The continued threat of tuberculosis

Structural characterization of glycinamide-RNase-transformylase T from Mycobacterium tuberculosis

Enzymes from the purine salvage pathway in Mycobacterium tuberculosis (Mtb) have been regarded as an attractive target for the development of anti-bacterial drugs. Although this pathway has not been extensively studied in Mtb, it has been identified as essential for growth and survival. Glycinamide-RNase-transformylase T (PurT) is found only in some specific bacteria including Mtb and utilizes ATP-dependent ligation to catalyze the formylation of 5′-phosphoribosyl-glycinamide (GAR) in the third reaction of the de novo purine salvage pathway. In the study, we determined the crystal structure of MtbPurT at a resolution of 2.79 Å. In contrast to Pyrococcus horikoshii OT3 PurT (phBCCPPurT), MtbPurT exhibits an “open” conformation, which results in a broader ATP-binding pocket and thus might facilitate the entry and exit of the cofactor. Additionally, active site superposition with E.coli PurT (EcPurT) showed that residues involved in the ATP-binding site in MtbPurT exhibited structural similarity but had notable difference in the GAR-binding site. The loop 383-389 in MtbPurT was much shorter and shifted 5.7 Å away from the phosphate of the GAR substrate. The different GAR-binding mode might result in a large conformational change in MtbPurT, and would provide a possible opportunity for anti-TB drug development.

Bovine tuberculosis disturbs parasite functional trait composition in African buffalo

Novel parasites can have wide-ranging impacts, not only on host populations, but also on the resident parasite community. Historically, impacts of novel parasites have been assessed by examining pairwise interactions between parasite species. However, parasite communities are complex networks of interacting species. Here we used multivariate taxonomic and trait-based approaches to determine how parasite community composition changed when African buffalo (Syncerus caffer) acquired an emerging disease, bovine tuberculosis (BTB). Both taxonomic and functional parasite richness increased significantly in animals that acquired BTB than in those that did not. Thus, the presence of BTB seems to catalyze extraordinary shifts in community composition. There were no differences in overall parasite taxonomic composition between infected and uninfected individuals, however. The trait-based analysis revealed an increase in direct-transmitted, quickly replicating parasites following BTB infection. This study demonstrates that trait-based approaches provide insight into parasite community dynamics in the context of emerging infections.

Novel high throughput pooled shRNA screening identifies NQO1 as a potential drug target for host directed therapy for tuberculosis

Chemical regulation of macrophage function is one key strategy for developing host-directed adjuvant therapies for tuberculosis (TB). A critical step to develop these therapies is the identification and characterization of specific macrophage molecules and pathways with a high potential to serve as drug targets. Using a barcoded lentivirus-based pooled short-hairpin RNA (shRNA) library combined with next generation sequencing, we identified 205 silenced host genes highly enriched in mycobacteria-resistant macrophages. Twenty-one of these "hits" belonged to the oxidoreductase functional category.

NAD(P)H

quinone oxidoreductase 1 (NQO1) was the top oxidoreductase "hit". NQO1 expression was increased after mycobacterial infection, and NQO1 knockdown increased macrophage differentiation, NF-κB activation, and the secretion of pro-inflammatory cytokines TNF-α and IL-1β in response to infection. This suggests that mycobacteria hijacks NQO1 to down-regulate pro-inflammatory and anti-bacterial functions. The competitive inhibitor of NQO1 dicoumarol synergized with rifampin to promote intracellular killing of mycobacteria. Thus, NQO1 is a new host target in mycobacterial infection that could potentially be exploited to increase antibiotic efficacy in vivo. Our findings also suggest that pooled shRNA libraries could be valuable tools for genome-wide screening in the search for novel druggable host targets for adjunctive TB therapies.

Anything to Stay Alive: The Challenges of a Campaign for an Experimental Drug

Drug-resistant tuberculosis (TB) has a high mortality rate. Most medicines used to treat it are poorly tested and have terrible side effects. Activists have campaigned for patients with drug-resistant TB to have access to experimental drugs, particularly one called bedaquiline, before these have been approved by regulatory authorities such as the Food and Drug Administration (FDA) in the United States (US) and the Medicines Control Council (MCC) in South Africa. Some activists have also campaigned for bedaquiline to be approved by regulatory authorities before testing of the drug is completed. These campaigns raise ethical concerns about whether patients should be offered experimental, unapproved, medicines for the treatment of life-threatening illnesses, and if authorities should approve drugs for life-threatening illnesses when vital questions about safety and efficacy remain outstanding.

