Effects of positive results for Mycobacterium avium subsp paratuberculosis as determined by microbial culture of feces or antibody ELISA on results of caudal fold tuberculin test and interferon-γ assay for tuberculosis in cattle

Objective-To determine whether cattle testing positive for Mycobacterium avium subsp paratuberculosis as determined by microbial culture of feces or antibody ELISA were more likely to have false-positive responses on the caudal fold tuberculin (CFT) test or interferon-gamma (IFN-gamma) assay for Mycobacterium bovis than cattle testing negative for M paratuberculosis. Animals-1,043 cattle from 10 herds in Michigan. Procedure-Feces and blood samples for plasma were collected from cattle less than or equal to 24 months old on the day the CIFT test was read. Fecal samples were submitted for microbial culture for M Para tuberculosis. Plasma samples were tested for antibody against M paratuberculosis, and IFN-gamma after stimulation with purified protein derivative tuberculin from M bovis or M avium. Results-Of 1,043 cattle, 180 (173%) had positive CFT test results (suspects) and 8 (0.8%) had positive IFN-gamma assay results after stimulation with purified protein derivative tuberculin from M bovis. Forty-five (4.3%) and 115 (11.0%) cattle tested positive for M paratuberculosis as determined by microbial culture of feces and antibody ELISA, respectively. Cattle with positive responses for M paratuberculosis appeared to have an increased likelihood of false-positive results on the CFT test, although this association was not significant. Conclusions and Clinical Relevance-No significant association was detected among cattle testing positive for M paratuberculosis as determined by microbial culture of feces and antibody ELISA and positive CFT test and IFN-gamma assay results for M bovis.