Occurrence of overlooked zoonotic tuberculosis: detection of Mycobacterium bovis in human cerebrospinal fluid

Mycobacterium bovis induced human tuberculosis in India: Current status, challenges & opportunities

Tuberculosis (TB) caused by Mycobacterium tuberculosis is a leading cause of human deaths due to any infectious disease worldwide. However, infection of Mycobacterium bovis, primarily an animal pathogen, also leads to the development of 'human tuberculosis'. Infected animals have been considered the major source of M. bovis infection and humans get exposed to M. bovis through close contact with infected animals or consumption of contaminated milk, unpasteurized dairy products and improperly cooked contaminated meat. The information on the global distribution of bovine TB (bTB) is limited, but the disease has been reported from all the livestock-producing middle- and low-income countries of the world. In recent years, there is a renewed interest for the control of bTB to minimize human infection worldwide. In India, while the sporadic presence of M. bovis has been reported in domestic animals, animal-derived food products and human beings from different geographical regions of the country, the information on the national prevalence of bTB and transmission dynamics of zoonotic TB is, however, not available. The present article reviewed published information on the status of M. bovis-induced zoonotic TB to highlight the key challenges and opportunities for intervention to minimize the risk of M. bovis infection in humans and secure optimum animal productivity in India.

Evaluation of ELISA and PCR in parallel to single intradermal cervical tuberculin test (SICT) for diagnosis of tuberculosis in buffaloes

Bovine tuberculosis is an economically important disease with very high zoonotic potential. Single intradermal cervical tuberculin test (SICT) is considered a gold standard assay for the diagnosis of bovine tuberculosis. However, bovines especially buffaloes may produce a false negative result when the animal becomes cell-mediated immune (CMI) anergic in the advanced stage of the disease. In the present study, ELISA and PCR assays were successfully demonstrated to be useful in diagnosing tuberculosis especially in the CMI anergic buffaloes infected with Mycobacterium bovis. ELISA and PCR assays are able to detect 8.94% and 8.13%, respectively, more animals as positive in comparison to standard SICT assay in a selected population of 123 buffaloes. The moderate agreement between SICT and ELISA (k: 0.528; 0.249-0.807), a substantial agreement between SICT and PCR (k: 0.648; 0.364-0.931), and high agreement between ELISA and PCR (k: 0.856; 0.697-1.0) highlight that ELISA and PCR, if used in parallel with SICT, will provide better sensitivity over single assay. Reduction of false negative reactors may help in minimizing the zoonotic threat from bovine tuberculosis especially in disease endemic region where human and livestock interface is quite high.

Diagnostic Challenges and Prospects Associated With Zoonotic Tuberculosis of Central Nervous System

Introduction:

The diagnosis of Tuberculous Meningitis (TBM) has remained a challenge due to its insidious onset and the failure of conventional diagnostic tests. The present study aimed to identify the mycobacterial pathogen in the CSF of patients with TBM and a poor prognosis.

Methods:

We retrospectively recruited 224 TBM and 34 non-TBM patients admitted to the Central India Institute of Medical Sciences, Nagpur, India, in 2014. The CSF samples of these patients were subjected to a duplex PCR assay for the species-specific identification of the causative pathogen.

Results:

M. bovis and infection with M.tuberculosis were detected in 7% (18) and 32.9% (85) of the patients, respectively. Moreover, 14% (36) of the study samples were culture positive; however, the mycobacterial pathogens could not be differentiated to the species level.

Conclusion:

The present study findings emphasized the potentially vital importance of M. bovis identification for appropriate patient management. The obtained data also demonstrated the persistent significance of M. bovis, as a zoonotic pathogen.

Reconsidering Mycobacterium bovis as a proxy for zoonotic tuberculosis: a molecular epidemiological surveillance study

Background

Zoonotic tuberculosis is defined as human infection with Mycobacterium bovis. Although globally, India has the largest number of human tuberculosis cases and the largest cattle population, in which bovine tuberculosis is endemic, the burden of zoonotic tuberculosis is unknown. The aim of this study was to obtain estimates of the human prevalence of animal-associated members of the Mycobacterium tuberculosis complex (MTBC) at a large referral hospital in India.

