Evaluation of single and comparative intradermal tuberculin tests for tuberculosis eradication in caprine flocks in Castilla y León (Spain)

Phylogenetic analysis of Mycobacterium caprae highlights past and present epidemiological links at the Iberian Peninsula scale

Mycobacterium caprae is linked to regular outbreaks of tuberculosis (TB) in geographically distinct caprine populations across Europe, namely Iberia where this ecovar may represent up to 8% of total animal TB cases, circulating in multi-host communities encompassing domestic ruminants and wildlife, representing severe financial losses. It also causes zoonotic human disease. In this work, we undertake the first phylodynamic and phylogeographic analyses of M. caprae to reconstruct past demography and transmission chains. First, we examined the worldwide diversity of M. caprae based on 229 unpublished and publicly available whole genome sequences, depicting Asian, Central-East European, and Iberian clades. Phylodynamic analyses of the SB0157 Iberian clade (n = 81) positioned the most recent common ancestor in goats, around 100 years ago. Host transition events were common between goats, wild boars, and humans, possibly resulting from mixed farming, extensive management, and close human proximity, facilitating interspecific transmission. We show the spread of M. caprae on multiple scales due to local and transnational animal trade, supporting historical and sustained cross-species transmission in Iberia. We highlight the value of intersecting genomic epidemiology with molecular ecology to resolve epidemiological links and show that an EU-official eradication program in goats is utterly needed to control TB in a multi-host scenario.

Effect of the topical administration of corticosteroids and tuberculin pre-sensitisation on the diagnosis of tuberculosis in goats

Background

Caprine tuberculosis (TB) is a zoonosis caused by members of the Mycobacterium tuberculosis complex (MTBC). Caprine TB control and eradication programmes have traditionally been based on intradermal tuberculin tests and slaughterhouse surveillance. However, this strategy has limitations in terms of sensitivity and specificity. Different factors may affect the performance of the TB diagnostic tests used in goats and, subsequently, the detection of TB-infected animals. In the present study, the effect of two of the factors that may affect the performance of the techniques used to diagnose TB in goats, the topical administration of corticosteroids and a recent pre-sensitisation with tuberculin, was analysed.

Methods

The animals (n = 151) were distributed into three groups: (1) a group topically treated with corticosteroids 48 h after intradermal tuberculin tests (n = 53); (2) a group pre-sensitised with bovine and avian purified protein derivatives (PPDs) 3 days before the intradermal tuberculin test used for TB diagnosis (n = 48); and (3) a control group (n = 50). All the animals were tested using single and comparative intradermal tuberculin (SIT and CIT, respectively) tests, an interferon-gamma release assay (IGRA) and a P22 ELISA.

Results

The number of SIT test reactors was significantly lower in the group treated with corticosteroids when compared to the pre-sensitised (p < 0.001) and control (p = 0.036) groups. In contrast, pre-sensitisation with bovine and avian PPDs did not cause a significant reduction in the number of SIT and CIT test reactors compared with the control group. In fact, a higher number of reactors was observed after the prior tuberculin injection in the pre-sensitised group (p > 0.05). No significant effect was observed on IGRA and P22 ELISA due to corticosteroids administration. Nevertheless, a previous PPD injection affected the IGRA performance in some groups.

Conclusions

The application of topical corticosteroid 24 h before reading the SIT and CIT tests can reduce the increase in skin fold thickness and subsequently significantly decrease the number of positive reactors. Corticosteroids used can be detected in hair samples. A previous pre-sensitisation with bovine and avian PPDs does not lead to a significant reduction in the number of intradermal tests reactors. These results are valuable in order to improve diagnosis of caprine TB and detect fraudulent activities in the context of eradication programs.

Serological detection of Mycobacterium Tuberculosis complex infection in multiple hosts by One Universal ELISA

