A field evaluation of serological and cellular diagnostic tests for bovine tuberculosis

A combined application of molecular docking technology and indirect ELISA for the serodiagnosis of bovine tuberculosis

BACKGROUND

There is an urgent need to find reliable and rapid bovine tuberculosis (bTB) diagnostics in response to the rising prevalence of bTB worldwide. Toll-like receptor 2 (TLR2) recognizes components of bTB and initiates antigen-presenting cells to mediate humoral immunity. Evaluating the affinity of antigens with TLR2 can form the basis of a new method for the diagnosis of bTB based on humoral immunity.

OBJECTIVES

To develop a reliable and rapid strategy to improve diagnostic tools for bTB.

METHODS

In this study, we expressed and purified the sixteen bTB-specific recombinant proteins in Escherichia coli. The two antigenic proteins, MPT70 and MPT83, which were most valuable for serological diagnosis of bTB were screened. Molecular docking technology was used to analyze the affinity of MPT70, MPT83, dominant epitope peptide of MPT70 (M1), and dominant epitope peptide MPT83 (M2) with TLR2, combined with the detection results of enzyme-linked immunosorbent assay to evaluate the molecular docking effect.

RESULTS

The results showed that interaction surface Cα-atom root mean square deviation of proteins (M1, M2, MPT70, MPT83)-TLR2 protein are less than 2.5 A, showing a high affinity. It is verified by clinical serum samples that MPT70, MPT83, MPT70-MPT83 showed good diagnostic potential for the detection of anti-bTB IgG and M1, M2 can replace the whole protein as the detection antigen.

CONCLUSIONS

Molecular docking to evaluate the affinity of bTB protein and TLR2 combined with ELISA provides new insights for the diagnosis of bTB.

Bayesian Estimation of Diagnostic Accuracy of Three Diagnostic Tests for Bovine Tuberculosis in Egyptian Dairy Cattle Using Latent Class Models

The aim of the present study was to calculate the sensitivity (Se) and specificity (Sp) of the single cervical tuberculin test (SCT), rapid lateral flow test (RLFT), and real-time polymerase chain reaction (RT-PCR) for the diagnosis of Mycobacterium bovis (M. bovis) infection in Egyptian dairy cattle herds within a Bayesian framework. The true M. bovis infection within-herd prevalence was assessed as a secondary objective. Data on the test results of SCT, RLFT, and RT-PCR for the detection of M. bovis were available from 245 cows in eleven herds in six major governorates in Egypt. A Bayesian latent class model was built for the estimation of the characteristics of the three tests. Our findings showed that Se of SCT (0.93 (95% Posterior credible interval (PCI): 0.89–0.93)) was higher than that of RT-PCR (0.83 (95% PCI: 0.28–0.93)) but was similar to the Se of RLFT (0.93 (95% PCI: 0.31–0.99)). On the contrary, SCT showed the lowest Sp estimate (0.60 (95% PCI: 0.59–0.65)), whereas Sp estimates of RT-PCR (0.99 (95% PCI: 0.95–1.00)) and RLFT (0.99 (95% PCI: 0.95–1.00)) were comparable. The true prevalence of M. bovis ranged between 0.07 and 0.71. In conclusion, overall, RT-PCR and RLFT registered superior performance to SCT, making them good candidates for routine use in the Egyptian bovine tuberculosis control program.

Comparing recombinant MPB70/SahH and native 20-kDa protein for detecting bovine tuberculosis using ELISA

Bovine tuberculosis (bTB) is a zoonosis caused by Mycobacterium bovis. Test-and-cull protocols and gross pathological examinations of abattoir animals as well as milk pasteurization have been implemented to prevent the spread of tuberculosis from animals to humans worldwide. Despite the importance of precise and rapid diagnostic tests, conventional methods including intradermal skin tests and γ-interferon assays are limited by the high rate of false-negative results for cattle in the late infectious stage and due to laborious and time-consuming procedures. Therefore, antibody detection methods such as enzyme-linked immunosorbent assay (ELISA) are urgently needed to supplement the established approaches and expand the diagnostic window. This study was conducted to develop a bTB ELISA by evaluating recombinant and native proteins and various assay parameters. We produced recombinant MPB70 and SahH (M70S) and a native 20-kDa protein (20K) and optimized the ELISA protocol. The 20K ELISA showed 94.4% sensitivity and 98.2% specificity with an optimal sample-to-positive ratio cut-off of 0.531. The sensitivity and specificity of M70S ELISA were 94.4% and 97.3%, respectively, with an optimal sample-to-negative ratio cut-off of 1.696. Both assays showed acceptable diagnostic efficiency and could be used for bTB diagnosis in combination with established methods for herd screening and to expand the diagnostic window.

Modeling the Accuracy of Two in-vitro Bovine Tuberculosis Tests Using a Bayesian Approach

Accuracy of new or alternative diagnostic tests is typically estimated in relation to a well-standardized reference test referred to as a gold standard. However, for bovine tuberculosis (bTB), a chronic disease of cattle, affecting animal and public health, no reliable gold standard is available. In this context, latent-class models implemented using a Bayesian approach can help to assess the accuracy of diagnostic tests incorporating previous knowledge on test performance and disease prevalence. In Uruguay, bTB-prevalence has increased in the past decades partially because of the limited accuracy of the diagnostic strategy in place, based on intradermal testing (caudal fold test, CFT, for screening and comparative cervical test, CCT, for confirmation) and slaughter of reactors. Here, we evaluated the performance of two alternative bTB-diagnostic tools, the interferon-gamma assay, IGRA, and the enzyme-linked immunosorbent assay (ELISA), which had never been used in Uruguay in the absence of a gold standard. In order to do so animals from two heavily infected dairy herds and tested with CFT-CCT were also analyzed with the IGRA using two antigens (study 1) and the ELISA (study 2). The accuracy of the IGRA and ELISA was assessed fitting two latent-class models: a two test-one population model (LCA-a) based on the analysis of CFT/CFT-CCT test results and one in-vitro test (IGRA/ELISA), and a one test-one population model (LCA-b) using the IGRA or ELISA information in which the prevalence was modeled using information from the skin tests. Posterior estimates for model LCA-a suggested that IGRA was as sensitive (75-78%) as the CFT and more sensitive than the serial use of CFT-CCT. Its specificity (90-96%) was superior to the one for the CFT and equivalent to the use of CFT-CCT. Estimates from LCA-b models consistently yielded lower posterior Se estimates for the IGRA but similar results for its Sp. Estimates for the Se (52% 95%PPI:44.41-71.28) and the Sp (92% 95%PPI:78.63-98.76) of the ELISA were however similar regardless of the model used. These results suggest that the incorporation of IGRA for detection of bTB in highly infected herds could be a useful tool to improve the sensitivity of the bTB-control in Uruguay.

Assessment of the bovine tuberculosis elimination protocol in the United States

In this study, we analyzed the performance of the USDA's bovine tuberculosis (bTB) elimination protocol in a 1,000-cow closed dairy herd using an agent-based simulation model under different levels of initial bTB infection. We followed the bTB test sensitivity and specificity values used by the USDA in its model assessment. We estimated the net present value over a 20-yr horizon for a bTB-free milking herd and for bTB-infected herds following the USDA protocol. We estimated the expected time to identify the infection in the herd once it is introduced, its elimination time, the reproductive number (R₀), and effective reproduction number (R_e) under the USDA protocol. The optimal number of consecutive negative whole-herd tests (WHT) needed to declare a herd bTB-free with a 95% confidence under different bTB prevalence levels was derived. Our results support the minimum number of consecutive negative WHT required by the USDA protocol to declare a herd bTB-free; however, the number of consecutive negative WHT needed to eliminate bTB in a herd depends on the sensitivity and specificity of the tests. The robustness of the protocol was analyzed under conservative bTB test parameters from the literature. The cost of implementing the USDA protocol when 1 infected heifer is introduced in a 1,000-cow dairy herd is about $1,523,161. The average time until detection and the time required to eliminate bTB-infected animals from the herd, after 1 occult animal is introduced in the herd, were 735 and 119 d, respectively.