Evaluation of Moxifloxacin ActivityIn VitroAgainstMycobacterium tuberculosis, Including Resistant and Multidrug-Resistant Strains

The new quinolone moxifloxacin was tested against 86 strains of Mycobacterium tuberculosis including 13 resistant and 4 multiresistant strains. The antimicrobial susceptibility was tested, in parallel, using two different liquid media, the radiometric Bactec 12B and the Mycobacteria Growth Indicator Tube (Becton Dickinson, USA). All strains but two were susceptible at 0.5 microg/ml of moxifloxacin; for the remaining two strains, both multidrugresistant, the minimal inhibitory concentrations (MIC) were =2 and >4 microg/ml respectively. Our data confirm the high antitubercular in vitro activity of moxifloxacin.

The value of effective public tuberculosis treatment: an analysis of opportunity costs associated with multidrug resistant tuberculosis in Latvia

BACKGROUND

A challenge to effective protection against tuberculosis is to sustain expensive and complex treatment public programs. Potential consequences of program failure include acquired drug resistance, poor patient outcomes, and potentially much higher system costs, however. In contrast, effective efforts have value illustrated by impacts they prevent. We compared the healthcare costs and treatment outcomes among multidrug-resistant tuberculosis (MDR-TB) and non MDR-TB patients in Latvia to identify benefits or costs associated with both.

METHODS

We measured and compared costs, healthcare utilization, and outcomes for patients who began treatment through Latvia's TB control program in 2002 using multivariate regression analysis and negative binomial regression.

RESULTS

We analyzed data for 92 MDR-TB and 54 non MDR-TB patients. Most (67%) MDR-TB patients had history of prior tuberculosis treatment. MDR-TB was associated with lower cure rates (71% vs. 91%) and greater resource utilization. MDR-TB treatment cost almost $20,000 more than non MDR-TB.

CONCLUSION

Up to 2/3 of MDR-TB treated in our sample was preventable at a potential savings of over $1.3 million in healthcare resources as well as substantial individual health.

Infectious Diseases: The Role of the Forensic Physician

Infections have plagued doctors for centuries, both in the diagnosis of the specific diseases, and the identification and subsequent management of the causative agents. There is a constant need for information as new organisms emerge, existing ones develop resistance to current drugs or vaccines and there are changes in epidemiology and prevalence. In the twenty-first century, obtaining this information has never been more important. Population migration, and the relatively low cost of flying, means that unfamiliar infectious diseases may be brought into industrialised countries. An example of this was an outbreak of severe acute respiratory syndrome (SARS), which was first recognised in 2003. Despite modern technology and a huge input of money, it took months for the agent to be identified, a diagnostic test to be produced, and a strategy for disease reporting and isolation to be established.

The societal cost of tuberculosis: Tarrant County, Texas, 2002

PURPOSE

Cost analyses of tuberculosis (TB) in the United States have not included elements that may be prevented if TB were prevented, such as losses associated with TB-related disability, personal and other costs to society. Unmeasured TB costs lead to underestimates of the benefit of prevention and create conditions that could result in a resurgence of TB. We gathered data from Tarrant County, Texas, for 2002, to estimate the societal cost due to TB.

METHODS

We estimated societal costs due to the presence or suspicion of TB using known variable and fixed costs incurred to all parties. These include costs for infrastructure; diagnostics and surveillance; inpatient and outpatient treatment of active, suspected, and latent TB infection (LTBI); epidemiologic activities; personal costs borne by patients and by others for lost time, disability, and death; and the cost of secondary transmission. A discount rate of 3% was used.

RESULTS

During 2002, 108 TB cases were confirmed in Tarrant County, costing an estimated $40,574,953. The average societal cost per TB illness was $ 376,255. Secondary transmission created 47% and pulmonary impairment after TB created 35.4% of the total societal cost per illness.

CONCLUSIONS

Prior estimates have concluded that treatment costs constitute most (86%) TB-related expenditures. From a societal perspective treatment and other direct costs account for little (3.3%) of the full burden. These data predict that preventing infection through earlier TB diagnosis and treatment of LTBI and expanding treatment of LTBI may be the most feasible strategies to reduce the cost of TB.

Regulation of type 1 diabetes, tuberculosis, and asthma by parasites

Helminth infection is a worldwide health problem. In addition to directly causing disease, helminthic infection also affects the incidence and progression of other diseases by exerting immune modulatory effects. In animal models, infection with helminthic parasites can prevent autoimmune diseases and allergic inflammatory diseases, but worsens protective immunity to certain infectious pathogens. In this review, we summarize current findings regarding the effects of helminth infection on type 1 diabetes, tuberculosis, and asthma and discuss possible mechanisms through which helminthic parasites modulate host immunity. Investigating these mechanisms could lead to treatment strategies that specifically modulate the immune response as well as address fundamental questions in immunobiology.

