Uniting to end the TB epidemic: advances in disease control from prevention to better diagnosis and treatment

Mixed infections in tuberculosis: The missing part in a puzzle

The mixed strains infection phenomenon is a major problem posing serious challenges in control of tuberculosis (TB). In patients with mixed infection, several different strains of Mycobacterium tuberculosis can be isolated simultaneously. Although different genotyping methods and various molecular approaches can be employed for detection of mixed infection in clinical samples, the MIRU-VNTR technique is more sensitive with higher discriminative power than many widely used techniques. Furthermore, the recent introduction of whole genome sequencing (WGS) promises to reveal more details about mixed infection with high resolution. WGS has been used for detection of mixed infection with high sensitivity and discriminatory, but the technology is currently limited to developed countries. Mixed infection may involve strains with different susceptibility patterns, which may alter the treatment outcome. In this report, we review the current concepts of mixed strains infection and also infection involving strains with a different susceptibility pattern in TB. We evaluate the importance of identifying mixed infection for diagnosis as well as treatment and highlight the accuracy and clinical utility of direct genotyping of clinical specimens.

Diagnosis of Tuberculosis in HIV Co-infected Individuals: Current Status, Challenges and Opportunities for the Future

Tuberculosis (TB) remains one of the most important causes of death among people co-infected with human immunodeficiency virus (HIV). The diagnosis of TB remains challenging in HIV co-infected individuals, due to a high frequency of smear-negative disease and high rates of extrapulmonary TB. Accurate, ease of use and rapid diagnosis of active TB are critical to the World Health Organization (WHO) End TB Strategy by 2050. Traditional laboratory techniques do not provide rapid and accurate results to effectively manage HIV co-infected patients. Over the last decade, molecular methods have provided significant steps in the fight against TB. However, many HIV co-infected patients do not have access to these molecular diagnostic tests. Given the costs closely related with confirming a TB diagnosis in HIV patients, an overtreatment for TB is used in this patient population. Nowadays, an estimated US $8 billion a year is required to provide TB treatment, which is very high compared with making an important strategy to improve the current diagnostic tests. This review focuses on current advances in diagnosing active TB with an emphasis on the diagnosis of HIV-associated TB. Also discussed are the main challenges that need to be overcome for improving an adequate initial diagnosis of active TB in HIV-positive patients.

Animal Models for Tuberculosis in Translational and Precision Medicine

Tuberculosis (TB) is a health threat to the global population. Anti-TB drugs and vaccines are key approaches for TB prevention and control. TB animal models are basic tools for developing biomarkers of diagnosis, drugs for therapy, vaccines for prevention and researching pathogenic mechanisms for identification of targets; thus, they serve as the cornerstone of comparative medicine, translational medicine, and precision medicine. In this review, we discuss the current use of TB animal models and their problems, as well as offering perspectives on the future of these models.

Diagnosis of opportunistic infections: HIV co-infections - tuberculosis

PURPOSE OF REVIEW

Tuberculosis (TB) incidence has declined ∼1.5% annually since 2000, but continued to affect 10.4 million individuals in 2015, with 1/3 remaining undiagnosed or underreported. The diagnosis of TB among those co-infected with HIV is challenging as TB remains the leading cause of death in such individuals. Accurate and rapid diagnosis of active TB will avert mortality in both adults and children, reduce transmission, and assist in timeous decisions for antiretroviral therapy initiation. This review describes advances in diagnosing TB, especially among HIV co-infected individuals, highlights national program's uptake, and impact on patient care.

RECENT FINDINGS

The TB diagnostic landscape has been transformed over the last 5 years. Molecular diagnostics such as Xpert MTB/RIF, which simultaneously detects Mycobacterium tuberculosis (MTB) resistance to rifampicin, has revolutionized TB control programs. WHO endorsed the use of Xpert MTB/RIF in 2010 for use in HIV/TB co-infected patients, and later in 2013 for use as the initial diagnostic test for all adults and children with signs and symptoms of pulmonary TB. Line probe assays (LPAs) are recommended for the detection of rifampicin and isoniazid resistance in sputum smear-positive specimens and mycobacterial cultures. A second-line line probe assay has been recommended for the diagnosis of extensively drug-resistant (XDR)-TB Assays such as the urine lateral flow (LF)-lipoarabinomannan (LAM), can be used at the point of care (POC) and have a niche role to supplement the diagnosis of TB in seriously ill HIV-infected, hospitalized patients with low CD4 cell counts of less than 100 cells/μl. Polyvalent platforms such as the m2000 (Abbott Molecular) and GeneXpert (Cepheid) offer potential for integration of HIV and TB testing services. While the Research and Development (R&D) pipeline appears to be rich at first glance, there are actually few leads for true POC tests that would allow for earlier TB diagnosis or rapid, comprehensive drug susceptibility testing, especially when considering the very high attrition rates observed between biomarker discovery and product market entry.

SUMMARY

In this review, we describe diagnostic strategies specifically for HIV and TB co-infected individuals. Molecular diagnostics in particular within the past 5 years have revolutionized and 'disrupted' this field. They lend themselves to integration of services with platforms capable of polyvalent testing. Impact on patient care is, however, still debatable. What has been highlighted is the need for health system strengthening and for true POC testing that can be used in active case finding.

