Assessment of defined antigens for the diagnosis of bovine tuberculosis in skin test‐reactor cattle

Abstract

The continued use of purified protein derivative (PPD) tuberculin is considered to be the main factor which limits the specificity of diagnostic tests for bovine tuberculosis (TB). This study evaluated a whole blood interferon-gamma (IFN-gamma) assay and compared the diagnostic potential of PPD with two tuberculosis-specific antigens, ESAT-6 and MPB70. To provide estimates of sensitivity and specificity, responses were measured in 180 skin test-reacting cattle, of which 131 were confirmed as tuberculous, and in 128 cattle from TB-free herds. For the skin test reactors, there was a positive correlation between the IFN-gamma responses to PPD from Mycobacterium bovis (PPDB) and PPD from Mycobacterium avium (PPDA), indicating cross-reactivity between these complex antigens which are the basis of the skin test. In comparisons of the ESAT-6 IFN-gamma test with a PPD IFN-gamma test (using PPDB compared with PPDA), there was a decrease in sensitivity (76.3 per cent vs 89.3 per cent), but a clear increase in specificity (99.2 per cent vs 92.2 per cent). The provision of high specificity, even with lower sensitivity, offers major benefits for testing in areas with a low incidence of TB.

Assessment of diagnostic tools for eradication of bovine tuberculosis in cattle co-infected withMycobacterium bovisandM. aviumsubsp.paratuberculosis

“…In this case, this common population was also small (40.9%). Therefore, and in agreement with other authors [13,28,32,39,45], the detection of the maximum number of infected animals is achieved by the combination of both tests. Both tests were complementary also in the way that the IDTB test performed better during the first part of the trial, while the IFN-γ test was the only method that detected the infected animals at the second part of the study (it detected the M. bovis culture positive cattle that failed to react to the IDTB test).…”

“…Although it is difficult to compare the results obtained in the published field trials because of the use of different methodology (sampling time, different PPD and ELISA kit), source of cattle, and criteria of interpretation, the sensitivity values obtained in this study for both the IDTB and the IFN-γ tests have been only moderate, and in general terms, they were lower than those found in other reports [13,18,28,31,32,45]. This low performance is more obvious regarding the IFN-γ assay since it is generally accepted to have a higher sensitivity.…”

“…In most of them, the sensitivity of the IFN-γ test was higher compared to the tuberculin tests [13,18,24,28,32,44,45]. The specificity of the IFN-γ assay was 90.6 to 98.6% [3,20,44].…”

Identification of Mycobacterium bovis antigens by analysis of bovine T-cell responses after infection with a virulent strain

“…In an attempt to identify individual antigens in antigenic fractions using a combination of methods, we determined that these stimulant fractions consisted of 85B, TRB-B, MPB70, TPX, CFP10 and ESAT6. 85B (22), ESAT6 (6,23) and MPB70 (24)(25)(26) are well known T-cell-stimulating antigens, while the antigenicity of CFP10 has only recently been demonstrated (23,25,27). These results support the view that low molecular weight proteins such as ESAT6 (6) play an important role in bovine immune responses to M. bovis.…”

Bovine tuberculosis as a model for human tuberculosis: advantages over small animal models

“…Alternatively, they can become infected and clear the infection. In this case, animals turn skin test positive and/or their blood cells release IFNg upon stimulation with PPD, but they show no clinical signs of disease, no visible lesions are present when slaughtered, and M. bovis cultures are negative [17]. The question to which extent animals that are effectively infected can remain clinically latent for years, will be discussed below.…”