Tuberculosis (TB), a contagious disease mainly caused by Mycobacterium tuberculosis (M. tb), Mycobacterium bovis (M. bovis), and Mycobacterium caprae (M. caprae), poses a major global threat to the health of humans and many species of animals. Developing an ante-mortem detection technique for different species would be of significance in improving the surveillance employing a One Health strategy. To achieve this goal, a universal indirect ELISA was established for serologically detecting Mycobacterium tuberculosis complex infection for multiple live hosts by using a fusion protein of MPB70, MPB83, ESAT6, and CFP10 common in M. tb, M. bovis, and M. caprae as the coating antigen (MMEC) and HRP-labeled fusion protein A and G as a secondary antibody. After testing the known positive and negative sera, the receiver operating characteristic curves were constructed to decide the cut-off values. Then, the diagnostic sensitivity and specificity of MMEC/AG-iELISA were determined as 100.00% (95% CI: 96.90%, 100.00%) and 100.00% (95% CI: 98.44%, 100.00%) for M. bovis infection of cattle, 100.00% (95% CI: 95.00%, 100.00%) and 100.0% (95% CI: 96.80%, 100.00%) for M. bovis infection of sheep, 90.74% (95% CI: 80.09%, 95.98%) and 98.63% (95% CI: 95.14%, 99.76%) for M. bovis infection of cervids, 100.00% (95% CI: 15.81%, 100.00%) and 98.81% (95% CI: 93.54%, 99.97%) for M. bovis infection of monkeys, 100.00% (95% CI: 86.82%, 100.00%) and 94.85% (95% CI: 91.22%, 97.03%) for M. tb infection of humans. Furthermore, this MMEC/AG-iELISA likely detects M. caprae infection in roe deer. Thus this method has a promising application in serological TB surveillance for multiple animal species thereby providing evidence for taking further action in TB control.

Effect of the Inoculation Site of Bovine and Avian Purified Protein Derivatives (PPDs) on the Performance of the Intradermal Tuberculin Test in Goats From Tuberculosis-Free and Infected Herds

The single and comparative intradermal tuberculin (SIT and CIT) tests are used for the ante-mortem diagnosis of caprine tuberculosis (TB). The tuberculin injection site has been associated with a different performance of the test in cattle. In contrast to that required in cattle in Europe (cervical injection), it can be carried out in the scapular region in goats. Nevertheless, there are no previous data concerning the effect of the injection site on the performance of the test in goats. The aim of the present study was to evaluate the effect of two different inoculation sites (cervical and scapular) on the performance of the SIT/CIT tests. This was done by intradermally inoculating 309 goats from two infected herds and one TB-free herd with both avian and bovine PPDs in the mid-cervical and scapular regions. None of the animals from the TB-free herd had positive reactions, and the number of reactors was not significantly higher, regardless of the inoculation site, in the high and low prevalence herds. However, significantly higher increases in skin fold thickness were observed on the cervical site when compared to the scapular site after the avian and bovine PPD inoculations in the TB-free herd (p < 0.001) and after the bovine PPD injection in the high prevalence herd (p = 0.003). The presence of clinical signs was also more evident on the cervical site when using avian and bovine PPDs in the high prevalence herd (p < 0.01). In contrast, increases in higher skin fold thickness were observed on the scapular site when compared to the cervical site after the bovine and avian PPD inoculations were employed in the low prevalence herd (p < 0.01). These results suggest that the cervical injection of PPDs may improve the sensitivity of the intradermal tuberculin test in high TB prevalence caprine herds, mainly owing to the increased presence of local clinical signs and a better performance of the CIT test. Moreover, specificity was not affected when using standard interpretations, although further analyses in a great number of herds are required in order to confirm these findings.

Tuberculosis caused by Mycobacterium caprae in a camel (Camelus dromedarius)

BACKGROUND

Animal tuberculosis (TB) is distributed worldwide and has a wide range of wild and domestic reservoirs. Few studies concerning TB in camelids have been published in the last decade, particularly as regards Old World Camelids (OWC), but the increase in reports of TB outbreaks in these species in recent years suggests a high susceptibility to the infection.

CASE PRESENTATION

We studied a dromedary camel (Camelus dromedarius) herd (n = 24) in which a Mycobacterium caprae infection was detected. The TB infection was confirmed in one animal at necropsy through the detection of TB lesions, mainly in the abdominal organs, and the subsequent isolation of M. caprae (SB0157 spoligotype). The whole herd was additionally tested using cellular and humoral based diagnostic techniques. The intradermal tuberculin test results were compared with those obtained using P22 ELISA for the detection of specific antibodies against the M. tuberculosis complex. The TB infected animal was a positive reactor to both the intradermal tuberculin tests and P22 ELISA, while the others were negative to all the diagnostic tests.

CONCLUSION

The present study found M. caprae infection in OWC. This is the first report of M. caprae infection in an OWC not living in a zoo. Since the animal was born in the herd and fed with goat's milk, this practice was suspected to be the potential source of TB infection, which was not confirmed in the other animals present in the herd. Moreover, our results highlight that the intradermal tuberculin test and the P22 ELISA could be valuable tools for the diagnosis of TB in OWC.

