Lecture on Tuberculosis

Epidemiology

• 30% of global population infected with tuberculosis (TB).
  • Mostly latent infections: bacteria present but not causing active disease.
• 10% of those with latent TB will experience disease reactivation over a lifetime.
  • 10 million people globally have active TB at any one time.
  • Results in about 1 million deaths annually.

Causes

• Caused by Mycobacterium tuberculosis.
  • Unusual bacteria: slow-growing, lipid-rich cell wall.
  • No environmental source; transmitted via infected individuals.
  • Subspecies include Mycobacterium bovis, Mycobacterium africanus.
• BCG vaccine developed from non-pathogenic Mycobacterium bovis.

Pathogenesis

• Transmission through inhalation of droplets from coughing individuals.
• Bacteria invade alveolar macrophages, resisting normal killing mechanisms.
  • Can remain latent for decades.
  • Potential for systemic spread via macrophages.
• Formation of granulomas, a hallmark of TB infection.

Types of Tuberculosis

• Pulmonary Tuberculosis: affects lungs.
• Extrapulmonary Tuberculosis: affects other body parts.

Risk Factors

• Immune system weakening: age, malnutrition, immunosuppressive drugs, HIV.
• Recent emigration: increases risk of reactivation.
• Higher prevalence in marginalized groups (homeless, alcoholics, drug addicts).

Clinical Manifestations

• Pulmonary Tuberculosis: cough, haemoptysis, systemic symptoms (fever, night sweats, weight loss).
• Extrapulmonary Tuberculosis: depends on site, e.g. cervical lymph nodes, gastrointestinal symptoms.

Diagnosis

• Often clinical, confirmed by culturing bacteria from samples.
• Microscopy: looking for acid-fast bacilli.
• Culture is slow, taking 3-4 weeks.
• PCR tests: faster identification.
• Biopsies: histological examination for granulomas.

Treatment

• Multi-drug antibiotic therapy (isoniazid, rifampicin, pyrazinamide, ethambutol).
• Treatment duration: minimum 6 months, longer for CNS or bone involvement.
• Corticosteroids for brain/pericardial involvement to reduce fibrosis.

Challenges

• Slow diagnosis, compliance issues, drug toxicity, resistance.
• Resistant strain treatment is prolonged and difficult.
• Untreated TB can cause lung damage leading to chronic issues like bronchiectasis.

Outcomes

• Non-resistant TB: 90-95% cure rate.
• Potential long-term lung damage from extensive untreated TB.

Case Studies

1. Indian patient with pulmonary TB: systemic symptoms, cough, chest X-ray showed cavitation.
2. Somalian patient with spinal TB: systemic symptoms, back pain, MRI showed vertebral changes.

Summary

• Key to TB recognition is systemic symptoms in high-risk groups.
• Diagnosis relies on clinical judgment, reinforced by laboratory tests where possible.
• Management involves long-term, multi-drug treatments with attention to resistance and patient compliance.