Development of vaccines to control bovine tuberculosis in cattle and relationship to vaccine development for other intracellular pathogens

Vaccination of cattle against bovine tuberculosis could be an important strategy for the control of disease either where there is a wildlife reservoir of Mycobacterium bovis infection or in developing countries where it is not economically feasible to implement a 'test and slaughter' control program. Advances in the understanding of protective immune responses to M. bovis infection in cattle and the advent of new molecular biological techniques, coupled with the sequencing of the M. bovis genome have provided opportunities for the rational development of improved tuberculosis vaccines. A number of new tuberculosis vaccines including attenuated M. bovis strains, killed mycobacteria, protein and DNA vaccines are under development and many are being assessed in cattle. Recent results have revealed several promising vaccine candidates and vaccination strategies. Ways of distinguishing between vaccinated and infected cattle are becoming available and the possibility of new approaches to the eradication of tuberculosis from domestic livestock is discussed. Similarities between the mechanisms of protective immunity against M. bovis and against other intracellular parasites continue to be found and discoveries from vaccine studies on bovine tuberculosis may provide helpful insights into requirements for vaccines against other intracellular pathogens.     

Extensively drug-resistant tuberculosis: current challenges and threats

Extensively drug-resistant tuberculosis (XDR-TB) is defined as tuberculosis caused by a Mycobacterium tuberculosis strain that is resistant to at least rifampicin and isoniazid among the first-line antitubercular drugs (multidrug-resistant tuberculosis; MDR-TB) in addition to resistance to any fluroquinolones and at least one of three injectable second-line drugs, namely amikacin, kanamycin and/or capreomycin. Recent studies have described XDR-TB strains from all continents. Worldwide prevalence of XDR-TB is estimated to be c. 6.6% in all the studied countries among multidrug-resistant M. tuberculosis strains. The emergence of XDR-TB strains is a reflection of poor tuberculosis management, and controlling its emergence constitutes an urgent global health reality and a challenge to tuberculosis control activities in all parts of the world, especially in developing countries and those lacking resources and as well as in countries with increasing prevalence of HIV/AIDS.     

Rapid culture-based methods for drug-resistance detection in Mycobacterium tuberculosis

Tuberculosis still represents a major public health problem, especially in low-resource countries where the burden of the disease is more important. Multidrug-resistant and extensively drug drug-resistant tuberculosis constitute serious problems for the efficient control of the disease stressing the need to investigate resistance to first- and second-line drugs. Conventional methods for detecting drug-resistance in Mycobacterium tuberculosis are slow and cumbersome. The most commonly used proportion method on L?wenstein-Jensen medium or Middlebrook agar requires a minimum of 3-4 weeks to produce results. Several new approaches have been proposed in the last years for the rapid and timely detection of drug-resistance in tuberculosis. This review will address phenotypic culture-based methods for rapid drug susceptibility testing in M. tuberculosis.     

Tuberculosis among immigrants related to length of residence in England and Wales. Report from the British Thoracic and Tuberculosis Association.

Between 1965 and 1971 the notifications of tuberculosis among lifetime residents of the British Isles declined, but among those born in India, Pakistan, and new Commonwealth countries in Africa tuberculosis notifications increased appreciably. Furthermore, the long-held suspicion that among these immigrants the most recent arrivals in England and Wales have higher rates of tuberculosis than those who have lived here longer was confirmed.     

Successful use of an inhalational phytochemical to treat pulmonary tuberculosis: a case report.

Multi-drug resistant strains of tuberculosis pose a serious threat in many third- and first-world countries. The aim of this case report is to describe a potential new method for treating those with primary pulmonary tuberculosis using phytochemicals via inhalation. We report the first case of using inhaled phytochemicals in treating primary pulmonary tuberculosis. A 28-year-old female presented with symptoms suggestive of primary pulmonary tuberculosis, and she was found to be positive via chest X-ray and sputum culture. She subsequently underwent treatment with conventional DOTS treatment. Ten days post-inhalation of the phytochemical, the patient is tuberculosis negative (via sputum culture), with no clinical symptoms. This may be a potential new method and type of treatment for pulmonary tuberculosis.     