Influence of vaccination against paratuberculosis on the diagnosis of caprine tuberculosis during official eradication programmes in Castilla y León (Spain)

The information generated from the official eradication programmes of caprine tuberculosis (TB) in Castilla y León, Spain, during 2018, has been used to assess the effect of vaccination against paratuberculosis (PTB) and the presence of this infection, on the single intradermal tuberculin (SIT) test results. Data from 121,665 goats belonging to 1936 different herds were analysed using generalized linear models. An epidemiological survey was conducted to know the herd immunization status against PTB and the date of last vaccination. All SIT test-positive animals were further investigated in order to confirm the diagnosis of TB, through bacterial culture, and PTB, by histopathological and qPCR analyses. SIT positivity was found in 39 (2.01%) herds and 507 (0.41%) goats. TB was confirmed by M. caprae or M. bovis isolation in 10 (0.51%) herds and 46 (0.038%) goats. PTB was diagnosed in 13 (33.33%) and 55 (10.84%) of the SIT test-positive herds and goats, respectively. Vaccination against PTB showed a significant influence on the results of the SIT test at herd level, with higher positivity detected among those herds vaccinated. However, this effect was not observed when the total number of animals was considered, where the highest positivity was found in unvaccinated goats. The time elapsed between vaccination and SIT test performance also influenced the results. The strongest effect was found when less than eight months elapsed between performing both activities, and to a lesser extent between 8 and 12 months. Conversely, no positive herds or animals were found when the time elapsed was higher than one year. No significant effect of the presence of PTB was observed. These findings demonstrate that the use of PTB vaccine does not result in false positives to a SIT test at individual level, provided that the time elapsed between the performance of both practices is higher than 12 months.

Accuracy of tuberculosis diagnostic tests in small ruminants: A systematic review and meta-analysis

Tuberculosis (TB) in small ruminants is a neglected disease despite its major impact on goat and sheep production and the global public health. The awareness of the role of small ruminants in the epidemiology of animal TB has increased in the last two decades, however, there is a lack of standardization of procedures and robust quantitative estimates on the accuracy of diagnostic TB tests in the scientific literature. To address this knowledge gap, all the available information regarding the use of ante-mortem diagnostic techniques in small ruminants was collected and summarized through a systematic review process. Furthermore, a random-effects meta-analysis was conducted to separately estimate the sensitivity (Se) and specificity (Sp) of cell-based tests among the retrieved studies in goats. Studies included in the meta-analysis were also evaluated using the Quality Assessment of Diagnostic Accuracy Studies included in systematic reviews adapted for animal diagnostic tests (VETQUADAS). Median pooled Se estimates of the single intradermal tuberculin (SIT) test (ranged from 0.51 to 0.59), the comparative intradermal tuberculin (CIT) test (ranged from 0.30 to 0.50) and the interferon-gamma (IFN-γ) release assay (IGRA) (ranged from 0.66 to 0.72) were lower than that reported previously in cattle, regardless the interpretation criteria and the reporting of MAP infection or vaccination. However, the specificity was adequate for all the tests (ranged from 0.95 to 0.99), except for the SIT test in MAP vaccinated herds (ranged from 0.78 to 0.90). This study provides an overview of the accuracy of diagnostic tests for TB in goats, however, the considerable between-study heterogeneity found hampered the conclusive interpretation of the pooled Se and Sp estimates. Therefore, further studies in small ruminants are necessary to optimize the diagnostic Se, which could help to design effective control strategies, accelerate the eradication of TB in these species and harmonize test procedures.

Evaluation of P22 Antigenic Complex for the Immuno-Diagnosis of Tuberculosis in BCG Vaccinated and Unvaccinated Goats

