Overview

  • Tuberculosis (TB) is an infectious disease primarily affecting the lungs, caused by the bacterium Mycobacterium tuberculosis.
  • TB can also affect other organs (extrapulmonary TB), such as the kidneys, spine, and brain.
  • It spreads through airborne droplets when an infected person coughs, sneezes, or speaks.

Transmission: Analogies & Real-World Examples

  • Analogy: TB spreads like glitter at a party. When someone with active TB coughs, tiny droplets (like glitter) float in the air. Anyone nearby can “catch” the glitter if they breathe it in.
  • Real-World Example: In crowded places (e.g., public transport, dormitories), one person with active TB can infect many others, especially if ventilation is poor.

Pathophysiology

  • Entry: M. tuberculosis enters the lungs via inhaled droplets.
  • Immune Response: The immune system forms granulomas (clusters of immune cells) to “wall off” the bacteria, similar to how a city builds walls to contain a threat.
  • Latent vs. Active TB:
    • Latent TB: The bacteria are contained and inactive. No symptoms, not contagious.
    • Active TB: The bacteria multiply, causing symptoms and contagiousness.

Clinical Presentation

  • Pulmonary TB Symptoms:
    • Persistent cough (>3 weeks)
    • Hemoptysis (coughing up blood)
    • Chest pain
    • Night sweats
    • Fever
    • Weight loss (“consumption”)
  • Extrapulmonary TB: Symptoms depend on affected organ (e.g., back pain for spinal TB).

Diagnosis

  • Tuberculin Skin Test (TST): Injection of TB proteins under the skin; swelling indicates exposure.
  • Interferon-Gamma Release Assays (IGRAs): Blood test measuring immune response to TB antigens.
  • Chest X-ray: Identifies lung abnormalities.
  • Sputum Microscopy & Culture: Detects M. tuberculosis in coughed-up mucus.

Key Equations

  • Incidence Rate:
    Incidence = (Number of new TB cases / Population at risk) × 100,000
  • Prevalence Rate:
    Prevalence = (Total number of TB cases / Total population) × 100,000
  • Basic Reproduction Number (R₀):
    R₀ = β × c × D
    Where:
    • β = transmission probability per contact
    • c = contact rate
    • D = duration of infectiousness

Treatment

  • First-Line Drugs: Isoniazid, Rifampicin, Ethambutol, Pyrazinamide (often given together for 6+ months).
  • Directly Observed Therapy (DOT): Health workers supervise patients taking medication, like a coach ensuring an athlete follows their training regimen.
  • Drug-Resistant TB: Requires second-line drugs, longer treatment, and more side effects.

Practical Applications

  • Public Health: TB screening in high-risk populations (e.g., healthcare workers, prisoners).
  • Vaccination: Bacillus Calmette-Guérin (BCG) vaccine is used in many countries to prevent severe forms of TB in children.
  • Contact Tracing: Identifying and testing people exposed to an active TB case.
  • CRISPR Technology:
    • Recent advances use CRISPR to detect M. tuberculosis DNA rapidly and with high specificity.
    • Example: CRISPR-based diagnostics can identify TB in under an hour, even in resource-limited settings (Kellner et al., 2020, Nature Protocols).

Common Misconceptions

  • Misconception 1: Only people with symptoms can spread TB.
    • Fact: Only those with active pulmonary TB are contagious, but many with latent TB have no symptoms and cannot spread the disease.
  • Misconception 2: TB is a disease of the past.
    • Fact: TB remains one of the top 10 causes of death worldwide, especially in low- and middle-income countries.
  • Misconception 3: TB only affects the lungs.
    • Fact: TB can affect almost any organ.
  • Misconception 4: BCG vaccine provides lifelong protection.
    • Fact: Protection wanes over time and is variable; it is most effective against severe childhood TB.
  • Misconception 5: Antibiotic treatment for TB is quick and easy.
    • Fact: Treatment is lengthy (at least 6 months), and incomplete treatment can lead to drug resistance.

Recent Research & News

  • CRISPR Diagnostics:
    • A 2020 study by Kellner et al. introduced a CRISPR-based test for TB, offering rapid, accurate, and affordable diagnosis (Nature Protocols, 2020).
  • Global TB Report 2023:
    • WHO reported that the COVID-19 pandemic disrupted TB services, leading to increased deaths and missed diagnoses (WHO Global TB Report 2023).

Summary Table

Aspect Key Points
Cause Mycobacterium tuberculosis
Transmission Airborne droplets
Symptoms Cough, fever, weight loss, night sweats
Diagnosis TST, IGRA, chest X-ray, sputum tests
Treatment 4-drug regimen, DOT, long duration
Prevention BCG vaccine, public health measures
Practical Applications Screening, CRISPR diagnostics, contact tracing
Misconceptions Latent vs. active, organ involvement, vaccine efficacy

Summary

  • TB is a major global health challenge with complex transmission and treatment.
  • Advances like CRISPR technology are improving diagnosis and control.
  • Understanding misconceptions is vital for effective prevention and management.
  • Ongoing research and public health efforts are crucial to reducing TB burden.