What You Need to Know About Eastern Equine Encephalitis

The mosquito-borne disease is potentially fatal—and exceedingly rare.

Medically reviewed in October 2021

From time to time, an illness called Eastern equine encephalitis (EEE) pops up in the news. In July 2019, for instance, the Florida Department of Health in Orange County reported that the virus that causes EEE had been detected in local chickens—and not for the first time.

Transmitted by infected mosquitos, EEE is a serious disease that may cause swelling of the brain, brain damage and death. Media coverage of EEE can be alarming, but it’s important to note: The illness is extremely rare in the United States, with an average of just seven cases reported each year. 

While the odds of developing EEE are low, here’s what you should know about this potentially fatal condition.

What is EEE?
In the U.S., most cases of EEE occur between late spring and early fall, commonly in Atlantic or Gulf Coast states, and sometimes around the Great Lakes. Between 2009 and 2018, Florida, Massachusetts, New York and North Carolina reported the largest number of cases. 

People who spend lots of time outside—whether for work or play—are at higher risk, simply due to more mosquito exposure. Those who visit, live or work in woodlands may have increased odds, as well. EEE doesn’t spread from human to human, or from animal (other than the mosquito) to human, though some animals can contract the infection. 
 
The vast majority of people infected with the EEE virus—95 to 96 percent—will not develop EEE. Those who do will typically experience symptoms within a few days of being bitten by a mosquito carrying the virus. Adults older than 50 and children younger than 15 are most susceptible to severe disease.

According to the Centers for Disease Control and Prevention (CDC), severe cases start with sudden headaches, chills, vomiting and a high fever, which may progress into disorientation, seizures and coma. More than a third of patients with EEE will die. Those who live are frequently left with brain damage.  

Can you keep EEE from happening?
There is no vaccine to prevent EEE or specific medication used to treat the disease. The best way to avoid it is by avoiding mosquito bites. So, when you’re outside, use an insect repellent containing at least 20 percent DEET or other CDC-recommended ingredients. Look for products with the Environmental Protection Agency (EPA) graphic, which means they’re both safe and effective. Weather permitting, dress in light pants, long-sleeve shirts and socks. 

At home, make sure screens fit securely into doors and windows. Take care to eliminate standing water—which mosquitos love to use as breeding grounds—in the surrounding area. Clean gutters and pools regularly, and drain pool covers after rainstorms. Dispose of or turn over outdoor items that can collect water, like used tires, wading pools, flower pots, buckets and other containers.

Though it’s very unlikely that you or your loved ones will develop EEE, a little extra attentiveness can drive the odds even lower. As a bonus, you may be less likely to develop other insect-borne diseases, too.

Medically reviewed in July 2019

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