Detection of Bovine Tuberculosis in Herds with Different Disease Prevalence and Influence of Paratuberculosis Infection on PPDB and ESAT-6/CFP10 Specificity

Bovine tuberculosis (BTB) is a major animal health problem with zoonotic implications. Current control programs are based on test and slaughter strategies utilizing skin tests with tuberculins as antigens. The low specificity and associated operative difficulties of these tests have driven the search for new antigens and diagnostic assays. In this multicenter study, using herds from Argentina, Mexico and Northern Ireland, we selected skin test positive and negative animals from herds with different prevalence's of BTB and compared tuberculin (PPDB) and ESAT-6+CFP10 as antigens ex vivo. In low prevalence herds, crossreactivity of PPDB was apparent since up to 60% of the PPDB skin test and ex vivo positive animals did not responded to ESAT-6+CFP10 ex vivo. The superior specificity of ESAT-6+CFP10 was confirmed in a Mycobacterium avium sp. paratuberculosis infected herd where several of the animals had strong crossreactivity to PPDB and PPDA but not to ESAT-6+CFP10. In high prevalence herds 85% of the skin test-positive animals, were confirmed ex vivo using either PPDB or ESAT-6+CFP10 as antigen. However, within this group 60% of the skin test negative animals were PPDB and ESAT-6+CFP10 positive ex vivo indicating that the skin test can in some herds yield a significant number of false negative results. In conclusion, the ex vivo test is recommended as an ancillary test to accelerate BTB eradication. In high prevalence herds, PPDB or ESAT-6+CFP10 can be used as antigen whereas in low and medium prevalence herds ESAT-6+CFP10 is the preferred choice.