COMPARISON OF THE SENSITIVITY OF THE CAUDAL FOLD SKIN-TEST AND A COMMERCIAL GAMMA-INTERFERON ASSAY FOR DIAGNOSIS OF BOVINE TUBERCULOSIS

A study to determine and compare the sensitivity of the caudal fold tu berculin test (CFT) and a commercial gamma-interferon (gamma-IFN) assa y for diagnosis of bovine tuberculosis was conducted. A dairy herd wit h approximately a third of the cattle infected with Mycobacterium bovi s was chosen for this study. AU cattle from this herd were slaughtered and tissue specimens for bacteriologic culturing and histologic exami nation were collected. Results of the CFT and gamma-IFN assay were com pared with results of bacteriologic culturing and histologic examinati on to determine test sensitivity. Results were analyzed, using each of the following 4 standards to classify cattle as infected: positive te st result by bacteriologic culturing only; histologic examination only ; bacteriologic culturing and histologic examination; and bacteriologi c culturing or histologic examination. Sensitivity of the CFT ranged f rom 80.4 to 84.4%, depending on the standard of comparison. Sensitivit y of the gamma-IFN assay ranged from 55.4 to 97.1%, depending on the s tandard of comparison and on the method of interpretation. The CFT was significantly (P < 0.001) more sensitive than the gamma-IFN assay for diagnosis of bovine tuberculosis when the gamma-IFN assay was conduct ed and interpreted as instructed by the manufacturer. Maximum overall sensitivity was achieved when results of the CFT and gamma-IFN assay w ere interpreted in parallel.