Overwintering and Early Season Amplification of EEE in Southeastern U.S.

The following is the abstract of the dissertation from Andrea Bingham, PhD candidate at the University of South Florida, entitled “Overwintering and Early Season Amplification of Eastern Equine Encephalitis Virus in the Southeastern United States.” You can read her dissertation online.


“Eastern equine encephalitis virus (EEEV) is a highly pathogenic arbovirus that causes severe disease, with a mortality rate of approximately 30-35% in humans and 80-90% in horses. Studies dating back to the 1930’s have identified many of the epidemiological and ecological aspects of the virus. However, there are several aspects of EEEV’s transmission cycle that remain unclear. In the northeastern states, transmission is seasonal, peaking in the late summer months, while in Florida there is year-round transmission of EEEV. Recent phylogenetic studies have also suggested that Florida may serve as a reservoir for EEEV; the virus may periodically be introduced from Florida to the northeastern US where it locally amplifies, overwinters, and can remain stable for several years. How EEEV is able to migrate from Florida and how it persists during the winter in North America is not yet known, however several theories exist and are examined further by this research. The first part of this study investigates the hypothesis that snakes may serve as overwintering reservoir hosts for EEEV. Rates of exposure and infection of wild snakes were examined by testing serum samples from wild snakes at a focus of EEEV in Alabama. Two species of vipers, the cottonmouth and the copperhead, were found to be positive for EEEV RNA. The second part of the study attempts to identify the hosts and vectors of enzootic winter transmission of EEEV in Florida, with a focus on avian host preference. EEEV was detected in two mosquito species, Culiseta melanura and Anopheles quadrimaculatus, and were both from the month of February. In addition, the results also suggest that EEEV vectors preferentially feed upon wading birds during the winter months.”

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