Current ante-mortem techniques for diagnosis of bovine tuberculosis

Evaluation of a new enzyme-linked immunosorbent assay for the diagnosis of tuberculosis in goat milk

Caprine tuberculosis (TB) is a zoonosis with sanitary and economic repercussions. Caprine TB control programs are based on a test and cull strategy using the intradermal tuberculin tests and slaughterhouse surveillance. However, this approach is not always feasible and may have a limited sensitivity under specific circumstances. In this study, performance of a new experimental test based on the P22 protein complex (P22 ELISA) was evaluated in two TB-infected herds using milk and serum samples and compared with cell-based diagnostic tests. Samples from a low (n = 62, herd 1) and a high (n = 52, herd 2) TB prevalence herd were selected. Moreover, bulk tank milk samples from both herds were analysed using the P22 ELISA. At the end of the study, a group of animals (n = 21) was euthanized and subjected to post-mortem analysis and bacteriological culture. Significant differences (p < .001) on the qualitative and quantitative (ODs) results were observed between herds using both serum and milk samples in the P22 ELISA. The correlation observed in the quantitative results obtained in serum and milk samples was very strong in animals from flock 2 (r_s = 0.91) and moderate in animals from flock 1 (r_s = 0.46). Among the slaughtered animals, the P22 ELISA detected a higher proportion of lesion-culture positive animals than cell-based diagnostic tests (61.9 and 66.7% using milk and serum samples, respectively). The P22 ELISA using milk samples demonstrated a similar sensitivity compared with serum samples, suggesting it might be a valuable test for TB control in dairy goats.

More insights about the interfering effect of Mycobacterium avium subsp. paratuberculosis (MAP) infection on Mycobacterium bovis (M. bovis) detection in dairy cattle

The estimated herd and within herd Mycobacterium bovis (M. bovis) infection prevalence in the southern Chile regions are 0.3 and 0.67%, respectively. However, higher rates of infection still remain in some herds. In parallel, it is well established that a big proportion of cattle herds are infected with Mycobacterium avium subsp. paratuberculosis (MAP), which has been also associated with a clear interference effect on M. bovis diagnosis. The present study aims to provide more insights about the diagnostic interference for Mycobacterium bovis detection due to co-infection with MAP. To better understand the dynamics of this identified interference, the effect of MAP genotype present, as well as MAP faecal shedding values (as proxy of the infection progression), for each of the CFT results was compared. No relationship was observed between MAP genotype with any type of differential response to the diagnostic tests of M. bovis infection. However, MAP shedding values in animals with positive CFT diagnostic results for M. bovis infection was significantly lower than animals with a negative CFT result, observing that as the MAP shedding load raises, the response to the bovine tuberculin test tends to be negative. The findings reported in this study allows to interpret that one of the causes of the prolonged elimination of M. bovis infection from some cattle herds may be due in part to the advanced MAP infection status in co-infected individuals affecting the outcome of screening in-vivo diagnostic techniques such as CFT. These false negative animals that show negative results to M. bovis detection tests, may maintain the infection at herd level and spread the pathogen to healthy individuals.

Biomarkers of cell-mediated immunity to bovine tuberculosis

Whole blood based assays, particularly interferon gamma (IFN-γ) release assays (IGRAs), are used for the diagnosis of both bovine and human tuberculosis (TB). The aim of the current study was to evaluate a panel of cytokines and chemokines for potential use as diagnostic readouts indicative of Mycobacterium bovis (M. bovis) infection in cattle. A gene expression assay was used to determine the kinetics of the response to M. bovis purified protein derivative and a fusion protein consisting of ESAT-6, CFP10, and Rv3615c upon aerosol infection with ∼10⁴ cfu of M. bovis. The panel of biomarkers included: IFN-γ, CXCL9, CXCL10, CCL2, CCL3, TNF-α, IL-1α, IL-1β, IL-1Ra, IL-22, IL-21 and IL-13. Protein levels of IFN-γ, CXCL9, and CXCL10 were determined by ELISA. Findings suggest that CXCL9, CXCL10, IL-21, IL-13, and several acute phase cytokines may be worth pursuing as diagnostic biomarkers of M. bovis infection in cattle.

The Role of Phosphatidylinositol Mannosides in the Serological Diagnosis of Mycobacterial Infections

Accurate diagnosis of mycobacterial infections, such as bovine tuberculosis and paratuberculosis, remains challenging. Available direct diagnostic tests aimed at detecting the pathogen are highly specific but lack sensitivity, depending on the stage of infection and the prevalence of infection in a population. The sensitivity of indirect diagnostic assays that measure the host immune response to infection is similarly affected by disease characteristics. The choice of antigen used to detect a host response to infection has a critical impact on test sensitivity and specificity. Many indirect tests rely on crude antigen preparations and cell-free extracts, of which the production is poorly standardized. Moreover, these preparations contain ample uncharacterized cross-reactive compounds. To enhance serological test specificity, existing assays depend on the pre-treatment of samples and a relatively high cut-off value, that in turn influences test sensitivity. Research therefore focuses on the identification of more specific, defined antigens to improve diagnostics. In the current study, we extracted phosphatidylinositol mannosides (PIMs) and investigated their potential use in antibody-based tests. Our results demonstrate that specific IgG class antibodies are generated against PIMs in cows, but this is unrelated to tuberculosis or paratuberculosis infection status, making these antigens unsuitable for diagnostic applications. In addition, we demonstrate that PIMs are widely present in crude antigen preparations and in serum pre-absorption buffer. Our results indicate that PIMs are cross-reactive compounds with immunodominant B cell epitopes that could impair serological test specificity.

