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Surveillance of bovine tuberculosis (bTB) is partly based on the sanitary inspection of carcasses at the abattoir to detect bTB-like lesions which, in compliance with EU recommendations, are analysed by bacteriology and histopathology to disclose Mycobacterium bovis (or M. caprae) infection. Moreover, since 2012, a PCR method with similar sensitivity and specificity values of histopathology and bacteriology respectively is additionally employed in France, partially compensating for the weaknesses of classical diagnostic methods. We analysed a collection of bTB-like lesions from cattle presenting positive histological results albeit with negative PCR results. We present here the results of these samples, recovered from 292 animals culled between 2013 and 2016, analysed with a second line molecular diagnosis approach that consists in a combination of PCRs targeting the M. tuberculosis-M. avium complexes as well as the Mycobacterium genus and sequencing of hsp65 gene. These molecular analyses disclosed to identify the presence of non-tuberculous bacteria which could be responsible for most of these non-specific TB lesions: non tuberculous mycobacteria (24%) or Actinomycetales (56%) such as Rhodococcus equi (53%); 24% of the samples were negative. M. bovis -or any other MTBC members- was neither detected by molecular methods nor isolated in any of them at the end of the 3 months of culture. In conclusion, these results highlight the lack of specificity of histopathology and the usefulness of a first line PCR with a second line molecular diagnostic test to circumvent it. This diagnostic strategy makes it possible to reduce the number of suspect bTB cases raised at the abattoir or shortening their lock-up periods. By simplifying diagnostic schemes, the use of this tool could improve bTB surveillance and make eradication programs more efficient in the future. [ABSTRACT FROM AUTHOR]

Bacteriology and histopathology are the most commonly used tests used for official confirmatory diagnosis of bovine tuberculosis (bTB) in cattle in most countries. PCR is also being used increasingly because it allows a fast diagnosis. This test could be applied as a supplement to or replacement for current bTB confirmatory diagnostic tests but its characteristics have first to be evaluated. The aim of this study was to estimate and compare sensitivities and specificities of bacteriology, histopathology and PCR under French field conditions, in the absence of a gold standard using latent class analysis. The studied population consisted of 5,211 animals from which samples were subjected to bacteriology and PCR (LSI VetMAX™ Mycobacterium tuberculosis Complex PCR Kit, Life Technologies) as their herd of origin was either suspected or confirmed infected with bTB or because bTB-like lesions were detected during slaughterhouse inspection. Samples from 697 of these animals (all with bTB-like lesions) were subjected to histopathology. Bayesian models were developed, allowing for dependence between bacteriology and PCR, while assuming independence from histopathology. The sensitivity of PCR was higher than that of bacteriology (on average 87.7% [82.5–92.3%] versus 78.1% [72.9–82.8%]) while specificity of both tests was very good (on average 97.0% for PCR [94.3–99.0%] and 99.1% for bacteriology [97.1–100.0%]). Histopathology was at least as sensitive as PCR (on average 93.6% [89.9–96.9%]) but less specific than the two other tests (on average 83.3% [78.7–87.6%]). These results suggest that PCR has the potential to replace bacteriology to confirm bTB in samples submitted from suspect cattle. [ABSTRACT FROM AUTHOR]