Evaluation of the Performance of the IDvet IFN-Gamma Test for Diagnosis of Bovine Tuberculosis in Spain

In Spain, the national bovine tuberculosis (bTB) eradication program is based on yearly skin testing of every ≥6 weeks old animal using the single or comparative tuberculin test and parallel use of the interferon-gamma (IFN-γ) assay as an ancillary diagnostic test in infected herds. There are several versions of the latter. Recently, a new commercial IDvet IFN-γ assay has been authorized for use in the program, but there is limited scientific evidence about its performance in different epidemiological settings. Therefore, two studies to evaluate the performance of the IDvet assay were conducted. In study 1, a concordance analysis between the new IDvet and the Bovigam IFN-γ assay in use in Spain for over 10 years was conducted. In study 2, results from the IDvet assay when applied in tandem with a single intradermal tuberculin (SIT) test were used to evaluate the concordance between both tests and to estimate their sensitivity (Se) and specificity (Sp) using a Bayesian latent-class model. Field data from cattle herds located in Madrid and Castilla y Leon (Spain) were collected. For study 1, herd selection was based on a high expected prevalence of reactors to the IFN-γ assay, while herds were selected at random to estimate Se and Sp of the new IDvet assay in study 2. Agreement between the results obtained with both kits for IFN-γ assay was poor (Kappa = 0.20), and a receiver operating characteristic (ROC) analysis indicated a low Se of the new IDvet relative to the Bovigam in a heavily bTB infected population. The Bayesian latent-class analysis estimated the Se of the IDvet assay to be 36.7% [95% probability posterior interval (PPI) 14.7-78.8%] with estimated Sp close to 100% when the cut-off recommended by the manufacturer (35) was applied. At the alternative cut-off values of 16 and 4, the estimated Se of the IDvet assay increased to 49.0% (PPI: 24.8-94.1%) and 56.0% (PPI: 30.8-96.3%), respectively, while maintaining a high specificity. The results suggest that the new IDvet assay may have lower sensitivity than the Bovigam for diagnosis of bTB in cattle herds in Spain, and that adjusting its cut-off might be considered.

Methodology and preliminary results of a systematic literature review of ante-mortem and post-mortem diagnostic tests for bovine tuberculosis

A systematic review was conducted to identify studies with data for statistical meta-analyses of sensitivity (Se) and specificity (Sp) of ante-mortem and post-mortem diagnostic tests for bovine tuberculosis (bTB) in cattle. Members of a working group (WG) developed and tested search criteria and developed a standardised two-stage review process, to identify primary studies with numerator and denominator data for test performance and an agreed range of covariate data. No limits were applied to year, language, region or type of test in initial searches of electronic databases. In stage 1, titles and available abstracts were reviewed. References that complied with stage 1 selection criteria were reviewed in entirety and agreed data were extracted from references that complied with stage 2 selection criteria. At stage 1, 9782 references were reviewed and 261 (2.6%) passed through to stage 2 where 215 English language references were each randomly allocated to two of 18 WG reviewers and 46 references in other languages were allocated to native speakers. Agreement regarding eligibility between reviewers of the same reference at stage 2 was moderate (Kappa statistic = 0.51) and a resolution procedure was conducted. Only 119 references (published 1934-2009) were identified with eligible performance estimates for one or more of 14 different diagnostic test types; despite a comprehensive search strategy and the global impact of bTB. Searches of electronic databases for diagnostic test performance data were found to be nonspecific with regard to identifying references with diagnostic test Se or Sp data. Guidelines for the content of abstracts to research papers reporting diagnostic test performance are presented. The results of meta-analyses of the sensitivity and specificity of the tests, and of an evaluation of the methodological quality of the source references, are presented in accompanying papers (Nuñez-Garcia et al., 2017; Downs et al., 2017).

Inferring biomarkers for Mycobacterium avium subsp. paratuberculosis infection and disease progression in cattle using experimental data

Available diagnostic assays for Mycobacterium avium subsp. paratuberculosis (MAP) have poor sensitivities and cannot detect early stages of infection, therefore, there is need to find new diagnostic markers for early infection detection and disease stages. We analyzed longitudinal IFN-γ, ELISA-antibody and fecal shedding experimental sensitivity scores for MAP infection detection and disease progression. We used both statistical methods and dynamic mathematical models to (i) evaluate the empirical assays (ii) infer and explain biological mechanisms that affect the time evolution of the biomarkers, and (iii) predict disease stages of 57 animals that were naturally infected with MAP. This analysis confirms that the fecal test is the best marker for disease progression and illustrates that Th1/Th2 (IFN-γ/ELISA antibodies) assays are important for infection detection, but cannot reliably predict persistent infections. Our results show that the theoretical simulated macrophage-based assay is a potential good diagnostic marker for MAP persistent infections and predictor of disease specific stages. We therefore recommend specifically designed experiments to test the use of a based assay in the diagnosis of MAP infections.

The Sensitivity of Gross Necropsy, Caudal Fold and Comparative Cervical Tests for the Diagnosis of Bovine Tuberculosis

Bovine tuberculosis (bTb) was diagnosed in 22 cattle herds in the northeast corner of Michigan's lower peninsula. Of these 22 herds, 494 animals in 7 herds were examined by gross necropsy, histopathologic exam, mycobacterial culture, and polymerase chain reaction (PCR) assay performed only on samples that were histologically compatible for bTb. Results of culture and PCR assay interpreted in parallel were used as the reference test for calculation of the sensitivity of 1) the caudal fold test (CFT), 2) the caudal fold and comparative cervical skin tests used in series (CFTCCTSER), and 3) gross necropsy. Mycobacterium bovis was isolated from 43 animals. Using all 7 herds, the sensitivities of the CFT, the CFTCCTSER, and gross necropsy were 93.02%, 88.37%, and 86.05%, respectively. When the data were stratified by low- and moderate-prevalence herds, the sensitivities were 83.33%, 75.0%, and 83.33% in low-prevalence herds and 96.77%, 93.55%, and 87.10% in moderate-prevalence herds. The sensitivities of the 2 skin tests were slightly higher when 2 or more gross lesions were present, and the sensitivity of gross necropsy was significantly higher ( P = 0.049). The sensitivity of the CFT was found to be notably higher than most estimates in other studies; however, a direct comparison was not possible because the amount of purified protein derivative and the reference methods were different in this study compared with other published studies. Although the sensitivities are high, 2 of the 7 herds (29%) would have had 1 or more positive animals left in the herd if a test-and-removal program had been used. This suggests that when positive herds are identified, selective culling of skin test reactors is a less acceptable disease control strategy than is complete depopulation.

A polymerase chain reaction and enzyme linked immunosorbent assay based approach for diagnosis and differentiation between vaccinated and infected cattle with Mycobacterium bovis

BACKGROUND

In most African and Arabic countries tuberculosis (TB) causes great economic losses in bovine species and constitutes serious zoonotic problem. As the traditional diagnostic method delay the research because of low sensitivity and specificity, a rapid method of diagnosis is of outmost importance.