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.

Serological reactivity to MPB83 and CFP10/ESAT-6 antigens in three suid hosts of Mycobacterium bovis infection

Domestic pigs and wild suids are susceptible to Mycobacterium bovis (M. bovis) infection and may even serve as reservoir hosts in some situations. Therefore, detection of infected animals is important for understanding their role in the epidemiology of the disease as well as for management and control of bovine tuberculosis. Infected suids develop strong humoral responses, making serological screening a feasible approach to disease surveillance. However, to optimize sensitivity of the antibody assays, it is necessary to identify and incorporate immunodominant antigens recognized by the target species. The objective of this study was to characterize the antigen recognition by three suid species in a commercially available serological test, DPP VetTB Assay. Serum samples from naturally M. bovis-infected domestic pigs, wild boar and common warthogs were tested. MPB83 protein appeared to be the immunodominant antigen recognized by antibodies in all three species. Overall test sensitivity was increased in wild suids when seroreactivity to CFP10/ESAT-6 antigen was included. Infected animals with visible lesions showed more robust antibody responses than those without gross lesions. The high sensitivity and specificity of the DPP VetTB Assay demonstrated in the present study supports the utility of antibody tests employing these antigens in serological screening of the suid species for M. bovis infection.

A lateral flow assay for the rapid diagnosis of Mycobacterium bovis infection in wild boar

The native Eurasian wild boar (Sus scrofa) is a reservoir of Mycobacterium bovis, the causative agent of animal tuberculosis (TB), a chronic disease in livestock, companion animals and wild mammals. Cases of M. bovis infection in wild boar or feral pig have been reported worldwide, making early detection a priority in the eradication of the disease. Point-of-care diagnostic tests, such as low cost lateral flow assays, provide high specificity and sensitivity and can be performed on site, an essential requirement for a rapid screening of wildlife. A lateral flow assay, LFA, (INgezim TB CROM Ab) for the detection of M. bovis-specific antibodies in wild boar serum and blood has been developed based on MPB83, one of the major immunogenic antigens of the bacterium. A total of 140 samples of wild boar serum, well-characterized by Mycobacterium tuberculosis complex culture and TB compatible post-mortem lesions, have been analysed with LFA, and results were compared with one in-house and two commercial Enzyme-linked Immunosorbent Assays (ELISA), INgezim TB Porcine and INgezim Tuberculosis DR. In experimental samples, the achieved values of sensitivity of the different techniques ranged from 84.3% to 92.1% and the specificity was 100% in all of them. In field animals, specificity ranged from 96% to 100%, whereas sensitivity ranged from 48% to 64% in juvenile wild boar, increasing to 93.3%-100% in adult wild boar. In particular, the total sensitivity and specificity values obtained with the new LFA were 83% and 97%, respectively, indicating that INgezim TB CROM Ab could be used as a first approach for the surveillance of TB in wild boar, with a special applicability for animal-side testing.

Potential efficiency of conventional and advanced approaches used to detect Mycobacterium bovis in cattle

The present study was aimed to assess the prevalence and efficiency of techniques for the diagnosis of bovine tuberculosis (bTB) including enzyme-linked immunosorbent assay (ELISA), Gamma interferon assay (IFN-γ) and polymerase chain reaction (PCR) in comparison to skin tuberculin test and culture technique. A total of 2600 cross-breed dairy cattle in Menoufia and Daqahlia governorates were tested by the single intradermal tuberculin test where the disease prevalence was 1.8%. Serum and whole blood samples were collected from positive tuberculin reactors for ELISA and IFN-γ assay, respectively. After slaughtering of positive tuberculin reactors, the post-mortem examination was carried out and tissue samples were collected for the bacteriological examination and PCR. The percentage of visible lesions of tuberculin reactors was 78.7%, while non-visible lesions were 21.27%. Culture technique revealed that the percentage of bTB was 63.8%. The ELISA and IFN-γ assay using short-term culture filtrate (ST-CF) prepared antigen revealed higher sensitivity (72.3% and 82.9%) than the bovine purified protein derivative (PPD-B) antigen. Although prepared ST-CF antigen has great efficiency and eligibility for the diagnosis of bTB, PCR appeared to have a higher sensitivity (85.1%) than other diagnostic methods when dealing with post-mortem samples. Gamma interferon assay using ST-CF antigen is recommended for antemortem diagnosis of bTB in cattle.

Determination of the sensitivity and specificity of bovine tuberculosis screening tests in dairy herds in Thailand using a Bayesian approach

Background

The objective of this study was to determine the sensitivity (Se) and specificity (Sp) of bovine tuberculosis (bTB) screening tests including a single intradermal tuberculin (SIT) test, interferon gamma (IFN-γ) assay, and a commercial ELISA test (M. bovis Ab) in dairy cattle, under field conditions, using a Bayesian approach.

