Survey of human and bovine tuberculosis infection on dairy farms in southwestern China

Abstract Abstract Background: Tuberculosis is a zoonotic chronic infectious disease caused by Mycobacterium tuberculosis complex (MTBC) that can be transmitted between humans and cattle. The aim of our study was to identify cross-infections of MTBC between humans and cattle on dairy farms in Sichuan Province, southwestern China. Results: We selected 6 large-scale and 5 small-scale dairy farms in Sichuan Province as research sites. A total of 378 dairy farm workers (except one pregnant woman) were screened for tuberculosis symptoms and examined by X-ray. One worker was diagnosed as tuberculosis, though the sputum culture was negative. In total, 99 of 10,224 (0.97%) cows showed positive results for the purified protein derivative (PPD) skin tests. Esophageal-pharyngeal (OP) secretions from PPD-positive cows were cultured and 21 isolates were obtained. Sequences of 16s rDNA , hsp65 and rpoB and 16s-23s rRNA spacer region were amplified and sequenced. BLAST analysis classified these isolates as nontuberculous mycobacteria (NTM) (18 M. nonchromogenicum , 1 M. hiberniae , 1 M. arupense, and 1 M. chitae isolates). Conclusion: This study indicates that the PPD-positive cows in these dairy farms were infected with NTM rather than MTBC. Tuberculosis cross-infection between humans and cows on dairy farms has been well controlled in this region.