Methods

We did a molecular epidemiological surveillance study of 940 positive mycobacteria growth indicator tube (MGIT) cultures, collected from patients visiting the outpatient department at Christian Medical College (Vellore, India) with suspected tuberculosis between Oct 1, 2018, and March 31, 2019. A PCR-based approach was applied to subspeciate cultures. Isolates identified as MTBC other than M tuberculosis or as inconclusive on PCR were subject to whole-genome sequencing (WGS), and phylogenetically compared with publicly available MTBC sequences from south Asia. Sequences from WGS were deposited in the National Center for Biotechnology Information Sequence Read Archive, accession number SRP226525 (BioProject database number PRJNA575883).

Findings

The 940 MGIT cultures were from 548 pulmonary and 392 extrapulmonary samples. A conclusive identification was obtained for all 940 isolates; wild-type M bovis was not identified. The isolates consisted of M tuberculosis (913 [97·1%] isolates), Mycobacterium orygis (seven [0·7%]), M bovis BCG (five [0·5%]), and non-tuberculous mycobacteria (15 [1·6%]). Subspecies were assigned for 25 isolates by WGS, which were analysed against 715 MTBC sequences from south Asia. Among the 715 genomes, no M bovis was identified. Four isolates of cattle origin were dispersed among human sequences within M tuberculosis lineage 1, and the seven M orygis isolates from human MGIT cultures were dispersed among sequences from cattle.

Interpretation

M bovis prevalence in humans is an inadequate proxy of zoonotic tuberculosis. The recovery of M orygis from humans highlights the need to use a broadened definition, including MTBC subspecies such as M orygis, to investigate zoonotic tuberculosis. The identification of M tuberculosis in cattle also reinforces the need for One Health investigations in countries with endemic bovine tuberculosis.

Funding

Bill & Melinda Gates Foundation, Canadian Institutes for Health Research.

Community, system and policy level drivers of bovine tuberculosis in smallholder periurban dairy farms in India: a qualitative enquiry

BACKGROUND

Rapid urbanization has led to expansion of peri-urban fringes, where intensive, industry-style livestock rearing has led to emerging vulnerabilities at the human-animal-environment interface. This study was undertaken to understand the health system and farm-level factors that influenced the risk of transmission of bovine Tuberculosis (bTB) in animals and humans in peri-urban smallholder dairy farms of India.

METHODS

Thematic guides were developing through literature review and expert consultation. In-depth interviews were conducted till attainment of saturation. Identification of core themes was followed by etiological enquiry and generation of a conceptual model.

RESULTS

Veterinarians were consulted as a last resort after home-remedies and quacks had failed. Damage control measures, especially with respect to- selling or abandoning sick animals, added to the risk of disease transmission. Although civic authorities believed in the adequacy of a functioning laboratory network, end users were aggrieved at the lack of services. Despite the presence of extension services, knowledge and awareness was limited, promoting risky behaviour. The absence of cogent policies in dealing with bTB was a significant barrier. Stakeholders did not consider bTB to be a major concern. It is possible that they underestimate the problem.

CONCLUSION

The current study helps to identify gaps which need to be addressed through collaborative research, and OneHealth interventions to build community awareness.

Culture positivity of smear negative pulmonary and extrapulmonary tuberculosis- A study from North Kerala, India

Introduction:

The identification of smear negative pulmonary and extrapulmonary tuberculosis continues to remain a diagnostic challenge. This study was conducted in a tertiary care setup in north Kerala to isolate and identify mycobacteria by culture from radiologically and clinically suspected cases of smear negative pulmonary and extrapulmonary tuberculosis.

Methods:

A total of 200 samples (100 pulmonary and 100 extrapulmonary) were processed and cultured by automated (MB/BacT) and conventional methods. Heat stable catalase test, nitrate reduction test and detection of MPT 64 antigen were done to aid species identification.

Results:

Overall culture positivity was 7% (14 isolates - 8 pulmonary and 6 extrapulmonary) of which 92.9% (13) of the isolates were Mycobacterium tuberculosis and 7.1% (1) was Mycobacterium fortuitum (identified by molecular typing). Detection rate by automated method was 7% (14) and by conventional method was only 1.5% (3).

Conclusion:

Despite its shortcomings and low positivity, culture still remains the gold standard for the diagnosis of EPTB and SNPT. However, automated liquid cultures have better isolation rates than the conventional LJ culture. Subjecting these isolates to rapid diagnostic tests like antigen detection and LPA can aid in the early institution of appropriate treatment regimen.

