Eastern equine encephalitis (EEE) virus and West Nile (WN) virus are disease agents of humans, horses, and birds and are transmitted among birds by bird-feeding mosquitoes. Bird populations serve as a reservoir for these viruses, and outbreaks occur when virus is transmitted from birds to horses and humans by species of mosquitoes that feed on both mammals and birds. Although we understand much about these viral cycles, the mechanism by which the viruses survive winter and are reinitiated within the bird population each spring in temperate climates is unknown. This is the greatest gap in our knowledge about each virus and the missing link in our ability to develop effective strategies for early detection and prevention. Field studies of EEE virus in free-ranging songbirds provide evidence that the virus may survive the winter in birds. Birds infected during previous years may maintain chronic infections that relapse and provide a source of infection for newly emerged mosquitoes in the spring. Relapse of latent infections in birds is likely initiated by increased levels of hormones associated with breeding or stressful events such as migration. Laboratory studies are needed to verify this hypothesis. Using a migratory songbird, the gray catbird, we will conduct laboratory experiments to test the prediction that gray catbirds chronically infected with EEE and WN virus will undergo relapse when subjected to migratory conditions and hormonal change associated with breeding. This study will contribute to society at large by addressing a biological problem that directly affects human and animal health.