High mortality among tuberculosis patients on treatment in Nigeria: a retrospective cohort study

Background

Tuberculosis (TB) remains a leading cause of death in much of sub-Saharan Africa despite available effective treatment. Prompt initiation of TB treatment and access to antiretroviral therapy (ART) remains vital to the success of TB control. We assessed time to mortality after treatment onset using data from a large treatment centre in Nigeria.

Methods

We analysed a retrospective cohort of TB patients that commenced treatment between January 2010 and December 2014 in Aminu Kano Teaching Hospital. We estimated mortality rates per person-months at risk (pm). Cox proportional hazards model was used to determine risk factors for mortality.

Results

Among 1,424 patients with a median age of 36.6 years, 237 patients (16.6%) died after commencing TB treatment giving a mortality rate of 3.68 per 100 pm of treatment in this cohort. Most deaths occurred soon after treatment onset with a mortality rate of 37.6 per 100 pm in the 1^st week of treatment. Risk factors for death were being HIV-positive but not on anti-retroviral treatment (ART) (aHR 1.39(1 · 04–1 · 85)), residence outside the city (aHR 3 · 18(2.28–4.45)), previous TB treatment (aHR 3.48(2.54–4.77)), no microbiological confirmation (aHR 4.96(2.69–9.17)), having both pulmonary and extra-pulmonary TB (aHR 1.45(1.03–2.02), and referral from a non-programme linked clinic/centre (aHR 3.02(2.01–4.53)).

Conclusions

We attribute early deaths in this relatively young cohort to delay in diagnosis and treatment of TB, inadequate treatment of drug-resistant TB, and poor ART access. Considerable expansion and improvement in quality of diagnosis and treatment services for TB and HIV are needed to achieve the sustainable development goal of reducing TB deaths by 95% by 2035.

Impact of the GeneXpert MTB/RIF Technology on Tuberculosis Control

Molecular technology revolutionized the diagnosis of tuberculosis (TB) with a paradigm shift to faster, more sensitive, clinically relevant patient care. The most recent molecular leader is the GeneXpert MTB/RIF assay (Xpert) (Cepheid, Sunnyvale, CA), which was endorsed by the World Health Organization with unprecedented speed in December 2010 as the initial diagnostic for detection of HIV-associated TB and for where high rates of drug resistance are suspected. South Africa elected to take an aggressive smear replacement approach to facilitate earlier diagnosis and treatment through the decision to implement the Xpert assay nationally in March 2011, against the backdrop of approximately 6.3 million HIV-infected individuals, one of highest global TB and HIV coinfection rates, no available implementation models, uncertainties around field performance and program costs, and lack of guidance on how to operationalize the assay into existing complex clinical algorithms. South Africa's national implementation was conducted as a phased, forecasted, and managed approach (March 2011 to September 2013), through political will and both treasury-funded and donor-funded support. Today there are 314 GeneXperts across 207 microscopy centers; over 8 million assays have been conducted, and South Africa accounts for over half the global test cartridge usage. As with any implementation of new technology, challenges were encountered, both predicted and unexpected. This chapter discusses the challenges and consequences of such large-scale implementation efforts, the opportunities for new innovations, and the need to strengthen health systems, as well as the impact of the Xpert assay on rifampin-sensitive and multidrug-resistant TB patient care that translated into global TB control as we move toward the sustainable development goals.

Adjunct Strategies for Tuberculosis Vaccines: Modulating Key Immune Cell Regulatory Mechanisms to Potentiate Vaccination

Tuberculosis (TB) remains a global health threat of alarming proportions, resulting in 1.5 million deaths worldwide. The only available licensed vaccine, Bacillus Calmette–Guérin, does not confer lifelong protection against active TB. To date, development of an effective vaccine against TB has proven to be elusive, and devising newer approaches for improved vaccination outcomes is an essential goal. Insights gained over the last several years have revealed multiple mechanisms of immune manipulation by Mycobacterium tuberculosis (Mtb) in infected macrophages and dendritic cells that support disease progression and block development of protective immunity. This review provides an assessment of the known immunoregulatory mechanisms altered by Mtb, and how new interventions may reverse these effects. Examples include blocking of inhibitory immune cell coreceptor checkpoints (e.g., programed death-1). Conversely, immune mechanisms that strengthen immune cell effector functions may be enhanced by interventions, including stimulatory immune cell coreceptors (e.g., OX40). Modification of the activity of key cell “immunometabolism” signaling pathway molecules, including mechanistic target of rapamycin, glycogen synthase kinase-3β, wnt/β-catenin, adenosine monophosophate-activated protein kinase, and sirtuins, related epigenetic changes, and preventing induction of immune regulatory cells (e.g., regulatory T cells, myeloid-derived suppressor cells) are powerful new approaches to improve vaccine responses. Interventions to favorably modulate these components have been studied primarily in oncology to induce efficient antitumor immune responses, often by potentiation of cancer vaccines. These agents include antibodies and a rapidly increasing number of small molecule drug classes that have contributed to the dramatic immune-based advances in treatment of cancer and other diseases. Because immune responses to malignancies and to Mtb share many similar mechanisms, studies to improve TB vaccine responses using interventions based on “immuno-oncology” are needed to guide possible repurposing. Understanding the regulation of immune cell functions appropriated by Mtb to promote the imbalance between protective and pathogenic immune responses may guide the development of innovative drug-based adjunct approaches to substantially enhance the clinical efficacy of TB vaccines.