Single-antigen serological testing for bovine tuberculosis

The problem that residual Mycobacterium bovis infection poses for the eradication of bovine tuberculosis

The dynamics of Mycobacterium bovis infection in cattle can influence the proportion of infected animals that are diagnosed by ante-mortem tests in routine bovine tuberculosis (bTB) surveillance and monitoring programmes. Although the current diagnostic tests based on cell-mediated or serological responses are imperfect, they are effective in diagnosing the majority of infected animals. However, the lack of perfect sensitivity and specificity also leads to failure to diagnose all infected animals leading to persistence of infection in herds. The terms residual, subclinical, latent and anergy have been used interchangeably to denote the presence of continued undiagnosed M. bovis infection within cattle herds, which ultimately hinders the eradication of bTB and imposes substantial financial burdens on farming communities and national economies. Epidemiological data suggests the existence of M. bovis-infected, but often undetected, cattle within herds that contribute to eradication failure. This has similarities with human tuberculosis, caused by Mycobacterium tuberculosis, where latent infection is defined as the persistence of viable but quiescent bacilli for extended periods in patients without clinical symptoms but with a detectable immune response to M. tuberculosis antigens. If a similar infection state exists in cattle infected with M. bovis, the persistence of such animals in disease-managed herds is unlikely to be common given that those found to have positive immune responses to M. bovis antigens are routinely culled to minimise future risk of transmission. Apart from contributing to the burden of herd infection, such residual infection without detection may also 'seed' recipient herds following animal movements, and potentially play an important role in the overall epidemiology of bTB as the prevalence of disease decreases and the attendant altered predictive value of the diagnostic tests result in a greater proportion of infected animals remaining undetected. This review examines how the different stages of M. bovis infection in cattle may contribute to the failure to diagnose infected animals using conventional testing methodologies and the attendant risk this poses in creating prolonged or recurrent herd breakdowns.

B Cell and Antibody Responses in Bovine Tuberculosis

The development of vaccines and effective diagnostic methods for bovine tuberculosis requires an understanding of the immune response against its causative agent, Mycobacterium bovis. Although this disease is primarily investigated and diagnosed through the assessment of cell-mediated immunity, the role of B cells and antibodies in bovine tuberculosis has been relatively undervalued and understudied. Current evidence indicates that circulating M. bovis-specific antibodies are not effective in controlling the disease. However, local humoral immune responses may contribute to either defence or pathology. Recent studies in animal models and cattle vaccine trials suggest a potential beneficial role of B cells in tuberculosis control. This review discusses the role of B cells and antibodies in bovine tuberculosis and explores antibody-based diagnostics for the disease, including traditional techniques, such as different ELISA, new platforms based on multiple antigens and point-of-care technologies. The high specificity and sensitivity values achieved by numerous antibody-based tests support their use as complementary tests for the diagnosis of bovine tuberculosis, especially for identifying infected animals that may be missed by the official tests.

Diagnostic accuracy of the Enferplex Bovine TB antibody test using individual milk samples from cattle

Bovine tuberculosis is usually diagnosed using tuberculin skin tests or at post-mortem. Recently, we have developed a serological test for bovine tuberculosis in cattle which shows a high degree of accuracy using serum samples. Here, we have assessed the performance of the test using individual bovine milk samples. The diagnostic specificity estimate using the high sensitivity setting of the test was 99.7% (95% CI: 99.2-99.9). This estimate was not altered significantly by tuberculin boosting. The relative sensitivity estimates of the test using the high sensitivity setting in milk samples from comparative skin test positive animals was 90.8% (95% CI: 87.1-93.6) with boosting. In animals with lesions, the relative sensitivity was 96.0% (95% CI: 89.6-98.7). Analysis of paired serum and milk samples from skin test positive animals showed correlation coefficients ranging from 0.756-0.955 for individual antigens used in the test. Kappa analysis indicated almost perfect agreement between serum and milk results, while McNemar marginal homogeneity analysis showed no statistically significant differences between the two media. The positive and negative likelihood ratio were 347.8 (95% CI: 112.3-1077.5) and 0.092 (95% CI: 0.07-0.13) respectively for boosted samples from skin test positive animals. The results show that the test has high sensitivity and specificity in individual milk samples and thus milk samples could be used for the diagnosis of bovine tuberculosis.

