IMMUNE RESPONSE AND PROTECTION IN RACCOONS (PROCYON LOTOR) FOLLOWING CONSUMPTION OF BAITS CONTAINING ONRAB®, A HUMAN ADENOVIRUS RABIES GLYCOPROTEIN RECOMBINANT VACCINE

Abstract

We investigated the immune response and protection conferred in raccoons (Procyon lotor) following consumption of ONRAB(®) oral rabies vaccine baits. Forty-two wild-caught, captive raccoons were each offered an ONRAB vaccine bait; 21 controls received no vaccine baits. Blood samples collected from all raccoons before treatment, and each week posttreatment for 16 wk, were assessed for the presence of rabies virus antibody. In the bait group, an individual was considered to have responded to vaccination if serum samples from three or more consecutive weeks were antibody-positive. Using this criterion, 77% (20/26) of raccoons that consumed ONRAB baits with no observed vaccine spillage (full dose) demonstrated a humoral immune response. In the group that received a partial dose (0.05-0.90 mL vaccine recovered), 50% (8/16) of raccoons responded to vaccination. Regardless of the vaccine dose received, among the 28 raccoons that responded to vaccination 18 had antibody initially detectable at week 2 and 22 remained antibody-positive for at least 10 consecutive weeks. Kinetics of the humoral immune response suggest that the best time to conduct postbaiting surveillance for evidence of vaccination would be 6-13 wk following bait deployment, with the highest antibody prevalence expected between weeks 8-10. A sub-sample of 29 raccoons (20 ONRAB, 9 controls) was challenged with raccoon rabies virus variant 350 days posttreatment. Eight of nine controls (89%) developed rabies whereas 15/20 vaccinates (75%) survived. Survival following rabies challenge was significantly higher in raccoons presented ONRAB vaccine baits.