Bayesian receiver operating characteristic estimation of multiple tests for diagnosis of bovine tuberculosis in Chadian cattle

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

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

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.

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.

Appraisal of interpretation criteria for the single intra-dermal comparative cervical tuberculin test for the diagnosis of tuberculosis in dromedary camels in Ethiopia

Dromedary camels are the main sources of milk, meat and income for the Ethiopian pastoralists as they withstand the harsh environments of the regions of the country. Tuberculosis (TB) affects dromedary camels causing morbidity and mortality in these animals. Hence, early diagnosis and identification of infected camels play a significant role in reducing the transmission of TB in camels. This study was conducted on 168 camels between October 2014 and July 2015 to evaluate the performance of single intra-dermal comparative cervical tuberculin (SICCT) to diagnose TB in camels. Gross pathology was used as a gold standard to define disease status of each camel. The result showed that at the cutoff value of ≥ 3 mm SICCT had optimum performance with sensitivity and specificity of 60.7 and 85%, respectively. Moreover, at a cutoff ≥ 3 mm, the receiver operating characteristics (ROC) revealed area under the ROC curve was 0.729 (0.615-0.842) which is statistically significant (p = 0.000). Thus, the result of the present study could suggest the use of ≥ 3 mm cutoff value for the diagnosis of TB in dromedary camels in Ethiopia.

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

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

The prevalence of brucellosis and bovine tuberculosis in ruminants in Sidi Kacem Province, Morocco

Bovine tuberculosis (BTB) and brucellosis are major endemic zoonoses in ruminants in Morocco that impact on both animal and human health. This study presents an assessment of the epidemiological and socioeconomic burden of bacterial zoonoses in Sidi Kacem Province in Northern Morocco from a cross-sectional survey of 125 cattle and/or small ruminant-owning households. In total, 1082 sheep and goats were examined from 81 households. The single intradermal comparative cervical test to screen for bovine tuberculosis was undertaken on 1194 cattle from 123 households and all cattle were blood sampled. Cattle and small ruminant sera were tested for brucellosis using the standard Rose Bengal Test (sRBT) and the modified Rose Bengal Test (mRBT). Bacteriology was performed on 21 milk samples obtained from cattle that were seropositive for brucellosis for isolation and phenotyping of circulating Brucella strains. Individual and herd prevalence for BTB in cattle of 20.4% (95% CI 18%-23%) and 57.7% (95% CI 48%-66%), respectively, were observed in this study. The prevalence of brucellosis in cattle at individual and herd level was 1.9% (95% CI 1.2%-2.8%) and 9% (95% CI 4.5%-1.5%), respectively. Brucella pathogens were isolated from three cattle milk samples and were identified as B. abortus using Bruceladder® multiplex PCR and B. abortus biovar 1 by classical phenotyping. All small ruminants were seronegative to sRBT, two were positive to mRBT. A higher risk of BTB and brucellosis was observed in cattle in intensive livestock systems, in imported and crossed breeds and in animals from larger herds (>15). The three risk factors were usually present in the same herds, leading to higher transmission risk and persistence of both zoonoses. These results highlight the importance of implementing control strategies for both BTB and brucellosis to reduce productivity losses and the risk of transmission to humans. Prioritising control for BTB and brucellosis in intensive livestock production systems is essential for human and animal health.

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.

Isolation and characterization of non tuberculous mycobacteria from humans and animals in Namwala District of Zambia

BACKGROUND

The genus Mycobacterium contains more than 100 species, most of which are classified as non-tuberculous mycobacteria (NTM). In Zambia, the NTM are slowly becoming recognized as pathogens of major public health significance with the advent of Human Immunodeficiency Virus (HIV) and Acquired Immunodeficiency Syndrome (AIDS). This study aimed at reporting the isolated NTM and ascertains their zoonotic potential and diagnostic significance in Zambia.

METHOD

A total of 100 sputum samples were collected from three health facilities from suspected pulmonary tuberculosis human patients. In addition, 67 lymph node tissue samples from cattle and 14 from Kafue lechwe (Kobus leche kafuensis) showing tuberculosis-like lesions were collected. The samples were appropriately decontaminated and cultured on Middlebrook 7H10 and Stone brink. The isolates were then identified accordingly using the 16S ribosomal RNA analysis method.

RESULTS

A total of 8 NTM were isolated from human sputum, 12 from cattle and 1 from the Kafue lechwe. The identified NTM included M. intracellulae, M. abscess, M. chimaera, M. bolleti, M. fortuitum and M. stomatopae sp. Nov.