Diagnostic accuracy of the Enferplex Bovine Tuberculosis antibody test in cattle sera

Bovine tuberculosis is a contagious bacterial disease of worldwide economic, zoonotic and welfare importance caused mainly by Mycobacterium bovis infection. Current regulatory diagnostic methods lack sensitivity and require improvement. We have developed a multiplex serological test for bovine tuberculosis and here we provide an estimate of the diagnostic accuracy of the test in cattle. Positive and negative reference serum samples were obtained from animals from Europe and the United States of America. The diagnostic specificity estimate was 98.4% and 99.7% using high sensitivity and high specificity settings of the test respectively. Tuberculin boosting did not affect the overall specificity estimate. The diagnostic sensitivity in samples from Mycobacterium bovis culture positive animals following tuberculin boosting was 93.9%.The relative sensitivity following boosting in tuberculin test positive, lesion positive animals and interferon gamma test positive, lesion positive animals was 97.2% and 96.9% respectively. In tuberculin test negative, lesion positive animals and in interferon gamma test negative, lesion positive animals, the relative sensitivity following tuberculin boosting was 88.2% and 83.6% respectively. The results show that the test has high diagnostic sensitivity and specificity and can detect infected animals that are missed by tuberculin and interferon gamma testing.

Improving the diagnosis of bovine tuberculosis using gold nanoparticles conjugated with purified protein derivative: special regard to staphylococcal protein A and streptococcal protein G

Different ancillary immunodiagnostic tests were traditionally-established for diagnosis of bovine tuberculosis (BTB) either cellular or humoral as tuberculin skin test (TST), gamma interferon (INF-γ), and indirect enzyme-linked immunosorbent assay (iELISA). These tests had been consumed more time and expensive, and needed sophisticated equipment. To dissolve these problems, serological diagnosis depending on humoral immunity is the aim of this work. Herein, slide-based agglutination test was chosen as a rapid and simple field test based on purified protein derivative (PPD) antigen in addition to some supplementation materials such as Staphylococcal protein A (SPA) and Streptococcal protein G (SPG) to improve detection of BTB antibody in serum samples. Gold nanoparticles (Au NPs) were synthesized by gamma ray, and after complete characterization, the synthesized Au NPs were spherical, small-sized, and stable without any impurities. Addition of such supplementation reagents for serodiagnosis of tuberculosis is of paramount important for the detection of serum antibodies against tuberculosis (TB) and it was considered an easily simple and possible way for improving TB diagnosis. In this work, 70 animals tested positive for TST as well as 20 animals tested negative for TST were used for the diagnosis of BTB depending on humoral immune response based on PPD slide agglutination test using reporter regents (SPA and/or SPG) either native or recombinant. The agglutination density was recorded and read in 4 degrees of positivity with scores ranging from negative (-) to very strong reaction (++++) occurred in different times of agglutination. Groups showed 100% positive reactivates employed in Exp. 1, 2, and 3 with differentiation of slide agglutination test density and was rated from moderate positivity (2+) to very strong (4+), with predominant positivity in density of (3+). Pink-colored intensity is associated with the strengthened reactions between PPD-conjugated Au NPs and serum antibody of each tested samples, which allows for visual rapid, simple, and effective attractive diagnosis of BTB. The specificity and sensitivity of the serological tests were characterized. TST offers the highest sensitivity (83.6%) among the other immunoassays, while the lowest specificity was recorded in TST (57.4%). SPA/SPG offers the best performance in term of combined sensitivity and specificity (performance index) of 175.4. Therefore, the development and uses of detection reagent (such as SPA and/or SPG) slide co-agglutination test (COAT), either native or recombinant (rSPA/SPG) for the detection of TB antibodies based on PPD antigen, as well as the uses of Au NPs rSPA/SPG as detection conjugate based on the same antigen, were also performed as a simple, rapid, sensitive, specific, eco-friendly, and low cost, which shows a great potential in field and lab diagnosis of BTB. So, high reduction in reagents that yields reactions similarly as traditional techniques was needed.

