Official websites use

A website belongs to an official government organization in the City of Boston.


Secure .gov websites use HTTPS

A lock or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Last updated:

Eastern Equine Encephalitis (EEE)

This fact sheet answers frequently asked questions about eastern equine encephalitis (EEE).

Eastern equine encephalitis (EEE) virus is a rare but serious disease.

The basics

How common is EEE in Boston?

In Massachusetts, infected mosquitos are most often found in and around freshwater swamps. EEE infected fewer than 100 people since identifying the virus in Massachusetts in 1938. Mosquitoes that carry EEE are rare in Boston but are much more common in areas such as Plymouth and Norfolk counties. EEE is a very rare disease.

How is the Boston Public Health Commission (BPHC) tracking and controlling EEE?

BPHC works with the Suffolk County Mosquito Control Project to trap and test mosquitoes around Boston for EEE. Trapping and testing happens during the summer and fall months. Mosquito control measures are also implemented during summer and fall months. The city treats wetlands, storm drains, and other areas to limit the number of mosquitoes. Click here for more information.

How is EEE virus spread?

The virus that causes EEE spreads through the bite of an infected mosquito. Mosquitoes become infected when they bite infected birds. Once infected, mosquitoes feed on horses, humans and other mammals. Humans, horses, and other types of mammals can become infected, but they do not spread the disease.


What are the signs and symptoms of EEE?

Some people infected with EEE do not become ill. When symptoms occur they range from flu-like symptoms such as a high fever and headache, to more serious illness. Other symptoms include muscle aches, lack of energy, neck stiffness, and confusion. Severe cases develop swelling of the brain (encephalitis) which can be dangerous. These symptoms show up four to ten days after a bite from an infected mosquito. Illness usually lasts about 1 to 2 weeks, but it often takes much longer to recover.

Who gets EEE virus infections?

Most mosquitoes do not transmit disease, but anyone bitten by an infected mosquito can get EEE. People of all ages are at risk of developing serious illness after infection with the EEE virus.

Is there a vaccine to protect humans from Eastern equine encephalitis?

No. There is no vaccine because the virus rarely occurs in people. There is a vaccine for use in horses.


How can I help protect myself from mosquitoes?

  • Use a mosquito repellent. Repellents approved by the EPA include those containing DEET, oil of lemon eucalyptus, Picaridin or IR3535. Follow the directions on the product label. After returning indoors, wash repellent off with soap and water and wash treated clothes before wearing again. Do not use these products on pets unless the label approves
  • If you use a product containing DEET, do not use concentrations of more than 30% on adults and use low concentrations of DEET on children. Apply DEET to exposed skin (not eyes or mouth) and on clothes, but do not use on open cuts or wounds. Do not apply underneath clothes
  • Do not let children apply repellants to themselves. Apply the repellant to your hands and rub it on your child. Do not apply repellants to children’s eye, mouth, or hands and use cautiously around ears. Do not apply DEET on infants. Instead use mosquito netting over infant carriers or oil of lemon eucalyptus on children under 3 years of age
  • Wear protective clothing such as long sleeved shirts, long pants and socks whenever possible. Tuck your shirt into your pants to keep mosquitoes from going under your clothes
  • Although mosquitoes can bite at any time of day, try to limit time outdoors between dusk to dawn when mosquitoes are most active
  • Make sure window and door screens don’t have holes in them. Screens in good condition will help prevent mosquitoes from getting inside your house

Follow these steps to help prevent mosquito breeding: Mosquitoes need water to breed. They can develop into adults in as little as a week. Make sure items around your home don’t collect water. Clean out items that do collect water once a week.

  • Containers: Turn over or cover unused flower pots, buckets, garbage cans, and wheelbarrows. Change water in bird baths once a week
  • Gutters: Remove leaves and other debris that can clog gutters and trap water
  • Pools: Cover unused swimming pools and turn over kiddie pools when not in use. Be sure to keep swimming pool covers clear of leaves and water. Keep large pools treated and circulating
  • Old tires: Cover or dispose of them. They are a favorite mosquito-breeding site

To learn more about EEE from the Centers for Disease Control and Prevention, click here


What is the treatment for EEE?

There is no specific treatment for EEE infection. A healthcare provider may prescribe medications to relieve the symptoms of the illness. Many cases will need hospitalization.

Back to top