Results

The study population consisted of 128 dairy cows from 25 bTB-infected herds in Chiang Mai and Chiang Rai provinces, Thailand. A single-population Bayesian model was implemented assuming conditional dependence between the SIT test and IFN-γ assays. The 95% posterior probability interval (PPI) of the SIT test (severe interpretation) Se ranged from 75.3 to 95.2% (median = 87.6%), while the Sp was slightly lower (median = 83.6%, PPI = 74.2–92.8%). The IFN-γ assay Se was moderate and the 95% PPI ranged from 38.6 to 74.4% (median = 55.7%) with higher Sp (median = 93.5.4%, PPI = 87.0–98.1%). The M. bovis Ab ELISA Se was low, with 95% PPI ranging between 30.0 and 71.2% (median = 47.4%); however, the Sp was high (median = 90.9%, PPI = 84.5–95.5%).

Conclusion

The SIT test sensitivity was similar to that demonstrated in other regions and can, therefore, be used effectively as part of control programs in this area. The IFN-γ and M. bovis Ab ELISA assays can be applied as supplementary techniques. The test performance of these tests when used as single tests without confirmation, however, are expected to continue to challenge disease eradication efforts.

Electronic supplementary material

The online version of this article (10.1186/s12917-019-1905-x) contains supplementary material, which is available to authorized users.

Investigation of field intradermal tuberculosis test practices performed by veterinarians in France and factors that influence testing

Bovine tuberculosis infection remains at a low but persistent level in French cattle herds and requires for its surveillance the use of tests with limited sensitivity and specificity. It thus appears essential to understand the reality of the field situation, to identify parameters which could affect how veterinarians perform these tests and how it can affect the sensitivity of the bovine tuberculosis surveillance system. We surveyed rural veterinarians (n = 1084), major stakeholders of the bovine tuberculosis surveillance system, after judgement (non-random) sampling to investigate their skin-test practices and their perception of the surveillance and control programs for this disease. The response rate was 19.4% (210/1084). The responses highlighted that veterinarians were aware of the importance of the fight against bovine tuberculosis and were resilient to the challenges and issues faced during fieldwork. However, we identified several areas of noncompliance with regulatory recommendations, particularly regarding the choice of injection site, verifying the quality of the injection, the method of test reading, and the reporting of non-negative test results. Multivariate analysis showed that veterinarians who had worked for fewer years in large-animal practice had better skin-test procedures. A higher proportion of performed comparative tests and a more positive perception of surveillance and control programs by veterinarians were associated with better skin-test practices. The areas of noncompliance identified in this study could be detrimental to the sensitivity of bovine tuberculosis surveillance but our results suggest that improving the information provided to veterinarians and increasing their awareness are feasible solutions to improve the surveillance efficacy.

A new test to detect antibodies against Mycobacterium tuberculosis complex in red deer serum

Red deer (Cervus elaphus) farming is a growing economic activity worldwide. However, the capacity of this species to act as reservoir of animal tuberculosis (TB) poses a threat to other wildlife and to livestock. Diagnostic assay accuracy in this species is therefore highly relevant for prevention and control measures. Our aim was to evaluate the diagnostic performance of the protein complex P22, obtained from Mycobacterium bovis derived purified protein derivative (bPPD), as a candidate antigen for the detection of antibodies against Mycobacterium tuberculosis complex (MTC). We assessed the performance of this new antigen in indirect enzyme-linked immunosorbent assays (ELISA) in TB-positive and TB-negative red deer, in comparison with a bPPD-based ELISA. The P22 ELISA achieved a higher specificity (Sp) and similar sensitivity (Se) in comparison with the bPPD ELISA at all the cut-off points considered. The P22 ELISA yielded optimal Sp (99.02%; 95% confidence intervals [CI_95%]: 96.5-99.8) and appropriate Se (70.1%; CI_95%: 63.6-76) at the selected cut-off point of 100%. These results suggest that P22 can be used as an alternative antigen in the immunodiagnosis of animal TB through the use of an ELISA-type detection of antibodies against MTC in red deer, thus contributing to the diagnosis of animal TB in this species as a measure for further disease prevention and control programs.

Cytokine and Chemokine Concentrations as Biomarkers of Feline Mycobacteriosis

Mycobacteriosis is an emerging zoonotic disease of domestic cats and timely, accurate diagnosis is currently challenging. To identify differential cytokine/chemokine concentrations in serum/plasma of cats, which could be diagnostic biomarkers of infection we analysed plasma/serum from 116 mycobacteria-infected cats, 16 healthy controls and six cats hospitalised for unrelated reasons was analysed using the Milliplex MAP Feline Cytokine Magnetic Bead multiplex assay. Three cytokines; sFAS, IL-13 and IL-4 were reduced while seven; GM-CSF, IL-2, PDGF-BB, IL-8, KC, RANTES and TNF-α were elevated in mycobacteria-infected cats compared to healthy controls. However, IL-8 and KC concentrations were not significantly different from cats hospitalised for other reasons. Elevations in TNF-α and PDGF-BB may have potential to identify M. bovis and M. microti infected cats specifically while GM-CSF, IL-2 and FLT3L were increased in MTBC infected cats. This study demonstrates potential use of feline tuberculosis as a spontaneously occurring model of this significant human disease. Cytokine profiling has clear diagnostic potential for mycobacteriosis of cats and could be used discriminate tuberculous from non-tuberculous disease to rapidly inform on zoonotic risk. Future work should focus on the in-field utility of these findings to establish diagnostic sensitivity and specificity of these markers.