AIM

The study was designed to evaluate the two rapid diagnostic methods of TB in cattle, further to differentiate between infected and bacillus Calmette-Guerin (BCG) vaccinated animals.

MATERIALS AND METHODS

Intradermal tuberculin test was applied to 300 cattle. Of these cattle, 15 cattle were vaccinated from cattle negative to tuberculin test with BCG. Blood samples were taken for lymphocyte separation to apply polymerase chain reaction (PCR) upon and for serum preparation for the enzyme-linked immunosorbent assay (ELISA) application, this blood collected from 65 cattle classified into three groups, viz. positive tuberculin test (35 animals), negative tuberculin test (15 animals), and vaccinated cow with BCG (15 animals). From blood samples lymphocytes were separated and the isolated lymphocytes were subjected to PCR and serum for ELISA application. Blood samples, specimens from lymph nodes and specific tissues were taken for PCR and for cultivation and isolation of Mycobacterium bovis.

RESULTS AND CONCLUSIONS

The results of this study revealed that PCR can be used as rapid efficient and accurate diagnostic test in detection of ruminant TB. Moreover, cattle's ELISA reading showed higher sensitivity in positive tuberculin animals. However, the differentiations between vaccinated and infected animals not clear by using a single antigen only.

Extent of Mycobacterium bovis infection in dairy cattle herds subject to partial culling as determined by an interferon-gamma assay

The interferon-gamma (IFN-γ) assay is employed as a complementary diagnostic test for bovine tuberculosis (BTB) in many countries. To simplify this assay, we established a 96-well plate format using the ESAT-6 and CFP-10 antigens and then employed it to determine the extent of Mycobacterium (M.) bovis infection in dairy herds with a history of BTB outbreaks in a country where only selective culling is practiced. The sensitivity and specificity of this IFN-γ assay were 85.9% and 100%, respectively, based on comparison with the conventional single intradermal tuberculin test (SIDT). The IFN-γ assay was also positive in 30.4% and 36.8% of SIDT-negative animals from herds with recent and remote BTB outbreaks, respectively. Of 14 SIDT-negative, IFN-γ positive cattle, five (35.7%) were culture positive and an additional six were positive based on a polymerase chain reaction-based test for M. bovis. Therefore, the IFN-γ assay has the potential to serve as a specific and sensitive test for M. bovis infection in dairy cattle. Further, the results indicated that a substantial portion of SIDT-negative animals in herds with previous BTB outbreaks were actually infected with M. bovis. Accordingly, the present selective-culling strategy may require modifications to include this more sensitive assay.

Towards risk-based test protocols: estimating the contribution of intensive testing to the UK bovine tuberculosis problem

Eradicating disease from livestock populations involves the balancing act of removing sufficient numbers of diseased animals without removing too many healthy individuals in the process. As ever more tests for bovine tuberculosis (BTB) are carried out on the UK cattle herd, and each positive herd test triggers more testing, the question arises whether ‘false positive’ results contribute significantly to the measured BTB prevalence. Here, this question is explored using simple probabilistic models of test behaviour. When the screening test is applied to the average UK herd, the estimated proportion of test-associated false positive new outbreaks is highly sensitive to small fluctuations in screening test specificity. Estimations of this parameter should be updated as a priority. Once outbreaks have been confirmed in screening-test positive herds, the following rounds of intensive testing with more sensitive, albeit less specific, tests are highly likely to remove large numbers of false positive animals from herds. Despite this, it is unlikely that significantly more truly infected animals are removed. BTB test protocols should become based on quantified risk in order to prevent the needless slaughter of large numbers of healthy animals.

Evaluation of the interferon-γ assay on blood collected at exsanguination of cattle under field conditions for surveillance of bovine tuberculosis

Development of point of concentration (POC) surveillance strategies for bovine tuberculosis (bTB) would facilitate global efforts to eradicate bTB. The interferon-gamma (IFNγ) assay can detect IFNγ responses to Mycobacterium bovis in blood collected at commencement of exsanguination (COE) of experimentally challenged cattle but has not been evaluated under field conditions. The current study was aimed at determining (i) whether blood collected at COE of cattle at slaughter, under field conditions, is practical to obtain and useful for identifying cattle as IFNγ positive for bTB, (ii) whether the results of the IFNγ assay obtained at COE reliably compare with results obtained from live animals in the field, and (iii) whether the identified animal(s) originated from bTB-infected or bTB-exposed herds. Cattle from three risk groups were used: the highest risk group consisted of 49 cattle from 3 bTB-infected herds; the medium risk group consisted of 24 cattle from a potentially exposed herd; and the lowest risk group consisted of 60 cattle from herds with no known history of bTB exposure. The IFNγ assay was performed on blood collected both before stunning and at COE of cattle at slaughter. An enhanced slaughter inspection for gross lesions consistent with bTB was performed on all cattle. In addition, lymph nodes were cultured for M. bovis for cattle that tested positive for bTB via the IFNγ assay and for most cattle that tested negative for bTB. Cattle, both with and without lesions consistent with bTB, were identified as positive for bTB by the IFNγ assay using blood collected at COE, but none of the positive cattle originated from the lowest risk group. The current study demonstrates that blood collected at COE of cattle is both a practical and moderately reliable sample for accessing bTB infection using the IFNγ assay.

Detection of interferon-γ response to tuberculosis in blood collected at commencement of exsanguination at slaughter from cattle sensitized with Mycobacterium bovis

OBJECTIVE

To determine whether an interferon (IFN)-γ response sufficient to categorize cattle as positive for tuberculosis can be detected in blood collected at commencement of exsanguination at slaughter.

ANIMALS

15 Holstein cows.

PROCEDURES

12 cows were experimentally sensitized by SC injection with inactivated Mycobacterium bovis in mineral oil, which induced an immune response that mimicked natural infection with M bovis. Three nonsensitized control cows were injected SC with mineral oil alone. By 5 weeks after injection, only the 12 sensitized cows had positive results for tuberculosis with whole blood IFN-γ assay. At that time, all 15 cows were sent to slaughter and samples of blood were collected from each cow immediately before stunning and at commencement of exsanguination (within 90 seconds after stunning). A whole blood IFN-γ assay was performed on the samples. Conditional probability and paired t tests were used to analyze changes in the categorical test interpretation and qualitative IFN-γ production, respectively.

RESULTS

All 12 sensitized cows had positive results for tuberculosis in samples obtained immediately before stunning, and 9 retained positive results for samples obtained at commencement of exsanguination. There was a significant decrease in the mean background-corrected IFN-γ ELISA optical density values for samples obtained at commencement of exsanguination.

CONCLUSIONS AND CLINICAL RELEVANCE

IFN-γ response sufficient to classify cattle as positive for tuberculosis could be detected in blood collected at commencement of exsanguination. These findings support further development and use of the IFN-γ assay on blood samples collected at exsanguination as part of a bovine tuberculosis surveillance program.

Opportunities for improved serodiagnosis of human tuberculosis, bovine tuberculosis, and paratuberculosis

Mycobacterial infections—tuberculosis (TB), bovine tuberculosis (bTB), and Johne's disease (JD)—are major infectious diseases of both human and animals. Methods presently in use for diagnosis of mycobacterial infections include bacterial culture, nucleic acid amplification, tuberculin skin test, interferon-γ assay, and serology. Serological tests have several advantages over other methods, including short turn-around time, relatively simple procedures, and low cost. However, current serodiagnostic methods for TB, bTB and JD exhibit low sensitivity and/or specificity. Recent studies that have aimed to develop improved serodiagnostic tests have mostly focused on identifying useful species-specific protein antigens. A review of recent attempts to improve diagnostic test performance indicates that the use of multiple antigens can improve the accuracy of serodiagnosis of these mycobacterial diseases. Mycobacteria also produce a variety of species-specific nonprotein molecules; however, only a few such molecules (e.g., cord factor and lipoarabinomannan) have so far been evaluated for their effectiveness as diagnostic antigens. For TB and bTB, there has been recent progress in developing laboratory-free diagnostic methods. New technologies such as microfluidics and “Lab-on-Chip” are examples of promising new technologies that can underpin development of laboratory-free diagnostic devices for these mycobacterial infections.

