Bayesian Assessment of the Accuracy of a PCR-Based Rapid Diagnostic Test for Bovine Tuberculosis in Swine

Limited usefulness of the IS6110 touchdown-PCR in blood for tuberculin skin test false-negative cattle with serological response to Mycobacterium bovis

Ante-mortem diagnosis of bovine tuberculosis (bTB) is based mainly on the tuberculin skin test (TST) and the ɣ-IFN release assay (IGRA). Some infected animals escape screening tests, thus, limit herd sanitation. Previous reports have suggested a predominant pattern of multi-organ lesions attributable to Mycobacterium bovis (the causative agent of bTB) bacteraemia. A case-control study was conducted to investigate blood PCR as an alternative tool for improving ante-mortem detection of TST false-negative bovines. Cases comprised 70 TST false-negative bovines (cases), which were serology positive, and controls included 81 TST positive bovines; all of them confirmed as infected with M. bovis. Detection of the IS6110 target through touchdown blood-PCR (IS6110 TD-PCR) was performed. The positivity of the blood-PCR was 27.2% in the control group. This performance was similar to the 15% obtained among cases (p = 0.134). Most cases identified by the IS6110 TD-PCR exhibited focalized lesions (p = 0.002). Results demonstrated that blood-PCR could detect TST false-negative cattle, even if they are negative for IGRA. Considering that cases exhibited humoral response to M. bovis, further studies conducted in a pre-serological stage could provide evidence about the real contribution of the technique in herds.

Worldwide Swine Tuberculosis-Positive Rate and Associated Risk Factors, 1966-2020: A Systematic Review and Meta-Analysis

Background: Tuberculosis (TB) is a chronic, zoonotic infectious disease caused by Mycobacterium tuberculosis that infects not only humans but also animals such as pigs, cows, buffaloes, sheep, and goats. Among them, pigs are one of the main food animals in the world. If pigs are infected with M. tuberculosis, meat products will be negatively affected, causing economic losses to the livestock industry. There is currently no systematic epidemiological assessment of swine TB in the world, so it is important to know the prevalence of swine, and these data are currently lacking, so we performed a statistical analysis. Results: We searched 6791 articles and finally included data from 35,303 pigs from 15 countries or territories, showing a combined prevalence of TB in pigs of 12.1% (95% confidence interval [CI]: 9.2 to 15.9). Among them, the prevalence rate of swine TB in Europe was 15.2% (95% CI: 11.1 to 20.7, 2491/25,050), which was higher compared with other continents, and the difference was significant; the positive rate of PCR method was higher in the detection method subgroup, which was 15.7% (95% CI: 8.0 to 31.0, 376/2261); Mycobacterium bovis was detected in pigs in the M. tuberculosis typing group (9.5%, 95% CI: 6.7 to 13.5, 1364/21,430). The positive rate is higher compared with Mycobacterium capris. Conclusion: This systematic review and meta-analysis is the first to determine the global prevalence of TB in swine herds. Although the seroprevalence of swine TB in this article is very low, the harm of TB cannot be ignored. It is important to take effective control and preventive measures to stop the spread of TB to reduce the impact of diseased pigs on animal husbandry and human health.

Optimization of real-time PCR protocols from lymph node bovine tissue for direct detection of Mycobacterium tuberculosis complex