Validation of a new serological assay for the identification of Mycobacterium tuberculosis complex-specific antibodies in pigs and wild boar

BACKGROUND AND OBJECTIVES

Animal tuberculosis (TB) is a multi-host disease involving a wide variety of domestic and wild mammals and causing a significant economic burden and sanitary problems. Wild boar and domestic pigs (Sus scrofa) are indicators of the circulation of the Mycobacterium tuberculosis complex (MTC) and can play a role in its maintenance. The proper diagnosis of MTC contact in these species is, therefore, a key factor as regards controlling TB. The objective of the current study is to evaluate the diagnostic performance of the protein complex P22 as a candidate for use in an in-house ELISA to identify M. tuberculosis complex-specific antibodies for the diagnosis of TB in comparison to the commonly used bPPD-based ELISA (bPPD ELISA) in suids.

METHODS

We conducted a retrospective study. Sera were collected from wild boar during hunting season and from domestic pigs during routine handling, and all the animals underwent reference standard tests (detailed necropsy followed by bacteriological culture and isolation). Animal TB was confirmed to be positive in 277 animals and negative in 366 animals based on both reference standard tests. Sera from those animals were tested by P22 ELISA as well as bPPD ELISA.

RESULTS

Both ELISAs yielded a good diagnostic value, however, a higher sensitivity (Se) and specificity (Sp) was achieved with the P22 ELISA (Se: 84.1%; CI_95%: 79.3-88.2% / Sp: 98.4%; CI_95%:96.5-99.4%) when compared to the bPPD ELISA (Se: 77.3%; CI_95%: 71.9-82.2% / Sp: 97.3%; CI_95%: 95-98.3%). An optimum Sp of 100% (CI_95%: 98.54-100%) was attained with white pigs for both the bPPD and the P22 ELISA.

DISCUSSION

The results suggest that serological tests for MTC-antibody detection, and particularly the P22 ELISA, are valuable tools in the diagnosis of TB in wild boar and domestic pigs when attempting to detect contact with MTC and thereby facilitate TB control and management.

Association of Fasciola gigantica Co-infection With Bovine Tuberculosis Infection and Diagnosis in a Naturally Infected Cattle Population in Africa

Bovine tuberculosis (bTB), caused by Mycobacterium bovis, remains a major livestock and public health problem in both high and low-income countries. With the current absence of an effective vaccine, control in cattle populations is reliant on regular testing and removal of positive animals. However, surveillance and control are hampered by imperfect diagnostic tests that have poorly described properties in naturally infected populations. Recent research in cattle co-infected with the temperate liver fluke, Fasciola hepatica, has raised concerns about the performance of the intradermal skin test in high fluke incidence areas. Further, recent studies of parasitic co-infections have demonstrated their impact on Th1 and Th2 responses, concurrent disease pathology and susceptibility to mycobacterial infections. Here we report for the first time the association of co-infection with the tropical liver fluke, Fasciola gigantica, with the presence of bTB-like lesions and the IFN-γ response in naturally infected African cattle. After adjusting for age and sex we observed a complex interaction between fluke status and breed. Fulani cattle had a higher risk of having bTB-like lesions than the mixed breed group. The risk of bTB-like lesions increased in the mixed breed group if they had concurrent evidence of fluke pathology but was less clear in the coinfected Fulani breed. Further, we observed a slight decline in the IFN-γ levels in fluke infected animals. Finally we explored factors associated with IFN-γ false negative results compared to the presence of bTB-like lesions. Fulani cattle had a higher risk of having a false negative result compared to the mixed breed group. Further, the mixed breed cattle had an increased risk of being false negative if also co-infected with fluke. Interesting, as with the risk of bTB-like lesions, this association was less clear in the Fulani cattle with weak evidence of a slight decrease in risk of having a false negative test result when fluke pathology positive. This interesting interaction where different breeds appear to have different responses to co-infections is intriguing but further work is needed to confirm and understand more clearly the possible confounding effects of different other co-infections not measured here, breed, management or exposure risks.

Immune response biomarkers in human and veterinary research

Biomarkers are increasingly utilised in biological research and clinical practice for diagnosis of disease, monitoring of therapeutic prognosis, or as end points in clinical studies. Cytokines are small molecules that orchestrate immune responses and as such have great potential as biomarkers for both human and veterinary fields. Given the ease of sampling in the blood, and their high prevalence in clinical applications we will focus on protein detection as an area for biomarker discovery. This is facilitated by new technological developments such as digital ELISA that have led to significant increases in sensitivity. Two highly relevant examples include type I interferons, namely IFNα, that is now directly quantifiable by digital ELISA from biological samples. The application of this approach to the study of the unique bat interferon response may reveal novel findings with applications in both human and veterinary research. As a second example we will describe the use of CXCL10 as a disease biomarker in Tuberculosis, highlighting findings from human and mouse studies that should be considered in veterinary research. In summary, we describe how cytokines may be applied as novel biomarkers and illustrate two key examples where human and veterinary research may complement each other in line with the One Health objectives.

