Epizootiology of eastern equine encephalomyelitis virus in upstate New York, USA. VI. Antibody prevalence in wild birds during an interepizootic period.

Abstract

Wild birds in and near Toad Harbor Swamp, Oswego Co., New York, USA, were screened for antibodies to EEE virus during 1978–1980 by hemagglutination-inhibition (HI) tests. Netted birds were banded and released, allowing long-term surveillance of individuals through multiple sampling. A total of 4273 sera from 3639 birds was tested. Prevalence of HI antibodies in birds hatched prior to the year of capture (AHY) decreased annually from 34.4 to 9.8 to 5.2%. Prevalence in birds hatched during the year of capture (HY) was ca. 1.0% all 3 years, indicating little on-site virus circulation during the study. EEE prevalence rates in AHYs of breeding species were compared by sex, nest heights, bird size, bird taxa, and nesting habitats. Prevalence was lower in smaller birds, in the taxa Parulinae and Tyrannidae, and in birds breeding in open-field habitats. Based on antibody prevalence, the virus was widespread during the previous epizootics (1976–1977) and birds at all heights in all habitats near the swamp were exposed. Serial bleedings of individual birds yielded no on-site seroconversions. Birds recaptured in more than 1 year showed a significantly higher antibody prevalence than that of the general population. HI antibody titers in individual birds decreased with time, some to undetectable levels. It is believed that the virus is enzootic, overwintering on site or in locally breeding birds, and that the role of migrating birds in its annual reappearance is minimal.