Prevalence of Latent and Active Tuberculosis among Dairy Farm Workers Exposed to Cattle Infected by Mycobacterium bovis

Background

Human tuberculosis caused by M. bovis is a zoonosis presently considered sporadic in developed countries, but remains a poorly studied problem in low and middle resource countries. The disease in humans is mainly attributed to unpasteurized dairy products consumption. However, transmission due to exposure of humans to infected animals has been also recognized. The prevalence of tuberculosis infection and associated risk factors have been insufficiently characterized among dairy farm workers (DFW) exposed in settings with poor control of bovine tuberculosis.

Methodology/Principal Findings

Tuberculin skin test (TST) and Interferon-gamma release assay (IGRA) were administered to 311 dairy farm and abattoir workers and their household contacts linked to a dairy production and livestock facility in Mexico. Sputa of individuals with respiratory symptoms and samples from routine cattle necropsies were cultured for M. bovis and resulting spoligotypes were compared. The overall prevalence of latent tuberculosis infection (LTBI) was 76.2% (95% CI, 71.4–80.9%) by TST and 58.5% (95% CI, 53.0–64.0%) by IGRA. Occupational exposure was associated to TST (OR 2.72; 95% CI, 1.31–5.64) and IGRA (OR 2.38; 95% CI, 1.31–4.30) adjusting for relevant variables. Two subjects were diagnosed with pulmonary tuberculosis, both caused by M. bovis. In one case, the spoligotype was identical to a strain isolated from bovines.

Conclusions

We documented a high prevalence of latent and pulmonary TB among workers exposed to cattle infected with M. bovis, and increased risk among those occupationally exposed in non-ventilated spaces. Interspecies transmission is frequent and represents an occupational hazard in this setting.     

New approaches in the diagnosis and treatment of latent tuberculosis infection

With nearly 9 million new active disease cases and 2 million deaths occurring worldwide every year, tuberculosis continues to remain a major public health problem. Exposure to Mycobacterium tuberculosis leads to active disease in only ~10% people. An effective immune response in remaining individuals stops M. tuberculosis multiplication. However, the pathogen is completely eradicated in ~10% people while others only succeed in containment of infection as some bacilli escape killing and remain in non-replicating (dormant) state (latent tuberculosis infection) in old lesions. The dormant bacilli can resuscitate and cause active disease if a disruption of immune response occurs. Nearly one-third of world population is latently infected with M. tuberculosis and 5%-10% of infected individuals will develop active disease during their life time. However, the risk of developing active disease is greatly increased (5%-15% every year and ~50% over lifetime) by human immunodeficiency virus-coinfection. While active transmission is a significant contributor of active disease cases in high tuberculosis burden countries, most active disease cases in low tuberculosis incidence countries arise from this pool of latently infected individuals. A positive tuberculin skin test or a more recent and specific interferon-gamma release assay in a person without overt signs of active disease indicates latent tuberculosis infection. Two commercial interferon-gamma release assays, QFT-G-IT and T-SPOT.TB have been developed. The standard treatment for latent tuberculosis infection is daily therapy with isoniazid for nine months. Other options include therapy with rifampicin for 4 months or isoniazid + rifampicin for 3 months or rifampicin + pyrazinamide for 2 months or isoniazid + rifapentine for 3 months. Identification of latently infected individuals and their treatment has lowered tuberculosis incidence in rich, advanced countries. Similar approaches also hold great promise for other countries with low-intermediate rates of tuberculosis incidence.     

Epidemic levels of drug resistant tuberculosis (MDR and XDR-TB) in a high HIV prevalence setting in Khayelitsha, South Africa

Background

Although multidrug-resistant tuberculosis (MDR-TB) is emerging as a significant threat to tuberculosis control in high HIV prevalence countries such as South Africa, limited data is available on the burden of drug resistant tuberculosis and any association with HIV in such settings. We conducted a community-based representative survey to assess the MDR-TB burden in Khayelitsha, an urban township in South Africa with high HIV and TB prevalence.

