Abstract
Rapid and accurate diagnostic tools, such as Real-Time PCR (qPCR), need to be implemented as a confirmatory test in the framework of bovine tuberculosis (bTB) surveillance and control programs, shortening the turnaround time to confirm bTB infection. The present study aimed to evaluate a direct qPCR from fresh tissue samples targeting the insertion sequence IS6110 using individually homogenized bovine lymph nodes compared with microbiological culture. Retropharyngeal, tracheobronchial, and mesenteric lymph nodes fresh tissue samples (n = 687) were collected from 230 different cattle carcasses at the slaughterhouse. Only 23 of the 230 examined animals showed tuberculosis-like lesions, with 62 of 230 considered as positive. Among these 62 animals, 61 resulted as culture-positive, whereas 48 were qPCR-positive. Thus, this qPCR targeting IS6110 showed an apparent diagnostic sensitivity and specificity values of 77.1% [95% confidence interval (CI): 66.5–87.6%] and 99.4% (95% CI: 98.3–100.6%), respectively, and a positive predictive value of 97.9% (95% CI: 93.9–102.0%) and negative predictive value of 92.3% (95% CI: 88.4–96.2%). Positive and negative likelihood ratios were 130.2 and 0.2, respectively, and the agreement between microbiological culture and this qPCR was almost perfect (κ = 0.82). These results highlight this qPCR targeting IS6110 as a suitable complementary method to confirm bTB in animals with either tuberculosis-like lesions or non-tuberculosis-like lesions, decreasing the number of samples subjected to microbiological culture and, hence, its overall associated costs and the turnaround time (under 48 h) to confirm bTB infection. Besides, sampling mesenteric lymph node, which is uncommonly sampled, together with tracheobronchial and retropharyngeal ones, is advisable during postmortem inspection in bTB surveillance programs at the slaughterhouse, especially in areas with a low bTB prevalence scenario.
Highlights
Bovine tuberculosis is a chronic infectious disease caused by Mycobacterium bovis and other members of the Mycobacterium tuberculosis complex (MTC) [1, 2] that affects various species of mammals, including humans [3, 4]. bovine tuberculosis (bTB) is still one of the largely neglected zoonotic diseases, in developing countries, as the control and surveillance programs for this disease are inadequate or are not carried out, and domestic and wild animals, which act as reservoirs, often share pasture areas
A total of 687 retropharyngeal, tracheobronchial, and mesenteric lymph node samples belonging to 230 cattle carcasses were analyzed to serve as evidence of the presence of MTC using microbiological culture and qPCR directly from lymph nodes
Every single tissue sample was subjected to a visual inspection to disclose gross lesions, with 26 of 26/687 (3.8%) tissue samples belonging to 23 different cattle (23/230, 10.0%) showing tuberculosis-like lesions (TBLs) (Table 1)
Summary
Bovine tuberculosis (bTB) is a chronic infectious disease caused by Mycobacterium bovis and other members of the Mycobacterium tuberculosis complex (MTC) [1, 2] that affects various species of mammals, including humans [3, 4]. bTB is still one of the largely neglected zoonotic diseases, in developing countries, as the control and surveillance programs for this disease are inadequate or are not carried out, and domestic and wild animals, which act as reservoirs, often share pasture areas. BTB is subjected to national eradication programs based on skin testing of all registered cattle herds, slaughtered policy, and abattoir surveillance (Council Directive 64/432/EEC). According to the EU legislation, the official diagnosis of bTB is based on the detection of the cellular immune response (single intradermal tuberculin testing) in reactor animals (skin test-positive animals), which is followed by slaughtering, histopathological examination of atypical or enlarged lymph nodes or parenchymatous organs with tuberculosis-like lesions (TBLs), and/or culture of MTC in primary isolation medium [6]. A substantial economic expenditure is addressed to ensure efficient surveillance systems and control programs, the detection and confirmation of bTB infection in cattle herds should be more reliable and swifter [7]
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