Evaluation of Mycobacterium tuberculosis lipoarabinomannan antigen assay and rapid serology blood test for the diagnosis of bovine tuberculosis in Ethiopia

Background

Bovine tuberculosis (bTB) is prevalent in dairy cattle in Ethiopia. Currently used diagnostic tools such as the single intradermal comparative tuberculin test (SICTT) are time consuming and labor intensive. A rapid, easy-to-use and cost-effective diagnostic test would greatly contribute to the control of bTB in developing countries like Ethiopia. In the present study, two point-of-care diagnostic tests were evaluated for the detection of bTB: LIONEX® Animal TB Rapid test, a membrane-based test for the detection of antibodies to Mycobacterium bovis in blood and ALERE® Determine TB Lipoarabinomannan (LAM) Ag, an immunoassay for the detection of lipoarabinomannan (LAM) antigen (Ag) of mycobacteria in urine. A combination of the SICTT and gamma interferon (IFN-γ) test was used as the gold standard for the validation of these point-of-care tests, as it was not feasible to slaughter the study animals to carry out the historical gold standard of mycobacterial culture. A total of 175 heads of cattle having three different bTB infection categories (positive SICTT, negative SICTT, and unknown SICTT status) were used for this study.

Result

The sensitivity and specificity of TB LAM Ag were 72.2% (95% CI = 62.2, 80.4) and 98.8% (95% CI = 93.6, 99.7), respectively, while the sensitivity and specificity of the LIONEX Animal TB rapid test assay were 54% (95% CI = 44.1 64.3) and 98.8% (95% CI = 93.6, 99.7) respectively. The agreement between TB LAM Ag and SICTT was higher (κ = 0.85; 95% CI = 0.65–0.94) than between TB LAM Ag and IFN-γ (κ = 0.67; 95% CI = 0.52–0.81). The agreement between LIONEX Animals TB Rapid blood test and SICTT was substantial, (κ = 0.63; 95% CI = 0.49–0.77) while the agreement between LIONEX Animal TB rapid blood test and IFN-γ test was moderate (κ = 0.53; 95% CI = 0.40–0.67). Analysis of receiver operating curve (ROC) indicated that the area under the ROC curve (AUC) for TB LAM Ag was 0.85 (95% CI = 0.79–0.91) while it was 0.76 (95% CI; =0.69–0.83) for LIONEX Animal TB rapid test assay.

Conclusion

This study showed that TB LAM Ag had a better diagnostic performance and could potentially be used as ancillary either to SICTT or IFN-γ test for diagnosis of bTB.

Association between results of diagnostic tests for bovine tuberculosis and Johne's disease in cattle

BACKGROUND

Bovine tuberculosis (bTB) diagnosis is impaired by numerous factors including cross-reactivity with Mycobacterium avium subspecies paratuberculosis, which causes Johne's disease (JD). In addition, the effect of repeated bTB-intradermal testing on the performance of JD diagnostic tests is not fully understood. This study aimed to evaluate the impact of repeated bTB-intradermal tests under field conditions in Spain on the JD serological status of cattle.

METHODS

bTB-positive herds (n=264) from Castilla-y-Leon region were selected and matched with officially tuberculosis-free control herds. The association between JD and bTB status at the herd level was assessed using conditional logistic regression and, in herds with both JD-positive and bTB-positive animals, a Bayesian hierarchical mixed-effect model was used for individual-level analysis.

RESULTS

A significantly higher risk of being JD positive (OR: 1.48; 95 per cent CI: 1.01 to 2.15) was found for bTB-positive herds compared with controls. Individual results indicated that cattle tested more than three times per year, within the last 90 days and more than 12 months were more likely to be JD positive. A skin test-related boost in antibody response could be the cause of an apparent increase of the sensitivity of the JD-absorbed ELISA.

CONCLUSION

The results demonstrate the interaction between bTB repeated testing and JD individual and herd-level results and this improved knowledge will facilitate the design of more effective control programmes in herds coinfected with two of the most important endemic diseases affecting cattle in Spain.

