Tuberculosis - aetiology, pathogenesis and pathological features

Question 1

Describe the sequence of events in cells/tissues after infection with TB

Answer 1

Macrophage ingestion
Spread to lymph nodes
Bacteraemia - organisms divides unchecked
-Inhibition of lysosomal fusion

Question 2

What are the sequences of events in TB infection, starting with inhalation

Answer 2

• Inhalation of the bacilli
• Implants in lower part of upper lobe of the lung, or upper part of the lower lobe
• Develops a Ghon focus, which undergoes central caseous necrosis
• Bacilli drain to regional lymph nodes, that also caseate, forming more Ghon processes
• At this stage, there is haematogenous and lymphatic dissemination
• Ghon complexes undergo fibrosis and form a Ranke complex

Question 3

What are clinical manifestations of primary TB?

Answer 3

Progressive lung disease with:

• Malaise, weight loss
• Fever, night sweats
• Cough, sputum
• Pleuritic pain
• Resembles acute bacterial pneumonia in some cases

Question 4

What % of TB deaths occur in low income countries?

Answer 4

90%

Question 5

How many times more likely are you to get TB in Australia if you are Aboriginal, compared to non-aboriginal?

Answer 5

8x

Question 6

Is Tb aerobic or anaerobic?

Answer 6

Aerobic

Question 7

Describe some TB testing

Answer 7

• Sputum, tissue ZNs stain, fluorescent staining
• Culture
• NAT
• Mantoux testing
• Quantiferon assay

Question 8

What are 3 virulence factors of Mycobacterium tuberculosis?

Answer 8

• Cord factor - a glycolipid in the cell wall
• Inhibition of phagolysosome formation
• Suppression of T-cell function
• Protection against complement activated killing

Question 9

What does secondary TB infection look like clinically?

Answer 9

Involves apex of the lung. Due to pre-existing hypersensitivity, there is little enlargement of the hilar lymph nodes
Tissue necrosis with cavitation is evident

Question 10

What type of inflammation do you see in TB?

Answer 10

Granulomatous

Question 11

Describe progressive pulmonary TB

Answer 11

Extension of the lung lesion, cavitation with central caseation that is not walled off by fibrous tissue
This erodes into bronchi and blood vessels, becoming ‘open TB’
The disease spreads through the blood and lymph nodes

Question 12

Describe Miliary TB

Answer 12

After dissemination through the lymph nodes, bacilli in venous blood get back to the lungs, and cause numerous small lesions throughout the lung

Question 13

Where can you get TB developing?

Answer 13

• lungs
• CNS
• Peritoneal
• Spine

Question 14

Which Mycobacterium species is involved in HIV disease?

Answer 14

Mycobacterium avium-intracelluare

Causes disseminated “MAC” infection