Emerging and reemerging diseases: a historical perspective

Summary: Between mid‐century and 1992, there was a consensus that the battle against infectious diseases had been won, and the Surgeon General announced that it was time to close the book. Experience with human immunodeficiency virus/acquired immunodeficiency syndrome, the return of cholera to the Americas in 1991, the plague outbreak in India in 1994, and the emergence of Ebola in Zaire in 1995 created awareness of a new vulnerability to epidemics due to population growth, unplanned urbanization, antimicrobial resistance, poverty, societal change, and rapid mass movement of people. The increasing virulence of dengue fever with dengue hemorrhagic fever and dengue shock syndrome disproved the theory of the evolution toward commensalism, and the discovery of the microbial origins of peptic ulcer demonstrated the reach of infectious diseases. The Institute of Medicine coined the term ‘emerging and reemerging diseases’ to explain that the world had entered an era in which the vulnerability to epidemics in the United States and globally was greater than ever. The United States and the World Health Organization took devised rapid response systems to monitor and contain disease outbreaks and to develop new weapons against microbes. These mechanisms were tested by severe acute respiratory syndrome in 2003, and a series of practical and conceptual blind spots in preparedness were revealed.

The anti-mycobacterial activity of Lantana camara a plant traditionally used to treat symptoms of tuberculosis in South-western Uganda

INTRODUCTION

Tuberculosis continues to be a devastating public health problem. Many communities in Uganda use medicinal plants to treat various infections, including respiratory tract infections. There are claims that some can treat tuberculosis. Verifying some of these claims could lead to discovery of lead compounds for development of a TB drug.

METHODS

Chloroform and methanol extracts of L. camara collected from South-western Uganda were screened against three strains of Mycobacterium tuberculosis using the agar-well diffusion method. H37Rv, the rifampicin-resistant TMC-331 and a non-resistant wild strain (28-25271). The MIC and MBC were determined using the Agar dilution method on Middle brook 7H11.

RESULTS

The methanol extract showed the highest activity against all the three strains used, with zones of inhibition of 18.0-22.5 mm and MIC values of 20 µg/ml for H37Rv and 15 µg/ml for both TMC-331 and wild stain. The values for rifampicin were 1.0 µg/ml for both H37Rv and wild strain but rifampicin hardly showed any activity on TMC-331. The MBC value for the methanol extract of L. camara was 30µg/ml for the H37Rv, and 20µg/ml for both the TMC-331 and wild strains of M. tuberculosis. The MBC for rifampicin was 2.0µg/ml for both H37Rv and the wild strain.

CONCLUSION

We conclude that L. camara contains principles active against M. tuberculosis, which merit further research.

BCG immunization age in urban and rural areas of Akita Prefecture, Japan

BCG immunization, utilizing whole-body coordination, is a highly cost-effective means of health intervention for preventing miliary tuberculosis (TB) and TB meningitis. In this study, we investigated the appropriate age by which a child should have completed his or her BCG immunization and discuss the current BCG immunization rate in Akita Prefecture, Japan. BCG immunization rates in urban and rural areas were 90.1% and 80.7%, respectively. Our immunization data were lower than the World Health Organization's (WHO) recommended rate. Immunization coverage rates in urban settings were higher than those in rural areas among infants four months to fifteen months of age, except for those six months old. We recommend: (1) completing BCG immunization by the age of twelve months, (2) preparing and educating parents for BCG immunization by means of a health policy, and (3) changing BCG immunization methods from group to individual inoculation. Immunization coverage rates may be increased or maintained to prevent miliary TB and TB meningitis.

What are the costs of suspected but not reported tuberculosis?

PURPOSE

Little is known regarding patients suspected, but not proven, to have tuberculosis before meeting reporting requirements. These patients generate unmeasured tuberculosis costs to the health care system. Elimination efforts are undervalued without fully quantifying the burden of tuberculosis. This may lead to decreased support and resurgence of this disease. This report provides a preliminary quantification of these costs.

METHODS

We used acid-fast bacillus (AFB) cultures completed as a proxy to estimate the number of patients with suspected tuberculosis who are never reported. We collected data on the number of AFB tests conducted in Tarrant County, TX, for calendar year 2002. We excluded all tests positive for Mycobacterium tuberculosis or secondary to growth of mycobacteria not M tuberculosis. We considered all AFBs conducted on an individual within 90 days to be single diagnostic episodes. We measured the number of diagnostic episodes, number of AFBs, number of AFBs meeting inclusion criteria, estimated cost incurred by testing, and individuals affected.