New serological platform for detecting antibodies against Mycobacterium tuberculosis complex in European badgers

European badgers (Meles meles) have been identified as wildlife reservoirs for Mycobacterium bovis in the UK and Ireland, and may also have a role in the epidemiology of animal tuberculosis in other European regions. Thus, detection of M. bovis‐infected badgers may be required for the purposes of surveillance and monitoring of disease levels in infected populations. Current serological assays to detect M. bovis infection in live badgers, while rapid and inexpensive, show limited diagnostic sensitivity. Here we describe and evaluate new ELISA platforms for the recognition of the P22 multiprotein complex derived from the purified protein derivative (PPD) of M. bovis. The recognition of IgG against P22 multiprotein complex derived from PPD‐B was tested by ELISA in the serum of badgers from the UK, Ireland and Spain. TB infection in the badgers was indicated by the presence of M. bovis in tissues by culture and histology at post‐mortem examination and TB‐free status was established by repeated negativity in the interferon γ release assay (IGRA). In experimentally infected badgers, humoral antibody responses against P22 developed within 45 days post‐infection. The ELISA tests showed estimated sensitivity levels of 74–82% in experimentally and naturally infected badgers with specificities ranging from 75% to 100% depending on the badger population tested. The P22 multi‐antigen based ELISAs provide a sensitive and specific test platform for improved tuberculosis surveillance in badgers.

Identification of Novel Antigens Recognized by Serum Antibodies in Bovine Tuberculosis

Bovine tuberculosis (TB), caused by Mycobacterium bovis, remains an important zoonotic disease posing a serious threat to livestock and wildlife. The current TB tests relying on cell-mediated and humoral immune responses in cattle have performance limitations. To identify new serodiagnostic markers of bovine TB, we screened a panel of 101 recombinant proteins, including 10 polyepitope fusions, by a multiantigen print immunoassay (MAPIA) with well-characterized serum samples serially collected from cattle with experimental or naturally acquired M. bovis infection. A novel set of 12 seroreactive antigens was established. Evaluation of selected proteins in the dual-path platform (DPP) assay showed that the highest diagnostic accuracy (∼95%) was achieved with a cocktail of five best-performing antigens, thus demonstrating the potential for development of an improved and more practical serodiagnostic test for bovine TB.

Proteomic characterisation of bovine and avian purified protein derivatives and identification of specific antigens for serodiagnosis of bovine tuberculosis

Background

Bovine purified protein derivative (bPPD) and avian purified protein derivative (aPPD) are widely used for bovine tuberculosis diagnosis. However, little is known about their qualitative and quantitative characteristics, which makes their standardisation difficult. In addition, bPPD can give false-positive tuberculosis results because of sequence homology between Mycobacterium bovis (M. bovis) and M. avium proteins. Thus, the objective of this study was to carry out a proteomic characterisation of bPPD, aPPD and an immunopurified subcomplex from bPPD called P22 in order to identify proteins contributing to cross-reactivity among these three products in tuberculosis diagnosis.

Methods

Trypsin digests of bPPD, aPPD and P22 were analysed by nanoscale liquid chromatography-electrospray ionization tandem mass spectrometry. Mice were immunised with bPPD or aPPD, and their serum was tested by indirect ELISA for reactivity against these preparations as well as against P22.

Results

A total of 456 proteins were identified in bPPD, 1019 in aPPD and 118 in P22; 146 of these proteins were shared by bPPD and aPPD, and 43 were present in all three preparations. Candidate proteins that may cause cross-reactivity between bPPD and aPPD were identified based on protein abundance and antigenic propensity. Serum reactivity experiments indicated that P22 may provide greater specificity than bPPD with similar sensitivity for ELISA-type detection of antibodies against M. tuberculosis complex.

Conclusion

The subpreparation from bPPD called P22 may be an alternative to bPPD for serodiagnosis of bovine tuberculosis, since it shares fewer proteins with aPPD than bPPD does, reducing risk of cross-reactivity with anti-M. avium antibodies.

Electronic supplementary material

The online version of this article (10.1186/s12014-017-9171-z) contains supplementary material, which is available to authorized users.

