Lecture Notes on Tuberculosis (TB)

Introduction

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Global Impact: Approximately 2 billion people infected worldwide.
Asymptomatic Cases: 90-95% do not show symptoms; infection often remains latent.

Structure: Slender, rod-shaped, oxygen-dependent (strict aerobes).
Cell Wall: Waxy due to mycolic acid; makes them acid-fast and hardy against disinfectants.

Transmission: Primarily through inhalation.
Defense Mechanisms: Mucus traps bacteria; macrophages digest foreign cells.
- TB evasion: TB inhibits fusion of phagosome and lysosome, allowing survival and proliferation.
- Primary Tuberculosis: Initial infection may be asymptomatic or mild flu-like symptoms.

Immune Response: After 3 weeks, cell-mediated immunity forms a granuloma.
- Caseous Necrosis: Central tissue death resembling cheese; forms a Gon Focus.
Gon Complex: Combination of Gon Focus and affected lymph nodes.
Radiological Findings: Fibrosis and calcification visible on x-ray forming Ranke Complex.

Reactivation: Occurs when the immune system is compromised (e.g., AIDS, aging).
Cavitations: TB can cavitate in upper lobes, leading to bronchopneumonia and systemic miliary TB.
- Systemic Spread: Can infect kidneys, brain (meningitis), spine (Pott's disease), adrenal glands, liver, lymph nodes (scrofula).

PPD Test: Intradermal injection of tuberculin; positive result indicates previous exposure.
IGRA Test: Blood test for TB proteins; no need for follow-up visits to read results.
Chest X-ray: Recommended for positive test results to check for active disease.
Sputum Sample: Collected for staining, culture, and PCR in symptomatic patients.

Latent TB: Typically treated with isoniazid for 9 months.
Active TB: Combination of antibiotics (isoniazid, rifampin, ethambutol, pyrazinamide).
- Infectious Period: Patients are usually non-infectious after a few weeks of treatment.
- Isolation Measures: Negative pressure rooms and protective masks for visitors.
Drug-Resistant TB: Multi-drug resistant (MDR-TB) and extensive drug-resistant (XDR-TB) strains require special regimens.
- New Treatments: Pritominid approved for XDR-TB; effective combination therapy is promising.

TB is caused by Mycobacterium tuberculosis, primarily affecting the lungs.
Immune response leads to granuloma formation, which can reactivate under compromised immunity.
Diagnosis involves PPD or IGRA tests, followed by chest x-rays and possibly sputum culture.
Treatment involves prolonged antibiotic courses; vigilance is required for drug-resistant strains.

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