Comparative assessment of fluorescence polarization and tuberculin skin testing for the diagnosis of bovine tuberculosis in Chadian cattle

Effective surveillance of bovine tuberculosis (BTB) in developing countries where reliable data on disease prevalence is scarce or absent is a precondition for considering potential control options. We conducted a slaughterhouse survey to assess for the first time the burden of BTB in Southern Chad. Altogether, 954 slaughter animals were consecutively sampled and tested using the single intra-dermal comparative cervical tuberculin (SICCT) test, a recently developed fluorescence polarization assay (FPA) and routine abattoir meat inspection after slaughter. Gross visible lesions were detected in 11.3% (CI: 9.4–13.5%) of the animals examined and they were mostly located in the lymph nodes and the lung. Significantly more Mbororo zebus (15.0%) were affected by lesions than Arab zebus (9.9%; OR = 2.20, CI: 1.41–3.41%; p < 0.001). Of all animals tested, 7.7% (CI: 6.2–9.6%) reacted positively to SICCT if OIE guidelines were applied. However, receiver operating characteristic (ROC) analysis using Mycobacterium tuberculosis complex (MTBC) infected animals as the positive population and lesion negative animals as the negative population, revealed a better SICCT performance if the cut-off value was decreased to >2 mm. SICCT reactor prevalence rose to 15.5% (CI: 13.3–18.0%) and FPA did not perform better than SICCT, when this setting adapted cut-off was applied.