Generation of Monoclonal Antibodies against Ag85A Antigen of Mycobacterium tuberculosis and Application in a Competitive ELISA for Serodiagnosis of Bovine Tuberculosis

The Ag85 complex functions as the main secretory protein of Mycobacterium tuberculosis (M. tuberculosis) and BCG. This complex is composed of the proteins, Ag85A, Ag85B, and Ag85C, with Ag85A thought to play the largest role within the complex. However, the lack of commercially available monoclonal antibodies (mAbs) against Ag85A still hinders the biological and applicative research on this protein. In this study, we developed and identified anti-Ag85A mAbs, and five hybridoma cells were established. Using the indirect immunofluorescence test, we found that two anti-Ag85A mAbs did not cross-react with Ag85B and/or Ag85C. In addition, we showed that all of the mAbs tested in this study are able to react with endogenous Ag85A protein in BCG and rBCG:Ag85A using indirect ELISA and Western blot analyses. A competitive ELISA (cELISA) based on mAb 3B8 was developed, the analyses of clinic serum samples from cattle with bovine tuberculosis (TB) and healthy cattle demonstrated that the sensitivity of the cELISA was 54.2% (26/48) and the specificity was 83.5% (167/200). This study demonstrated that the mAbs against Ag85A will provide useful reagents for further investigation into the function of the Ag85 complex and can be used for serodiagnosis of bovine TB.

Potential for rapid antibody detection to identify tuberculous cattle with non-reactive tuberculin skin test results

BACKGROUND

Bovine tuberculosis (TB) control programs generally rely on the tuberculin skin test (TST) for ante-mortem detection of Mycobacterium bovis-infected cattle.

RESULTS

Present findings demonstrate that a rapid antibody test based on Dual-Path Platform (DPP^®) technology, when applied 1-3 weeks after TST, detected 9 of 11 and 34 of 52 TST non-reactive yet M. bovis-infected cattle from the US and GB, respectively. The specificity of the assay ranged from 98.9% (n = 92, US) to 96.0% (n = 50, GB) with samples from TB-free herds. Multi-antigen print immunoassay (MAPIA) revealed the presence of antibodies to multiple antigens of M. bovis in sera from TST non-reactors diagnosed with TB.

CONCLUSIONS

Thus, use of serologic assays in series with TST can identify a significant number of TST non-reactive tuberculous cattle for more efficient removal from TB-affected herds.

Effects of Serial Skin Testing with Purified Protein Derivative on the Level and Quality of Antibodies to Complex and Defined Antigens in Mycobacterium bovis-Infected Cattle

Several serological tests designed to detect antibodies to immunodominant Mycobacterium bovis antigens have recently emerged as ancillary tests for the detection of bovine tuberculosis in cattle, particularly when used after the injection of purified protein derivative (PPD) for skin testing, which significantly boosts M. bovis-specific antibody responses. The present findings demonstrate the onset and duration of boosted antibody responses after the injection of M. bovis PPD for the caudal fold test (CFT) and Mycobacterium avium and M. bovis PPDs for the comparative cervical test (CCT), administered in series in cattle experimentally infected with M. bovis. While skin tests boosted the responses to certain antigens (i.e., MPB83 and MPB70), they did not affect the responses to other antigens (e.g., ESAT-6, CFP10, MPB59, and MPB64). Administration of the CCT 105 days after the CFT resulted in an even greater secondary boost in antibody responses to MPB83 and MPB70 and to a proteinase K-digested whole-cell sonicate (WCS-PK) of M. bovis. Both IgM and IgG contributed to the initial boost in the MPB83/MPB70-specific antibody response after the CFT. The secondary boost after the CCT was primarily due to increased IgG levels. Also, the avidity of antibodies to MPB83 and MPB70 increased after the CCT in M. bovis-infected cattle. The avidity of antibodies to the WCS-PK antigens increased in the interval between the CFT and the CCT but did not increase further after the CCT. Together, these findings demonstrate that the administration of PPDs for skin tests results in additive enhancement (i.e., when the CFT and CCT are performed in series), both qualitative and quantitative, of MPB83/MPB70-specific antibody responses.

Evaluation of ethanol vortex ELISA for detection of bovine tuberculosis in cattle and deer

Background

The use of serological assays for diagnosis of bovine tuberculosis (TB) has been intensively studied and use of specific antigens have aided in improving the diagnostic accuracy of the assays. In the present study, we report an in-house enzyme linked immunosorbent assay (ELISA), developed by using ethanol extract of Mycobacterium bovis (M. bovis). The assay, named (ethanol vortex ELISA [EVELISA]), was evaluated for detection of anti- M. bovis antibodies in the sera of cattle and white-tailed deer.

