Eastern Equine Encephalitis Virus

Eastern Equine Encephalitis is an infection caused by Eastern Equine Encephalitis (EEE) virus, which is spread to people by the bite of a mosquito infected with the virus. Viruses that are spread to people by mosquitoes are called arboviruses. EEE virus infections generally occur during warm weather months when mosquitoes are active. EEE occurs very infrequently in people with an average of 5 cases a year reported in the U.S. The disease also affects horses and is found primarily east of the Mississippi River in the U.S. It is among the most serious of a group of mosquito-borne virus diseases that can affect the central nervous system and cause severe complications and even death. Other similar diseases are Western Equine Encephalitis, St. Louis Encephalitis, and LaCrosse Encephalitis.

The EEE virus has a complex life cycle involving birds and a specific type of mosquito, Culiseta melanura, which lives in freshwater swamp habitats. These mosquitoes feed only on birds; they do not feed on humans and other mammals. In rare cases, however, the virus can escape from its normal habitat in other mosquitoes that feed on both birds and mammals (including horses and humans). These mosquitoes can transmit the virus to animals and people. After infection, the virus invades the central nervous system, including the spinal cord and brain.

Infection can cause a range of illnesses. Most people have no symptoms; others get only a mild flu-like illness with fever, headache, and sore throat. For people with infection of the central nervous system, a sudden fever and severe headache can be followed quickly by seizures and coma. About half of these patients die from the disease. Of those who survive, many suffer permanent brain damage and require lifetime institutional care. Unfortunately, there is no specific treatment for EEE virus infection. A physician may prescribe medications to relieve the symptoms of the illness. Additionally, there is no vaccine because the virus occurs so infrequently in people. (There is a vaccine for use in horses.)

Chatham County Mosquito Control routinely monitors for the presence of EEE virus in mosquitoes though trapping and subsequent testing of adult mosquitoes as well as testing of avian blood samples.

More information about EEE can be found at the following sites: