Serological and Molecular Evidence Indicates Widespread Mycobacterium avium Subsp. paratuberculosis Exposure in Large-Scale Dairy Farms in Xinjiang, Northwest China

Johne’s disease is a chronic progressive enteritis in cattle caused by Mycobacterium avium subsp. paratuberculosis (MAP). It causes substantial economic losses and has been suggested to be related to human Crohn’s disease. This study investigated MAP exposure and molecular detection in large-scale dairy herds in Xinjiang, China. A total of 1817 milk and 988 fecal samples were collected from 30 herds located across ten regions. Anti-MAP-specific antibodies were measured in milk samples using a commercially available enzyme-linked immunosorbent assay (ELISA), while MAP DNA was assessed in fecal samples by quantitative PCR (qPCR). The apparent individual seroprevalence was 6.66% (121/1817) based on milk ELISA. At the herd level, 25 of the 30 herds (83.3%) examined by milk ELISA had at least one animal positive for MAP-specific antibodies. MAP DNA was detected in 2.53% (25/988) of fecal samples, and bacterial culture of the qPCR-positive samples yielded 12 MAP isolates, which were confirmed by F57-targeted qPCR and Ziehl–Neelsen staining. Age-related differences were observed according to the diagnostic method, with the highest qPCR positivity recorded in older animals. These findings provide evidence of widespread MAP exposure and molecular detection among large-scale dairy herds in Xinjiang, and support continued monitoring and improved control measures.