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

An attenuated Mycobacterium bovis RD1 deletion (Delta RD1) mutant of the Ravenel strain was constructed, characterized, and sequenced. This M. bovis Delta RD1 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 Delta RD1- 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 Delta RD1 or BCG prior to challenge correlated with reduced pathology and bacterial colonization. Neither Delta RD1 or BCG elicited IFN-gamma responses to rESAT-6:CFP-10 prior to challenge, an emerging tool for modern TB surveillance programs. The Delta RD1 strain may prove useful for bovine TB vaccine programs, particularly if additional mutations are included to improve safety and immunogenicity. Published by Elsevier Ltd.