An experimental
beta-propiolactone (BPL)-inactivated rabies virus
vaccine was evaluated for the oral immunization of captive raccoons (Procyon lotor) and red foxes (Vulpes vulpes). None of 10 red foxes administered a single 1.0 ml dose of BPL-inactivated rabies virus
vaccine (PM strain; 100 or 500 micrograms
protein) per os developed detectable anti-rabies virus-
neutralizing antibodies (VNA) at any time over 8 wk of observation. Foxes were excluded from further study. In two different groups of five to six raccoons, each administered a single 1.0 ml dose of BPL-inactivated rabies virus
vaccine (ERA strain) per os, at concentrations of 100 or 400 micrograms
protein, only a single animal in each group demonstrated evidence of seroconversion within 4 wk. In contrast, instillation of a single dose (500 micrograms
protein) of BPL-inactivated rabies virus
vaccine (ERA strain), directly into the small intestine via fiberoptic
endoscope, or ERA
vaccine (800 micrograms
protein) instillation to the buccal cavity by needle-less syringe, resulted in the production of
rabies-specific VNA and protection against lethal
rabies infection in three of six, and in four of six raccoons, respectively; all seven control raccoons succumbed to street virus challenge. These preliminary challenge studies, while somewhat encouraging, demonstrate that considerable quantities of purified
viral antigen are required for even minimal oral efficacy against lethal
rabies infection. At the present time, therefore, potent, self-replicating, attenuated, or recombinant viruses offer the most versatile, economic, efficacious, and safe solutions to terrestrial
rabies control of free-ranging carnivores.