Mucosal adjuvants to improve wildlife rabies vaccination

RABORAL V-RG(®)a is a recombinant vaccine used in oral rabies vaccination (ORV) programs for wildlife in the United States. Vaccination rates for raccoons are substantially lower than vaccination rates for gray foxes and coyotes. Research suggests that the low viscosity of the oral vaccine may preclude animals from receiving an effective dose when biting into the vaccine bait delivery system. We evaluated the possibility of using two benign compounds, chitosan and N,N,N-trimethylated chitosan (TMC), to increase the viscosity of the vaccine and potentially act as adjuvants to improve the immune response in raccoons (Procyon lotor). Forty mildly sedated raccoons were orally vaccinated via needleless syringe with either RABORAL V-RG (n = 12), chitosan+RABORAL V-RG (n = 12), TMC+ RABORAL V-RG (n = 12), or no vaccine (n = 4), on day 0 and again on day 90. We collected sera every 2-4 wk for 4 mo and evaluated rabies virus-neutralizing antibodies (rVNA). Raccoons were considered responders if rVNA titers were ≥ 0.1 IU/mL. Eleven of 12 raccoons vaccinated with TMC+RABORAL V-RG responded after one dose of vaccine, as did eight of 12 vaccinated with RABORAL V-RG, and three of 12 vaccinated with chitosan+ RABORAL V-RG. Our results suggest that the inclusion of an adjuvant, such as TMC, could increase vaccine efficacy to aid in controlling rabies virus spread in wildlife reservoirs.