Analysis of the diagnostic accuracy of the gamma interferon assay for detection of bovine tuberculosis in U.S. herds

The goal of this study was to evaluate the test sensitivity (SE) and specificity (SP) of the gamma interferon (G-IFN) assay used for the detection of bovine tuberculosis (bTB) in U.S. cattle herds. In addition, the study assessed the association between G-IFN test results and bTB status of cattle, and explored different cut off values for classification of test results in adult cattle using receiver operating characteristics (ROC) curve analysis. Test SE was estimated using a population of 87 confirmed infected cattle from 14 herds distributed in 6 states. Test SP was estimated using a population of 4123 cattle representing 3000 premises in 3 states. These animals were from bTB free areas, accredited bTB free herds, or herds that were historically bTB free based on the absence of lesions found at slaughter and historical records of negative tests performed for bTB surveillance. The distribution of G-IFN results and its association with bTB infection status was also explored in a group of 914 exposed cattle in which infection was not confirmed. The results showed that the SE of the G-IFN for a cut-off value ≥0.1 was 83.9% (76.1, 91.6). The SP of the G-IFN was 90.7% (95% CI: 89.8, 91.6), 97% (95% CI: 96.5, 97.5), and 98.6%(95% CI: 98.2, 98.9), for cut off values of 0.1, 0.3, and 0.5, respectively. For a cut off value ≥0.1, the likelihood ratio of a positive G-IFN test was 9.03 (95% CI: 7.90, 10.31), and the likelihood ratio of a negative G-IFN test was 0.18 (95% CI: 0.11, 0.29). The area under the ROC curve was 0.976 (95% CI: 0.97, 0.98), characteristic of a highly accurate test. ROC analysis also showed that lower cut-off values, such as 0.1, have high SE with suitable SP for use in parallel testing, while cut-off values ranging between 0.3 and 0.6 provide the high SP desired in series-testing protocols with lower SE values. Findings from this study indicated that the G-IFN performs with high accuracy in the field, yielding SE and SP estimates comparable to those reported in previous evaluations (Ryan et al., 2000; Ameni et al., 2000; de la Rua-Domenech et al., 2006; Gormley et al., 2006).

ExperimentalMycobacterium bovisinfection of cattle: Effect of dose ofM. bovisand pregnancy on immune responses and distribution of lesions

Groups of 18-month-old cattle were inoculated intratracheally with 5 x 10(5) colony forming units (high dose) or 500 colony forming units (low dose) of Mycobacterium bovis to determine an appropriate dose to induce lesions similar to those seen in the natural disease. An additional group of 21-28 weeks pregnant cattle were inoculated with the high dose of M. bovis to determine if pregnancy increased the susceptibility of cattle to M. bovis infection. By 23-24 weeks after challenge, the high dose of M. bovis had induced extensive lung lesions, and tuberculous lesions were observed in the lymph nodes of the head, neck, and thoracic and abdominal cavities. In contrast, the low dose of M. bovis induced predominantly small lesions (< 1 cm diameter) which were localised to the lungs and pulmonary lymph nodes. The lesions induced by the low dose were similar to those seen in the natural disease in cattle. The majority of the high dose group cattle produced strong antibody responses to M. bovis culture filtrate, while only one low dose animal produced a detectable response. All of the M. bovis-inoculated cattle produced strong cellular immune responses to bovine PPD (skin test and interferon-gamma responses). Pregnancy did not appear to affect the susceptibility to M. bovis infection, and immune responses of the cattle in this group at the end of the study were similar to those in the high dose non-pregnant group. However, from the first test after calving, the interferon-gamma responses of peripheral blood cultures to bovine PPD were low compared with the responses prior to calving.

Eurasian wild boar response to skin-testing with mycobacterial and non-mycobacterial antigens

Eurasian wild boar (Sus scrofa) are able to maintain bovine tuberculosis (bTB) in the wild and are most probably able to transmit the disease to other species, thus acting as a true wildlife reservoir. Translocation of wild boar is a common practice in European countries. Therefore, identifying effective tools for bTB diagnosis in living wild boar is crucial for the implementation of control measures. We describe for the first time the sex and origin related differences in the skin-test response to mycobacterial antigens (bPPD and aPPD) and to a non-mycobacterial antigen (PHA, a plant derived mitogen) in wild and farmed wild boar, and used a small sample of known M. bovis infected wild boar to establish whether skin-testing is an option for bTB diagnosis in living wild boar. The highest skinfold increase response was detected at the PHA injection site, evidencing that the PHA test could be useful in monitoring cell mediated immunity (CMI) in wild boar populations. A clear age-increasing trend of the PHA response indicated that age should be taken into account when measuring CMI in wild boar. Origin related differences in the response against mycobacterial antigens could reflect differential exposure to mycobacterial antigens. Skin testing in BCG immunized wild boar showed low sensitivity (43-57%), while the sensitivity was good in the culture positive controls (75-100%), depending on the reading criterion. Specificity improved when the criterion was a response to bPPD larger than 2 mm and bPPD response larger than aPPD response (77%). Although a limited sample, our results indicated the potential of skin test as a bTB diagnostic tool in Eurasian wild boar. However, handling of wild boar is dangerous, specificity is low, and more effort is needed in order to define the sensitivity of this technique.

Bovine tuberculosis: a review of current and emerging diagnostic techniques in view of their relevance for disease control and eradication

Existing strategies for long-term bovine tuberculosis (bTB) control/eradication campaigns are being reconsidered in many countries because of the development of new testing technologies, increased global trade, continued struggle with wildlife reservoirs of bTB, redistribution of international trading partners/agreements, and emerging financial and animal welfare constraints on herd depopulation. Changes under consideration or newly implemented include additional control measures to limit risks with imported animals, enhanced programs to mitigate wildlife reservoir risks, re-evaluation of options to manage bTB-affected herds/regions, modernization of regulatory framework(s) to re-focus control efforts, and consideration of emerging testing technologies (i.e. improved or new tests) for use in bTB control/eradication programs. Traditional slaughter surveillance and test/removal strategies will likely be augmented by incorporation of new technologies and more targeted control efforts. The present review provides an overview of current and emerging bTB testing strategies/tools and a vision for incorporation of emerging technologies into the current control/eradication programs.

Diagnostic accuracy and optimal use of three tests for tuberculosis in live badgers

BACKGROUND

Accurate diagnosis of tuberculosis (TB) due to infection with Mycobacterium bovis is notoriously difficult in live animals, yet important if we are to understand the epidemiology of TB and devise effective strategies to limit its spread. Currently available tests for diagnosing TB in live Eurasian badgers (Meles meles) remain unvalidated against a reliable gold standard. The aim of the present study was to evaluate the diagnostic accuracy and optimal use of three tests for TB in badgers in the absence of a gold standard.

