Efficacy and immunogenicity of Mycobacterium bovis ΔRD1 against aerosol M. bovis infection in neonatal calves

An attenuated Mycobacterium bovisRD1 deletion (ΔRD1) mutant of the Ravenel strain was constructed, characterized, and sequenced. This M. bovis ΔRD1 vaccine strain administered to calves at 2 weeks of age provided similar efficacy as M. bovis bacillus Calmette Guerin (BCG) against low dose, aerosol challenge with virulent M. bovis at 3.5 months of age. Approximately 4.5 months after challenge, both ΔRD1- and BCG-vaccinates had reduced tuberculosis (TB)-associated pathology in lungs and lung-associated lymph nodes and M. bovis colonization of tracheobronchial lymph nodes as compared to non-vaccinates. Mean central memory responses elicited by either ΔRD1 or BCG prior to challenge correlated with reduced pathology and bacterial colonization. Neither ΔRD1 or BCG elicited IFN-γ responses to rESAT-6:CFP-10 prior to challenge, an emerging tool for modern TB surveillance programs. The ΔRD1 strain may prove useful for bovine TB vaccine programs, particularly if additional mutations are included to improve safety and immunogenicity.