CONCLUSION

The isolation of NTM from humans and animals at the interface in Namwala district has highlighted the clinical significance and diagnostic challenge. The epidemiological investigation of NTM in the study area is therefore recommended. This should include sampling from environmental sources such as water and soil.

Bayesian estimation of the seroprevalence of brucellosis in humans and livestock in Kyrgyzstan

Kyrgyzstan reported 77.5 new cases of human brucellosis per 100,000 inhabitants in 2007, which is one of the highest incidences in the world. However, because this number is based on official records, it is very likely that the incidence is underreported. The diagnostic tests most commonly used in Kyrgyzstan are the Rose Bengal test in ruminants and the Huddleson test in humans. The sensitivity and specificity of these tests have never been evaluated under field conditions in Kyrgyzstan, where the strains circulating in livestock and humans are unknown. Therefore, a representative national cross-sectional serological study was undertaken in humans, cattle, sheep and goats to assess the true seroprevalence and to compare different serologicaltests. In the year of study (2006), few animals were vaccinated against brucellosis in Kyrgyzstan. A total of 5,229 livestock sera and 1,777 human sera from three administrative regions were collected during spring 2006 and submitted to a range of serological tests. The true seroprevalence of brucellosis, estimated using Bayesian methodology, was 7% (95% credibility interval 4%-9%) in humans, 3% (1%-5%) in cattle, 12% (7%-23%) in sheep and 15% (7%-30%) in goats. The Rose Bengal test was confirmed as a useful screening test in livestock and humans, although its sensitivity was lower than that of other tests. The estimates of specificity of all tests were significantly higher than those for sensitivity. The high seroprevalence of brucellosis in humans, cattle and small ruminants in Kyrgyzstan was confirmed. Bayesian statistical approaches were demonstrated to be useful for simultaneously deriving test characteristics and true prevalence estimates in the absence of a gold standard.

Bovine tuberculosis: within-herd transmission models to support and direct the decision-making process

Use of mathematical models to study the transmission dynamics of infectious diseases is becoming increasingly common in veterinary sciences. However, modeling chronic infectious diseases such as bovine tuberculosis (bTB) is particularly challenging due to the substantial uncertainty associated with the epidemiology of the disease. Here, the methodological approaches used to model bTB and published in the peer-reviewed literature in the last decades were reviewed with a focus on the impact that the models' assumptions may have had on their results, such as the assumption of density vs. frequency-dependent transmission, the existence of non-infectious and non-detectable stages, and the effect of extrinsic sources of infection (usually associated with wildlife reservoirs). Although all studies suggested a relatively low rate of within-herd transmission of bTB when test-and-cull programs are in place, differences in the estimated length of the infection stages, sensitivity and specificity of the tests used and probable type of transmission (density or frequency dependent) were observed. Additional improvements, such as exploring the usefulness of contact-networks instead of assuming homogeneous mixing of animals, may help to build better models that can help to design, evaluate and monitor control and eradication strategies against bTB.

Prevalence of bovine tuberculosis and risk factor assessment in cattle in rural livestock areas of Govuro District in the Southeast of Mozambique

Background

Bovine tuberculosis (bTB), caused by Mycobacterium bovis, is an infectious disease of cattle that also affects other domestic animals, free-ranging and farmed wildlife, and also humans. In Mozambique, scattered surveys have reported a wide variation of bTB prevalence rates in cattle from different regions. Due to direct economic repercussions on livestock and indirect consequences for human health and wildlife, knowing the prevalence rates of the disease is essential to define an effective control strategy.

Methodology/Principal findings

A cross-sectional study was conducted in Govuro district to determine bTB prevalence in cattle and identify associated risk factors. A representative sample of the cattle population was defined, stratified by livestock areas (n = 14). A total of 1136 cattle from 289 farmers were tested using the single comparative intradermal tuberculin test. The overall apparent prevalence was estimated at 39.6% (95% CI 36.8–42.5) using a diagnostic threshold cut-off according to the World Organization for Animal Health. bTB reactors were found in 13 livestock areas, with prevalence rates ranging from 8.1 to 65.8%. Age was the main risk factor; animals older than 4 years were more likely to be positive reactors (OR = 3.2, 95% CI: 2.2–4.7). Landim local breed showed a lower prevalence than crossbred animals (Landim × Brahman) (OR = 0.6, 95% CI: 0.4–0.8).