Methodology/Principal Findings

A cross-sectional survey was conducted among adult clinic attendees suspected for pulmonary tuberculosis in two large primary care clinics, together constituting 50% of the tuberculosis burden in Khayelitsha. Drug susceptibility testing (DST) for isoniazid and rifampicin was conducted using a line probe assay on positive sputum cultures, and with culture-based DST for first and second-line drugs. Between May and November 2008, culture positive pulmonary tuberculosis was diagnosed in 271 new and 264 previously treated tuberculosis suspects (sample enriched with previously treated cases). Among those with known HIV status, 55% and 71% were HIV infected respectively. MDR-TB was diagnosed in 3.3% and 7.7% of new and previously treated cases. These figures equate to an estimated case notification rate for MDR-TB of 51/100,000/year, with new cases constituting 55% of the estimated MDR-TB burden. HIV infection was not significantly associated with rifampicin resistance in multivariate analyses.

Conclusions/Significance

There is an extremely high burden of MDR-TB in this setting, most likely representing ongoing transmission. These data highlight the need to diagnose drug resistance among all TB cases, and for innovative models of case detection and treatment for MDR-TB, in order to interrupt transmission and control this emerging epidemic.     

牛结核病的传播特点和风险因素及防控

牛结核病是一种世界分布的人畜共患传染病,被世界动物卫生组织列为法定报告疾病。其传播风险影响着畜牧业持续发展和人类的健康。本文概述了牛结核病的宿主范围、传播特点、风险因素及其防控措施等方面,旨在为我国牛结核病疫情传播和预防控制提供理论研究。     

Metabolism of Nicotinamide Adenine Dinucleotide in Human and Bovine Strains of Mycobacterium tuberculosis

A marked difference was found to exist between the nicotinamide adenine dinucleotide (NAD) glycohydrolase activity of human strains of Mycobacterium tuberculosis as compared with bovine strains. Human strains had from 6- to 20-fold higher NAD glycohydrolase activity than bovine strains. This finding explains the accumulation of free nicotinic acid in the culture medium by human strains and not by bovine strains. The biosynthetic intermediates nicotinic acid mononucleotide and deamido-NAD were not degraded by either human or bovine strains of M. tuberculosis; hence these nucleotides do not represent a source of the nicotinic acid accumulated by the human strains.     

Further study of the problem of specific cellular receptors in delayed hypersensitivity]

The work presents the materials obtained as a result of the further study of specific T lymphocyte receptors with the use of so-called receptor antisera, i. e. antisera against the lymphoid cells of mice sensitized with one of the two antigens (Macobacterium tuberculosis or bovine gamma globulin); thus these differed from control antisera against the lymphoid cells of intact mice. These mouse antisera reacted with the lymphoid cells of guinea pigs in experiments of delayed-type hypersensitivity transfer. The cells of sensitized guinea pigs lost their ability to transfer hypersensitivity if, prior to their injection into the recipient guinea pigs, these cells were treated with the above-mentioned mouse antisera, i. e. antisera against the lymphoid cells of mice had a blocking effect on the lymphoid cells of guinea pigs. The blocking action of the antisera proved to be specific: antisera against the lymphoid cells of mice sensitized to bovine gamma gloublin blocked the cells of guinea pigs, also sensitized to bovine gamma globulins, but did not block the cells sensitized to Mycobacterium tuberculosis. The control antisera, taken in the same doses as the factor antisera, did not show a blocking effect on the specific activity of lymphoid cells.     

Multidrug resistant to extensively drug resistant tuberculosis: What is next?

