Evaluation of an oral vaccination program to control raccoon rabies in a suburbanized landscape

Abstract

We evaluated the efficacy of an oral rabies vaccination (ORV) program conducted in Erie County, New York, from July through September, 2002–2005. Ingress of the raccoon (Procyon lotor) rabies variant first occurred along the southern border of Erie County, New York, during 1992 and began to spread northward at a velocity of 31 km/year. Fixed-wing aircraft dropped ORV baits in rural landscapes; helicopters, hand baiting, and bait stations distributed baits in suburban landscapes ( bait densities ranged 59–118 baits/km2). Our study objectives were to quantify rabies case densities, evaluate efficacy of intervention efforts, and determine biological, census, geographical, and weather variables potentially affecting oralrabies vaccination of raccoons in Erie County. Overall, 16% and 9% of the raccoons in Erie County tested positive for virus-neutralizing antibodies (VNA) at the 0.125 and 0.5 international units (IU)/ml levels, respectively. We found no differences between baiting strategies and frequencies of antibody-positive raccoons. However, adult males generally consumed baits most often, and the probability of seropositivity increased with raccoon age. Seroprevalence of VNA differed among raccoon sex and age classes, and vaccination year. A post-hoc kernel density estimation of rabies-positive raccoons and skunks (Mephitis mephitis) from 1992– 2006 (n = 364) revealed clustering in northeastern Erie County. Our results should help ORV managers maximize limited resources.