A comprehensive study of mycobacterial infections in reactor-positive bovines across different regions of Iran

Although several studies have investigated the prevalence of Mycobacterium bovis in Iran, limited information exists on the concurrent presence of M. bovis and nontuberculous mycobacteria (NTM) species in tuberculin-positive cattle. Accurate identification of mycobacterial species in specific geographic regions is crucial, especially in countries like Iran, where food security and livestock-dependent economies are vital. The often-overlooked contribution of NTM species to false-positive tuberculin skin test (TST) results highlights the need for improved diagnostic approaches. In this study, 237 reactor-positive cattle were selected from a screened population of 3,000 animals across 10 provinces. Tissue samples from lymph nodes and lungs were examined using Ziehl–Neelsen staining, culture on Löwenstein–Jensen medium, and PCR assays targeting IS6110 , hsp65 , rpoB , and ITS regions. M. bovis was confirmed in 90 cases (38.0%), while NTM species, including M. fortuitum , M. porcinum , and M. avium , were identified in 35 cases (14.7%). Statistical analysis revealed significant associations between M. bovis infection and variables such as farm type, husbandry system, animal age, and production purpose. These findings underscore the necessity of molecular confirmation in reactor-positive cattle to prevent diagnostic misclassification, minimize economic losses, and strengthen bovine tuberculosis (bTB) control efforts.