Evaluation of comparative intradermal tuberculin and interferon gamma release tests for prediction of tuberculous lesion development in slaughtered cattle

Abstract

Bovine tuberculosis (BTB) is a chronic contagious disease of cattle which has economical, public health and veterinary importance worldwide. So far, test and slaughter is the most feasible method to control the disease but identification of lesions from slaughtered animals does not always coincide with ante-mortem test results. Fifty four animals which were found positive by comparative intradermal tuberculin test (CIDT) or INF-γ release assay or both were slaughtered and post mortem examination (PME) was conducted to identify tuberculous (TB) lesions. The animals were composed of four age groups (≤ 3; 4-6; 7-9 and ≥ 10 years) the two sexes and two breeds (Boran, Boran-Friesian cross). Out of all the slaughtered animals, lesions were detected from 70.3% (38/54) of them. No significant difference was observed among the four age groups and two sexes of both breeds of animals on the level of TB lesion detection. Higher proportion of the lesion was observed by mediastinal (40.4%) followed by bronchial (34.8%), retropharyngeal (17.9%) and lastly miliary form and mesenteric lymph nodes in equal proportion (3.3%). Among the CIDT positive animals, 59.2% of them had lesions. Similarly, 46.2% of INF-γ release assay positive animals had lesions during postmortem examination. Of the total CIDT (+) and INF-γ (-) animals, postmortem lesions were detected from 22.2% of them, and in the vice-versa, of the CIDT (-) and INF-γ (+) animals, 9.2% of them contain TB lesions. Using the PME as reference test, sensitivity of CIDT was 84.2% and the specificity was 6.2%. Similarly, the sensitivity and specificity of the INF-γ release assay was 65.7 and 37.5% respectively. It is concluded that, both tests predict the development of TB lesions. However, in our condition, CIDT was found more predictable for detection of TB lesions as compared to INF-γ release assay. Key words: Bovine tuberculosis (BTB), comparative intradermal tuberculin test (CIDT), interferon gamma (INF-γ) release, post mortem examination (PME), tuberculous (TB) lesion