Intraduodenal vaccination of brushtail possums with bacille Calmette-Guerin enhances immune responses and protection against Mycobacterium bovis infection

SETTING: An effective oral bacille Calmette-Guerin (BCG) vaccine would have advantages for use in humans and as an oral bait vaccine for protecting wild-life against bovine tuberculosis. OBJECTIVE: To compare the level of protection against tuberculosis in intraduodenally BCG-vaccinated possums with those vaccinated intragastrically in order to determine whether degradation of BCG in the stomach lowers vaccine efficacy. DESIGN: Three groups of five possums were vaccinated with BCG by the intraduodenal, intragastric or subcutaneous routes, with a fourth group serving as unvaccinated controls. The animals were later challenged intratracheally with a low dose of virulent Mycobacterium bovis. RESULTS: Possums vaccinated intraduodenally with BCG had significantly greater lymphocyte blastogenic responses to bovine purified protein derivative (PPD) and lower lung bacterial counts in comparison with intragastrically vaccinated animals. In comparison with unvaccinated animals, all. of the BCG-vaccinated groups had significant protection against M. bovis infection as assessed by changes in body weight, lung weight and reduction in numbers of mycobacteria and granulomas in the spleen. CONCLUSION: The enhanced immune responses and protection against bovine tuberculosis observed in the intraduodenally BCG-vaccinated possums indicated that if BCG vaccine is protected from degradation in the stomach its efficacy should improve.