EVALUATION OF ORAL RABIES VACCINATION: PROTECTION AGAINST RABIES IN WILD CAUGHT RACCOONS ( PROCYON LOTOR)

Area of Science:

• Veterinary immunology
• Wildlife disease ecology
• Zoonotic disease control

Background:

• Oral rabies vaccination (ORV) is crucial for controlling wildlife rabies, especially at epizootic fronts.
• Evaluating the efficacy of ORV programs in free-ranging raccoons (Procyon lotor) in the US is ongoing.
• Understanding antibody levels and their correlation with protection is key to assessing ORV program success.

Purpose of the Study:

• To evaluate rabies protection in raccoons with varying pre-existing neutralizing antibody levels after ORV.
• To determine the correlation between antibody titers at different time points and survival rates post-rabies virus challenge.
• To assess the validity of using lower antibody titer cutoffs for measuring immunization coverage in ORV management zones.

Main Methods:

• 37 free-ranging raccoons from ORV-baited areas in Pennsylvania were live-trapped and transferred to captivity.
• Raccoons were held for 86-199 days before rabies virus challenge.
• Antibody titers were measured at capture and challenge; survival rates were analyzed based on titer levels and timing relative to vaccination.

Main Results:

• At capture, 24% of raccoons were seronegative, while 76% had detectable antibody titers.
• At challenge, 68% of raccoons were seronegative, with an overall survival rate of 46%.
• Survivorship was 24% for seronegative animals, but 100% for low positive, 83% for medium positive, and 100% for high positive animals at challenge.

Conclusions:

• High-titer seroconversion post-vaccination is a strong indicator of rabies survival.
• Any detectable antibody titer at challenge (>3 months post-vaccination) appears to be a reliable surrogate for survival.
• Lower titer cutoffs may be a valid approach for estimating herd immunity in ORV management zones, balancing sensitivity and specificity.