Conclusions/Significance

The findings reveal an urgent need for intervention with effective, area-based, control measures in order to reduce bTB prevalence and prevent its spread to the human population. In addition to the high prevalence, population habits in Govuro, particularly the consumption of raw milk, clearly may potentiate the transmission to humans. Thus, further studies on human tuberculosis and the molecular characterization of the predominant strain lineages that cause bTB in cattle and humans are urgently required to evaluate the impact on human health in the region.

Bovine tuberculosis in South Darfur State, Sudan: an abattoir study based on microscopy and molecular detection methods

Bovine tuberculosis (BTB) is a widespread zoonosis in developing countries but has received little attention in many sub-Saharan African countries including Sudan and particularly in some parts such as Darfur states. This study aimed to detect bovine tuberculosis among caseous materials of cattle slaughtered in abattoirs in South Darfur State, Sudan by using microscopic and PCR-based methods. The study was a cross-sectional abattoir-based study which examined a total of 6,680 bovine carcasses for caseous lesions in South Darfur State between 2007 and 2009. Collected specimens were examined for the presence of acid-fast bacilli (AFB) by using microscopic and culture techniques. Isolated mycobacteria were identified by selected conventional cultural and biochemical tests in comparison to a single tube multiplex PCR (m-PCR) assay which detect Mycobacterium bovis-specific 168-bp amplicons. Of the total 6,680 slaughtered cattle examined in South Darfur, 400 (6 %) showed caseations restricted to lymph nodes (86.8 %) or generalized (13.2 %). Bovine tuberculosis was diagnosed in 12 (0.18 %), bovine farcy in 59 (0.88 %), unidentified mycobacteria in 6 (0.09 %), and missed or contaminated cultures in 7 (0.1 %). Out of 18 cultures with nonbranching acid-fast rods, 12 amplified unique 168-bp sequence specific for M. bovis and subsequently confirmed as M. bovis. With the exception of the reference M. tuberculosis strains, none of the remaining AFB amplified the 337-bp amplicon specific for M. tuberculosis. It could be concluded that bovine tuberculosis is prevalent among cattle in South Darfur representing 4.5 % from all slaughtered cattle with caseous lesions. The study sustains microscopy as a useful and accessible technique for detecting AFB. m-PCR assay proved to be valuable for confirmation of BTB and its differentiation from other related mycobacteriosis, notably bovine farcy.

Polymorphisms of the SLC11A1 gene and resistance to bovine tuberculosis in African Zebu cattle

Bovine tuberculosis (BTB) is a considerable health threat to livestock keepers and general communities in many developing countries. Information on genetic resistance or susceptibility because of polymorphisms of candidate genes could be used in making selection decisions for breeding disease tolerant/resistant animals. Here, we investigated associations between polymorphisms at the solute carrier family 11 (proton-coupled divalent metal ion transporters), member 1 gene (SLC11A1, previously known as natural resistant associated macrophage protein 1, NRAMP1), with BTB phenotypes in Chadian cattle. Phenotypes were (i) single intradermal comparative cervical tuberculin test (SICCT) outcome, (ii) presence of gross visible lung lesions, (iii) a bacteriological culture test outcome and (iv) a predicted true BTB infection status using a Bayesian model. All traits were recorded as binary (presence or absence) traits. A total of 211 cattle were genotyped for a microsatellite within the SLC11A1 candidate gene. Standard linear and threshold-liability models regressing BTB traits on copy number of SLC11A1 alleles revealed statistically significant effects of SLC11A1 alleles (P < 0.001) on most BTB traits. Polymorphisms (alleles 211, 215 and 217) are significantly related to lower incidence of BTB traits in Chadian cattle. This is the first study to report the association of SLC11A1 gene polymorphisms with BTB traits in Chadian or any other African cattle breeds.

Diagnostic efficiency of abattoir meat inspection service in Ethiopia to detect carcasses infected with Mycobacterium bovis: implications for public health

Background

Bovine Tuberculosis (BTB) is a widespread and endemic disease of cattle in Ethiopia posing a significant threat to public health. Regular surveillance by skin test, bacteriology and molecular methods is not feasible due to lack of resource. Thus, routine abattoir (RA) inspection will continue to play a key role for national surveillance. We evaluated efficiency of RA inspection for diagnosis of Mycobacterium bovis infection and discussed its public health implications in light of a high risk of human exposure.

