Eastern Equine Encephalitis
Information for Health Professionals

All EEE and West Nile virus disease cases should be reported to the Vermont Department of Health.

Cause of EEE

EEE is caused by the most neuropathogenic arbovirus present in the United States. For patients that develop encephalitis, the mortality rate is high and survivors often have severe neurological damages.


EEE is relatively rare with only 5 to 10 cases reported nationally each year.

As of the beginning of September 2012, two cases of Eastern Equine Encephalitis (EEE) in Vermont have been confirmed. Both are adults from the Addison and Rutland County area where mosquito pools have recently tested positive for EEE and West Nile virus. Both of the patients have died.

In the northeast, Massachusetts has had the most human cases, and outbreaks have historically occurred in the southeastern part of the state every 10 to 20 years. New Hampshire has had a recent increase in reported cases. Since 2005, New Hampshire has recorded 9 human cases.

For more information about EEE in Vermont, go to Surveillance and Data.


The virus is maintained in a bird-mosquito cycle that occasionally spills over to cause illness in mammals, including humans. Mammals are dead-end hosts and do not contribute to the transmission cycle of the virus. Vermont has the birds and mosquito species necessary to perpetuate the enzootic cycle, so it is possible that Vermonters could see this disease in people and susceptible animals. In 2010, deer and moose blood collected during hunting season tested positive for antibodies against EEE virus. Out of almost 500 samples tested, about 11% were positive. Positive samples came from deer and moose from all parts of the state. This is the first evidence that EEE virus is present in Vermont.


 EEE virus infection in people can be asymptomatic, or it can result in either a systemic or encephalitic infection. Systemic infection has an abrupt onset and is characterized by chills, fever, malaise, arthralgia, and myalgia. The illness lasts 1 to 2 weeks. Recovery is complete when there is no central nervous system involvement.

Most of the reported cases are caused by an encephalitic infection. In infants, the encephalitic form is characterized by abrupt onset; in older children and adults, encephalitis occurs after a few days of systemic illness. Signs and symptoms in encephalitic patients include fever, headache, irritability, restlessness, drowsiness, anorexia, vomiting, diarrhea, cyanosis, convulsions, and coma. Approximately 1/3 of people that develop encephalitis die, and 50% of those who recover have significant neurologic sequelae.

Testing and Diagnosis

Arboviral Diseases

All EEE and West Nile virus disease cases should be reported to the Vermont Department of Health.

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More Information

Contact Us

Department of Health
Tel: 800-640-4374 (Vermont only) or 802-863-7240
Email the Department of Health (general mailbox)

Public Health Laboratory
Tel: 800-660-9997, extension 7560

Epidemiology Field Unit
800-640-4374 (in VT only), or 802-863-7240.

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