Methods

By using the EVELISA, we tested sera obtained from two species of animals; cattle (n = 62 [uninfected, n = 40; naturally infected, n = 22]) and white-tailed deer (n = 41 [uninfected, n = 25; naturally infected, n = 7; experimentally infected, n = 9]). To detect species specific molecules, components in the ethanol extract were analyzed by thin layer chromatography and western blotting.

Results

Among the tested animals, 77.2% of infected cattle and 87.5% of infected deer tested positive for anti- M. bovis antibody. There were only minor false positive reactions (7.5% in cattle and 0% in deer) in uninfected animals. M. bovis -specific lipids and protein (MPB83) in the ethanol extract were detected by thin layer chromatography and western blotting, respectively.

Conclusion

The results warrant further evaluation and validation of EVELISA for bovine TB diagnosis of traditional and alternative livestock as well as for free-ranging animal species.

Current ante-mortem techniques for diagnosis of bovine tuberculosis

Bovine tuberculosis (TB), mainly caused by Mycobacterium bovis, is a zoonotic disease with implications for Public Health and having an economic impact due to decreased production and limitations to the trade. Bovine TB is subjected to official eradication campaigns mainly based on a test and slaughter policy using diagnostic assays based on the cell-mediated immune response as the intradermal tuberculin test and the gamma-interferon (IFN-γ) assay. Moreover, several diagnostic assays based on the detection of specific antibodies (Abs) have been developed in the last few years with the aim of complementing the current diagnostic techniques in the near future. This review provides an overview of the current ante-mortem diagnostic tools for diagnosis of bovine TB regarding historical background, methodologies and sensitivity (Se) and specificity (Sp) obtained in previous studies under different epidemiological situations.

Relevance of bovine tuberculosis research to the understanding of human disease: historical perspectives, approaches, and immunologic mechanisms

Pioneer studies on infectious disease and immunology by Jenner, Pasteur, Koch, Von Behring, Nocard, Roux, and Ehrlich forged a path for the dual-purpose with dual benefit approach, demonstrating a profound relevance of veterinary studies for biomedical applications. Tuberculosis (TB), primarily due to Mycobacterium tuberculosis in humans and Mycobacterium bovis in cattle, is an exemplary model for the demonstration of this concept. Early studies with cattle were instrumental in the development of the use of Koch's tuberculin as an in vivo measure of cell-mediated immunity for diagnostic purposes. Calmette and Guerin demonstrated the efficacy of an attenuated M. bovis strain (BCG) in cattle prior to use of this vaccine in humans. The interferon-γ release assay, now widely used for TB diagnosis in humans, was developed circa 1990 for use in the Australian bovine TB eradication program. More recently, M. bovis infection and vaccine efficacy studies with cattle have demonstrated a correlation of vaccine-elicited T cell central memory (TCM) responses to vaccine efficacy, correlation of specific antibody to mycobacterial burden and lesion severity, and detection of antigen-specific IL-17 responses to vaccination and infection. Additionally, positive prognostic indicators of bovine TB vaccine efficacy (i.e., responses measured after infection) include: reduced antigen-specific IFN-γ, iNOS, IL-4, and MIP1-α responses; reduced antigen-specific expansion of CD4(+) T cells; and a diminished activation profile on T cells within antigen stimulated cultures. Delayed type hypersensitivity and IFN-γ responses correlate with infection but do not necessarily correlate with lesion severity whereas antibody responses generally correlate with lesion severity. Recently, serologic tests have emerged for the detection of tuberculous animals, particularly elephants, captive cervids, and camelids. B cell aggregates are consistently detected within tuberculous lesions of humans, cattle, mice and various other species, suggesting a role for B cells in the immunopathogenesis of TB. Comparative immunology studies including partnerships of researchers with veterinary and medical perspectives will continue to provide mutual benefit to TB research in both man and animals.

