Detection of live M. bovis BCG in tissues and IFN-[gamma] responses in European badgers vaccinated by oropharyngeal instillation or directly in the ileum

Background Oral vaccination with Mycobacterium bovis Bacille of Calmette and Guerin (BCG) has provided protection against M. bovis to badgers both experimentally and in the field. There is also evidence suggesting that the persistence of live BCG within the host is important for maintaining protection against TB. Here we investigated the capacity of badger inductive mucosal sites to absorb and maintain live BCG. The targeted mucosae were the oropharyngeal cavity (tonsils and sublingual area) and the small intestine (ileum). Results We showed that significant quantities of live BCG persisted within badger in tissues of vaccinated badgers for at least 8 weeks following oral vaccination with only very mild pathological features and induced the circulation of IFN[gamma]-producing mononuclear cells. The uptake of live BCG by tonsils and drainage to retro-pharyngeal lymph nodes was repeatable in the animal group vaccinated by oropharyngeal instillation whereas those vaccinated directly in the ileum displayed a lower frequency of BCG detection in the enteric wall or draining mesenteric lymph nodes. No faecal excretion of live BCG was observed, including when BCG was delivered directly in the ileum. Conclusions The apparent local loss of BCG viability suggests an unfavorable gastro-enteric environment for BCG in badgers, which should be taken in consideration when developing an oral vaccine for use in this species. Keywords: BCG, Badger, Vaccine, Mucosa, Capsule, Tonsil, Lymphatic drainage