What You Need to Know About Eastern Equine Encephalitis Virus

Although not as widely discussed as other mosquito-borne diseases, the rare Eastern Equine Encephalitis virus (EEE) is one of the most serious and deadly diseases transmitted by mosquitoes. Symptoms typically appear between four and ten days after infection and include headache, vomiting, chills, and fever. While most human cases are mild or asymptomatic, severe cases of EEE can lead to brain damage, seizures, or coma. With no specific treatment, cure, or vaccine available for humans, EEE is extremely dangerous. According to the Centers for Disease Control and Prevention (CDC), approximately 30% of humans who contract EEE and develop severe cases die, and many survivors suffer permanent neurological damage.

Map EEE

Human Cases and Geographical Spread

From 2003 to 2023, there were 196 reported human cases of EEE in the United States. Most cases have been reported in the Atlantic and Gulf Coast states, where the virus primarily occurs from late spring through early fall. The disease is transmitted by several mosquito species, including some from the Aedes, Coquillettidia, and Culex genera, which thrive around freshwater hardwood swamps in the Atlantic and Gulf Coast states, as well as the Great Lakes region.

As of January 14, 2025, 19 human cases of EEE were reported by the CDC in 2024 in the United States. The affected states include Wisconsin, North Carolina, New York, New Jersey, Rhode Island, Massachusetts, New Hampshire, Vermont and Maine.

Impact on Horses

EEE is significantly more severe in horses, with a mortality rate as high as 90%. Between 2008 and 2021, there were 2,149 confirmed equine cases in the U.S. A vaccine is available for horses and is typically recommended by veterinarians. Preventative measures for horse owners include changing the water in troughs at least twice a week to prevent mosquito development.

Preventing EEE in Humans

The only way to prevent EEE in humans is to avoid mosquito bites. Since there is no cure or treatment, bite prevention is crucial. Effective measures include:

  • Applying mosquito repellents containing DEET or other EPA-recommended active ingredients and wearing loose-fitting clothing outdoors.
  • Removing standing water from artificial containers like buckets, old tires, gutters, birdbaths, and flower pots to eliminate breeding sites.
  • Using air conditioning and maintaining window screens to prevent mosquitoes from entering homes.

Mosquito Control Strategies

Mosquito abatement professionals emphasize an integrated mosquito management (IMM) approach, targeting mosquitoes at every stage of their life cycle. This includes:

  • Surveillance and Larvicides: Mosquito surveillance and disease testing provide IMM program managers critical information to guide the targeted application of both larvicides and adulticides. Early use of larvicides like Altosid®, which contains our pioneering Insect Growth Regulator (S)-methoprene, or FourStar® Microbials, which use naturally occurring bacteria to kill mosquito larvae, can help control mosquito populations and reduce the risk of mosquito-borne diseases.
  • Adulticides: For addressing adult mosquito populations, Zenivex® adulticides, featuring Etofenprox and classified as reduced risk by the EPA, are recommended.

Effective vector control can significantly reduce the threat of EEE and other mosquito-borne diseases, safeguarding public health.

For more information, contact a representative near you.