Bovine tuberculosis (bTB) is a zoonotic disease and a global health problem that is subjected to obligatory eradication programs in the European Union. Microbiological culture is an imperfect technique for bTB diagnosis. This study aims to compare and validate two DNA isolation protocols and three different specific DNA targets, IS6110, IS4, and mpb70, to confirm Mycobacterium tuberculosis complex (MTC) infection by real-time PCR directly from fresh tissue samples. Fresh lymph node samples were collected from 81 cattle carcasses at the slaughterhouse. A comparison of both extraction protocols was performed with IS6110-real-time PCR, showing an adjusted sensitivity (SE) of 78.34% and 95.9% for protocols 1 and 2, respectively, while the specificity (SP) was 100% in both cases. Afterward, the comparison between IS4 and mpb70 targets was performed from the samples extracted with protocol 2, obtaining an adjusted SE of 90.87% and 83.3%, respectively, and an SP of 100% in both cases. The positive likelihood ratio was ∞ for the three targets, and the negative likelihood ratio was 0.04, 0.091, and 0.16 for IS6110, IS4, and mpb70, respectively. Negative predictive values were ≥90%, ≥85%, and ≥80% for real-time PCR targeting IS6110, IS4, and mpb70, respectively, when the true prevalence is ≤60%, and the positive predictive value is 100% in any scenario of true prevalence. According to these results, the DNA extraction protocol 2 and real-time PCR targeting IS6110 or IS4 could be potential first-choice molecular assays to detect MTC directly in fresh bovine tissue samples. IMPORTANCE Bovine tuberculosis (bTB), a chronic infectious and zoonotic disease caused by Mycobacterium tuberculosis complex (MTC), is considered a neglected disease of global importance, causing a detrimental impact on public health, particularly in developing countries where tuberculosis remains a major health problem. However, debate around the efficacy of control measures is still an ongoing matter of concern, with poor diagnostic performance being considered one of the most relevant factors involved in the failure to eradicate the disease since many truly infected animals will be misclassified as bTB-free. This study highlights a DNA extraction protocol and real-time PCR targeting IS6110 or IS4 as potential first-choice molecular assays to detect MTC directly in fresh bovine tissue samples, providing rapid, highly sensitive, and specific diagnostic tools as an alternative to microbiology, which could take up to 3 months to complete, shortening the turnaround time for decision makers to be promptly informed.

Molecular detection of Mycobacterium tuberculosis complex in a captive aguará popé (Procyon cancrivorus) with macroscopic tuberculosis like-lesions

Tuberculosis is a chronic and contagious infectious disease caused by multi-host species of the genus Mycobacterium grouped within the Mycobacterium tuberculosis complex. These pathogenic bacteria mainly affect mammals, including humans. The most recognized species is Mycobacterium bovis, the causative agent of bovine tuberculosis in livestock. Although livestock is the main host of M. bovis, this species is frequently isolated from wild animals. Wild native mammals from Central and South America, as the crab-eating raccoon or "aguará popé" (Procyon cancrivorus), may act as a source of tuberculosis and may represent a human health risk, especially in captive scenarios, due to closer animal-human interaction. However, the only presence of infection in wild animals is not enough to determine their epidemiological role in the disease. Here we identify tuberculosis in a captive aguará popé with clinical signs and lung macroscopic tuberculosis-like lesions during necropsy. We detected tuberculosis by polymerase chain reaction assay. DNA was extracted directly from lung tissue and the amplification target was the insertion sequence 6110. This study contributes to investigate the presence of the disease in wild native animals of Argentina and supports the knowledge that wild mammals may act as a source of TB for humans and domestic animals.

Real-Time PCR Validation for Mycobacterium tuberculosis Complex Detection Targeting IS6110 Directly From Bovine Lymph Nodes

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.

Intra-vitam Diagnosis of Tuberculosis in Pigs: Concordance Between Interferon-Gamma Release Assay and Comparative Tuberculin Skin Test

The role of pigs in the maintenance of bovine tuberculosis caused by Mycobacterium bovis has been demonstrated in many settings; however, the current control programs usually do not state any intra-vitam diagnostic procedure in this species, as for the cattle. Carcass inspection has shown to be insufficient to detect infection in swine; thus, the assessment of intradermal tuberculin test and interferon-gamma release assay (IGRA) in this species is mandatory. The current study compares the performances of the single intradermal comparative cervical tuberculin (SICCT) test and IGRA. A total of 628 Nebrodi Black pigs raised in free-roaming farms were subjected to the two tests simultaneously. Besides, 124 animals underwent postmortem examination for the detection of tuberculous lesions and isolation of mycobacteria from target organs. The two tests showed a concordance of 94.42% with a Cohen's k coefficient of 0.786 and McNemar chi-square of 4.83 (P = 0.03). Slightly lower levels of concordance (90.32%) between SICCT and IGRA were obtained in the group of 124 animals, with a Cohen's k = 0.797 and McNemar chi-squared value of 0.69 with a non-significant P = 0.41. Moreover, the results showed how IGRA tends to result positive in higher rates, mostly when non-tuberculous mycobacteria (NTM) were isolated, suggesting a possible impairment of specificity in the event of coinfections in the swine. In conclusion, the results obtained support the possibility of the strategic use of IGRA or SICCT in combination or alternatively one to the other, particularly IGRA which showed lower specificity but has evident advantages over SICCT.