Evaluation of the agreement between comparative intra-dermal tuberculin and gamma interferon tests for the diagnosis of bovine tuberculosis in Ethiopia

The control of bovine tuberculosis is difficult in developing countries because of the high cost of a sustainable testing programs and the lack of a diagnostic assays with high sensitivity and specificity to detect animals at all stages of infection. A cross-sectional study was conducted to evaluate the test agreement between comparative intra-dermal tuberculin test (CIDT) and interferon gamma (INF-y) tests for the diagnosis of bovine tuberculosis (BTB) at Holeta, Ethiopia from December, 2012 to May, 2013. In this study, a total of 114 cattles were tested both by CIDT and INF-y tests. The agreement between INF-y (PPDB-PPDA) and CIDT tests was fair (k=0.288). On the other hand, a moderate agreement (k=0.44) was observed between INF-y test (PPDB-PPDA) and INF-y test (ESAT6/CFP10-Nil). The difference between reaction sizes at the bovine PPD injection site and the avian PPD injection site was significant (t test; P0.05) in INF-y response to bovine PPD and avian PPD. INF-y response was stronger for ESAT6-CFP10 protein cocktails compared to PPD (B-A). Logistic regression analysis showed a significant association of animal age group with the responses of CIDT and INFy tests. In conclusion, the fair agreement between the CIDT and INF-y tests could indicate that the two tests are not completely overlapping and thus in addition to detecting a similar stage of the disease they also detect the different stages of the disease. Hence, it is advisable to use the two tests in combination.