Tuberculosis and Schistosomiasis Notes

Tuberculosis (TB)

Definition

• Infectious disease primarily affecting lung parenchyma.

• Caused by Mycobacterium tuberculosis.

• Spreads through airborne droplets (coughing, sneezing).

Risk Factors

• Weakened immune system (HIV/AIDS, malnutrition, diabetes, immunosuppressive therapy).

• Close contact with infected individuals.

• Living in crowded or unsanitary conditions.

• Substance abuse.

• Healthcare workers exposed to TB patients.

Latent vs. Active TB

• Latent TB: No symptoms, cannot spread the disease.

• Active TB: Shows symptoms, can spread the disease.

Epidemiology

• WHO: TB remains a top infectious disease killer worldwide.

• 2022: 10.6 million people developed TB, 1.3 million died.

• More prevalent in low- and middle-income countries (South-East Asia, Africa, Western Pacific).

• Guyana: 48 new TB cases per 100,000 population in 2022 (decline from 2020).

Pathophysiology

• Inhalation of Mycobacterium tuberculosis leads to:

  • Immediate clearance

  • Latent infection

  • Active disease (primary)

  • Reactivation disease

• Cavities in lungs allow spread through coughing.

• Reactivation can occur after immunosuppression, HIV infection, or smoking.

Clinical Features

• Systemic: Fever, sweats, weight loss.

• Respiratory: Chronic cough, haemoptysis, chest pain, dyspnoea.

• Other: Bone/joint pain, neurological symptoms, enlarged lymph nodes.

Diagnosis

• Clinical evaluation: Persistent cough, fever, night sweats, weight loss.

• Laboratory tests:

  • Sputum Smear Microscopy: Detects acid-fast bacilli (AFB).

  • GeneXpert (PCR): Detects Mycobacterium tuberculosis DNA and rifampicin resistance.

  • Sputum Culture: Confirms TB and checks drug resistance.

  • IGRAs: Detect latent TB.

  • Tuberculin Skin Test (TST/Mantoux Test): Identifies TB exposure.

• Imaging: Chest X-ray, CT Scan (lung abnormalities).

• Biopsy: For extrapulmonary TB (lymph node, pleural).

Macroscopic Morphology

• Primary Tuberculosis: Ghon focus, Ghon complex, caseous necrosis.

• Secondary Tuberculosis: Cavitary lesions (upper lobes), fibrosis, calcification (Ranke complex).

• Miliary Tuberculosis: Small nodules throughout lungs and other organs.

• Extrapulmonary Tuberculosis:

  • Lymph Nodes (Scrofula): Enlarged, caseous necrotic lymph nodes.

  • Bone (Pott’s Disease): Vertebral destruction.

  • Kidneys: Caseous nodules.

  • Meninges: Gelatinous exudate (tuberculous meningitis).

Histopathology

• Granuloma Formation (Tubercle):

  • Epithelioid cells (activated macrophages).

  • Langhans giant cells (fused macrophages).

  • Lymphocytes (T cells).

  • Fibroblasts (chronic cases).

• Caseous Necrosis: Amorphous, eosinophilic debris in the granuloma center.

Special Stains

• Ziehl-Neelsen (ZN) stain (acid-fast bacilli stain): Detects Mycobacterium tuberculosis.

• Kinyoun's method: Another stain to detect tuberculosis.

• Fite stain: Modification of ZN stain.

Treatment

• Isoniazid (H): Bactericidal, targets growing bacilli. kills >90\%

• Rifampicin (R): Bactericidal. High potency.

• Pyrazinamide (Z): Bactericidal with a low potency. Achieves its sterilising action.

• Ethambutol (E): Bacteriostatic. Low potency. Minimises drug resistance

• Streptomycin (S): Bactericidal with a low potency.

Complications

• Lung complications: Lung damage, acute respiratory distress syndrome, pneumothorax, bronchiectasis.

• Brain and spinal cord complications: Tubercular meningitis, spinal TB.

• Other: Infection/damage of bones, lymph nodes, skin; inflammation of heart tissues; hemoptysis; aspergilloma; fibrothorax; empyema.

Prevention

• Primary: Block infection (avoid close contacts, maintain ventilated houses, vaccination).

• Secondary: Block progression to active disease (cough etiquette, avoid smoking/drinking, consult doctor for symptoms).