Pathogenesis of tuberculosis

Question 1

What is tuberculosis and how is it spread?

Answer 1

• A contagious bacterial disease
• Caused by myobacterium tuberculosis (slow growing, difficult to kill, aerobe)
• Spread by airbourne droplet

Question 2

What are the symptoms of TB?

Answer 2

• Cough (blood)
• Weight loss
• Night sweats
• Fever
• Tiredness/ fatigue

Question 3

What are the differences between active TB and latent TB?

Answer 3

Latent TB:
- No symptoms
- Cannot spread TB to other
- Normal chest X-ray and negative sputum test

Active TB:
- Has symptoms
- May spread TB to others
- Abnormal chest x-ray and positive culture

Both have positive skin test

Question 4

What are risk factors for reactivation of TB?

Answer 4

• Immunosupression
• Old age
• Malnutrition
• Poverty
• Diabetes
• HIV

Question 5

How is TB spread and what are common sites of infection?

Answer 5

• TB can spread through airways (broncho-pneumonia) or vascular system (systemic milary TB)
  
  • Systemic milary TB can affect kidneys (WBCs in urine), brain (meningitis), liver (hepatitis), adrenal glands (addisons disease), cervical lymph nodes (scrofula), skeletal (Potts disease)

Question 6

What is the Ghon complex?

Answer 6

Initial infection of TB in upper region of lower lobe of lung producing a lesion called a Ghon focus

Ghon focus and lymph node lesion = Ghon complex

Question 7

What type of necrosis is involved in TB

Answer 7

Caseous necrosis

Question 8

How do you get secondary and primary Intestinal TB?

Answer 8

Intestinal TB can be secondary to pulmonary TB from swallowed infected sputum

Primary intestinal TB develops in people who drink milk infected with M.bovis

Question 9

Explain how the immune system play a positive and negative effect with a TB infection?

Answer 9

Good:
- Innate immunity: alveolar macrophages kill ingested bacilli
- Th1 adaptive immune response: CD8 and CD4 T cells, IFN-gamma –> controls infection

Bad:
- Excessive immune response leads to overproduction of TNF-alpha and healthy tissue damage by macrophages

Question 10

Describe the pathogenesis of TB

Answer 10

1) Inhalation
2) Alveolar macrophages
3) Lymph nodes
4) Haematogenous spread to other parts of lung via lymphatics and capillaries
5) Acute inflammatory response
6) Recruitment of CD4, CD8 and NK cells - production of IFN-gamma
7) Chronic inflammation
8) Formation of granuloma - immune containment
9) Ceseation
10) Liquifacation, cavitation and release
11) Transmission

Question 11

What is a TB granuloma?

Answer 11

• Spherical collection of lymphocytes, macrophages and epitheloid cells
• With a small area of central caseation necrosis

Question 12

How to diagnose TB?

Answer 12

• Interferon IFN-gamma blood test
• Chest x-ray
• Sputum