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About Eastern Equine Encephalitis

Eastern equine encephalitis virus (EEEV) is transmitted to humans through the bite of an infected mosquito. Human EEEV cases occur relatively infrequently, largely because the primary transmission cycle takes place in and around swampy areas where human populations tend to be limited. All residents of and visitors to areas where EEEV activity has been identified are at risk of infection. People who engage in outdoor work and recreational activities in endemic areas are at increased risk of infection. Persons over age 50 and under age 15 seem to be at greatest risk for developing severe disease when infected with EEEV. Overall, only about 4-5% of human EEEV infections result in EEE. EEEV infection is thought to confer life-long immunity against re-infection. It does not confer significant cross-immunity against other alphaviruses (e.g., western equine encephalitis virus), and it confers no cross-immunity against flaviviruses (e.g., West Nile virus) or bunyaviruses (e.g., La Crosse virus).

In the United States, an average of 11 human cases of EEE are reported annually. To ensure standardization of reporting across the country, CDC recommends that the national surveillance case definition be consistently applied by all state health departments.

From 2012-2021, most cases of EEE have been reported from Massachusetts, Michigan, Florida, Georgia, and North Carolina. EEEV transmission is most common in and around freshwater hardwood swamps in the Atlantic and Gulf Coast states and the Great Lakes region.