Rapid clearance of SAG-2 rabies virus from dogs after oral vaccination

This study investigated the safety, efficacy, and clearance of SAG-2, an attentuated rabies virus, after oral vaccination in dogs. Nineteen dogs consumed baits containing lyophilized vaccine, but residual SAG-2 virus was recovered in only one of 57 oral swabs, collected one hour post-vaccination. Seven vaccinates were euthanized between 24 and 96 h after consuming a bait. Rabies virus RNA was detected in tonsils from all seven dogs by nested RT-PCR, with primers to the viral glycoprotein. Genomic, sense-transcripts, and m-RNAs were detected in five of seven tonsil samples using primers to the rabies virus nucleoprotein gene, as well as in four of seven samples from the buccal mucosa and one of seven from the tongue. Rabies virus antigen was detected in all tonsils by an immunohistochemistry test, confirming the RT-PCR results. In addition, virus was isolated from one tonsil sample collected at 96 h, providing supportive evidence of viral replication. Ten of 12 (83%) of the vaccinated dogs demonstrated an anamnestic response, with viral neutralizing antibody titers (> or =0.5 IU/ml), after rabies virus challenge. These ten dogs survived, whereas all control dogs succumbed to rabies. Attenuated rabies viruses, such as SAG-2, replicate in local tissues of the oral cavity and can be cleared relatively quickly, without viral excretion, leading to protective immunity against the disease.