Sentinel Chicken Seroconversions Track Tangential Transmission of West Nile Virus to Humans in the Greater Los Angeles Area of California

In Los Angeles, California, West Nile virus (WNV) has followed a pattern of emergence, amplification, subsidence, and resurgence. A time series cross-correlation analysis of human case counts and sentinel chicken seroconversions revealed temporal concordance indicating that chicken seroconversions tracked tangential transmission of WNV from the basic passeriform-Culex amplification cycle to humans rather than antecedent enzootic amplification. Sentinel seroconversions provided the location and time of transmission as opposed to human cases, which frequently were reported late and were assumed to be acquired 2-14 days before disease onset at their residence. Cox models revealed that warming degree-days were associated with the increased risk of seroconversion, whereas elevated herd immunity in peridomestic birds dampened seroconversion risk. Spatially, surveillance data collected within a 5 km radius of flock locations 15-28 days before the bleed date were most predictive of a seroconversion. In urban Los Angeles, sentinel chicken seroconversions could be used as an outcome measure in decision support for emergency intervention.