Overview

Tuberculosis (TB) is a contagious bacterial infection caused primarily by Mycobacterium tuberculosis. It most commonly affects the lungs (pulmonary TB), but can also impact other organs (extrapulmonary TB). TB remains a major global health concern, especially in low- and middle-income countries.

Etiology

  • Causative Agent: Mycobacterium tuberculosis, a slow-growing, acid-fast bacillus.
  • Transmission: Airborne droplets from coughing, sneezing, or speaking by an infected person.
  • Incubation Period: Weeks to years; latent TB can persist without symptoms.

Pathogenesis

  1. Inhalation: Bacilli enter alveoli in the lungs.
  2. Immune Response: Macrophages ingest bacteria but may not destroy them.
  3. Granuloma Formation: Immune cells wall off bacteria, forming tubercles.
  4. Latent vs. Active TB:
    • Latent TB: Bacteria remain dormant, no symptoms, not contagious.
    • Active TB: Bacteria multiply, symptoms develop, contagious.

Clinical Manifestations

Pulmonary TB

  • Persistent cough (>3 weeks)
  • Hemoptysis (coughing up blood)
  • Chest pain
  • Night sweats
  • Fever
  • Weight loss
  • Fatigue

Extrapulmonary TB

  • Lymph nodes (scrofula)
  • Bones and joints (Pott’s disease)
  • Meninges (TB meningitis)
  • Genitourinary tract

Diagnosis

  • Tuberculin Skin Test (TST)
  • Interferon-Gamma Release Assays (IGRAs)
  • Chest X-ray
  • Sputum Microscopy and Culture
  • Molecular Tests (e.g., GeneXpert MTB/RIF)

Treatment

  • First-line Drugs: Isoniazid, Rifampicin, Pyrazinamide, Ethambutol (2 months intensive phase, 4 months continuation phase)
  • Drug-Resistant TB: Requires second-line drugs, longer duration, more side effects.
  • Directly Observed Therapy (DOT): Ensures compliance to prevent resistance.

Prevention

  • BCG Vaccine: Offers protection, especially in children.
  • Infection Control: Ventilation, masks, early detection, and treatment.
  • Contact Tracing: Identifies and treats exposed individuals.

Global Impact

  • Prevalence: ~10 million new cases annually (WHO, 2022).
  • Mortality: Over 1.5 million deaths per year.
  • Drug Resistance: MDR-TB and XDR-TB are rising threats.
  • Socioeconomic Factors: Poverty, malnutrition, and HIV increase risk.
  • COVID-19 Impact: Disrupted TB services, increased mortality (Lancet Infectious Diseases, 2022).

Recent Research

A 2022 study published in Nature Communications identified new host genetic factors influencing susceptibility to TB, suggesting personalized medicine could improve outcomes (Zhou et al., 2022).

Mind Map

TB Mind Map

Diagram: TB Pathogenesis

TB Pathogenesis Diagram

Surprising Facts

  1. Silent Epidemic: Nearly one-quarter of the world’s population has latent TB, with potential to develop active disease.
  2. Bioluminescent TB: Researchers use bioluminescent M. tuberculosis strains to track infection in live animals, improving drug development and monitoring.
  3. TB and Diabetes: Diabetes triples the risk of developing active TB, creating a dangerous synergy in affected populations.

TB and Health

  • Public Health: TB is a leading cause of death from infectious disease, surpassing HIV/AIDS.
  • One Health Perspective: TB affects humans, cattle (bovine TB), and wildlife, requiring cross-sectoral control strategies.
  • Comorbidities: HIV, diabetes, and malnutrition worsen outcomes and complicate management.

References

  • Zhou, X. et al. (2022). “Host genetic factors influencing tuberculosis susceptibility.” Nature Communications, 13, 1234. Link
  • World Health Organization. (2022). “Global Tuberculosis Report.” Link
  • The Lancet Infectious Diseases. (2022). “Impact of COVID-19 on TB services.” Link

Summary Table

Aspect Details
Cause Mycobacterium tuberculosis
Transmission Airborne droplets
Symptoms Cough, fever, weight loss, night sweats
Diagnosis TST, IGRA, sputum, molecular tests
Treatment 6-month regimen, DOT, second-line for resistance
Prevention BCG vaccine, infection control
Global Impact 10M cases/year, 1.5M deaths/year, MDR/XDR-TB rising
Recent Research Host genetics, bioluminescent tracking

Additional Resources