METHODOLOGY/PRINCIPAL FINDINGS

A Bayesian approach was used to evaluate the diagnostic accuracy and optimal use of mycobacterial culture, gamma-interferon assay and a commercially available serological test using multiple samples collected from 305 live wild badgers. Although no single test was judged to be sufficiently sensitive and specific to be used as a sole diagnostic method, selective combined use of the three tests allowed guidelines to be formulated that allow a diagnosis to be made for individual animals with an estimated overall accuracy of 93% (range: 75% to 97%). Employing this approach in the study population of badgers resulted in approximately 13 out of 14 animals having their true infection status correctly classified from samples collected on a single capture.

CONCLUSIONS/SIGNIFICANCE

This method of interpretation represents a marked improvement on the current procedure for diagnosing M. bovis infection in live badgers. The results should be of use to inform future test and intervention strategies with the aim of reducing the incidence of TB in free-living wild badger populations.

Performance of the Enferplex TB assay with cattle in Great Britain and assessment of its suitability as a test to distinguish infected and vaccinated animals

Rapid, simple, and accurate antemortem tests for tuberculosis (TB) in cattle need to be developed in order to augment the existing screening methods. In particular, as cattle vaccines are developed, such tests would allow the continuation of test-and-slaughter policies alongside vaccination. Therefore, the development of an assay that distinguishes infected from vaccinated animals (a DIVA test) is an urgent research requirement. In this study, we assessed the performance of a novel multiplex serological test with sera collected from 96 skin-tested animals with bovine tuberculosis, 93 TB-free animals, and 39 cattle vaccinated with Mycobacterium bovis BCG. Our results indicate that the test has a relative sensitivity range of 77.0% to 86.5% at corresponding specificity levels of 100.0% to 77.6%. Comparison with the Bovigam gamma interferon antemortem test revealed that this serology test was significantly more sensitive at specificities above 97.9%, while the Bovigam test was, on average, about 10% more sensitive when the test specificity was set below 97%. Importantly, this serological multiplex assay does not react with sera from BCG-vaccinated calves and is therefore suitable as a DIVA test alongside BCG-based vaccine strategies.

Accuracy of three diagnostic tests for determining Mycobacterium bovis infection status in live-sampled wild meerkats (Suricata suricatta)

Accurate diagnosis of Mycobacterium bovis infection (bovine tuberculosis [bTB]) in live animals is notoriously problematic. The aim of the present study was to evaluate the diagnostic potential of 2 new serologic tests (multiantigen print immunoassay [MAPIA] and lateral flow immunoassay rapid test [RT]) in comparison with mycobacterial culture of tracheal washes for determining M. bovis infection status in a free-ranging population of wild meerkats (Suricata suricatta). During a longitudinal study lasting 2.5 years, 240 individually identifiable meerkats were each sampled up to 8 times under anesthesia every 3 months. Diagnostic accuracy was determined through Bayesian and maximum likelihood estimations of sensitivity, specificity, and likelihood ratios for each diagnostic test when used independently and in parallel to classify the disease status of individual meerkats in the absence of a gold standard. Culture of tracheal washes was highly specific (0.99; 95% confidence interval [CI] = 0.77, 1.00) but of low sensitivity (0.36; 95% CI = 0.24, 0.50) for diagnosing M. bovis-infected individuals. The longitudinal nature of the study with repeated sampling of the same individual animals served simultaneously to improve chances of detecting infection and increase confidence in a negative result in individual animals repeatedly testing negative. Although MAPIA and RT were individually of limited diagnostic use, interpreting the results of these 2 tests in parallel produced estimates of sensitivity (0.83; 95% CI = 0.67, 0.93) and specificity (0.73; 95% CI = 0.62, 0.82) high enough to usefully inform decision making when determining exposure to bTB in wild meerkats and potentially other species in which bTB poses a diagnostic challenge.

Development and validation of an enzyme-linked immunosorbent assay for antibodies against Mycobacterium bovis in European wild boar

Background

Bovine tuberculosis (bTB) remains a significant problem in some parts of Spain largely because of contacts between cattle and wildlife reservoirs in extensive grazing systems. European Wild boar (Sus scrofa) is one of the species involved in the transmission of the disease to other species. Fast and simple detection methods would be critical for assessing infection prevalence, study the mechanisms of pathogen transmission and monitoring the effects of TB control measures.

Results

An enzyme-linked immunosorbent assay (ELISA) to detect antibodies against Mycobacterium bovis in wild boar serum was developed and validated on 185 sera from TB positive and negative wild boar. Based on antigen inoculation of captive animals as well as tuberculosis compatible lesions, culture results and molecular analysis of hunted individuals, animals were allocated into two groups: tuberculosis positive group and tuberculosis negative group. After optimization of the positive to negative ratio using different combinations of serum dilutions and conjugate concentrations, the test yielded a sensitivity of 72.60% and a specificity of 96.43% for the best cut-off.

Conclusion

Although some negative group animals showed an ELISA positive reaction (< 3%), this assay showed a high potential for accurate diagnosis of TB in wild boar, as its large dynamic range supported a good discriminatory power and a satisfactory balance between sensitivity and specificity.

Multiplex immunoassay for serological diagnosis of Mycobacterium bovis infection in cattle

Efforts to develop a better diagnostic assay for bovine tuberculosis have shown that the sensitivity and specificity of an assay can be improved by the use of two or more antigens. As reported here, we developed a multiplex chemiluminescent immunoassay that can simultaneously detect antibody activity to 25 antigens in a single well in a 96-well plate array format. The chemiluminescent signal is captured with a digital imaging system and analyzed with a macro program that tracks each serum for its pattern of antibody activity for Mycobacterium bovis antigens. The comparison of sera from 522 infected and 1,489 uninfected animals showed that a sensitivity of 93.1% and a specificity of 98.4% can be achieved with a combination of antigens. The assay system is rapid and can be automated for use in a centralized laboratory.

Enhanced protection against bovine tuberculosis after coadministration of Mycobacterium bovis BCG with a Mycobacterial protein vaccine-adjuvant combination but not after coadministration of adjuvant alone

Current efforts are aimed at optimizing the protective efficacy of Mycobacterium bovis BCG by the use of vaccine combinations. We have recently demonstrated that the protection afforded by BCG alone is enhanced by vaccinating cattle with a combination of vaccines comprising BCG and a protein tuberculosis vaccine, namely, culture filtrate proteins (CFPs) from M. bovis plus an adjuvant. In the current study, three different adjuvant systems were compared. The CFP was formulated with a depot adjuvant, dimethyldioctadecyl ammonium bromide (DDA), together with one of three different immunostimulants: monophosphoryl lipid A (MPL), a synthetic mycobacterial phosphatidylinositol mannoside-2 (PIM2), and a synthetic lipopeptide (Pam3Cys-SKKKK [Pam(3)CSK(4)]). Groups of cattle (n = 10/group) were vaccinated with BCG-CFP-DDA-PIM2, BCG-CFP-DDA-MPL, or BCG-CFP-DDA-Pam(3)CSK(4). Two additional groups (n = 10) were vaccinated with BCG alone or BCG-adjuvant (DDA-MPL), and a control group was left unvaccinated. Protection was assessed by challenging the cattle intratracheally with M. bovis. Groups of cattle vaccinated with BCG-CFP-DDA-PIM2, BCG-CFP-DDA-MPL, BCG-CFP-DDA-Pam(3)CSK(4), and BCG alone showed significant reductions in three, three, five, and three pathological and microbiological disease parameters, respectively, compared to the results for the nonvaccinated group. Vaccination with the combination of BCG and the DDA-MPL adjuvant alone abrogated the protection conferred by BCG alone. The profiling of cytokine gene expression following vaccination, prior to challenge, did not illuminate significant differences which could explain the latter result. Vaccination of cattle with a combination of BCG and protein tuberculosis vaccine enhances protection against tuberculosis.

