Transmissibility study of two vaccine candidates against bovine tuberculosis

Aims & Objective: We studied the transmissibility in mice of two candidate vaccine M. bovis strains, M. bovis Δmce2 and M. bovis Δmce2ΔphoP, attenuated by gene knock out. The parental strain M. bovis UK (NCTC10772) and a M. bovis wild boar isolate (Mb04-303) were inoculated as controls. Methods: Groups of animals including 3 non-inoculated + 3 subcutaneously inoculated with every strain (1.10 5 CFU) were placed in the same cage (in duplicate). Necropsy was performed at 60 and 90 days post inoculation (dpi) in search of visible tuberculosis lesions (VTL) in lungs and spleens. Organs were analyzed to determine the bacterial load. Results: None of the animals presented VTL and no M. bovis was detectable in the non-inoculated group at 60 and 90 dpi. M. bovis was isolated from spleen of all the inoculated mice and from lungs of mice inoculated with control strains. The candidate vaccines were not isolated from lungs. Conclusions: This study shows the absence of transmissibility up to 90 days. Recovery of viable control strains from lungs and spleen suggests that the administration route would not alter the capacity of virulent strains to colonize organs. Contrasting, the candidate vaccines were only isolated from spleen. Longer periods should be assayed to evaluate transmissibility of these strains in mice.