Prevalence of exposure to eastern equine encephalomyelitis virus in domestic and feral swine in Georgia.

Abstract

Eastern equine encephalomyelitis (EEE) is endemic in the eastern United States. The number of cases during the summer of 1991 reached epizootic proportions in horses, and 2 human cases were diagnosed in Georgia (Fig. 1). In addition, 2 outbreaks of EEE virus infection were diagnosed in swine and confirmed by isolation of EEE virus at the Veterinary Diagnostic and Investigational Laboratory (VDIL) in Tifton, Georgia. Eastern equine encephalomyelitis virus infection in pigs has been described in Georgia, and antibodies to EEE virus in swine have been reported from other states in the USA. The clinical disease in swine probably is underdiagnosed in swine-producing areas with high incidence of EEE in horses or other species because cell lines routinely used to isolate virus from porcine tissues do not readily propagate EEE virus. Financial losses to swine producers due to EEE have not been estimated but were substantial in cases reported in Georgia and in 1994 in Florida. In the Florida outbreak, a 16-year-old farm worker also had clinical signs consistent with EEE virus infection. The objective of this study was to determine prevalence of exposure to EEE virus in selected populations of domestic swine in Georgia and in feral swine on Ossabaw Island, a barrier island in the Atlantic Ocean off the Georgia coast. Serum samples from domestic swine received in accessions for pseudorabies and brucellosis testing at the VDIL from June to September 1991 and from April to July 1992 were analyzed for neutralizing antibodies to EEE virus. An accession is defined as a collection of specimens from 1 locale (farm or stockyard) on 1 date. Accessions were selected nonrandomly for testing to reflect close spatial (same or neighboring county) and temporal (within 1 week) proximity to clinical EEE cases in all species (Fig. 1, 2). A total of 1,247 specimens in 65 accessions were tested: 46 accessions with 1,064 specimens were from 45 farms, 16 accessions with 151 specimens were from 6 stockyards/salesbarns, and 3 acces-