Development and evaluation of a test for tuberculosis in live European badgers (Meles meles) based on measurement of gamma interferon mRNA by real-time PCR

A real-time PCR assay for the measurement of gamma interferon (IFN-gamma) mRNA in European badger (Meles meles) blood cultures was developed. The levels of IFN-gamma mRNA in blood cultures stimulated with either bovine or avian tuberculin or specific mycobacterial antigens were compared with those in a nonstimulated control blood culture as the basis for determining the tuberculosis (TB) status of live badgers. The assay was validated by testing 247 animals for which there were matching data from postmortem examination and culture of tissues. Relative changes in the levels of IFN-gamma mRNA in response to bovine tuberculin and specific antigens were found to be greater among badgers with tissues positive for TB on culture. The test was at its most accurate (87% of test results were correct) by using blood cultures containing bovine tuberculin as the antigen and when the response to avian tuberculin was taken into account by subtracting the avian tuberculin response from the bovine tuberculin response. At a specificity of 90.7%, the test was 70.6% sensitive. At the same specificity, the current serological enzyme-linked immunosorbent assay for TB in badgers was only 53% sensitive. This work demonstrates that measurement of IFN-gamma mRNA by real-time PCR is a valid method for the detection of TB in live badgers and may provide an alternative to the current serological methods of diagnosis, the Brock test. The testing procedure can be completed within 5 h of receipt of the blood culture samples. In addition, the use of a molecular biology-based test offers the potential to fully automate the testing procedure through the use of robotics.

The immunology of bovine tuberculosis and progression toward improved disease control strategies

Failure to remove cattle diseased with Mycobacterium bovis has immense financial implications for disease control, animal health and agricultural trade as well as the zoonotic risk to human health. Current disease control strategies based on DTH skin testing fail to detect all diseased cattle and additional measures are urgently needed to improve detection of disease and to prevent naïve animals becoming exposed to infection. Experimental models of bovine TB traditionally based on intra-nasal instillation, intra-tracheal inoculation or placed in-contact with infected cattle, have been further developed using aerosolised bacteria delivered to the respiratory tract, allowing field-like bovine TB to be recreated under controlled, experimental conditions. Experimental infection models have already been used to improve diagnostic tests. Specificity of DTH skin testing can be improved under experimental conditions, using recombinant ESAT-6, while laboratory assays such as IFN-gamma release have benefited from the use of defined proteins to improve assay specificity. In combination, antigen cocktails may also improve test sensitivity. There is a concerted international effort to evaluate vaccines for use in cattle populations and to define vaccination strategies which will eliminate disease from infected herds. DNA, protein and genetically modified vaccines inoculated in a single dose, given as prime-boost or injected concurrently, will elicit significant protection against challenge with M. bovis under controlled conditions. However, vaccines and vaccination strategies require evaluation under field conditions. Furthermore, complementary strategies are under development to differentiate immune responses that follow vaccination from those following disease. This paper describes those recent advances which may lead to the introduction of improved disease control strategies.

Cattle husbandry in Ethiopia is a predominant factor affecting the pathology of bovine tuberculosis and gamma interferon responses to mycobacterial antigens

Bovine tuberculosis is a major economic problem and a potential public health risk. Improved diagnostics like the gamma interferon (IFN-gamma) test with ESAT6 and/or CFP10 could contribute to the control program. We assessed IFN-gamma responses in zebu (Ethiopian Arsi breed) and Holstein cattle kept indoors or in a pasture to tuberculin purified protein derivative (PPD) and an ESAT6-CFP10 protein cocktail. Furthermore, the intensity and distribution of pathology of bovine tuberculosis were compared between the two breeds. Our data demonstrated significantly (all P < 0.02) higher IFN-gamma responses to avian PPD, bovine PPD, and the ESAT6-CFP10 protein cocktail in Holstein than in zebu cattle, while lesion severities in infected animals and tuberculin skin test responses did not differ significantly (P > 0.05) between the two breeds. Holstein cattle that were kept indoors produced significantly (all P < 0.01) higher IFN-gamma levels in response to avian PPD, bovine PPD, and the ESAT6-CFP10 protein cocktail than did Holstein cattle kept in a pasture. Moreover, lesion severity was significantly higher in Holstein cattle kept indoors (P = 0.001) than in those kept in the pasture. Lesions were localized predominantly in the digestive tract in cattle kept in a pasture, while they were localized in the respiratory tract in cattle kept indoors. In conclusion, in Holstein cattle, husbandry was a dominant factor influencing the severity of tuberculosis lesions and IFN-gamma responses to mycobacterial antigens compared to breed. A difference in the cellular immune response between zebu and Holstein cattle was observed, while tuberculosis lesion severities were identical in the two breeds, when both were kept in a pasture.

Fluorescence polarization assay for the detection of antibodies to Mycobacterium bovis in bovine sera

The performance of a fluorescence polarization assay (FPA) that detects antibodies to Mycobacterium bovis in bovine sera is described. The FPA reported here is a direct binding primary screening assay using a small polypeptide derived from the M. bovis MPB70 protein. A secondary inhibition assay confirms suspect or presumed positive samples. Specificity studies involved five different veterinary laboratories testing 4461 presumed negative bovine samples. FPA specificity was 99.9%. The FPA was used to identify herd status as either M. bovis infected or non-infected. Herd surveillance studies (nine herds) were performed in Mexico and South Africa. The FPA had a specificity of 100% (two negative herds), and correctly identified six of seven infected herds. Finally, sera from 105 slaughter animals that had gross lesions in lymph nodes similar to those seen with bovine tuberculosis were tested by the FPA. Thin sections from the associated formalin-fixed paraffin-embedded samples of lymph nodes were stained using hematoxylin and eosin (H&E) for morphologic examination and using the Ziehl-Neelsen (ZN) method for detection of acid-fast bacilli. Of the 105 animals, 78 were classified as TB suspect based on lesion morphology, 21 were positive by ZN, 9 were positive by FPA and 13 were positive by PCR for the tuberculosis group of Mycobacterium. Among the 21 ZN positives, 11 (52.4%) were PCR positive. Among the 9 FPA positives, 8 (88.9%) were PCR positive. For the 13 PCR positives, 8 (61.5%) were FPA positive and 11 (84.6%) were ZN positives. These results show that use of the FPA for detection of M. bovis infection of cattle has value for bovine disease surveillance programs.

A novel fusion protein-based indirect enzyme-linked immunosorbent assay for the detection of bovine tuberculosis

Enzyme-linked immunosorbent assay (ELISA) for diagnosis of bovine tuberculosis has been widely explored over the years. Three Mycobacterium bovis-specific antigen genes, namely, mpb70, mpb83, and esat-6 were recombined in tandem by spliced overlap extension technology and expressed in Escherichia coli to obtain the fusion protein (rM70-83-E6). Western blot analysis showed that rM70-83-E6 can specifically react with bovine tuberculosis-positive sera but not those from cattle infected with other bovine diseases such as bovine paratuberculosis. An indirect ELISA (iELISA) method was established with rM70-83-E6 as the diagnostic antigen. The diagnostic criteria were determined using 150 serum samples from healthy cattle. Analyses of 85 serum samples from cattle with bovine tuberculosis and 100 serum samples from healthy cattle demonstrated that the sensitivity of the iELISA was 69.4% (59/85) and the specificity was 96.0% (96/100). Moreover, 46 out of 67 purified protein derivative (PPD) skin test-positive samples were also positive by iELISA, giving a positive coincidence of 68.7%, while all 50 PPD skin test-negative samples were negative by iELISA, giving a negative coincidence of 100%. The total coincidence between iELISA and the PPD skin test was 82.1%. This study demonstrated that iELISA using rM70-83-E6 antigen is simple, sensitive and easy to perform and can be used to analysis of a large number of samples for serodiagnosis of bovine tubercuiosis.

