Interferon-gamma (IFN-γ) detection assay is being applied as an ancillary test to tuberculin tests in the diagnosis of bovine tuberculosis to detect the maximum number of infected animals. Among possible factors influencing the performance of tuberculosis-diagnostic tests, paratuberculosis, a widespread disease in Spain and other European countries, has been pointed out as a cause of false positive reactions. Still, its effect on the sensitivity of these tests in cattle has yet to be fully characterized. The impact of paratuberculosis in the apparent sensitivity of IFN-γ assay was studied in a bullfighting cattle herd with a mixed tuberculosis-paratuberculosis infection, using culture of Mycobacterium bovis and Mycobacterium avium paratuberculosis as the gold standard to determine the infection status of every animal. A total of 218 animals were slaughtered and sampled for bacteriology after blood sampling. IFN-γ assay showed a lower apparent sensitivity in animals with a mixed infection (50%) compared to all animals suffering tuberculosis (78.3%). This finding indicates that the presence of paratuberculosis in tuberculosis-infected herds could imply a serious impairment in the sensitivity of IFN-γ detection test.
Bibliographical noteFunding Information:
This research was funded by project AGL2006-06206 of the Spanish Ministry of Science and Technology, ParaTBTools (STREP 23106) of the European Union, and the Spanish Ministry of Agriculture, Food and Fisheries. J. Álvarez was the recipient of a predoctoral grant assigned by the Spanish Ministry of Education and Culture. The group is a partner of the coordination action “Veterinary European Network on Mycobacteria (VENoMYC)” funded by the European Union.