Current eradication strategies of tuberculosis (TB) in goats mainly rely on the single intradermal tuberculin test (SIT) and single intradermal cervical comparative tuberculin tests (SICCTs). TB vaccination has been proposed as a cost-effective option in high-prevalence herds or countries where economic compensation for the slaughter of positive animals is not affordable. However, TB vaccination compromises the efficiency of tuberculin-based diagnostic tests. In this study, the performance of a new diagnostic platform, based on the P22 antigenic complex, was assessed for skin test (ST), interferon-gamma release assay (IGRA), and serology under different TB scenarios. The sensitivity (Se) of diagnostic tests was assessed in TB-infected goats from the same farm (herd A, N = 77). The specificity (Sp) was assessed in two TB-negative farms (both vaccinated against paratuberculosis): one TB unvaccinated (herd B, N = 77) and another vaccinated with bacille Calmette-Guérin (BCG) (herd C, N = 68). The single (s) P22-IGRA showed the highest Se among IGRA tests (91%), and the comparative (c) P22-ST showed the highest Sp (100% in herd B and 98% in herd C). Combined interpretation of techniques enabled the best diagnostic performances. Combining the SICCT + sP22-IGRA improved Se (97%) compared to SICCT + tuberculin-based IGRA (95%), with a reduction of Sp (95 and 100%, respectively). Besides, combination of P22-ELISA with cP22-ST or SICCT elicited a similar performance in the non-vaccination context (Se: 94 and 95%; Sp: 95 and 95%, respectively), but Sp was significantly higher for the combination with cP22-ST compared to SICCT in the TB vaccination context (95 and 79%, respectively). The combination of serological tests based on P22 and MPB83 showed higher complementarity and improved 13 percentage points the Se of P22-ELISA alone. These findings suggest that either cell-mediated or antibody-based diagnostic techniques, using the P22 antigen complex, can contribute to improve the immunodiagnostics of TB in goats under different TB control strategies.

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.

Polyclonal infection as a new scenario in Mycobacterium caprae epidemiology

Portugal is one of the European Union countries with an ongoing eradication program for bovine tuberculosis (TB), which does not include systematic goat testing. However, surveillance in small ruminants is increasingly important, since goat and sheep can harbour Mycobacterium caprae and be an infection source to cattle with impact in the success of bovine TB control. Furthermore, the information regarding the epidemiology and biology of M. caprae is quite limited comparing to the cognate bovine-adapted ecotype, M. bovis. In this work, we applied spoligotyping and MIRU-VNTR (Mycobacterial Interspersed Repetitive Units-Variable Number of Tandem Repeats) to M. caprae obtained between 2003 and 2014 from 55 animal hosts, including goat (n = 29), cattle (n = 21), sheep (n = 1) and wild boar (n = 4) from Portugal. The molecular analysis revealed a unique spoligotyping pattern (SB0157) and 24 MIRU types. Genotyping of serial M. caprae from herds with recurrent outbreaks enabled further discrimination of epidemiologically related isolates, supporting a clonal structure in Portugal and denoting the emergence of clonal diversity at the herd level, more apparent for MIRU4. Results suggest a founder effect and adaptive genotypic divergence, paving the way for sympatric speciation. Double allele findings at MIRU4 in over 20 % of infected animals indicates that co-infection and in vivo microevolution may be frequent in the goat-adapted ecotype. While polyclonal infection appears common in M. caprae epidemiology, the functional significance of subtle genotypic variations remains to be disclosed, namely at the interface with the host, to expand knowledge on the epidemiology and biology of this neglected ecotype.

The rapid detection and differentiation of Mycobacterium tuberculosis complex members from cattle and water buffaloes in the delta area of Egypt, using a combination of real-time and conventional PCR

Mycobacterium tuberculosis complex (MTBC) has the potential to cause infections in animals and human beings. The combination of real-time PCR targeting atpE or lpqT and RD1, and conventional PCR targeting regions of difference (RD) was rigorously evaluated as a descriptive molecular epidemiology tool. A total of 2100 cattle and buffaloes from the Menoufia, Sharkia, Gharbia, Dakahlia, Elbuhaira, and Cairo Governorates were tested by single intradermal comparative cervical tuberculin test (SICCT). The frequency was 74/2100 (3.5%); thereafter, on post-mortem examination (PM), 49/74 (66.21%) showed visible lesions, while only 25/74 (33.78%) were non-visible with a significant difference of (p < .0001). Real-time PCR using atpE or lpqT and RD1 similarly detected the frequency of infection, sensitivity, specificity, positive predictive value, negative predictive value, and accuracy, which represented 73/74 (98.65%), 98.65, 100, 100, 90.91, and 98.81%, respectively. Multiplex conventional PCR targeting RD1, 4, 9, and 12 confirmed that 49/74 (66.21%) were M.bovis, while the simplex conventional PCR targeting RD4 and RD9 confirmed mycobacteria in 71/74 (95.94%) samples, which included 61/74 (82.4%) M.bovis and 2/74 (2.7%) M.tuberculosis. Additionally, 8/74 (10.8%) exhibited mixed patterns of M.bovis and M.tuberculosis, and 3/74 (4.05%) were negative. There was a significant difference between the results of simplex and multiplex conventional PCR (p < .0001). Moreover, simplex conventional PCR targeting RD4 and RD9 proved higher sensitivity, specificity, positive predictive value, negative predictive value, and accuracy, which were 95.95, 100, 100, 76.92, and 96.43%, respectively, when compared with the values of multiplex conventional PCR targeting RD1,4,9, and 12 which were 66.22, 100, 100, 28.57, and 70.24%, respectively. The repeatability results of real-time PCR using atpE or lpqT and RD1, and simplex conventional PCR targeting RD4 and RD9 were acceptable. In conclusion, a combination of real-time PCR using atpE or lpqT and RD1 as the first step with simplex conventional PCR targeting RD4 and RD9 as the second step was reliable as a diagnostic tool.

