Complex Epidemiological Dynamics of Eastern Equine Encephalitis Virus in Florida.

Eastern equine encephalitis virus (EEEV) infection results in high mortality in infected horses and humans. Florida has been identified as an important source of EEEV epidemics to other states in the United States. In this study, we further characterized the epidemiological and evolutionary dynamics of EEEV in Florida. Epidemiological analysis of sentinel chicken seroconversion rates to EEEV infections during 2005-2016 suggested significant seasonality of EEEV activity in Florida. We observed significant annual activity of EEEV in the North and North Central regions, with little significant seasonality in the Panhandle region. Phylogenetic analysis of complete EEEV genome sequences from different host sources and regions in Florida during 1986-2014 revealed extensive genetic diversity and spatial dispersal of the virus within Florida and relatively more clustering of the viruses in the Panhandle region. We found no significant association between EEEV genetic variation and host source. Overall, our study revealed a complex epidemiological dynamic of EEEV within Florida, implicating the Panhandle region as a possible source of the virus with sustained year-round transmission. These findings will help in implementing targeted control measures that can have the most impact in reducing or eliminating EEEV and other mosquito-borne viral infections within Florida and in the rest of the United States.

Humoral response to an equine encephalitis vaccine in healthy alpacas.

OBJECTIVE: To determine humoral responses to an equine encephalitis vaccine in healthy alpacas. DESIGN: Clinical trial. ANIMALS: 39 healthy alpacas on 1 farm and 86 healthy alpacas on a second farm. PROCEDURES: All alpacas were given 3 doses IM of a bivalent, killed-virus equine encephalitis vaccine, with 4 weeks between doses. Eastern equine encephalitis (EEE) virus neutralizing antibody responses were determined with a plaque reduction neutralization assay every 14 days in alpacas on the first farm and 70 days after the first dose of vaccine on the second farm. RESULTS: For alpacas on the first farm, geometric mean virus neutralizing antibody titer peaked 2 weeks after the third vaccine dose was given (ie, day 70). At this time, 29 of 38 (76%) animals were seropositive for antibodies against EEE virus, and percentage of animals 6 years old that were seropositive (1/5). For alpacas on the second farm, 76 (88%) were seropositive on day 70, and percentage of animals 6 years old that were seropositive (27/33). For both farms, geometric mean titer on day 70 was significantly higher in animals < 2 years old than in animals > 6 years old. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that inoculation of alpacas with 3 doses of a bivalent, killed-virus equine encephalitis vaccine induced a humoral antibody response against EEE virus.