Abstract
Germany has been officially free of bovine tuberculosis since 1996. However, in the last years there has been an increase of bovine tuberculosis cases, particularly in the southern part of Germany, in the Allgäu region. As a consequence a one-time tuberculosis surveillance program was revisited with different premortal and postmortal tests. The aim of this paper was to estimate diagnostic sensitivities and specificities of the different tests used within this surveillance program. In the absence of a perfect test with 100% sensitivity and 100% specificity, thus in the absence of a gold standard, a Bayesian latent class approach with two different datasets was performed. The first dataset included 389 animals, tested with single intra-dermal comparative cervical tuberculin (SICCT) test, PCR and pathology; the second dataset contained 175 animals, tested with single intra-dermal cervical tuberculin (SICT) test, Bovigam® assay, pathology and culture. Two-way conditional dependencies were considered within the models. Additionally, inter-laboratory agreement (five officially approved laboratories) of the Bovigam® assay was assessed with Cohen's kappa test (21 blood samples). The results are given in posterior means and 95% credibility intervals. The specificities of the SICT test, SICCT test, PCR and pathology ranged between 75.8% [68.8–82.2%] and 99.0% [96.8–100%]. The Bovigam® assay stood out with a very low specificity (6.9% [3.6–11.1%]), though it had the highest sensitivity (95.7% [91.3–99.2%]). The sensitivities of the SICCT test, PCR, SICT test, pathology and culture varied from 57.8% [48.0–67.6%] to 88.9% [65.5–99.7%]. The prevalences were 19.8% [14.6–26.5%] (three-test dataset) and 7.7% [4.2–12.3%] (four-test dataset). Among all pairwise comparisons the highest agreement was 0.62 [0.15–1]). In conclusion, the specificity of the Bovigam® assay and the inter-laboratory agreement were lower than expected.
Highlights
Bovine tuberculosis which is caused by Mycobacterium caprae and Mycobacterium bovis is an important public and animal health problem and an international trade issue in Europe and worldwide [1,2,3,4,5,6]
Regarding the Bovigam1 assay agreement between blood samples tested by five different laboratories and between blood samples taken from two different anatomical locations was assessed with Cohen’s kappa coefficient
There was no evidence, based on DIC and visual inspection of covariance histograms that including any covariance term led to a better model fit (S3 Table and S1 Fig)
Summary
Bovine tuberculosis (bTB) which is caused by Mycobacterium caprae and Mycobacterium bovis is an important public and animal health problem and an international trade issue in Europe and worldwide [1,2,3,4,5,6]. Infected animals are detected with tuberculin skin tests or the Bovigam gamma-interferon (IFN-γ) assay. The Bovigam assay is supposed to have the ability to detect bTB earlier in the course of infection [11, 12]. In many countries it is used for serial or parallel testing together with the intradermal skin tests [7, 13]. For post-mortem diagnosis of previously positive-tested animals, bacteriological culture and PCR can be used following necropsy [1, 14, 15]
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