An outbreak of tuberculosis due to Mycobacterium bovis infection in a pack of English Foxhounds (2016-2017)

Mycobacterium bovis can cause tuberculosis (TB) in social mammals including lions, cattle and man, but canine infections are considered rare. In 2016/17 we investigated a M. bovis TB outbreak in a pack of approximately 180 Foxhounds within the bovine TB Edge Area of England. We employed a combination of immunological tests including an interferon gamma release assay (IGRA) and a serological assay (DPP VetTB, Chembio). Test‐positive hounds were euthanased and subjected to post‐mortem examination (PME). Overall 164 hounds were tested; 97 (59%) responded positively to at least one test. Eighty‐five (52%) dogs responded to M. bovis antigens by IGRA while only 21 (12.9%) had detectable serological responses. At PME three hounds (3.1%) had visible lesions (VL) due to M. bovis infection, later confirmed by culture. Samples from 24 non‐VL hounds were cultured and M. bovis infection was confirmed in a further three hounds (11%). This study is the first investigation and report of an outbreak of M. bovis TB in a canine species. We establish that, in principle, diagnostic tests used for identifying infected individuals of other species can effectively be used in the dog. Further work is urgently needed to establish the sensitivity and specificity of the testing approach used in this study for future clinical application.

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.

Development and evaluation of an interferon gamma assay for the diagnosis of tuberculosis in red deer experimentally infected with Mycobacterium bovis

BACKGROUND

Red deer (Cervus elaphus) is regarded as an epidemiologically relevant host for Mycobacterium bovis (M. bovis) and closely related members of the Mycobacterium tuberculosis complex that cause animal tuberculosis (TB). The standard antemortem screening test for the detection of TB in deer is the intradermal tuberculin skin test, but the detection of interferon-gamma (IFNγ) produced by white blood cells exposed to M. bovis antigens can be used as an alternative or supplemental assay in most TB eradication/control programs. This study aims to develop an in-house sandwich ELISA for deer IFNγ, based on the cross-reactivity of the antibodies to both cervid and bovine IFNγ, and to evaluate the potential of this assay to detect M. bovis-infected red deer in response to the in vitro stimulation of whole-blood cells with bovine purified protein derivative (bPPD), p22 protein complex derived from bPPD or using the specific tuberculous mycobacterial proteins ESAT-6/CFP-10, Rv3615c and Rv3020c. The positive control stimulant used in this study was pokeweed mitogen, which resulted in a consistent induction of IFNγ in samples from red deer, thus allowing the interpretation of the assay.

RESULTS

The percentage of animals correctly classified by this technique as M. bovis non-infected was 100%. The detection of infected animals as positive was high and ranged widely depending upon the antigen and the cut-off value applied, as well as the time after infection. Our findings indicate that this protocol may serve as a reliable assay for the antemortem diagnosis of TB from the initial stage of M. bovis-infection, and may also be adequately sensitive.

CONCLUSIONS

The suggested optimal antigens and cut-off are bPPD, p22 and the combination of ESAT-6/CFP-10 and Rv3020c with a 0.05 Δ optical density, which yielded a up to 100% correct classification of TB positive and negatve red deer under our experimental conditions. This technique will aid in TB testing of farmed and translocated deer. Future studies should evaluate the ability of this IFNγ assay to detect specific responses under field conditions.

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).

Evaluating diagnostic tests for bovine tuberculosis in the southern part of Germany: A latent class analysis

Germany has been officially free of bovine tuberculosis since 1996. However, in the last years there has been an increase of bovine tuberculosis cases, particularly in the southern part of Germany, in the Allgäu region. As a consequence a one-time tuberculosis surveillance program was revisited with different premortal and postmortal tests. The aim of this paper was to estimate diagnostic sensitivities and specificities of the different tests used within this surveillance program. In the absence of a perfect test with 100% sensitivity and 100% specificity, thus in the absence of a gold standard, a Bayesian latent class approach with two different datasets was performed. The first dataset included 389 animals, tested with single intra-dermal comparative cervical tuberculin (SICCT) test, PCR and pathology; the second dataset contained 175 animals, tested with single intra-dermal cervical tuberculin (SICT) test, Bovigam® assay, pathology and culture. Two-way conditional dependencies were considered within the models. Additionally, inter-laboratory agreement (five officially approved laboratories) of the Bovigam® assay was assessed with Cohen's kappa test (21 blood samples). The results are given in posterior means and 95% credibility intervals. The specificities of the SICT test, SICCT test, PCR and pathology ranged between 75.8% [68.8-82.2%] and 99.0% [96.8-100%]. The Bovigam® assay stood out with a very low specificity (6.9% [3.6-11.1%]), though it had the highest sensitivity (95.7% [91.3-99.2%]). The sensitivities of the SICCT test, PCR, SICT test, pathology and culture varied from 57.8% [48.0-67.6%] to 88.9% [65.5-99.7%]. The prevalences were 19.8% [14.6-26.5%] (three-test dataset) and 7.7% [4.2-12.3%] (four-test dataset). Among all pairwise comparisons the highest agreement was 0.62 [0.15-1]). In conclusion, the specificity of the Bovigam® assay and the inter-laboratory agreement were lower than expected.

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.

Early Detection of Circulating Antigen and IgM-Associated Immune Complexes during Experimental Mycobacterium bovis Infection in Cattle

The presence of circulating antigen in cattle experimentally infected with Mycobacterium bovis was demonstrated using dual-path platform (DPP) technology. The antigen capture immunoassays employed rabbit polyclonal antibody recognizing predominantly M. tuberculosis complex-specific epitopes and were able to detect soluble substances and whole cells of mycobacteria. The antigen found in serum appeared to be mostly bound to IgM, but not to IgG, within the immune complexes formed at early stages of M. bovis infection. The antigen was also detected in bile and urine, indicating possible clearance pathways. The data correlation analyses supported the idea of the role of IgM responses in antigen persistence during M. bovis infection. The antigen was detectable in serum months prior to detectable antibody seroconversion. This proof-of-concept study suggested the potential for improved immunodiagnostics for bovine tuberculosis.

