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FAQs - "B" Agents

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Eastern Equine Encephalitis (EEE)

What is Eastern Equine Encephalitis?

Eastern Equine Encephalitis (EEE) is a mosquito-borne viral disease. As the name suggests, EEE occurs in the eastern half of the US. Because of the high case fatality rate, it is regarded as one of the more serious mosquito-borne diseases in the United States.

How do people become infected with EEE virus?

EEE virus is transmitted to humans through the bite of an infected mosquito. Several species of mosquitoes can become infected with EEE virus. The main EEE transmission cycle is between birds and mosquitoes. Horses can also become infected with, and die from, EEE virus infection.

What causes EEE?

EEE is caused by a virus that is a member of the family Togaviridae, genus Alphavirus. It is closely related to Western and Venezuelan equine encephalitis viruses.

What type of illness can occur?

Symptoms can range from mild flu-like illness to encephalitis (inflammation of the brain), coma, and death. Among those who are recognized to have infection the death rate is 50-75%, making it one of the most deadly mosquito-borne diseases in the US. It is estimated that 30% of people who survive EEE will have neurologic deficits.

How common is EEE?

Human cases occur relatively infrequently, largely because the cycle of infection between mosquito and birds takes place in swamp areas that humans tend to avoid. There are an average of 4 EEE cases in the US each year. The states with most cases are Florida, Georgia, Massachusetts, and New Jersey.

Who is at risk for developing EEE?

Persons over age 50 and younger than age 15 seem to be at greatest risk for developing severe disease. Residents of and visitors to areas with an established presence of the virus are at increased risk, as are people who engage in outdoor work and recreational activities.

How can people avoid infection with EEE virus?

Though a vaccine is available to protect horses, there is no licensed vaccine for human use.

To avoid infection people should avoid mosquito bites by employing personal and household protection measures, such as using insect repellent containing DEET, wearing protective clothing, taking precautions from dusk to dawn when mosquitoes are most likely to bite, and controlling standing water that can provide mosquito breeding sites.

Find the PDF version of this FAQ in the Zebra Manual.