Introduction

Tuberculosis (TB) is a chronic infectious disease primarily affecting the lungs but capable of involving multiple organ systems. Caused by the bacterium Mycobacterium tuberculosis, TB remains a global health challenge, with complex interactions between host immunity, pathogen biology, and socio-economic factors. The World Health Organization (WHO) reported approximately 10.6 million new TB cases and 1.6 million deaths in 2021, underscoring its significance in public health and biomedical research.

Main Concepts

1. Etiology and Pathogenesis

  • Causative Agent: Mycobacterium tuberculosis is an acid-fast, slow-growing bacillus with a lipid-rich cell wall, conferring resistance to desiccation and many antibiotics.
  • Transmission: Primarily airborne via droplet nuclei expelled when an infected individual coughs, sneezes, or speaks.
  • Infection Process:
    • Primary Infection: Inhaled bacilli reach alveoli, where they are phagocytosed by macrophages. The bacteria can survive and replicate intracellularly.
    • Latent TB: Most infected individuals develop a latent infection, with bacteria contained but not eradicated by the immune system.
    • Active TB: Occurs when immune containment fails, leading to symptomatic disease and tissue destruction.

2. Clinical Manifestations

  • Pulmonary TB: Chronic cough, hemoptysis, chest pain, fever, night sweats, weight loss.
  • Extrapulmonary TB: Can affect lymph nodes, pleura, bones (Pott’s disease), CNS (TB meningitis), genitourinary tract, and more.
  • Latent vs. Active Disease: Latent TB is asymptomatic and non-contagious; active TB is symptomatic and contagious.

3. Diagnosis

  • Microbiological Tests:
    • Sputum smear microscopy for acid-fast bacilli.
    • Culture (gold standard, but slow).
    • Nucleic acid amplification tests (e.g., GeneXpert MTB/RIF).
  • Immunological Tests:
    • Tuberculin skin test (TST).
    • Interferon-gamma release assays (IGRAs).
  • Imaging: Chest X-ray, CT scans for pulmonary and extrapulmonary involvement.

4. Treatment

  • First-Line Drugs: Isoniazid, rifampicin, ethambutol, pyrazinamide (typically for 6 months).
  • Drug-Resistant TB:
    • Multidrug-resistant TB (MDR-TB): Resistant to at least isoniazid and rifampicin.
    • Extensively drug-resistant TB (XDR-TB): Resistant to first-line and key second-line drugs.
  • New Therapies: Bedaquiline, delamanid, and repurposed drugs are expanding options for resistant cases.

5. Prevention and Control

  • Vaccination: Bacillus Calmette-Guérin (BCG) vaccine offers variable protection, especially in children.
  • Public Health Strategies: Early detection, contact tracing, directly observed therapy (DOT), and addressing social determinants.

Interdisciplinary Connections

  • Immunology: TB provides a model for studying host-pathogen interactions, immune evasion, and granuloma formation.
  • Genomics: Whole-genome sequencing aids in tracking transmission, resistance mutations, and epidemiology.
  • Public Health: TB control involves social sciences, economics, and policy, addressing poverty, HIV co-infection, and healthcare access.
  • Pharmacology: Drug development for TB is challenged by unique bacterial physiology and resistance mechanisms.
  • Bioinformatics: Data analysis for TB surveillance, outbreak investigation, and personalized medicine.

Common Misconceptions

  • TB is eradicated: Despite progress, TB remains prevalent, especially in low- and middle-income countries.
  • Only affects lungs: TB can be extrapulmonary, affecting various organs.
  • Latent TB is not important: Latent infections represent a reservoir for future active cases.
  • BCG vaccine prevents all TB: BCG is not fully protective, especially against adult pulmonary TB.
  • Antibiotic treatment is straightforward: Drug resistance and lengthy treatment regimens complicate management.

Recent Research

A pivotal 2022 study published in The Lancet Infectious Diseases (Dheda et al., 2022) highlighted the efficacy of a shortened 4-month regimen for drug-susceptible TB, demonstrating non-inferiority to the conventional 6-month protocol. This could improve adherence and reduce healthcare costs. Source

Conclusion

Tuberculosis is a multifaceted disease with profound implications for global health. Understanding its biology, clinical features, and control strategies is essential for effective management. Ongoing research into diagnostics, therapeutics, and vaccines is critical, especially in the face of rising drug resistance and persistent socio-economic barriers.

Further Reading

  • World Health Organization. Global Tuberculosis Report 2023. WHO TB Report
  • Pai, M., et al. (2022). “Tuberculosis.” Nature Reviews Disease Primers, 8, Article 45.
  • Dheda, K., et al. (2022). “A four-month rifapentine-based regimen for treatment of tuberculosis.” The Lancet Infectious Diseases.
  • CDC Tuberculosis Resources: CDC TB

Revision Checklist

  • Understand TB pathogenesis and transmission.
  • Differentiate between latent and active TB.
  • Know diagnostic modalities and treatment regimens.
  • Recognize drug resistance challenges.
  • Appreciate interdisciplinary approaches to TB control.
  • Be aware of recent advances and ongoing research.