Meta-analyses of the sensitivity and specificity of ante-mortem and post-mortem diagnostic tests for bovine tuberculosis in the UK and Ireland

Bovine Tuberculosis (bTB) in cattle is a global health problem and eradication of the disease requires accurate estimates of diagnostic test performance to optimize their efficiency. The objective of this study was, through statistical meta-analyses, to obtain estimates of sensitivity (Se) and specificity (Sp), for 14 different ante-mortem and post-mortem diagnostic tests for bTB in cattle. Using data from a systematic review of the scientific literature (published 1934-2009) diagnostic Se and Sp were estimated using Bayesian logistic regression models adjusting for confounding factors. Random effect terms were used to account for unexplained heterogeneity. Parameters in the models were implemented using Markov Chain Monte Carlo (MCMC), and posterior distributions for the diagnostic parameters with adjustment for covariates (confounding factors) were obtained using the inverse logit function. Estimates for Se and/or Sp of the tuberculin skin tests and the IFN-γ blood test were compared with estimates published 2010-2015. Median Se for the single intradermal comparative cervical tuberculin skin (SICCT) test (standard interpretation) was 0.50 and Bayesian credible intervals (CrI) were wide (95% CrI 0.26, 0.78). Median Sp for the SICCT test was 1.00 (95% CrI 0.99, 1.00). Estimates for the IFN-γ blood test Bovine Purified Protein Derivative (PPD)-Avian PPD and Early Secreted Antigen target 6 and Culture Filtrate Protein 10 (ESAT-6/CFP10) ESAT6/CFP10 were 0.67 (95% CrI 0.49, 0.82) and 0.78 (95% CrI 0.60, 0.90) respectively for Se, and 0.98 (95% CrI 0.96, 0.99) and 0.99 (95% CrI 0.99, 1.00) for Sp. The study provides an overview of the accuracy of a range of contemporary diagnostic tests for bTB in cattle. Better understanding of diagnostic test performance is essential for the design of effective control strategies and their evaluation.

Serological Analysis of Tuberculosis in Goats by Use of the Enferplex Caprine TB Multiplex Test

Tuberculosis in goats is usually diagnosed clinically, at postmortem, or by a positive skin test. However, none of these approaches detects all infected animals. Serology offers an additional tool to identify infected animals missed by current tests. We describe the use of the Enferplex Caprine TB serology test to aid the management of a large dairy goat herd undergoing a tuberculosis breakdown. Initial skin and serology testing showed that IgG antibodies were present in both serum and milk from 100% of skin test-positive animals and in serum and milk from 77.8 and 95.4% of skin test-negative animals, respectively. A good correlation was observed between serum and milk antibody levels. The herd had been vaccinated against Mycobacterium avium subsp. paratuberculosis, but no direct serological cross-reactions were found. Subsequent skin testing revealed 13.7% positive animals, 64.9% of which were antibody positive, while 42.1% of skin test-negative animals were seropositive. Antibody responses remained high 1 month later (57.1% positive), and the herd was slaughtered. Postmortem analysis of 20 skin test-negative goats revealed visible lesions in 6 animals, all of which had antibodies to six Mycobacterium bovis antigens. The results provide indirect evidence that serology testing with serum or milk could be a useful tool in the diagnosis and management of tuberculosis in goats.

Evaluation of five serologic assays for bovine tuberculosis surveillance in domestic free-range pigs from southern Spain

In countries where bovine tuberculosis (bTB) is still prevalent the contact among different animal species in extensive systems contributes to the circulation of Mycobacterium bovis (M. bovis) and other members of the Mycobacterium tuberculosis complex (MTC). Thus, free-range pigs can develop subclinical infections and may contribute to disease spread to bovine and wildlife. Serodiagnosis has been proposed as a screening tool for detecting infected pig herds; however, the value of this method to obtain an accurate diagnosis in this species is still not clear. In this study, sensitivity (Se) and specificity (Sp) estimates of four ELISAs and a lateral flow immunochromatographic antibody assay based on different M. bovis antigens, including MPB70 and MPB83 proteins, were evaluated in naturally infected domestic free-range pigs. For this purpose, submandibular lymph nodes and blood samples from 217 pigs from both TB-infected and historically negative farms were sampled at slaughterhouse and analysed by gross examination, histopathology, bacteriological culture and qPCR. Se and Sp estimates of the 5 evaluated assays ranged from 66.1% to 78% (CI₉₅ from 52.6 to 87.7%) and from 98.9% to 100% (CI₉₅ from 93.8 to 100%), respectively. Results of our study suggest that all the evaluated assays could be used as a first screening tool to conduct bTB surveillance in domestic pigs at population level; however, animals from seropositive herds should later be surveyed by other methods in order to reduce false negative results.