Risk factors for human Mycobacterium bovis infections in an urban area of Brazil

BACKGROUND

The World Health Organization (WHO) has classified human zoonotic tuberculosis (TB) due to Mycobacterium bovis as a neglected issue in the developing world. In a recent cross-sectional study in Brazil, three of 189 TB patients presented with a coinfection of M. bovis and M. tuberculosis and were selected as cases for this study.

OBJECTIVE

The aim was to evaluate risk factors (RF) for zoonotic TB in an urban area of Brazil in order to guide preventive programmes.

METHODS

A matched case-control study was carried out nested within a cross-sectional study. For each of the three cases, 14 age- and sex-matched controls (TB due to M. tuberculosis) were selected.

FINDINGS

Zoonotic potential exposures (ZE) and extrapulmonary TB (EPTB) were independently associated with zoonotic TB in multivariate analyses.

CONCLUSIONS

ZE by occupation and consumption of raw milk and derivative products that place individuals in direct and indirect contact with animals and their excretions/secretions increase the risk for zoonotic TB in Brazil, especially among those with EPTB. Therefore, measures such as efficient control of bovine TB, distribution of pasteurised milk and its derivative products, and the diagnosis and monitoring of zoonotic TB in humans are essential steps, especially in developing countries where bovine TB is enzootic, and further studies are necessary.

Prevalence of zoonotic tuberculosis and associated risk factors in Central Indian populations

In the present study, we aimed to estimate the occurrence of bovine tuberculosis (TB) and examine the determinants of distribution of the disease in three high-risk populations of Central India. A prospective cohort study was conducted in Central India between March 2014 and June 2015. Based on the requisite inclusion criteria, we recruited a total of 301 participants whose blood samples were subjected to polymerase chain reaction-based detection and differentiation of Mycobacterium bovis and Mycobacterium tuberculosis. M. bovis was detected in 11.4%, 8.9%, and 12.6% of the recruited participants belonging to three distinct population groups (Groups A, B, and C, respectively). The highest proportion of cases infected with M. bovis was observed in Group C, who lived in the high TB endemic region. Previous contact with active TB cases (odds ratio = 3.7; 95% confidence interval, 0.9612–14.4533) and raw milk consumption (odds ratio = 5.3472; 95% confidence interval, 1.9590–14.5956) were found to be important determinants of bovine TB in this population. The high incidence rates of bovine TB in the Central Indian populations indicate the substantial consequences of this disease for some population groups and settings. However, more research is necessary to identify the main transmission drivers in these areas.

Antimycobacterial activity of Pichia pastoris-derived mature bovine neutrophil β-defensins 5

Tuberculosis (TB) is an ongoing threat to global health, and the lack of effective therapies for treating it is also a global problem. Previous studies have shown that human cathelicidin and defensins have effective antimicrobial activity against Mycobacterium spp. To our knowledge, there are no reports on the antimycobacterial effects of bovine neutrophil β-defensins so far. Here, we identified the antimicrobial effect of mature bovine neutrophil β-defensins (mBNBD) 5 against Mycobacterium infection both in vitro and in vivo. The mBNBD5 protein was expressed in Pichia pastoris. To increase the yield of β-defensins, a purification method was employed by adding a 6-His·tag to the C-terminus of the mBNBD5 gene. Our results indicated that recombinant mBNBD5 protein was successfully expressed and purified from Pichia pastoris with intact antimicrobial activity. The recombinant protein exhibited potent bactericidal activity in vitro against M. smegmatis and M. bovis, with a dose-dependent manner and a time-dependent manner. The electron microscope results showed that the bacterial cell wall of M. bovis was disrupted when incubated with mBNBD5 for 72 h. Our data also indicated that the exogenous addition of mBNBD5 could reduce the survival of Mycobacterium spp., especially M. tuberculosis and M. bovis in RAW 264.7 macrophages. These results provide foundations for the development of mBNBD5 as a potential new therapeutic agent for TB treatment.

Detection of IS6110 and HupB gene sequences of Mycobacterium tuberculosis and bovis in the aortic tissue of patients with Takayasu's arteritis

BACKGROUND

Takayasu's arteritis (TA) is a chronic inflammatory disease affecting the large arteries and their branches; its etiology is still unknown. In individuals suffering from TA, arterial inflammation progresses to stenosis and/or occlusion, leading to organ damage and affecting survival. Relation of TA with Mycobacterium tuberculosis has been known, but there have been only a few systematic studies focusing on this association. The IS6110 sequence identifies the Mycobacterium tuberculosis complex and the HupB establishes the differences between M. tuberculosis and M. bovis. Our objective was to search the presence of IS6110 and HupB genes in aorta of patients with TA.

