What is Eastern equine encephalitis?

Definition

Eastern equine encephalitis (EEE) is a virus affecting wild birds. It is
carried by certain mosquitoes and is occasionally
transmitted to horses and, rarely, to humans. EEE affects the brain and central nervous system.

Although EEE is more dangerous to horses than to humans (many people infected with the EEE virus do not have any apparent health problems), in some cases, people infected can become suddenly and seriously ill and may experience severe injury to the nervous system; death sometimes follows.

In areas where EEE is known to be present, one should take extra precaution to avoid mosquitoes and to protect against mosquito bites.

Causes

EEE, an arbovirus, is spread by infected invertebrate animals, mostly blood-sucking (hematophagous) insects. Arboviruses are usually spread by infected mosquitoes. Mosquitoes most often get the EEE virus by biting infected birds, and then spreading the virus to horses and other mammals, including humans.

Risk Factors

Because the only known way for humans to contract EEE is by being bitten by an
infected mosquito, the risk factor most commonly associated with EEE is exposure
to mosquito bites, or living near or visiting a wetland area or an area known to
have incidents of EEE. People age fifteen years and younger and age fifty years
and older seem to be more susceptible to the infection.

Symptoms

If a person experiences any of the symptoms for EEE, he or she should not assume it is caused by EEE. These symptoms may be caused by other, less serious health conditions. However, one should consult a doctor if any of the following symptoms are present: fatigue; fever; headache; nausea; restlessness or irritability; difficulty walking or unstableness; confusion, impaired judgment, or an altered mental state; or seizures.

Screening and Diagnosis

A doctor will ask about symptoms and medical history, will perform a physical
exam, and may order the following tests: blood tests to check if the virus is
present; a spinal tap to remove a small amount of spinal fluid to check for signs
of infection; an electroencephalogram (EEG) to measure the brain’s activity; a
neurological exam to access reflexes, memory, and other brain function; a
magnetic
resonance imaging (MRI) scan (a scan that uses radio waves
and a powerful magnet to produce detailed computer images); and a computed tomography (CT)
scan (a detailed X-ray picture that identifies abnormalities
of fine tissue structure).

Treatment and Therapy

There are no drug options to treat the EEE virus in humans, so medical treatment focuses on the symptoms of the infection. Such treatments may include antibiotics for secondary infections; anticonvulsants to treat seizures; a respirator to help with breathing; pain relievers to treat headache, fever, and body aches; corticosteroids to reduce swelling in the brain; and sedatives for restlessness or irritability.

Prevention and Outcomes

To help reduce the chance of getting EEE, one should avoid areas of mosquito activity, if possible, and stay inside when mosquitoes are most active (at dawn and at dusk). When outside, one should wear insect repellent, long pants, and long-sleeved shirts to limit exposure to bites. To help limit mosquito populations in and around the home, one should eliminate the insects’ breeding areas, such as standing water in ponds, bowls for pets, rain barrels, and other containers.

Bibliography

Booss, John, Margaret Esiri, and Margaret M. Esin, eds. Viral Encephalitis in Humans. Washington, D.C.: ASM Press, 2003.

Centers for Disease Control and Prevention. “Eastern Equine Encephalitis Virus (EEEV).” Available at http://www.cdc.gov/easternequineencephalitis.

Marquardt, William C., ed. Biology of Disease Vectors. 2d ed. New York: Academic Press/Elsevier, 2005.

North Carolina Department of Health and Human Services. “Arboviruses: Eastern Equine Encephalitis.” Available at http://www.epi.state.nc.us/epi/arbovirus/eee.html.

Stull, J. W., et al. “Eastern Equine Encephalitis—New Hampshire and Massachusetts, August-September 2005.” Journal of the American Medical Association 296 (2006): 645-646. Available at http://jama.ama-assn.org/cgi/content/full/296/6/645.