Effects of repeated comparative intradermal tuberculin testing on test results: a longitudinal study in TB-free red deer

BACKGROUND

Diagnosing tuberculosis (TB) in farmed red deer (Cervus elaphus) is challenging and might require combining cellular and humoral diagnostic tests. Repeated skin-testing with mycobacterial purified protein derivatives (PPDs) might sensitize or desensitize the subjects to both kinds of diagnostic tools. We evaluated the effect of repeated (every 6 months) comparative tuberculin skin testing on skin test and ELISA responsiveness in farmed red deer hinds from a TB-free herd. Eighteen 8-month old hinds were inoculated with bovine and avian PPDs and the mitogen phytohaemagglutinin (PHA), as positive control and concurrently tested by ELISA for antibodies against avian (avian PPD, aPPD and protoplasmatic antigen 3, PPA3) and bovine antigens (bPPD and MPB70). Blood serum was also sampled three weeks after each skin testing round and tested for antibodies against aPPD and bPPD, in order to detect eventual antibody level boosts. Testing took place every six months from winter 2012 until winter 2015.

RESULTS

The skin test response to both PPDs peaked during the second and third test round, returning to standard values thereafter. Individual variability was particularly high at the first year and early second year testing rounds (first intradermal test and blood sampling; first winter). The antibody response to avian antigens increased through time, while no such increase was recorded for bovine antigens. The antibody boost three weeks after skin testing was more marked for avian PPD. However, there was no consistent trend in the boosting response through time.

CONCLUSION

Repeated comparative skin testing at six month intervals did not cause progressive increments in skin test responsiveness or antibody production. Specifically, we observed no loss of the skin test response to bPPD and also no progressive loss of the boosting effect in the ELISA responses. However, we recorded increases through time in the antibody levels against avian mycobacterial antigens, possibly due to the progressive exposure to MAP or to other cross-reacting environmental mycobacteria. These findings should be taken into account in designing and interpreting TB testing schemes in farmed deer.

Mycobacterium bovis Infection of Cattle and White-Tailed Deer: Translational Research of Relevance to Human Tuberculosis

Tuberculosis (TB) is a premier example of a disease complex with pathogens primarily affecting humans (i.e., Mycobacterium tuberculosis) or livestock and wildlife (i.e., Mycobacterium bovis) and with a long history of inclusive collaborations between physicians and veterinarians. Advances in the study of bovine TB have been applied to human TB, and vice versa. For instance, landmark discoveries on the use of Koch's tuberculin and interferon-γ release assays for diagnostic purposes, as well as Calmette and Guérin's attenuated M. bovis strain as a vaccine, were first evaluated in cattle for control of bovine TB prior to wide-scale use in humans. Likewise, recent discoveries on the role of effector/memory T cell subsets and polyfunctional T cells in the immune response to human TB, particularly as related to vaccine efficacy, have paved the way for similar studies in cattle. Over the past 15 years, substantial funding for development of human TB vaccines has led to the emergence of multiple promising candidates now in human clinical trials. Several of these vaccines are being tested for immunogenicity and efficacy in cattle. Also, the development of population-based vaccination strategies for control of M. bovis infection in wildlife reservoirs will undoubtedly have an impact on our understanding of herd immunity with relevance to the control of both bovine and human TB in regions of the world with high prevalence of TB. Thus, the one-health approach to research on TB is mutually beneficial for our understanding and control of TB in humans, livestock, and wildlife.

Antemortem Detection of Chronic Wasting Disease Prions in Nasal Brush Collections and Rectal Biopsy Specimens from White-Tailed Deer by Real-Time Quaking-Induced Conversion

Chronic wasting disease (CWD), a transmissible spongiform encephalopathy of cervids, was first documented nearly 50 years ago in Colorado and Wyoming and has since spread to cervids in 23 states, two Canadian provinces, and the Republic of Korea. The expansion of this disease makes the development of sensitive diagnostic assays and antemortem sampling techniques crucial for the mitigation of its spread; this is especially true in cases of relocation/reintroduction of farmed or free-ranging deer and elk or surveillance studies of private or protected herds, where depopulation is contraindicated. This study sought to evaluate the sensitivity of the real-time quaking-induced conversion (RT-QuIC) assay by using recto-anal mucosa-associated lymphoid tissue (RAMALT) biopsy specimens and nasal brush samples collected antemortem from farmed white-tailed deer (n= 409). Antemortem findings were then compared to results from ante- and postmortem samples (RAMALT, brainstem, and medial retropharyngeal lymph nodes) evaluated by using the current gold standardin vitroassay, immunohistochemistry (IHC) analysis. We hypothesized that the sensitivity of RT-QuIC would be comparable to IHC analysis in antemortem tissues and would correlate with both the genotype and the stage of clinical disease. Our results showed that RAMALT testing by RT-QuIC assay had the highest sensitivity (69.8%) compared to that of postmortem testing, with a specificity of >93.9%. These data suggest that RT-QuIC, like IHC analysis, is an effective assay for detection of PrP(CWD)in rectal biopsy specimens and other antemortem samples and, with further research to identify more sensitive tissues, bodily fluids, or experimental conditions, has potential for large-scale and rapid automated testing for CWD diagnosis.

