Pulmonary Tuberculosis

Question 1

How prevalent is TB world-wide? In Canada?

Answer 1

• it is the #1 cause of death from an infectious agent in the world
• 750 people in Canada die from TB every year

Question 2

What causes TB?

Answer 2

bacteria

Question 3

What are the two types of TB bacteria? How are they spread?

Answer 3

1) mycobacterium tuberculosis hominis
- airborne spread via droplet nuclei

2) mycobacterium tuberculosis bovis
- spread by drinking milk from infected cows, infects the GI tract

Question 4

What is unique about the TB bacterium?

Answer 4

1) it is resistant to destruction and can live in dead and calcified lesions for a long time
2) it has no antigens to stimulate an antibody response (in other words, the body relies on a cell-mediated response to wall off/destroy the bacteria)

Question 5

What is the difference between primary TB and secondary TB?

Answer 5

primary exposure = first exposure

secondary exposure = reinfection or reactivation

Question 6

What happens in primary TB?

Answer 6

1) bacteria INHALED into lungs
2) bacteria PHAGOCYTOSED by macrophages but not killed
3) CELL-MEDIATED IMMUNE RESPONSE is initiated, helps make activated macrophages with increased ability to destroy bacteria but takes 3-6 weeks, will contain the infection
4) circumscribed granulomatous lesion forms, called GHON FOCUS, in subpleural area, in upper parts of lower lobes or lower parts of upper lobe
- Ghon focus contains bacteria, modified macrophages, other immune cells
5) cell-mediated reaction will necrose the middle of the Ghon focus = CASEOUS NECROSIS
6) some bacteria and macrophages drain into local lymph node, causes CASEOUS GRANULOMA IN NODE
7) Ghon focus and granuloma in node = GHON COMPLEX
8) in most people there is healing but some bacteria will remain
9) if immune response is inadequate (5%) = PRIMARY PROGRESSIVE TB:
- CONTINUAL DESTRUCTION of lung tissue
- bacteria SPREADS TO MULTIPLE SITES IN LUNGS
- may gain access to blood vessels and spread to organs = MILIARY TB
- may spread to sputum = INFECTIOUS

Question 7

What happens in secondary TB?

Answer 7

• reinfection or reactivation (can be from a decreased immune system)
• cell mediated hypersensitivity reaction occurs, attacks bacteria but keeps attacking some of the tissue around it, creates cavities as lung tissue is destroyed

Question 8

What are the common manifestations of TB?

Answer 8

• fever
• weight loss
• night sweats
• fatigue

Question 9

If secondary TB progresses, what other manifestations can occur?

Answer 9

• dry cough progressing to a productive, purulent or blood-tinged cough
• dyspnea, orthopnea if advanced

Question 10

How is TB diagnosed?

Answer 10

• screening:
  1) TB skin test (but a false negative can occur in those who are immuno-suppressed)
  2) chest x-ray
• positive diagnosis is based on identification from a culture or DNA/RNA

Question 11

Who is treated for TB?

Answer 11

• people with active TB
• people in close contact with TB
• those at increased risk of TB or with latent TB

Question 12

How is TB treated?

Answer 12

• multiple drugs (develops resistance easily)
• chemo
• bacillus Calmette-Guerin (BCG) = vaccine, given intradermally, causes local reaction for about 3 months, only given to people with a negative skin test, those at high risk… NOT recommended in Canada because of low risk