Drug resistant tuberculosis is a man made problem. While tuberculosis is hundred percent curable, multidrug resistant tuberculosis (MDR-TB) is difficult to treat. Inadequate and incomplete treatment and poor treatment adherence has led to a newer form of drug resistance known as extensively drug resistant tuberculosis (XDR-TB). XDR-TB is defined as tuberculosis caused by Mycobacterium tuberculosis strain, which is resistant to at least rifampicin and isoniazid among the first line anti tubercular drugs (MDR-TB) in addition to resistance to any fluroquinolones and at least one of three injectable second line anti tubercular drugs i.e. amikacin, kanamycin and/or capreomycin. Mismanagement of tuberculosis paves the way to drug resistant tuberculosis. Emergence of XDR-TB is reported world wide. Reported prevalence rates of XDR-TB of total MDR cases are; 6.6% overall worldwide, 6.5% in industrialized countries, 13.6% in Russia and Eastern Europe, 1.5% in Asia, 0.6% in Africa and Middle East and 15.4% in Republic of Korea. Better management and control of tuberculosis specially drug resistant TB by experienced and qualified doctors, access to standard microbiology laboratory, co-morbitidy of HIV and tuberculosis, new anti-TB drug regimens, better diagnostic tests, international standards for second line drugs (SLD)-susceptibility testing, invention of newer antitubercular molecules and vaccines and knowing the real magnitude of XDR-TB are some of the important issues to be addressed for effective prevention and management of XDR-TB.     

The metapopulation dynamics of an infectious disease: tuberculosis in possums

An SEI metapopulation model is developed for the spread of an infectious agent by migration. The model portrays two age classes on a number of patches connected by migration routes which are used as host animals mature. A feature of this model is that the basic reproduction ratio may be computed directly, using a scheme that separates topography, demography, and epidemiology. We also provide formulas for individual patch basic reproduction numbers and discuss their connection with the basic reproduction ratio for the system. The model is applied to the problem of spatial spread of bovine tuberculosis in a possum population. The temporal dynamics of infection are investigated for some generic networks of migration links, and the basic reproduction ratio is computed-its value is not greatly different from that for a homogeneous model. Three scenarios are considered for the control of bovine tuberculosis in possums where the spatial aspect is shown to be crucial for the design of disease management operations.     

Culling-induced social perturbation in Eurasian badgers Meles meles and the management of TB in cattle: an analysis of a critical problem in applied ecology

The Eurasian badger (Meles meles) is implicated in the transmission of bovine tuberculosis (TB) to cattle in the UK and Republic of Ireland. Badger culling has been employed for the control of TB in cattle in both countries, with varying results. Social perturbation of badger populations following culling has been proposed as an explanation for the failure of culling to consistently demonstrate significant reductions in cattle TB. Field studies indicate that culling badgers may result in increased immigration into culled areas, disruption of territoriality, increased ranging and mixing between social groups. Our analysis shows that some measures of sociality may remain significantly disrupted for up to 8 years after culling. This may have epidemiological consequences because previous research has shown that even in a relatively undisturbed badger population, movements between groups are associated with increases in the incidence of Mycobacterium bovis infection. This is consistent with the results from a large-scale field trial, which demonstrated decreased benefits of culling at the edges of culled areas, and an increase in herd breakdown rates in neighbouring cattle.     

Control and prevention of tuberculosis in Britain: an updated code of practice. Subcommittee of the Joint Tuberculosis Committee of the British Thoracic Society.

A subcommitte was appointed by the Joint Tuberculosis Committee of the British Thoracic Society to review and bring up to date guidelines on control measures for tuberculosis. The updated code of practice emphasises that all cases of tuberculosis must be notified. A minority of patients need admission, and those with positive sputum smears should be regarded as infectious until they have received two weeks of chemotherapy. NHS staff at risk should be protected, and evidence of infectious tuberculosis should be sought as routine among certain prospective NHS employees, schoolteachers, and others. Contact tracing should be vigorously pursued, and all entrants to Britain from countries where tuberculosis is common should be screened. BCG vaccination should be offered in selected instances, and local organisation of tuberculosis services should be extended.     

Urogenital tuberculosis: update and review of 8961 cases from the world literature

The AIDS epidemic caused unexpected worldwide levels of tuberculosis, even in developed countries where the incidence used to be low. Patients with urogenital tuberculosis in developed countries have fewer specific symptoms and lower rates of delayed diagnoses compared with patients from other countries. As a result, the disease tends to be less serious, with more patients presenting without significant lesions of the upper urinary tract on diagnosis. These data point to a correlation of the timing of diagnosis with the severity of urogenital tuberculosis. A systematic search for urogenital tuberculosis, regardless of symptoms, is warranted for early detection.     

