Session 7 - TB and lung cancer

Question 1

Describe the features of mycobacterium tuberculosis. how is it transmitted?

Answer 1

• Aerobic
• Acid and alcohol fast bacilli
• Transmitted by aerosolized droplets – Unit of infection called a droplet nucleus.

Question 2

Describe the pathology of a TB infection

Answer 2

1) Mycobacterium tuberculosis (MTB) enters the airways and deposits in alveoli
2) Alveolar macrophages phagocytose the MTB but are unable to kill them due to cell wall lipids of MTB blocking fusion of phagosome with lysosomes
a. These macrophages initiate development of activated macrophages with ability to kill MTB, takes 6 weeks,
3) Ingestion of MTB by macrophages causes a granulomatous reaction. A spherical granuloma with central caseation forms (Caseous necrosis)
4) Primary infections occurs on first exposure

Question 3

What happens in a primary infection of TB?

Answer 3

1) Primary infection occurs on first exposure
2) Deposition of TB bacilli in alveoli is followed by the development of sub-pleural focus of tubercles called the primary focus
3) From the primary focus the TB bacilli can drain into hilar lymph nodes. Primary focus + infected hilar lymph nodes together called the primary complex.
4) Primary infection heals with or without calcification of primary complex, however, TB enters the blood stream and seeding of TB in order parts of the lung and other organs can occur.
5) Development of cell mediated immunity results in contained infection but organisms still viable, Known as latent TB.

Question 4

How can latent TB be reactivated?

Answer 4

Immunosuppression

Question 5

How would you identify latent TB?

Answer 5

Skin test can reveal latent TB – Hypersensitivity to TB proteins suggests immunity has developed and therefore latent TB.