Eastern Equine Encephalitis - Frequently Asked Questions

What is Eastern Equine Encephalitis?

Eastern Equine Encephalitis (EEE) is a rare but serious disease caused by EEE virus.

What are the symptoms of EEE?

Most people infected with EEE virus do not become ill. When symptoms do occur they can range from mild fever and headache to coma. Other symptoms include high fever, fatigue, muscle aches, neck stiffness, tremors, or confusion. Severe cases include inflammation of the brain (encephalitis) which can lead to coma, convulsions, and death.

How soon after being bitten by a mosquito infected with EEE virus do symptoms occur?

Symptoms usually occur 3 to 10 days after an infected mosquito bites a person.

What is the treatment for EEE?

There is no cure for EEE, and 3 of every 10 people who get the disease die from it. Doctors provide supportive treatment, lower the fever, and ease the pressure on the brain and spinal cord. Some people who survive this disease will be permanently disabled and only about half recover completely.

Is there a vaccine to protect humans from EEE?

No. There is no vaccine because the EEE virus occurs so infrequently in people. (There is a vaccine for use in horses.)

How common are human cases of EEE in the United States?

In the United States, an average of 6 human cases of EEE are reported annually.

Have there been any human cases of EEE in Connecticut?

In 2013, the first human case of EEE infection in Connecticut was identified. This case involved an adult resident of eastern Connecticut who was hospitalized with encephalitis and died in fall 2013. In 2019, Connecticut had four human cases of EEE, three of which were fatal. All four were most likely exposed to infected mosquitoes sometime between mid-August and early September 2019, which was the peak period of mosquito activity in the state. All four residents lived in a part of eastern Connecticut where EEE activity had not been previously detected before summer 2019.

Have there been any horse cases of EEE in Connecticut?

Horse cases occur sporadically in Connecticut and are believed to have occurred among horses as far back as 1928 when there was a severe outbreak in New London County with about 100 cases. Symptoms may include appetite loss, drooping eyelids and lower lip, aimless wandering, and circling, blindness, and inability to stand. The infection is fatal to horses in more than 90 percent of cases, and death usually occurs in 2 to 3 days. A vaccine is available for use in horses.

How is EEE spread?

Mosquitoes spread the EEE virus. The virus is carried by birds that live in freshwater swamps and is generally found only in these birds and in mosquitoes that feed on birds but not people. In some years, however, many birds get infected and other types of mosquitoes pick up the virus that also bite people and horses. The risk of getting EEE is highest from late July through September. The virus is spread by adult mosquitoes, which are killed by frost in the fall. The EEE virus is not spread by people and horses with the disease.

Can any mosquito spread EEE to people?

No. In Connecticut, there are 52 different mosquito species. Since 1996, EEE virus has been isolated from mosquitoes in Connecticut every year except 1999, usually during September and early October. The virus is generally maintained by an exclusive bird-biting mosquito called Culiseta melanura, but has been found in 9 other mosquito species in Connecticut, 6 of which are known to bite people.

How can I lower my risk of getting EEE?

You should try to reduce the risk of being bitten by mosquitoes. If EEE is found in your area, you should:

• Minimize time spent outdoors between dusk and dawn when mosquitoes are most active.
• When it is necessary to be outdoors, use mosquito repellents containing an EPA-registered active ingredient, including DEET, Picaridin, IR3535, oil of lemon eucalyptus, para-menthane-diol (PMD), or 2-undecanone. EPA registration of skin-applied repellent products indicates that they have been evaluated and approved for human safety and effectiveness when applied according to instructions on the label.
• Wear shoes, socks, long pants, and a long-sleeved shirt when outdoors for long periods of time, or when mosquitoes are more active. Clothing should be light-colored and loose-fitting and made of tightly woven materials that keep mosquitoes away from the skin.
• Wear clothing and gear treated with permethrin. Permethrin is an insecticide that kills or repels mosquitoes and ticks.
• Be sure door and window screens are tight-fitting and in good repair.
• When sleeping outdoors, use tents or mosquito netting in an unscreened structure. Treat camping gear with permethrin when possible.
• Cover strollers and baby carriers with mosquito nets when outside.

NOTE: These measures also help to protect against infection with West Nile virus, another virus transmitted by mosquitoes.

Should I stay indoors if EEE is confirmed in my town?

It is usually not necessary to limit outdoor activities. However, you can and should try to reduce your risk of being bitten by mosquitoes by reducing standing water in your yard and taking personal precautions to prevent mosquito bites.

What is being done in my community to control mosquitoes?

The State of Connecticut has prepared a plan to address the public health threat posed by diseases that are carried by mosquitoes and has devised a preventive strategy to minimize the impact. Local communities are implementing various control measures based on geographic location and level of risk. For more information regarding activities in your specific area, contact your local health department.

How can I get more information on EEE?

Contact your local health department. For specific questions on human infections, contact the Connecticut Department of Public Health at 860-509-7994.

Content last updated in September 2024.