Doing something about tuberculosis

The phenomenal success public health officials enjoyed in controlling tuberculosis (TB) in developed countries has not been mirrored in developing countries, where TB still accounts for 25% of preventable deaths in adults. The fact that there are 8 million new cases each year (95% in developing countries) and 3 million deaths (98% in developing countries) led to the 1993 declaration by the World Health Organization (WHO) that TB poses a global emergency. Because TB is predominantly a disease of impoverished people, indifference has led to the fallacious and naive view that eradication of TB simply requires socioeconomic development. In response to this indifference, the WHO is promoting a "Stop TB--Use DOTS" campaign. DOTS, a strategy based on directly observed therapy, also requires government commitment, a regular supply of drugs, effective diagnoses, and an audit of the efficacy of the strategy. While the treatment of TB is among the most cost-effective of all medical interventions in terms of years of healthy life saved, the DOTS campaign requires a considerable dedication of funds. Renewed interest in TB is leading the US and the UK to increase support for control programs. In addition, a new UK-based charity, "TB Alert," hopes to play a major role in advocating for political commitment to and funding for TB control.     

Bacillus Calmette-Guérin vaccination reduces the severity and progression of tuberculosis in badgers

Control of bovine tuberculosis (TB) in cattle has proven particularly challenging where reservoirs of infection exist in wildlife populations. In Britain and Ireland, control is hampered by a reservoir of infection in Eurasian badgers (Meles meles). Badger culling has positive and negative effects on bovine TB in cattle and is difficult, costly and controversial. Here we show that Bacillus Calmette-Guérin (BCG) vaccination of captive badgers reduced the progression, severity and excretion of Mycobacterium bovis infection after experimental challenge. In a clinical field study, BCG vaccination of free-living badgers reduced the incidence of positive serological test results by 73.8 per cent. In common with other species, BCG did not appear to prevent infection of badgers subjected to experimental challenge, but did significantly reduce the overall disease burden. BCG vaccination of badgers could comprise an important component of a comprehensive programme of measures to control bovine TB in cattle.     

Vitamin D supplementation promotes macrophages' anti-mycobacterial activity in type 2 diabetes mellitus patients with low vitamin D receptor expression

The increasing number of people with type 2 diabetes (DM2) is alarming and if it is taken into account that the relative odds of developing tuberculosis in diabetic patients ranges from 2.44 to 8.33 compared with non-diabetic patients, thus in developing countries where these two diseases are encountering face to face, there is a need for prophylaxis strategies. The role of vitamin D has been widely implicated in growth control of Mycobacterium tuberculosis (Mtb) during primary infection mainly through the induction of certain antimicrobial peptides (AMPs). In this study we evaluated the vitamin D serum levels, CYP27B1-hydroxylase enzyme, vitamin D receptor (VDR) and AMPs gene expression in Healthy donors, DM2 and TB patients. Results showed that DM2 group has lower VDR and AMPs expression levels. When Monocytes Derived Macrophages (MDM) from DM2 patients with low VDR expression were supplemented with vitamin D, MDMs eliminate efficiently M. tuberculosis. This preliminary study suggests the use of vitamin D as prophylaxis for tuberculosis in high DM2 endemic countries.     

Molecular models of tryptophan synthase from Mycobacterium tuberculosis complexed with inhibitors

The development of new therapies against infectious diseases is vital in developing countries. Among infectious diseases, tuberculosis is considered the leading cause of death. A target for development of new drugs is the tryptophan pathway. The last enzyme of this pathway, tryptophan synthase (TRPS), is responsible for conversion of the indole 3-glycerol phosphate into indol and the condensation of this molecule with serine-producing tryptophan. The present work describes the molecular models of TRPS from Mycobacterium tuberculosis (MtTRPS) complexed with six inhibitors, the indole 3-propanol phosphate and five arylthioalkyl-phosphonated analogs of substrate of the alpha-subunit. The molecular models of MtTRPS present good stereochemistry, and the binding of the inhibitors is favorable. Thus, the generated models can be used in the design of more specific drugs against tuberculosis and other infectious diseases.