Avian serology in a St. Louis encephalitis epicenter before, during, and after a widespread epidemic in south Florida, USA

(B)lood and serum fr om 3.915 wild and domestic birds (2,590 resident, 139 migrant, and 1,186 captive), representing 56 species collected in central F lorida from 1989 through 1997, were analyzed for evidence of St. Louis ence phalitis (SLE) virus transmission. All sera were tested for SLE hemagglutin ation inhibition (HI) antibody. Selected sera and bloods were tested for SL E neutralizing (NT) antibody and virus. The reproductive success of residen t birds was highest from 1990-1992 and lowest from 1994-1997. Transmission of SLE to resident birds, especially mourning doves (Zenaida macroura). pea ked during the summer of 1990, a year during which a widespread SLE epidemi c was recorded in central Florida. The SLE antibody-positive resident birds ist appeared during September of the epidemic) ear. Some SLE, WI antibody- positive resident birds were captured throughout 1991, but only 5% were yea rlings, compared with 36% in 1990. By 1993, wild resident birds expressing HI and NT antibodies to SLE had nearly disappeared. None of the migrant bir ds tested were SLE-positive. Sentinel chickens maintained in Indian River C ounty during the epidemic year seroconverted to SLE starting in early July with peak seroconversion rates in August, September, and October. High (gre ater than or equal to 50%) SLE seroconversion rates in sentinel chickens pr eceded those in wild birds by 10 wk and preceded peak human SLE transmissio n by at least 8 wk. Major SLE epidemics in south Florida depend on abundant wild bird populations, especially during the amplification phase of the tr ansmission cycle. We propose that hard winter freezes along the temperate-s ubtropical climatic zone interface in central Florida. at;approximate to 27 degrees 30' North Latitude, opens foraging and nesting habitats for ground -feeding birds, resulting: in high reproductive success and an abundance of seronegative individuals that rapidly amplify the SLE later in the year.