Bovine tuberculosis in Central Ethiopian slaughterhouses and the identification of causative mycobacteria by multiplex real-time PCR.

BACKGROUND: Bovine tuberculosis (bTB) is a chronic disease caused by members of the Mycobacterium tuberculosis complex (MTBC) that ultimately leads to the development of progressive granulomatous lesions. Although the disease is widespread, especially in crossbred cattle 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 = 11.8, 95% CI: 6.4, 21.2, p < 0.001). Animals slaughtered at Adama (OR = 3.2, 95% CI: 1.2, 7.3, p = 0.009) or Burayu (OR = 5.8, 95% CI: 3.9, 8.9, p < 0.001) 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 = 7.1; 95% CI: 2.7, 24.5, p < 0.001) and the head lymph node (OR = 5.6; 95% CI: 1.8, 21.7; p = 0.006) compared to gut associated lymph nodes. Among the 173 TBL-positive animals, 36% (95% CI = 28.8, 43.2), and among the 388 TBL-positive tissues, 24.2% (95% CI = 20, 29) were culture and mRT-PCR positive. All the culture-generated isolates were positive for M. bovis in mRT-PCR. Among them, two animals had mixed infections including one zebu cattle tested positive for both M. caprae and M. bovis, and a crossbred cow tested positive for both M. tuberculosis and M. bovis in mRT-PCR. This suggests persistent transmission within the cattle population, posing a substantial public health threat. CONCLUSION: This study revealed an eleven-fold greater risk of bTB-related lesions in crossbred cattle compared to local zebu cattle. This finding highlights the necessity for targeted interventions, continuous vigilance, and thorough carcass inspection to mitigate public health risks.

Epidemiology of Bovine Tuberculosis and Its Zoonotic Implication in Addis Ababa Milkshed, Central Ethiopia.

Bovine tuberculosis (bTB) continues to be one of the most widely distributed chronic infectious diseases of zoonotic importance, which causes a significant economic loss in animal production. A cross-sectional study was conducted to estimate the prevalence of bTB and its associated risk factors and type the Mycobacterium bovis isolated in central Ethiopia. A total of 65 dairy farms and 654 cattle were tested for bTB using a single intradermal comparative cervical tuberculin (SICCT) test. Data on farm management, animal-related characteristics, and the owner's knowledge of the zoonotic importance of bTB were collected using a structured questionnaire. In addition, a total of 16 animals from different farms were identified for postmortem examination. Lowenstein Jensen (LJ) culture was also conducted, and spoligotyping was used to type the M. bovis strains isolated. Chi-square test and logistic regression models were used to analyze the herd- and animal-level risk factors. Herd- and animal-level prevalence rates of bTB were 58.5% (95% CI: 46.2%-69.2%) and 39.3% (95% CI: 35.5%-43.5%), respectively. At the herd level, poor farm management was the predictor for bTB positivity (p < 0.05). Animal breed, poor BCS, farm type, and poor farm management conditions were significant predictors of bTB positivity (p < 0.05) at an individual animal level. All animals identified for postmortem examination were found to have gross TB-like lesions. A total of 14 M. bovis strains were identified from 12 animals that were positive for LJ culture. The strain with the largest number of clusters (five isolates) was SB1176, followed by SB0134 (three isolates), SB0192 (two isolates), and SB2233 (two isolates), and two new strains, each consisting of only one isolate. The majority (58.5%) of the respondents did not know the zoonotic importance of bTB. The result of this study showed a high prevalence of bTB in the Addis Ababa milkshed and a low level of consciousness of the owners on its transmission to humans. Therefore, the launching of acceptable control measures of bTB and the creation of public awareness about its zoonotic transmission and prevention measures are required.