Methods

The study was conducted in five abattoirs: Addis Ababa, Adama, Hawassa, Yabello and Melge-Wondo abattoirs. The efficiency of routine abattoir (RA) inspection was validated in comparison to detailed abattoir (DA) inspection, followed by culture and microscopy (CM) and region of difference (RD) deletion analysis. Diagnostic accuracies (with corresponding measures of statistical uncertainty) were determined by computing test property statistics (sensitivity and specificity) and likelihood estimations using web-based SISA diagnostic statistics software. Post-test probability of detecting TB infected carcasses was estimated using nomograms. Agreement between RA and DA inspections was measured using kappa statistics. The study was conducted and reported in accordance with standards for reporting of diagnostic accuracy (STARD) requirements. Both routine and detailed meat inspection protocols were performed on a subpopulation of 3322 cattle selected randomly from among 78,269 cattle slaughtered during the study period. Three hundred thirty seven carcasses identified through detailed meat inspection protocols were subjected to culture and microscopy; of the 337, a subset of 105 specimens for culture and microscopy were subjected to further molecular testing.

Results

There was a substantial agreement between RA and DA inspections in Addis Ababa (Kappa = 0.7) and Melge-Wondo abattoirs (Kappa = 0.67). In Adama, Hawassa and Yabello abattoirs, the agreement was however poor (Kappa ≤ 0.2). RA inspection was able to detect only 117 of the total 3322 carcasses inspected (3.5%). The sensitivity (Sn) and specificity (Sp) of RA inspection were 28.2% (95/337) [95%CI: 23.4-33.0] and 99.3% (2963/2985) [95%CI: 99.0-99.6], respectively, when DA inspection was considered as reference test. When culture and microscopy (CM) was considered as reference test, the Sn and Sp of RA were 55.2% (58/105) [95%CI: 45.7-64.7] and 84.1% (195/232) [95%CI: 79.3-88.8]. RA inspection failed to detect 71.8% (242/337) and 44.8% (47/105) of TB infected carcasses as judged by DA inspection and CM, respectively. On the other hand, a much higher sensitivity of DA was obtained when CM and RD deletion analysis were considered as reference tests (96.3% (105/109) and 100.0% (24/24), respectively).

Conclusions

The study results indicate that meat inspection protocols currently utilized in abattoirs are insufficient to detect the majority of TB lesions at the gross level. DA inspection protocols were demonstrated to improve the detection level by approximately 3-fold. The failure of current inspection techniques to detect approximately 70% of carcasses presented with grossly-visible lesions of TB at the slaughter-plants indicates the magnitude of meat-borne zoonotic TB as an on-going risk to public health. Standardization of abattoir inspection protocols (in line with international sanitary requirements), enhanced training and proficiency testing of meat inspections, and raising public awareness are recommended as essential and cost-effective interventions to improve meat inspection service in Ethiopia, with subsequent protection of consumers' health.

Mixed infections of Corynebacterium pseudotuberculosis and non-tuberculous mycobacteria in South African antelopes presenting with tuberculosis-like lesions

Routine meat inspection of antelope carcasses from a South African game reserve revealed a high prevalence of tuberculosis-like lesions. This study aimed to identify the causative agent of this disease and to describe its pathological features. In total, 139 antelopes were randomly harvested from the game reserve and subjected to meat inspection. Of these animals, 46 (33%) showed gross visible, tuberculosis-like lesions. Histopathological examination revealed the presence of encapsulated necrogranulomas in organs and/or lymph nodes of 22 of 27 animals tested. Tissue samples from lesions were processed for both non-selective bacterial culture and mycobacterial culture following decontamination. In non-selective cultures of lesions from 25 of 31 animals tested, Corynebacterium pseudotuberculosis was detected. Isolation of C. pseudotuberculosis was closely associated with the presence of necrogranulomas. In mycobacterial cultures of lesions from 9 of 41 animals tested, different species of non-tuberculous mycobacteria (NTMs) were detected. In 5 instances, depending on the culture procedure that was applied, either C. pseudotuberculosis or NTMs were isolated from the same tissue sample. Our results suggest that the disease has been caused by infections with C. pseudotuberculosis. In sub-Saharan Africa, the role of pathogens other than Mycobacterium bovis may be underestimated in causing tuberculosis-like lesions. In cases where potentially pathogenic NTMs are isolated from mycobacterial cultures of tuberculosis-like lesions, the non-use of additional non-selective culture techniques could lead to misinterpretations of the diagnostic test results.