Epidemiology of Eastern Equine Encephalitis in Connecticut

Abstract

Outbreaks of eastern equine encephalitis (EEE) have occurred sporadically among horses and domestic pheasants in Connecticut since 1938 but no human cases have ever been confirmed. The majority of epizootics have occurred in the eastern portion of the state during the late summer and early fall and they have almost always coincided with major outbreaks in neighboring Massachusetts and Rhode Island. Most sites where EEE has occurred have been in or adjacent to fresh-water swamp (red maple/white cedar) or swamp-forest border locations that support a wide variety of wild bird life and numerous woodland mosquito species. Based on virus isolations and the seasonal prevalence and host feeding preferences of local mosquito populations, Culiseta melanura is presumed to be the enzootic vector while Aedes canadensis and Aedes vexans are the most likely vectors to horses. Epidemiological investigations suggest that Connecticut's numerous suburban forests, which comprise 60% of the state, provide a "sylvan" swampland ecology in which wild bird reservoirs and potential mosquito vectors are too widely dispersed to enable the build-up of infection in mosquitoes and subsequent transmission to man.

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