METHODS

We analyzed aorta tissues embedded in paraffin from 5760 autopsies obtained from our institution, we divided the selected samples as cases and controls;

CASES

aortic tissues of individuals with Takayasu's arteritis. Control positive: aortic tissues (with tuberculosis disease confirmed) and control negative with other disease aortic (atherosclerosis).

RESULTS

Of 181 selected aorta tissues, 119 fulfilled the corresponding criteria for TA, TB or atherosclerosis. Thus 33 corresponded to TA, 33 to tuberculosis (TB) and 53 to atherosclerosis. The mean age was 22 ± 13, 41 ± 19, and 57 ± 10, respectively. IS6110 and HupB sequences were detected in 70% of TA tissues, 82% in tuberculosis, and in 32% with atherosclerosis. Important statistical differences between groups with TA, tuberculosis versus atherosclerosis (p = 0.004 and 0.0001, respectively) were found.

CONCLUSION

We identified a higher frequency of IS6110 and HupB genes in aortic tissues of TA patients. This data suggests that arterial damage could occur due to previous infection with M. tuberculosis.

Extra pulmonary tuberculosis: a diagnostic dilemma

Tuberculosis remains a major public health problem globally, with India being one of the high burden countries. The common causative agent is Mycobacterium tuberculosis but in developing countries M. bovis is reported as a potential human pathogen. Almost 20% of all reported cases of tuberculosis are of extra pulmonary form of disease. Diagnosis of extra pulmonary tuberculosis (EPTB) is not always possible with conventional methods, due to the long time required and the paucibacillary nature of samples; hence the need of rapid molecular methods. A prospective study was conducted on 300 patients of EPTB over a period of 5 years. These patients were suspected cases of tubercular meningitis, tubercular ascites and tubercular lymphadenitis. Samples analyzed were cerebrospinal fluid, ascitic fluid and lymph node fine needle aspirate. A two step PCR targeting hup B gene was used. Clinical response to anti tubercular therapy (ATT) was taken as positive (gold standard). PCR for hup B gene was positive in 147 samples out of 155 ATT responders. Of these 85.71% were infected with M. tuberculosis, 9.52% with M. bovis alone and 4.76% showed co infection with both M.tb and M. bovis. The sensitivity and specificity of PCR was 90.32 and 94.48% respectively.

PCR-Based Evaluation of Tuberculous Endometritis in Infertile Women of North India

BACKGROUND

Tuberculous endometritis is often a diagnostic dilemma for gynecologists in the evaluation of infertility. This study evaluated and compared different diagnostic methods in tuberculous endometritis.

METHODS

100 infertile women were investigated for tuberculous endometritis. The endometrial samples obtained by curettage were evaluated by Ziehl-Neelsen (ZN) staining of the smears for acid-fast bacilli (AFB), the samples were also cultured on Lowenstein-Jensen medium, and histopathological examination and nested PCR targeting 'hupB' gene (Rv 2986c in M. tuberculosis and Mb3010c in M. bovis) which can differentiate between M. tuberculosis and M. bovis were performed. Antibodies against 38-kDa and 16-kDa mycobacterial antigens were detected in serum using ELISA. Statistical analysis was done by online GraphPad Prism software, version 5.0. McNemar's test was applied and Kappa agreement coefficient was calculated for agreement between various methods. A p-value < 0.05 was considered significant.

RESULTS

Among the 100 evaluated endometrial samples, one was AFB smear positive, none was positive by culture, four were positive by histopathology and 13 were positive by PCR. Of the 13 PCR-positive cases, 38.4% were positive for M. tuberculosis, 23.07% for M. bovis, and 38.4% showed co-infection with both species. 40% of the patients had raised IgG against M. tuberculosis 38-kDa antigen. McNemar's test was applied to PCR and the conventional methods of TB diagnosis (AFB, Culture and histopathology) and the p-value was < 0.001 (highly significant) for PCR. Detection by PCR showed a fair agreement with detection by Mantoux test and ELISA.