Optimizing antigen cocktails for detection of Mycobacterium bovis in herds with different prevalences of bovine tuberculosis: ESAT6-CFP10 mixture shows optimal sensitivity and specificity

Bovine tuberculosis is a major problem in many countries; hence, new and better diagnostic tools are urgently needed. In this work, we have tested ESAT6, CFP10, PE13, PE5, MPB70, TB10.4, and TB27.4 for their potentials as diagnostic markers in field animals from Northern Ireland, Mexico, and Argentina, regions with low, medium, and high prevalences of bovine tuberculosis, respectively. At all three sites, ESAT6 and CFP10 were superior diagnostic antigens, while their combination performed even better at the two sites where the combination was tested, providing the best coverage for the detection of diseased populations. The high sensitivity in the skin test reactor groups, combined with the high specificity in the tuberculosis-free groups, indicated that a diagnosis could correctly be made for 85% of the infected animals, based on their responses to these two antigens. Furthermore, TB10.4, PE13, and PE5 have the potential to supplement ESAT6 and CFP10 in a future five-component diagnostic cocktail.

Effects of different tuberculin skin-testing regimens on gamma interferon and antibody responses in cattle experimentally infected with Mycobacterium bovis

Although tuberculin skin testing has been a hallmark of bovine tuberculosis eradication campaigns, it lacks sensitivity, can be confounded by exposure to nontuberculous mycobacteria, and cannot be repeated for 60 days due to desensitization. To overcome these difficulties, an effective whole-blood cellular immunoassay for bovine gamma interferon (IFN-gamma) has been developed. The IFN-gamma test is commonly used in conjunction with tuberculin skin testing as a confirmatory test following a positive response to the caudal fold test (CFT). The present study was conducted to determine the effect of different tuberculin skin-testing regimens on IFN-gamma and antibody production by using calves that were experimentally infected with Mycobacterium bovis. Holstein calves were CFT tested 60 days after inoculation and the comparative cervical test (CCT) was conducted 7 (7-day CCT) or 55 (55-day CCT) days after the CFT. In both the 7-day CCT and 55-day CCT groups, IFN-gamma responses increased 3 days after the CFT; this was immediately followed by a decrease to pre-skin test levels 7 days after the CFT. In both groups, the application of the CCT at 7 or 55 days after the CFT resulted in no significant increase in IFN-gamma production. The administration of the CFT and the CCT to M. bovis-inoculated cattle boosted antibody responses to M. bovis PPD, rMPB83, ESAT-6, and the fusion protein Acr1-MPB83. The boosting effect was more pronounced in the 55-day CCT group. Increases in either IFN-gamma or antibody production were not seen in noninoculated cattle. Measurement of both IFN-gamma and antibody responses after skin testing may be useful in identifying M. bovis-infected cattle; however, the timing of collection of such samples may influence interpretation.

Assessment of diagnostic tools for eradication of bovine tuberculosis in cattle co-infected withMycobacterium bovisandM. aviumsubsp.paratuberculosis

The intradermal tuberculin (IDTB) test and the interferon-gamma (IFN-gamma) assay are used worldwide for detection of bovine tuberculosis in cattle, but little is known about the effect of co-infecting agents on the performance of these diagnostic tests. This report describes a field trial conducted in a cattle herd with dual infection (bovine tuberculosis and paratuberculosis) during 3.5 years. It has been based on a strategic approach encompassing serial parallel testing (comparative IDTB test, the IFN-gamma assay and serology of paratuberculosis) that was repeated 8 times over the period, and segregation of animals into two herds. The IDTB test detected 65.2% and the IFN-gamma test detected 69.6% of the Mycobacterium bovis culture-positive cattle. However, the IDTB test performed better during the first part of the trial, while the IFN-gamma test was the only method that detected infected animals during the following three samplings. The number of false positive reactors with the IDTB and/or the IFN-gamma tests was remarkably high compared to other reports, and could be caused by cross-reactivity with M. avium subsp. paratuberculosis. Also, the M. bovis isolates from cattle and wildlife from the same property were characterised using molecular techniques to disclose an epidemiological link. The IDTB test may not be appropriate to eradicate bovine tuberculosis in herds with dual mycobacterial infections. This report highlights the need to use several diagnostic techniques for the accurate detection of M. bovis infected animals in these herds.

Ante mortem diagnosis of tuberculosis in cattle: a review of the tuberculin tests, gamma-interferon assay and other ancillary diagnostic techniques

The early, preclinical stages of bovine TB can be detected in live animals by the use of tests of cellular immunity (the skin, gamma-interferon and lymphocyte transformation tests). Tests of humoral (antibody) immunity, Mycobacterium bovis PCR probes on early tissue cultures or live cattle specimens, and tests based on "electronic nose" technology have been developed more recently. The key measure of diagnostic test accuracy is the relationship between sensitivity and specificity, which determines the false-positive and false-negative proportions. None of the tests currently available for the diagnosis of bovine TB allow a perfectly accurate determination of the M. bovis infection status of cattle. Although various factors can reduce the sensitivity and specificity of the skin tests, these remain the primary ante mortem diagnostic tools for TB in cattle, providing a cost-effective and reliable means of screening entire cattle populations. Despite the inescapable limitations of existing diagnostic tests, bovine TB has been effectively eradicated from many developed countries and regions with the implementation of sound programmes of regular tuberculin skin testing and removal of reactors, coupled with slaughterhouse surveillance for undetected infections, repeat testing and culling of infected herds, cattle movement restrictions to prevent introduction of infected animals and occasional slaughter of entire herds with intractable breakdowns. This is likely to remain the mainstay of bovine TB control programmes for the foreseeable future. Additionally, newer ancillary in vitro diagnostic assays are now available to TB control programme managers to supplement the skin tests in defined circumstances according to the specific disease situation in each country or region. The strategic deployment of ancillary in vitro tests alongside the primary skin tests has enhanced the detection of M. bovis-infected cattle and reduced the number of animals slaughtered as false positives.

Advances in bovine tuberculosis diagnosis and pathogenesis: What policy makers need to know

The mainstay of tuberculosis diagnosis in cattle and deer has been the tuberculin skin test. Recent advances have allowed the incorporation of blood based assays to the diagnostic arsenal for both cattle and deer. Use of defined and specific antigens has allowed for improved specificity of cell mediated assays in both cattle and deer and advances in antibody tests for tuberculosis have potential for use in free-ranging and captive cervid populations. Combined use of blood-based assays with skin testing will require further understanding of the effect of skin testing on the accuracy of blood based assays. Models of experimental infection of cattle have allowed for increased understanding of natural disease pathogenesis. Differences likely exist; however, between cattle and deer in both disease distribution and primary route of inoculation in naturally infected animals.

Diagnosis of Mycobacterium bovis infection in cattle by use of the gamma-interferon (Bovigam®) assay

The strategic use of the gamma-interferon (IFN-gamma) assay (Bovigam) can provide a means for the early identification of Mycobacterium bovis infected cattle, thus ensuring their removal from an infected herd. When used in parallel with the tuberculin test, it is capable of identifying infected cattle, which might otherwise not be detected until later, if at all. The early detection and removal of these animals reduces the risk that they will become a source of infection for other cattle. When targeted in herds of high prevalence the benefits to the herd owner directly concerned can be considerable as the assay provides a means of shortening the period of restriction for such herds. This serves to generate confidence among herd owners and other stakeholders that effective schemes, based on sound scientific principles, can be developed to eradicate tuberculosis from infected cattle populations.

