What is tuberculosis?

What is Tuberculosis (TB)?

Tuberculosis (TB) is a chronic infectious disease caused by the bacterium Mycobacterium tuberculosis. It primarily affects the lungs (pulmonary TB), but can also involve other organs (extrapulmonary TB).

Causative Agent

  • Mycobacterium tuberculosis

    • Acid-fast, rod-shaped bacillus

    • Aerobic and slow-growing

    • High lipid content in cell wall → resists desiccation and immune killing

Mode of Transmission

  • Airborne transmission: Spread by inhalation of droplets (from cough, sneeze, or talk of infected person)

  • Not spread via touching or sharing food

Pathogenesis (Basic Overview)

  1. Inhalation of bacilli into lungs

  2. Bacilli are phagocytosed by alveolar macrophages

  3. Granuloma formation: body walls off infection

  4. Can lead to:

    • Latent TB (asymptomatic, not contagious)

    • Active TB (symptomatic, contagious)

  5. In immunocompromised individuals: risk of reactivation or dissemination (miliary TB)

Clinical Features (Pulmonary TB)

Symptom Details
Chronic cough With sputum, may be blood-streaked (hemoptysis)
Fever Especially low-grade, evening rise
Night sweats Common and characteristic
Weight loss Unintentional and significant
Fatigue and weakness General ill-health
Chest pain Sometimes pleuritic in nature

Diagnosis

  • Sputum AFB stain (Ziehl-Neelsen stain)

  • Sputum culture (gold standard but slow)

  • Mantoux tuberculin skin test (TST)

  • Interferon gamma release assays (IGRAs)

  • Chest X-ray: cavitations, infiltrates, or miliary pattern

  • GeneXpert MTB/RIF: rapid test for detection and drug resistance

Treatment

  • Standard anti-TB therapy (6–9 months):

    • Intensive phase (2 months): Isoniazid, Rifampicin, Pyrazinamide, Ethambutol (HRZE)

    • Continuation phase (4–7 months): Isoniazid + Rifampicin (HR)

  • DOTS (Directly Observed Treatment, Short-course) is a global WHO strategy

Prevention

  • BCG vaccine (given at birth in endemic areas)

  • Early detection and treatment

  • Isolation of active cases in early phase

  • Screening contacts and high-risk populations

Quick Facts

  • TB is one of the top 10 causes of death worldwide.

  • Latent TB can persist for years without symptoms.

  • HIV co-infection increases the risk of TB activation.

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