Differentiation between Mycobacterium bovis BCG-vaccinated and M-bovis-infected cattle by using recombinant mycobacterial antigens

Tuberculosis continues to be a worldwide problem for both humans and animal s, The development of tests to differentiate between infection with Mycobac terium tuberculosis or Mycobacterium bovis and vaccination with M, bovis BC G could greatly assist in the diagnosis of early infection as well as enhan ce the use of tuberculosis vaccines on a wider scale. Recombinant forms of four major secreted proteins of M. bovis-MPB59, MPB64, MPB70, and ESAT-6-we re tested in a whole-blood gamma interferon (IFN-gamma) assay for different iation between cattle vaccinated with BCG and those experimentally infected with M, bovis, BCG vaccination induced minimal protection in the present s tudy, with similar numbers of animals infected with M. bovis in BCG-vaccina ted and nonvaccinated groups. Following vaccination with BCG, the animals p roduced moderate LFN-gamma responses to bovine purified protein derivative (PPDB) but very weak responses to the recombinant antigens, Cattle from bot h the BCG-vaccinated and nonvaccinated groups which were M. bovis culture p ositive following challenge produced IFN-gamma responses to PPDB and ESAT-6 which were significantly stronger than those observed in the corresponding M, bovis culture-negative animals. IFN-gamma responses to MPB59, MPB64, an d MPB70 were significantly weaker, and these antigens could not discriminat e between vaccinated animals which develop disease and the culture-negative animals. The results of the study indicate that of the four antigens teste d in the IFN-gamma assay, only ESAT-6 would be suitable for differentiating BCG-vaccinated animals from those infected with bovine tuberculosis.