Protection against bovine tuberculosis induced by oral vaccination of cattle with Mycobacterium bovis BCG is not enhanced by co-administration of mycobacterial protein vaccines

Abstract

Mycobacterium bovis bacille Calmette-Guérin (BCG) delivered to calves by the oral route in a formulated lipid matrix has been previously shown to induce protection against bovine tuberculosis. A study was conducted in cattle to determine if a combination of a low dose of oral BCG and a protein vaccine could induce protective immunity to tuberculosis while not sensitising animals to tuberculin. Groups of calves (10 per group) were vaccinated by administering 2 × 10 7 colony forming units (CFU) of BCG orally or a combination of 2 × 10 7 CFU oral BCG and a protein vaccine comprised of M. bovis culture filtrate proteins (CFP) formulated with the adjuvants Chitin and Gel 01 and delivered by the intranasal route, or CFP formulated with Emulsigen and the TLR2 agonist Pam 3CSK 4 and administered by the subcutaneous (s.c.) route. Two further groups were vaccinated with the CFP/Chitin/Gel 01 or CFP/Emulsigen/Pam 3CSK 4 vaccines alone. Positive control groups were given 10 8 CFU oral BCG or 10 6 CFU s.c. BCG while a negative control group was non-vaccinated. All animals were challenged with M. bovis 15 weeks after vaccination and euthanized and necropsied at 16 weeks following challenge. Groups of cattle vaccinated with s.c. BCG, 10 8 CFU or 2 × 10 7 CFU oral BCG showed significant reductions in seven, three and four pathological or microbiological disease parameters, respectively, compared to the results for the non-vaccinated group. There was no evidence of protection in calves vaccinated with the combination of oral BCG and CFP/Emulsigen/Pam 3CSK 4 or oral BCG and CFP/Chitin/Gel 01 or vaccinated with the protein vaccines alone. Positive responses in the comparative cervical skin test at 12 weeks after vaccination were only observed in animals vaccinated with s.c. BCG, 10 8 CFU oral BCG or a combination of 2 × 10 7 CFU oral BCG and CFP/Chitin/Gel 01. In conclusion, co-administration of a protein vaccine, administered by either systemic or mucosal routes with oral BCG did not enhance the protection conferred by administration of oral BCG alone.