RESULTS

The Tarrant County hospitals sampled completed 6935 AFB cultures on an inpatient volume of 142,356 patients. One hundred ninety-three cultures confirmed tuberculosis or other mycobacteria, and 6742 AFBs were collected on persons suspected, but not proved, to have tuberculosis at an estimated $114.06 per culture. The total cost of eliminating tuberculosis as a cause of illness was $768,993. Laboratory costs for each patient with suspected, but not confirmed, tuberculosis averaged $364.11. One hundred forty-eight AFB cultures costing $16,830 were needed to confirm one case of tuberculosis.

CONCLUSIONS

The suspicion of tuberculosis incurs significant burdens and cost in the US health care system. More fully valuing tuberculosis elimination is important for tuberculosis management and will help maintain support for tuberculosis elimination.

A nose-only apparatus for airborne delivery of Mycobacterium tuberculosis to mice: calibration of biological parameters

Mycobacterium tuberculosis is the main cause of tuberculosis and is still a public health concern worldwide. This mycobacterium is transmitted through aerosols from human beings suffering from pulmonary tuberculosis to susceptible persons. To study this natural route of infection, we designed a new nose-only aerosol apparatus--system of aerosolisation of microorganisms (SAM)--in a carefully designed biohazard facility. For safety reasons, Mycobacterium smegmatis was first used to calibrate several parameters, such as inoculum density, atmospheric conditions (i.e. hygrometry) and particle size distribution. We present evidence that our apparatus is totally adapted to airborne delivery; the particle size of generated aerosol ranges from 1 to 7 microm, which is ideal for an infection by inhalation. We found that 99% of generated particles (<7 microm) could be retained by the respiratory tract, and among these particles, 62-79% (<3.3 microm) were able to reach pulmonary compartments. The next step was to simultaneously challenge 48 mice with M. tuberculosis in a highly reproducible way. We showed that a moderate dose (4 log10 colony-forming units (CFU) per mice) of M. tuberculosis was capable of causing progressive lung pathology and death in mice 30 days post-aerosolisation. Therefore, our apparatus, once calibrated, is easy to handle, safe, and can be used with any pathogen, which is spread by aerosol.

Major factors affecting the emergence and re-emergence of infectious diseases

The diversity of infectious disease threats currently facing humanity is unprecedented because of the remarkable emergence and reemergence of pathogens worldwide. Because of population mobility, globalization of commerce and the food supply, and the effects of the HIV/AIDS pandemic, infections in the developing world must be addressed to prevent infections in industrialized countries. Because pathogens do not recognize national boundaries, the rapidity with which individuals can circumnavigate the globe incubating infections makes the control of communicable diseases an enormous challenge for governments as well as for the public and primary health care systems. A global strategy for dealing with infectious disease threats must be developed and implemented as soon as possible.

Stable association between strains of Mycobacterium tuberculosis and their human host populations

Mycobacterium tuberculosis is an important human pathogen in virtually every part of the world. Here we investigate whether distinct strains of M. tuberculosis infect different human populations and whether associations between host and pathogen populations are stable despite global traffic and the convergence of diverse strains of the pathogen in cosmopolitan urban centers. The recent global movement and transmission history of 100 M. tuberculosis isolates was inferred from a molecular epidemiologic study of tuberculosis that spans 12 years. Genetic relationships among these isolates were deduced from the distribution of large genomic deletions, which were identified by DNA microarray and confirmed by PCR and sequence analysis. Phylogenetic analysis of these deletions indicates that they are unique event polymorphisms and that horizontal gene transfer is extremely rare in M. tuberculosis. In conjunction with the epidemiological data, phylogenies reveal three large phylogeographic regions. A host's region of origin is predictive of the strain of tuberculosis he or she carries, and this association remains strong even when transmission takes place in a cosmopolitan urban center outside of the region of origin. Approximate dating of the time since divergence of East Asian and Philippine clades of M. tuberculosis suggests that these lineages diverged centuries ago. Thus, associations between host and pathogen populations appear to be highly stable.

Homopseudopteroxazole, a new antimycobacterial diterpene alkaloid from Pseudopterogorgia elisabethae

In the course of our study to find novel antimycobacterial secondary metabolites from Caribbean gorgonian octocorals, we have isolated a new diterpene alkaloid, namely, homopseudopteroxazole (1), as a minor constituent of the hexane extract from the sea plume Pseudopterogorgia elisabethae. Its structure was deduced by interpretation of combined spectroscopic data, including extensive 1D and 2D NMR measurements, and NMR spectral comparisons with known amphilectane models. Biological screening studies indicate that homopseudopteroxazole (1) is a strong growth inhibitor of Mycobacterium tuberculosis H(37)Rv.