Evaluation of a commercial enzyme-linked immunosorbent assay for the diagnosis of bovine tuberculosis from milk samples from dairy cows

Milk samples from dairy cows provide a ready source of material for measuring antibody responses to Mycobacterium bovis antigens. In this study, we evaluated the IDEXX enzyme-linked immunosorbent assay (ELISA) for the measurement of antibody responses to M. bovis antigens MPB70 and MPB83 in milk samples from New Zealand cattle. Test sensitivities for individual milk and serum samples were assessed in samples collected from 44 M. bovis-infected cows, and test specificities were assessed in milk samples collected from 356 cows from tuberculosis (TB)-free herds. Milk vat samples were collected from 505 herds from regions with relatively high or low prevalences of infection. The ELISA had a sensitivity of 50% and a specificity of 97.5% for milk samples, and the test sensitivities for milk and serum samples were the same. Dilution of the positive test milk samples in milk from noninfected cows at 1/10, 1/20, and 1/50 dilutions reduced the proportions of positive responses to 13/21, 9/21, and 4/21, respectively. Small differences were observed in the ELISA responses of milk samples from individual TB-free cows collected at different times during lactation. No significant differences were detected in the ELISA responses of milk vat samples collected from infected and noninfected herds. This study shows that milk samples can be substituted for serum samples for screening individual cows for M. bovis infection, and pooling of milk samples from 10 to 20 animals can result in a reduction in the sensitivity by approximately 50%. However, screening of milk vat samples is unlikely to be useful in countries with low prevalences of M. bovis in cattle and large herd sizes.

Facts and dilemmas in diagnosis of tuberculosis in wildlife

Mycobacterium bovis, causing bovine tuberculosis (BTB), has been recognized as a global threat at the wildlife-livestock-human interface, a clear "One Health" issue. Several wildlife species have been identified as maintenance hosts. Spillover of infection from these species to livestock or other wildlife species may have economic and conservation implications and infection of humans causes public health concerns, especially in developing countries. Most BTB management strategies rely on BTB testing, which can be performed for a range of purposes, from disease surveillance to diagnosing individual infected animals. New diagnostic assays are being developed for selected wildlife species. This review investigates the most frequent objectives and associated requirements for testing wildlife for tuberculosis at the level of individual animals as well as small and large populations. By aligning those with the available (immunological) ante mortem diagnostic assays, the practical challenges and limitations wildlife managers and researchers are currently faced with are highlighted.

The secreted lipoprotein, MPT83, of Mycobacterium tuberculosis is recognized during human tuberculosis and stimulates protective immunity in mice

The long-term control of tuberculosis (TB) will require the development of more effective anti-TB vaccines, as the only licensed vaccine, Mycobacterium bovis bacille Calmette-Guérin (BCG), has limited protective efficacy against infectious pulmonary TB. Subunit vaccines have an improved safety profile over live, attenuated vaccines, such as BCG, and may be used in immuno-compromised individuals. MPT83 (Rv2873) is a secreted mycobacterial lipoprotein expressed on the surface of Mycobacterium tuberculosis. In this study, we examined whether recombinant MPT83 is recognized during human and murine M. tuberculosis infection. We assessed the immunogenicity and protective efficacy of MPT83 as a protein vaccine, with monophosphyl lipid A (MPLA) in dimethyl-dioctadecyl ammonium bromide (DDA) as adjuvant, or as a DNA vaccine in C57BL/6 mice and mapped the T cell epitopes with peptide scanning. We demonstrated that rMPT83 was recognised by strong proliferative and Interferon (IFN)-γ-secreting T cell responses in peripheral blood mononuclear cells (PBMC) from patients with active TB, but not from healthy, tuberculin skin test-negative control subjects. MPT83 also stimulated strong IFN-γ T cell responses during experimental murine M. tuberculosis infection. Immunization with either rMPT83 in MPLA/DDA or DNA-MPT83 stimulated antigen-specific T cell responses, and we identified MPT83_127–135 (PTNAAFDKL) as the dominant H-2^b-restricted CD8⁺ T cell epitope within MPT83. Further, immunization of C57BL/6 mice with rMPT83/MPLA/DDA or DNA-MPT83 stimulated significant levels of protection in the lungs and spleens against aerosol challenge with M. tuberculosis. Interestingly, immunization with rMPT83 in MPLA/DDA primed for stronger IFN-γ T cell responses to the whole protein following challenge, while DNA-MPT83 primed for stronger CD8⁺ T cell responses to MPT83_127–135. Therefore MPT83 is a protective T cell antigen commonly recognized during human M. tuberculosis infection and should be considered for inclusion in future TB subunit vaccines.

