Response of house finches to infection with sympatric and allopatric strains of western equine encephalomyelitis and St. Louis encephalitis viruses from California

Adult house finches from Kern County were inoculated subcutaneously with re cent sympatric and allopatric isolates of western equine encephalomyelitis and St. Louis encephalitis (SLE) viruses made from Culex tarsalis Coquillet t collected in Kern County and Coachella Valley, CA, respectively. Virulenc e, as measured by the amplitude of the viremia response during days 1 and 2 postinfection, varied significantly among strains, but independently of ge ographic origin. The intensity of the immune response, as measured by an en zyme immunoassay and a plaque reduction neutralization test, seemed to be i ndependent of virulence, especially for SLE where some strains failed to pr oduce a detectable viremia but elicited a strong antibody response. Our pre liminary data indicated that strain Virulence may be associated with the le vel of enzootic activity during the year of isolation.