A first insight into the application of high discriminatory MIRU-VNTR typing using QIAxcel technology for genotyping Mycobacterium bovis isolated from the Delta area in Egypt

Mycobacterium bovis is a notorious infectious agent leading to serious economic losses for cattle farms worldwide. Analysis of the widely spreading genotypes is vital for tracing infections, understanding transmission dynamics, and controlling the cluster growth. This study aimed to evaluate the discrimination ability of 15 mycobacterial interspersed repetitive unit-variable number tandem repeats (MIRU-VNTR) loci and to assess the extremely efficient loci subset for molecular epidemiological investigations of M.bovis from farms in the Delta area of Egypt. The discriminating ability of MIRU-VNTR genotyping using 15 loci {2 exact tandem repeat (ETR) loci, 6 MIRU loci, 4 Mtub loci, and 3 Queen's University of Belfast (QUB) group loci)} were evaluated on 61 M.bovis isolates from cattle (Holstein Frisian) and buffaloes. The results indicate that there are 48 genotypes: 3 unique genotypes and 45 genotypes with shared similarities. Using the MIRU-VNTRplus database, M.bovis ID 7540/01 and ID 5346/02 were the nearest lineages to both groups. Six loci (MIRU10, QUB11b, QUB26, ETRA, Mtub30, and Mtub39) were highly discriminating, seven other loci (Mtub21, MIRU26, QUB4156, MIRU04 (ETRD), MIRU16, MIRU 40, and ETRC) gave moderate discriminatory power, and the last two loci (Mtub04 and MIRU31) were poorly discriminative. MIRU-VNTR typing generally proved efficacy and high discriminatory power, with a collective allele's diversification of 0.9641. Both the six highly discriminating (DI = 0.9492) and the seven moderately discriminating loci (DI = 0.9269) evidenced to be suitable for M.bovis first-step initial genotyping from cattle herds in Egypt. MIRU-VNTR is rapid and effective in the genotyping of M.bovis from cattle and buffaloes in Egypt.

Oral Vaccination with Heat-Inactivated Mycobacterium bovis Does Not Interfere with the Antemortem Diagnostic Techniques for Tuberculosis in Goats

Vaccination against tuberculosis (TB) is prohibited in cattle or other species subjected to specific TB eradication campaigns, due to the interference that it may cause with the official diagnostic tests. However, immunization with a heat-inactivated (HI) Mycobacterium bovis vaccine via the oral route has been suggested to overcome this issue. In this study, the main goal was to assess the interference of the HI vaccine by different routes of administration using a previous vaccination and re-vaccination (boosting) protocol. TB-free kid goats were divided into three groups: oral (n = 16), intramuscular (IM; n = 16), and control (n = 16). Results showed that there was a significant difference in the percentage of animals positive to the single intradermal test (SIT) and blood based interferon-gamma release assay (IGRA) caused by vaccination when performed in the IM group compared to the oral group (p < 0.001). Nevertheless, no positivity to the SIT or IGRA test was observed in orally vaccinated goats regardless of the different interpretation criteria applied. None of the groups presented positive antibody titers using an in-house ELISA and samples collected 2 months after the boost. These results suggest the potential usefulness of the HI vaccine by the oral route in goats to minimize the interference on diagnostic tests (skin and IGRA tests) and reducing the necessity of defined antigens to replace the traditional purified protein derivatives for diagnosis. Finally, the results pave the way to future efficacy studies in goats using different routes of HI vaccination.

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.

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.