Development and evaluation of an enzyme-linked immunosorbent assay for use in the detection of bovine tuberculosis in cattle

As a consequence of continued spillover of Mycobacterium bovis into cattle from wildlife reservoirs and increased globalization of cattle trade with associated transmission risks, new approaches such as vaccination and novel testing algorithms are seriously being considered by regulatory agencies for the control of bovine tuberculosis. Serologic tests offer opportunities for identification of M. bovis-infected animals not afforded by current diagnostic techniques. The present study describes assay development and field assessment of a new commercial enzyme-linked immunosorbent assay (ELISA) that detects antibody to M. bovis antigens MPB83 and MPB70 in infected cattle. Pertinent findings include the following: specific antibody responses were detected at ∼90 to 100 days after experimental M. bovis challenge, minimal cross-reactive responses were elicited by infection/sensitization with nontuberculous Mycobacterium spp., and the apparent sensitivity and specificity of the ELISA with naturally infected cattle were 63% and 98%, respectively, with sensitivity improving as disease severity increased. The ELISA also detected infected animals missed by the routine tuberculin skin test, and antibody was detectable in bulk tank milk samples from M. bovis-infected dairy herds. A high-throughput ELISA could be adapted as a movement, border, or slaughter surveillance test, as well as a supplemental test to tuberculin skin testing.

Overt Mycobacterium avium subsp. paratuberculosis Infection: An Infrequent Occurrence in Archived Tissue from False TB Reactor Cattle in Michigan, USA

The objective of this study was to retrospectively determine whether or not cattle from the state of Michigan which were classified as bovine tuberculosis reactors, based on currently approved field and laboratory testing methods, were overtly infected with Mycobacterium avium subsp. paratuberculosis (MAP). Included in this study were 384 adult cattle submitted to the Diagnostic Center for Population and Animal Health over a seven-year period. Cattle were tested utilizing standard methods to confirm that all cattle were lesion and culture negative for infection with Mycobacterium bovis at postmortem examination. Retrospective analysis of formalin-fixed, paraffin-embedded sections of ileum and ileocecal lymph node were evaluated by histopathology, acid-fast staining, and PCR assays to detect MAP. Overall, only 1.04 percent of cattle showed overt infection with MAP on visual examination of sections of ileum and/or ileo-cecal lymph node. This increased slightly to 2.1 percent of cattle likely infected with MAP after additional testing using a PCR assay. Based on these results, we found no evidence that overt infection with MAP plays a major role in the false tuberculosis reactor test results for cattle examined in this study.

Use of recombinant proteins MPB70 or MPB83 as capture antigens in ELISAs to confirm bovine tuberculosis infections in Brazil

The objective was to evaluate the use of two indirect IgG-ELISA tests (with recombinant proteins MPB70 or MPB83, respectively, as capture antigens) as confirmatory tests for diagnosis of bovine tuberculosis in a herd of naturally infected dairy cows. Results for ELISA-MPB70 and ELISA-MPB83 were similar (kappa statistic=0.92) on Days 0 (day of intradermal injection with purified protein derivatives, PPD), 7, and 21. The kappa statistic between ELISA and the Comparative Intradermal Tuberculin Test, as well as ELISA sensitivity and specificity (relative to culture or PCR as standards) were: 0.7, 34.4% and 75% on Day 0; 0.25, 53.8% and 66.6% on Day 7; and 0.01, 1.8% and 77.7% on Day 21, respectively. In conclusion, although ELISAs using MPB70 or MPB83 as antigens were not reliable indicators of infection status, especially on Days 7 and 21, they were of potential value as complementary tools to intradermal PPD testing.

Mycobacterium bovis antigens for the differential diagnosis of vaccinated and infected cattle

The urgency for new and improved cattle vaccines and diagnostic reagents for Bovine tuberculosis (TB) has made their development a research priority in Great Britain (GB). Significant progress has been made to develop specific antigens that allow the differentiation of BCG vaccinated and Mycobacterium bovis infected cattle (DIVA test). This has been greatly facilitated by the completion of the genome sequences of M. tuberculosis, M. bovis and BCG Pasteur and the subsequent application of comparative genome and transcriptome analysis to define DIVA antigens that complemented the prototype DIVA antigens ESAT-6 and CFP-10 by increasing their test sensitivity. Finally, we present an up-date of our current approaches in this area.

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.

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.