Evaluation of the immunogenicity and diagnostic interference caused by M. tuberculosis SO2 vaccination against tuberculosis in goats

The immunogenicity and diagnostic interference caused by M. tuberculosis SO2, a prototype vaccine first time tested in goats was evaluated. Tuberculosis-free goats were distributed in four groups: [1], non-vaccinated; [2], subcutaneously (SC) BCG vaccinated; [3], intranasally (IN) SO2 vaccinated and [4], SC SO2 vaccinated. Intradermal tuberculin and IFN-γ tests using PPDs and alternative antigenic cocktails containing mainly ESAT-6 and CFP-10 (E/C) were applied at different times post-vaccination. Results showed a significant (p<0.05) increase in the number of reactors detected using both PPD-based intradermal and IFN-γ tests at different times in all the vaccinated groups. No intradermal reactivity was detected in the vaccinated goats using a cocktail containing E/C, Rv3615c and Rv3020c. A higher overall reactivity was observed in the group [4] in comparison with the other vaccinated groups. Results showed that antigens used to differentiate BCG vaccinated animals could be potentially used to differentiate SO2 vaccinated ones.

Goats challenged with different members of the Mycobacterium tuberculosis complex display different clinical pictures

Tuberculosis (TB) in goats (Capra hircus) is due to infection with members of the Mycobacterium tuberculosis complex (MTC), mainly Mycobacterium bovis and Mycobacterium caprae. We report a comparative experimental infection of goats with M. bovis, M. caprae and M. tuberculosis strains. We hypothesized that goats experimentally infected with different members of the MTC would display different clinical pictures. Three groups of goats were challenged with either M. bovis SB0134 (group 1, n=5), M. caprae SB0157 (group 2, n=5) and M. tuberculosis SIT58 (group 3, n=4). The highest mean total lesion score was observed in M. bovis challenged goats (mean 15.2, range 9-19), followed by those challenged with M. caprae (10.8, 2-23). The lowest score was recorded in goats challenged with M. tuberculosis (3, 1-6). Culture results coincided with the lesion scores in yielding more positive pools (7/15) in M. bovis challenged goats. By contrast, only three pools were positive from goats challenged M. tuberculosis (3/12) and with M. caprae (3/15), respectively. Differences in the performance of the intradermal and gamma-interferon (IFN-γ) tests depending of the group were observed since all goats from group 1 were diagnosed using intradermal test and these goats reacted earlier to the IFN-γ assay in comparison to the other groups. This study confirmed that goats experimentally infected with different members of the MTC display different clinical pictures and this fact may have implications for MTC maintenance and bacterial shedding.

Effect of the inoculation site of bovine purified protein derivative (PPD) on the skin fold thickness increase in cattle from officially tuberculosis free and tuberculosis-infected herds

The official technique for diagnosis of bovine tuberculosis (bTB) worldwide is the tuberculin skin test, based on the evaluation of the skin thickness increase after the intradermal inoculation of a purified protein derivative (PPD) in cattle. A number of studies performed on experimentally infected or sensitized cattle have suggested that the relative sensitivity of the cervical test (performed in the neck) may vary depending on the exact location in which the PPD is injected. However, quantitative evidence on the variation of the test accuracy associated to changes in the site of inoculation in naturally infected animals (the population in which performance of the test is most critical for disease eradication) is lacking. Here, the probability of obtaining a positive reaction (>2 or 4 millimeters and/or presence of local clinical signs) after multiple inoculations of bovine PPD in different cervical and scapular locations was assessed in animals from five bTB-infected herds (818 cattle receiving eight inoculations) using a hierarchical Bayesian logistic regression model and adjusting for the potential effect of age and sex. The effect of the inoculation site was also assessed qualitatively in animals from four officially tuberculosis free (OTF) herds (two inoculations in 210 animals and eight inoculations in 38 cattle). Although no differences in the qualitative outcome of the test were observed in cattle from OTF herds, a statistically important association between the test outcome and the inoculation site in animals from infected herds was observed, with higher probabilities of positive results when the test was performed in the neck anterior area. Our results suggest that test sensitivity may be maximized by considering the area of the neck in which the test is applied, although lack of effect of the inoculation site in the specificity of the test should be confirmed in a larger sample.

Diagnosis of bovine tuberculosis using a metal oxide-based electronic nose

Electronic noses (e-noses) have been used for environmental monitoring, standardization of medicinal flavourings, food safety tests and diagnosis of infectious diseases based on the statistical analysis of volatile organic compounds (VOCs). Bovine tuberculosis (bTB) is officially diagnosed using the intradermal skin test (IST), which is time-consuming and labour-intensive. Therefore, a more convenient and rapid test with greater sensitivity would be advantageous as prescreening test. In this study, we used a metal oxide sensor (MOS) type e-nose to analyse VOCs in a bTB-infected (n = 11) and bTB-free (n = 10) sera, from cattle whose health status was confirmed using the IST, and pathological and bacteriological examinations. The differences in VOCs from bTB-infected and bTB-free sera detected by the e-nose were statistically analysed using principal components and discriminant factor analyses. bTB-infected and bTB-free sera could be discriminated by MOS type e-nose, and analysing time per sample was only 20 min. VOC analysis using a MOS e-nose was a rapid and automated prescreening method to diagnose bTB, and can be used to select bTB-suspect cattle for IST confirmation. Further studies are required to estimate test sensitivity and specificity. Significance and impact of the study: Bovine tuberculosis (bTB) in cattle is diagnosed using the intradermal skin test (IST); however, this method is very time-consuming and labour-intensive. We analysed volatile organic compounds that are obtained from serum using a metal oxide sensor type of electronic nose to discriminate between TB-infected and TB-free sera. This simple and automated technique will be useful to prescreen bTB-suspects and reduce the time and labour required to perform the IST.

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.