Mycobacteria that interfere with the diagnosis of tuberculosis

13 March 2023

The occurrence of animals in which tuberculosis infection is not confirmed by means of laboratory techniques, but which react non-specifically to tuberculins, represents a still unresolved problem. This leads to the slaughter of animals that are not really infected (false positives) and the application of restrictive measures on the farm of origin. These reactions can be due, among other things, to a previous exposure of the animals to non-tuberculous mycobacteria (NTM) or, although currently not allowed in cattle, to the use of vaccines against tuberculosis or paratuberculosis. For this reason, one of the goals we pursue at INNOTUB is to identify non-tuberculous microorganisms capable of causing cross-reactions in diagnostic tests and to characterize the degree of interference, which will allow the development of new diagnostic techniques or criteria.

In this way, we have been able to demonstrate in guinea pigs that most of the MNTs studied can induce cross-reactions with bovine tuberculin and with the P22 reagent, that the comparative interpretation (also using avian tuberculin) would solve the problem in some cases and that the degree of interference may depend on the dose of MNT to which the animals are exposed. As a positive finding of the study, it should be noted that only animals exposed to Mycobacterium bovis and Mycobacterium caprae (the main causes of animal tuberculosis) reacted to PCL and FP reagents, so they could supplement bovine tuberculin or replace the in the future. In this way, the specificity of the diagnostic test would be improved, avoiding the appearance of false positives but without losing the ability to identify truly infected animals (sensitivity).

This study, led by NEIKER, has been funded by the projects: INNOTUB (EFA359/19/INNOTUB, FEDER co-funded) and GoatTBfree (PID2019-105155RB-C33), and  has been published in the journal Scientific Reports and is freely accessible at the following link.

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