Immune Responsiveness Induced by Administration of Heat-Inactivated M. bovis and BCG Prior to Experimental Infection in African Buffalo.

African buffalo (Syncerus caffer) are the primary wildlife reservoir for bovine tuberculosis (BTB) in Africa. Infected buffalo populations spread BTB to numerous species in conservation areas as well as to cattle at park boundaries. Quarantine requirements for BTB complicate wild animal metapopulation management. Considerable interest has arisen in the vaccination of cattle and indigenous wildlife species against BTB as an additional control strategy. This pilot trial aimed to evaluate cell-mediated and humoral immune responses in African buffalo immunised against BTB. Twenty-one sub-adult African buffalo were divided into four treatment groups, and received either Bacillus Calmette-Guérin (BCG; 106 CFU) intra-muscularly, a heat-inactivated Mycobacterium bovis vaccine intra-muscularly (HIMB-IM; 107 CFUs; followed by a boost after 4 months) or orally (HIMB-O; 107-108 CFU), or 1 mL phosphate-buffered saline (PBS) intra-muscularly (control group). 7 months after immunisation, all animals were intratracheally challenged with M. bovis (2 × 105 CFU). Monthly Bovigam interferon-gamma (IFNγ) assays and M. bovis-specific ELISAs were conducted and in addition, comparative intra-dermal tuberculin testings (CITTs) were performed at study start and termination 5 months after experimental infection. Over the study period, each treatment group showed distinct cell-mediated responses which differed in strength and temporal dynamics. In the post-immunisation stage, HIMB-IM animals produced a strong increase in bovine-avian purified protein derivative (PPD) IFNγ release after booster immunisation while HIMB-O and BCG groups showed relatively fewer numbers of positive responses. The experimental infection triggered significant elevations in bovine-avian PPD IFNγ release in all treatment groups. All animals were converted to bovine reactors. Both HIMB groups showed stronger IFNγ responses compared to the BCG and control groups in the early post-infection period, suggesting superior immune priming. Antibody responses showed marked individual variation, episodic interference from non-tuberculous mycobacterial (NTM) species and low test sensitivity and specificity.