CONCLUSION

In paucibacillary endometrial tuberculosis, the positive detection rate was found to be significantly higher for PCR compared to other methods. The 'in-house' nested PCR assay targeting the hupB gene and used in this study, can serve as a rapid diagnostic aid for tubercular endometritis. It can also differentiate between members of the Mycobacterium tuberculosis complex, namely M. tuberculosis and M. bovis.

Assessment of the N-PCR assay in diagnosis of pleural tuberculosis: detection of M. tuberculosis in pleural fluid and sputum collected in tandem

BACKGROUND

The nonspecific clinical presentation and paucibacillary nature of tuberculous pleuritis remains a challenge for diagnosis. Diagnosis of tuberculous pleural effusion depends on the demonstration of the presence of tubercle bacilli in the sputum, pleural fluid, or pleural biopsy specimen, or demonstration of granuloma in pleura by histological examination. We examined the clinical utility of the diagnosis of pleural tuberculosis using the in house N-PCR assay, AFB smear microscopy and culture. Besides pleural fluid the inclusion of sputum in the efficacy of diagnosis of pleural tuberculosis was scrutinized.

METHODOLOGY/PRINCIPAL FINDINGS

Pleural fluid and sputum samples of 58 tuberculous and 42 non-tuberculous pleural effusion patients were processed for AFB smear microscopy, culture and the N-PCR assay. Mycobacteria were detected exclusively in tuberculous pleural effusion samples. None of the non-tuberculous pleural effusion samples were positive for mycobacteria. Comparative analysis showed that the N-PCR assay had the highest sensitivity. Inclusion of sputum along with pleural fluid increased N-PCR sensitivity from 51.7 to 70.6% (p<0.0001).This improved sensitivity was reflected in AFB smear microscopy and isolation by culture. The sensitivity enhanced on inclusion of sputum from 3.4 (p = 0.50) to 10.3% (p = 0.038) for AFB smear microscopy and for isolation of mycobacteria from 10.3(p = 0.03) to 22.4% (p = 0.0005). Thirteen isolates were obtained from 58 pleural tuberculosis patients. Eleven mycobacterial isolates were identified as M. tuberculosis and two as M. fortuitum and M. chelonae. Complete concordance was seen between the biochemical identification of isolates and the N-PCR identification of mycobacterial species prior to isolation.

CONCLUSIONS/SIGNIFICANCE

To the best of our knowledge this is the first PCR based report on utility of sputum for diagnosis of pleural tuberculosis. The present study demonstrates that a combination of pleural fluid with sputum sample and N-PCR improved the diagnosis of pleural tuberculosis.

Visual format for detection of Mycobacterium tuberculosis and M. bovis in clinical samples using molecular beacons

A real-time polymerase chain reaction (PCR) assay for the direct identification of Mycobacterium tuberculosis and M. bovis using molecular beacons was developed. The assay was modified for use in regular thermal cyclers. Molecular beacons that were specific for M. tuberculosis (Tb-B) and M. bovis (Bo-B) were designed. The fluorescence of the target PCR product-molecular beacon probe complex was detected visually using a transilluminator. The results were then compared with those of conventional multiplex PCR (CM-PCR) assays and biochemical identification. The detection limit of Tb-B and Bo-B beacons was 500 fg and 50 fg by the visual format and real-time PCR assay, respectively, compared with 5 pg by CM-PCR assay. Pulmonary and extrapulmonary samples were examined. The agreement between culture and the two assays was very good in sputum samples and fair in extrapulmonary samples. The agreement between clinical diagnoses with the two assays was moderate in extrapulmonary samples. There was very good agreement between CM-PCR and visual format assays for all samples used in the study. Concordance in the identification of isolates by the visual, CM-PCR assay, and biochemical identification was seen. Hence, the use of molecular beacon detection of M. tuberculosis and M. bovis in clinical samples is feasible by setting up two asymmetric PCRs concurrently. The assay is sensitive, specific, simple to interpret, and takes less than 3 hours to complete.

Association of tuberculous endometritis with infertility and other gynecological complaints of women in India

Endometrial biopsy samples derived from 393 patients with assorted gynecological complaints were investigated for mycobacterial infection. By employment of four different techniques, mycobacterial pathogens were detected irrespective of the nature/type of clinical complaint. Mycobacterium tuberculosis was the predominant pathogen detected among the samples investigated.