Introduction

Tuberculosis (TB) is a contagious, airborne infectious disease primarily caused by the bacterium Mycobacterium tuberculosis. TB predominantly affects the lungs (pulmonary TB) but can also impact other organs (extrapulmonary TB). Despite being preventable and curable, TB remains a significant global health challenge, with millions affected annually. According to the World Health Organization (WHO), TB is among the top 13 causes of death worldwide, and drug-resistant strains pose increasing threats to public health.

Main Concepts

1. Etiology and Transmission

  • Causative Agent: Mycobacterium tuberculosis, a slow-growing, acid-fast bacillus.
  • Transmission: Primarily airborne, via droplets expelled when an infected person coughs, sneezes, or speaks.
  • Reservoir: Humans are the principal reservoir; zoonotic TB can occur with M. bovis.
  • Infectious Dose: Inhalation of as few as 1ā€“10 bacilli can initiate infection.

2. Pathogenesis

  • Primary Infection: Bacilli reach alveoli, are phagocytosed by macrophages, and may evade destruction.
  • Latent TB: The immune system contains the bacteria, which remain dormant. No symptoms, not infectious.
  • Active TB: Bacteria multiply, causing tissue damage and symptoms; contagious.
  • Granuloma Formation: Immune cells wall off bacteria, forming granulomas; central necrosis (caseation) is typical.

3. Clinical Manifestations

Pulmonary TB

  • Persistent cough (>3 weeks)
  • Hemoptysis (coughing blood)
  • Chest pain
  • Fever, night sweats
  • Weight loss, fatigue

Extrapulmonary TB

  • Lymphatic TB (most common extrapulmonary form)
  • TB meningitis
  • Skeletal TB (Pottā€™s disease)
  • Genitourinary TB

4. Diagnosis

  • Tuberculin Skin Test (TST): Detects immune response to TB antigens.
  • Interferon-Gamma Release Assays (IGRAs): Blood tests measuring immune reactivity.
  • Chest Radiography: Identifies lung lesions.
  • Microbiological Testing: Sputum smear microscopy, culture, and nucleic acid amplification tests (NAATs).
  • Drug Susceptibility Testing: Determines resistance to first-line drugs.

5. Treatment

  • First-line Drugs: Isoniazid, rifampicin, ethambutol, pyrazinamide.
  • Duration: Standard regimen is 6 months for drug-susceptible TB.
  • Drug-resistant TB: Requires second-line agents, longer treatment (up to 20 months).
  • Directly Observed Therapy (DOT): Ensures adherence, reduces resistance.

6. Prevention

  • BCG Vaccine: Bacillus Calmetteā€“GuĆ©rin; protects against severe forms in children, variable efficacy in adults.
  • Infection Control: Ventilation, masks, isolation of infectious cases.
  • Contact Tracing: Identifying and screening individuals exposed to TB.

Emerging Technologies

Molecular Diagnostics

  • GeneXpert MTB/RIF: Rapid, automated NAAT for TB and rifampicin resistance, results in <2 hours.
  • Whole Genome Sequencing (WGS): Identifies resistance mutations, tracks transmission pathways.
  • CRISPR-based Detection: Experimental platforms for ultra-sensitive, rapid diagnosis.

Therapeutics

  • New Drugs: Bedaquiline, delamanid, pretomanidā€”target multi-drug resistant TB.
  • Host-Directed Therapies: Modulate immune response to improve outcomes.

Vaccines

  • M72/AS01E Vaccine: Phase IIb trial showed ~50% efficacy in preventing active TB among latently infected adults (Lancet, 2019).
  • Next-Generation Candidates: Focus on broader, longer-lasting immunity.

Digital Health

  • Mobile Health (mHealth): Smartphone apps for treatment adherence, symptom tracking.
  • AI-based Radiology: Automated chest X-ray interpretation for screening in low-resource settings.

Data Table: Global TB Burden (WHO, 2022)

Indicator Value Notes
Estimated new cases 10.6 million Includes all forms
TB deaths (HIV-negative) 1.3 million
TB deaths (HIV-positive) 0.4 million
Drug-resistant TB cases ~450,000 Rifampicin-resistant/multidrug-resistant
Highest burden regions South-East Asia, Africa Over 80% of global cases
BCG coverage (children) ~85% Varies by country

Tuberculosis and Health

TBā€™s impact on health is multifaceted:

  • Individual Health: Causes chronic illness, disability, and death; exacerbates malnutrition and comorbidities (e.g., HIV/AIDS, diabetes).
  • Public Health: Airborne transmission enables rapid spread, especially in crowded or poorly ventilated settings.
  • Socioeconomic Impact: Long treatment duration and stigma can lead to loss of income, education, and social isolation.
  • Drug Resistance: Multidrug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB) complicate treatment, increase costs, and threaten control efforts.

Recent Research

A 2023 study published in Nature Medicine (ā€œGlobal emergence and spread of multidrug-resistant tuberculosisā€) used whole genome sequencing to map MDR-TB transmission across continents, revealing that resistance is often acquired locally rather than imported. This finding underscores the need for rapid diagnostics and tailored public health interventions (Nature Medicine, 2023).

Conclusion

Tuberculosis remains a major global health threat, driven by persistent transmission, drug resistance, and disparities in healthcare access. Advances in molecular diagnostics, new therapeutics, and vaccine development offer hope for improved control and eventual eradication. Ongoing research, robust public health strategies, and international collaboration are essential to reduce TBā€™s burden and protect vulnerable populations.

References:

  • World Health Organization. Global Tuberculosis Report 2022.
  • Nature Medicine, 2023: ā€œGlobal emergence and spread of multidrug-resistant tuberculosisā€ (link).