The interferon-gamma (IFN-gamma) assay is employed as a complementary diagnostic test for bovine tuberculosis (BTB) in many countries. To simplify this assay, we established a 96-well plate format using the ESAT-6 and CFP-10 antigens and then employed it to determine the extent of Mycobacterium (M.) bovis infection in dairy herds with a history of BTB outbreaks in a country where only selective culling is practiced. The sensitivity and specificity of this IFN-gamma assay were 85.9% and 100%, respectively, based on comparison with the conventional single intradermal tuberculin test (SIDT). The IFN-gamma assay was also positive in 30.4% and 36.8% of SIDT-negative animals from herds with recent and remote BTB outbreaks, respectively. Of 14 SIDT-negative, IFN-gamma positive cattle, five (35.7%) were culture positive and an additional six were positive based on a polymerase chain reaction-based test for M. bovis. Therefore, the IFN-gamma assay has the potential to serve as a specific and sensitive test for M. bovis infection in dairy cattle. Further, the results indicated that a substantial portion of SIDT-negative animals in herds with previous BTB outbreaks were actually infected with M. bovis. Accordingly, the present selective-culling strategy may require modifications to include this more sensitive assay.
Animals ; Antigens, Bacterial/*diagnostic use ; Bacterial Proteins/diagnostic use ; Cattle ; Female ; Interferon-gamma Release Tests/*veterinary ; Mycobacterium bovis/*isolation & purification ; Polymerase Chain Reaction/veterinary ; Republic of Korea/epidemiology ; Tuberculosis, Bovine/*diagnosis/*epidemiology/microbiology