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.
Prevalence
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.
Transmission
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.
Symptoms
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
All EEE and West Nile virus disease cases should be reported to the Vermont Department of Health.
Criteria for Arboviral Testing
In the summer and fall, patients with asceptic encephalitis or meningitis should be tested for both West Nile virus and Eastern equine encephalitis virus. Patients with Guillain-Barré syndrome should also be tested for West Nile virus. Testing is not recommended for persons with mild illness, such as fever or headache, because levels of WNV and EEEV activity in the community would have to be very high for such symptoms to likely be due these viral infections.
Diagnostic testing
Serologic testing remains the primary method for diagnosing WNV and EEEV infection. Combined with a consistent clinical presentation in an endemic area, a rapid and accurate diagnosis of acute arboviral disease can be made by the detection of virus-specific IgM antibody in serum or CSF. However, samples taken early in the course of illness may be negative, and a convalescent sample may be necessary for accurate diagnosis.
Ideal timing of specimens for serology:
| Specimen |
Timing |
|---|---|
Acute |
3 to 10 days after onset of symptoms |
Convalescent |
2-3 weeks after acute sample |
At least 1.0 of serum and/or 1.0 mL of CSF is required for serology testing
WNV and EEE virus antibody tests are available commercially. However, a positive IgM test result should be confirmed by neutralizing antibody testing at a state public health laboratory or CDC.
Samples can be sent to the Vermont Department of Health Laboratory. Serum should be refrigerated and shipped with an ice pack, and CSF samples should be submitted frozen. All specimens should be accompanied by a completed Department of Health Laboratory Clinical Test Request Form.
Mark "WNV and or EEE virus antibody" under the heading "Serology Tests (Misc.)." Date of onset must be included.
Forms and serology mailers can be obtained by contacting the Vermont Department of Health Laboratory at 800-660-9997, extension 7560.
More Information
- EEE in Vermont
- Vermont Arbovirus Surveillance & Data
- Eastern Equine Encephalitis information from CDC
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
Website
Epidemiology Field Unit
800-640-4374 (in VT only), or 802-863-7240.