Sensitivity of human gamma interferon assay and tuberculin skin testing for detecting infection with Mycobacterium tuberculosis in patients with culture positive tuberculosis

SETTING

Nine university-affiliated chest clinics in Australia.

OBJECTIVE

To evaluate the sensitivity of a whole blood human gamma-interferon assay (HGIA, QuantiFERON-TB) for specific T lymphocyte responses and Tuberculin skin testing (TST) for the detection of Mycobacterium tuberculosis infection in subjects with culture-proven M. tuberculosis disease (TBCP).

DESIGN

Prospective testing of 129 patients with recent TBCP and 100 patients with non-tuberculosis lung disease (NTBLD).

RESULTS

Using a defined level of specific IFN-gamma production and TST 10mm as positive cut-offs, the sensitivity of HGIA was 81% compared to 89% for TST (p=0.06). When positive responses in both TST and HGIA were combined, 96% of TB patients were detected. For the NTBLD group, 43% of whom were born overseas, 73% were negative for both the HGIA and TST. Prior immunization with M. bovis (bacille Calmette-Guerin) (BCG) or the type of TB had no effect on the sensitivities of the assays. For those treated for <2 months, the sensitivities for both assays were 84%, but for those treated for >2 months the sensitivity of TST (90%) tended to be higher than for HGIA (81%) (p=0.07). The distribution of TST results in TB patients showed a broad peak between 10 and 25 mm, while the results in the HGIA were bimodal in both TB and NTBLD patients.

CONCLUSION

HGIA may prove an alternative to skin testing for detecting M. tuberculosis infection in certain settings.

Vaccination of cattle with Mycobacterium bovis culture filtrate proteins and CpG oligodeoxynucleotides induces protection against bovine tuberculosis

Culture filtrate protein (CFP) vaccines have been shown to be effective in small animal models for protecting against tuberculosis while immunisation with these types of vaccines in cattle has been less successful. A study was conducted in cattle to evaluate the ability of selected adjuvants and immunomodulators to stimulate protective immune responses to tuberculosis in animals vaccinated with Mycobacterium bovis CFP. Seven groups of cattle (n=5) were vaccinated with M. bovis CFP formulated with either Emulsigen or Polygen adjuvant alone or in combination with a specific oligodeoxynucleotides (ODN), polyinosinic acid: polycytidylic acid (poly I:C) or poly I:C and recombinant granulocyte-macrophage colony stimulating factor. Two additional groups were vaccinated subcutaneously with BCG or non-vaccinated. In contrast to the strong interferon-gamma (IFN-gamma) responses induced by BCG, the CFP vaccines induced strong antibody responses but weak IFN-gamma responses. The addition of CpG ODN to CFP significantly enhanced cell-mediated responses and elevated antibody responses to mycobacterial antigens. Of the CFP vaccinated groups, the strongest IFN-gamma responses to CFP vaccines were measured in animals vaccinated with CFP/Emulsigen+CpG or CFP/Polygen+CpG. The animals in these two groups, together with those in the BCG and non-vaccinated groups were challenged intratracheally with virulent M. bovis at 13 weeks after the first vaccination and protection was assessed, by examination for presence of tuberculous lesions in the lungs and lymph nodes, 13 weeks later at postmortem. While BCG gave the best overall protection against tuberculosis, significant protection was also seen in animals vaccinated with CFP/Emulsigen+CpG. These results establish an important role for CpG ODN in stimulating protective Th1 responses to tuberculosis in cattle and indicate that a sub-unit protein vaccine can protect these animals against tuberculosis.

Vaccination of cattle with a CpG oligodeoxynucleotide-formulated mycobacterial protein vaccine and Mycobacterium bovis BCG induces levels of protection against bovine tuberculosis superior to those induced by vaccination with BCG alone

The development of a subunit protein vaccine for bovine tuberculosis which could be used either in combination with Mycobacterium bovis BCG (to improve the efficacy of that vaccine) or alone would offer significant advantages over currently available strategies. A study was conducted with cattle to determine the protective efficacy of a strategy based on concurrent immunization with an M. bovis culture filtrate (CFP) vaccine and BCG compared to vaccination with either vaccine alone. One group of calves (10 animals per group) was vaccinated subcutaneously with CFP formulated with Emulsigen and combined with a CpG oligodeoxynucleotide (ODN). A second group was vaccinated with both the CFP vaccine and BCG injected at adjacent sites (CFP-BCG). One further group was vaccinated subcutaneously with BCG, while another group served as nonvaccinated control animals. Vaccination with CFP-BCG induced levels of antigen-specific gamma interferon (IFN-gamma) and interleukin-2 (IL-2) in whole-blood cultures that were higher than those induced by vaccination with BCG alone. The combination of CFP and BCG did not enhance the production of antibodies to M. bovis CFP compared to vaccination with CFP alone. Vaccination with CFP alone led to delayed antigen-specific IFN-gamma and IL-2 responses. Vaccination with CFP-BCG induced a high level of protection against an intratracheal challenge with virulent M. bovis, based on a significant enhancement of six pathological and microbiological parameters of protection compared with the nonvaccinated group. In contrast, vaccination with BCG alone induced a significant enhancement of protection in only one parameter, while CFP alone induced no protection. These results suggest that a combination of a CpG ODN-formulated protein vaccine and BCG offers better protection against bovine tuberculosis than does BCG alone.

The diagnosis of tuberculosis

Diagnostic testing for tuberculosis has remained unchanged for nearly a century, but newer technologies hold the promise of a true revolution in tuberculosis diagnostics. New tests may well supplant the tuberculin skin test in diagnosing latent tuberculosis infection in much of the world. Tests such as the nucleic acid amplification assays allow more rapid and accurate diagnosing of pulmonary and extrapulmonary tuberculosis. The appropriate and affordable use of any of these tests depends on the setting in which they are employed.

Effects of positive results for Mycobacterium avium subsp paratuberculosis as determined by microbial culture of feces or antibody ELISA on results of caudal fold tuberculin test and interferon- assay for tuberculosis in cattle

OBJECTIVE

To determine whether cattle testing positive for Mycobacterium avium subsp paratuberculosis as determined by microbial culture of feces or antibody ELISA were more likely to have false-positive responses on the caudal fold tuberculin (CFT) test or interferon-gamma (IFN-gamma) assay for Mycobacterium bovis than cattle testing negative for M paratuberculosis.

ANIMALS

1043 cattle from 10 herds in Michigan.

PROCEDURE

Feces and blood samples for plasma were collected from cattle > or =24 months old on the day the CFT test was read. Fecal samples were submitted for microbial culture for M paratuberculosis. Plasma samples were tested for antibody against M paratuberculosis, and IFN-gamma after stimulation with purified protein derivative tuberculin from M bovis or M avium.

RESULTS

Of 1043 cattle, 180 (17.3%) had positive CFT test results (suspects) and 8 (0.8%) had positive IFN-gamma assay results after stimulation with purified protein derivative tuberculin from M bovis. Forty-five (4.3%) and 115 (11.0%) cattle tested positive for M paratuberculosis as determined by microbial culture of feces and antibody ELISA, respectively. Cattle with positive responses for M paratuberculosis appeared to have an increased likelihood of false-positive results on the CFT test, although this association was not significant.

CONCLUSIONS AND CLINICAL RELEVANCE

No significant association was detected among cattle testing positive for M paratuberculosis as determined by microbial culture of feces and antibody ELISA and positive CFT test and IFN-gamma assay results for M bovis.