Bovine Tuberculosis in Central Ethiopian Slaughterhouses and Identification of Causative Mycobacteria by Multiplex Real-Time PCR

Abstract

Background Bovine tuberculosis (bTB) is a chronic disease primarily caused by Mycobacterium bovis that ultimately leads to the development of progressive granulomatous lesions. Although the disease is widespread, especially on intensive dairy farms in Ethiopia, routine investigations and surveillance are lacking. Thus, the aim of this study was to determine the prevalence, associated risk factors, and species of mycobacteria causing bTB in slaughtered cattle at four slaughterhouses in Central Ethiopia. Methods Postmortem examination of 7,640 cattle was conducted using a cross-sectional slaughterhouse survey. A total of 388 tuberculous-like lesions (TBLs) were collected from 173 animals and cultured. Six target genes were used to differentiate mycobacterial species using multiplex real-time PCR (mRT-PCR). Multivariate logistic regression analyses and related odds ratios (ORs) were used to gauge the strength of the associations between risk factors, TBL incidence and culture growth. Results The prevalence of TBL was 2.3% (95% CI = 2.0-2.6). Logistic regression analysis indicated an increased risk of TBL in crossbred cattle (OR = 11.0, 95% CI: 6.1, 19.8). Animals slaughtered at Adama (OR = 2.99, 95% CI: 1.25, 7.14) or Burayu (OR = 5.65, 95% CI: 3.76, 8.47) had a greater risk of TBL than those slaughtered at Sululta. There were significantly more TBL-positive lesions in the lungs and lymph nodes related to the lung (OR = 6.35; 95% CI: 2.46, 16.4) and the head lymph node (OR = 3.05; 95% CI: 1.05, 8.93). Among the 173 TBL-positive animals, 36% (95% CI = 28.8, 43.2) were culture positive, and among the 388 TBL-positive tissues, 24.2% (95% CI = 20, 29) were culture positive. All the culture-generated isolates were M. bovis positive according to mRT-PCR, suggesting persistent transmission among the cattle population, posing a serious public health threat. Conclusion This study revealed an eleven-fold greater risk of bTB-related lesions in crossbred cattle than in local zebu cattle. This finding highlights the necessity for targeted interventions, continuous vigilance, and thorough meat inspection to mitigate public health risks.