about the virus, including how to protect yourself during mosquito season.

1. Symptoms appear several days after a bite

Eastern equine encephalitis virus infection can result in fever or neurologic disease. The type of illness will depend on the age of the person and other factors. Adults 50 and older are among the groups at highest risk for a severe infection.

Symptoms usually appear between four to 10 days after being infected from a mosquito bite. According to the CDC, mild symptoms lasting a week or two can include:

Fever
Chills
Body aches
Joint pain

More severe cases involve neurologic disease, including encephalitis or meningitis (inflammation of the membrane that surrounds the brain and spinal cord). Signs and symptoms of neurologic disease might occur after several days of systemic illness and can include:

Fever
Headache
Vomiting
Diarrhea
Seizures
Behavioral changes
Drowsiness
Coma

2. Common mosquitoes can carry the virus

Eastern equine encephalitis is caused by a virus that is found in North America and the Caribbean. The virus circulates in the environment between mosquitoes and birds typically found in freshwater hardwood swamps. It can be transmitted to people (and horses) through other types of mosquitoes, including the common house mosquito, that feed on infected birds, according to the CDC.

3. People and horses are considered “dead-end” hosts

The virus circulates between birds and mosquitoes, so if a person gets bitten by an infected mosquito, the chain of transmission stops there because, unlike birds, the concentration of virus that develops in people (and horses) is insufficient to pass the virus on to other biting mosquitoes. The virus has been transmitted from person to person through organ transplantation, according to the CDC.

4. There are things you can do to help prevent an infection

There are no vaccines or medicines that can prevent illness from the virus, but there are a few things you can do to lower your risk of infection.

Use an insect repellent registered with the Environmental Protection Agency (EPA).
Wear long-sleeve shirts and long pants.
Wear clothing that’s been treated with permethrin.
In areas of high risk, minimize outdoor activities during evening or early morning when mosquitoes are most active.
Eliminate or empty water-holding containers around your home, where mosquitoes can lay eggs. This includes buckets, toys, flowerpots and trash containers.
Install or repair window screens to keep mosquitoes out of your home.

More mosquito-borne illnesses

Here are a few more mosquito-borne diseases to pay attention to this season:

West Nile virus: As of Aug. 27, there have been 289 reported cases this year in 33 states. But that is likely just the tip of the iceberg because 8 in 10 people bitten by a mosquito and infected do not develop symptoms that otherwise can include headache, body aches, joint pain, vomiting, diarrhea and rash. Older adults are at greater risk of developing a severe infection. Read more about West Nile virus on AARP.org.

Dengue: U.S. health officials are monitoring a “higher than expected” number of dengue cases in the United States and popular travel destinations. An infection can cause mild flu-like symptoms. However, in some people, a dengue infection can become severe — even life-threatening. Read more about dengue on AARP.org.

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Peter Urban is a contributing writer and editor who focuses on health news. Urban spent two decades working as a correspondent in Washington, D.C., including a stint as Washington bureau chief for the Las Vegas Review-Journal, and for daily newspapers in Connecticut, Massachusetts, Ohio, California and Arkansas, His freelance work has appeared in Scientific American, Bloomberg Government and CTNewsJunkie.com.