Partial protection against oral challenge with Mycobacterium bovis in ferrets (Mustela furo) following oral vaccination with BCG

SETTING: Ferrets (Mustela furo) are important wildlife vectors of bovine tuberculosis (TB) in New Zealand. Protective vaccination of ferrets may limit the potential of transmission to livestock.OBJECTIVE: To determine whether orally-delivered Mycobacterium bovis BCG can confer protection against oral challenge with virulent M. bovis.DESIGN: Ten ferrets were vaccinated by feeding measured doses of live BCG, and subsequently challenged with virulent M. bovis via the oral route. Ten non-vaccinated (control) ferrets were similarly challenged. Live body weights and lymphocyte reactivity were monitored longitudinally, and ferrets were killed 20 weeks following challenge. Necropsy, histological examination and bacterial culture of alimentary tract lymphatic tissues were undertaken.RESULTS: There was a significant reduction in the incidence of gross tuberculous lesions among vaccinated ferrets compared to control animals, and fewer vaccinated ferrets had histologically-detectable acid-fast organisms in mesenteric lymph node (LN) tissues. There were significantly fewer vaccinated ferrets with culture-positive retropharyngeal LNs, and the mean bacterial burden was significantly lower for retropharyngeal LNs isolated from vaccinated animals than from controls.CONCLUSION: These results demonstrate that oral BCG vaccination of ferrets can confer partial protection against M. bovis, and suggest that systemic immune responses may be less important in mediating this degree of protection than local immunity.