A vaccinia-vectored rabies vaccine field trial: ante- and post-mortem biomarkers

During the field safety evaluation of a vaccinia-rabies glycoprotein recombinant virus vaccine for wildlife, two biomarkers were used to identify potential contact with vaccine-laden baits. Tetracycline, a commonly used and reliable calciphilic tissue marker, was included in a fish-meal polymer bait matrix and was evaluated from post-mortem bone samples. Additionally, an ante-mortem marker was needed to identify, for prospective study, raccoons which had contacted baits and thus, potentially, vaccine. Sulfadimethoxine (SDM) was included in an attractant slurry surrounding the bait, as a novel short-term seromarker. Preliminary laboratory studies in raccoons demonstrated SDM residues for up to one week following ingestion of a single 250 mg dose. During the first six days after bait distribution, 49 individual raccoons were live-trapped in the vaccination area. SDM was detectable in 38 of 49 (77.5%) serum samples. Similarly, 47 of 56 (83.9%) bone samples from raccoons collected in the vaccination area throughout the twelve-month study were tetracycline-positive. Conversely, none of the serum samples (n = 12) from the first six days of the trial nor any of the bone samples (n = 34) from raccoons in the surveillance area were biomarker-positive.