Influence of oral rabies vaccine bait density on rabies seroprevalence in wild raccoons

The effect of different oral rabies vaccine (ORV) bait densities (75, 150, and 300 baits/km2) on the seroprevalence of rabies virus neutralizing antibodies (RVNAs) in raccoons (Procyon lotor) was assessed at a 15% seroprevalence difference threshold in rural areas of northeast Ohio. Results (n = 588 raccoons) indicated that seropositivity for RVNAs was associated with both bait density and bait campaign frequency. Associations were not detected for raccoon gender, age, or macro-habitat. The odds of being seropositive were greater for raccoons originating from 300 bait/km2 treatment areas relative to those coming from the 75 bait/km2 areas (odds ratio [OR] = 4.4, probability [P] < 0.001, 95% confidence interval [CI] = 2.4-7.9), while accounting for cumulative ORV campaigns. No statistical advantage in seroprevalence was detected when comparing 150-75 baits/km2. These results indicate that a relatively extreme bait density when evenly distributed may be necessary to obtain a significant increase in seroprevalence. Higher bait densities may be more appropriate and less costly to address focused outbreaks than labor intensive trap-vaccinate-release and local population reduction campaigns. Finally, dramatic increases in seroprevalence of RVNA were not observed in raccoons between sequential, semi-annual campaigns, yet cumulative ORV campaigns were associated with gradual increases in seroprevalence.