Lecture 11: Tuberculosis

Question 1

What pathogen causes Tuberculosis

Answer 1

Mycobacteria:
M tuberculosis and M bovis are in NZ while there are 2 not in NZ. There is non TB mycobacteria that can be rapid or non rapid growing and can cause other disease

Question 2

How does TB infection progress (7 steps)

Answer 2

1. Aerosolised TB particle is inhaled which impacts on the distal airway (nose and throat cells resistant to TB)
2. LAM on the surface of cell binds to the complement receptor of pulmonary macrophages to get phagocytosed by resists lysis by lysosome
3. Once inside, TB prevents signalling for macrophages apoptosis and antigen presenting to T cells.
4. TB is carried to local lymph node where local wbcs release cytokines
5. Dendritic cells with the antigen stimulate T cell proliferation and differentiation.
6. T cells follow cytokines to site of infection
7. Macrophages and help T cells surround the dormant or slowly replicating TB becoming a granuloma

Question 3

Describe the general structure of a granuloma

Answer 3

Central necrosis containing the persistent antigen surrounded by a layer of epithelioid macrophages and then a zone of CD4 lymphocytes

Question 4

After primary infection and formation of a NECTROSING granuloma in the lymph node and the lungs what are the two main outcomes

Answer 4

1. There is immune containment in the granuloma leading to
   a) no disease and latent TB infection
   b) reactivation of TB bc of age, hiv, cancer, steroidal treatment or immune suppressant.

This leads to the 2nd outcome: illness if TB can’t be contained by the granuloma

• Miliary TB which is spotty everywhere
• Pulmonary/thoracic TB leading to bronchopneumonia
• Extra pulmonary TB- pleural, pericardial,

Question 5

How is TB transmitted

Answer 5

Through droplet and airborne transmission

Question 6

Who is most at risk for catching TB and who is more likely

Answer 6

Most likely: spouse
At risk
- children, immune supression, ppl in institutional care, healthcare workers

Question 7

What are signs for increased risk of transmission

Answer 7

Having the pulmonary disease

• Million TB visible in sputum
• Cavitation (dissolving of healthy tissue) visible on X ray
• Not cover mouth when coughing
• delayed diagnosis

Question 8

What are the 5 ways to help diagnose TB

Answer 8

1. Suspicion
2. Chest x ray- cavitiation
3. Sputum specimens- visualising the bacteria using the Ziehl neelsen stain (may be any mycobacterium)
4. TB PCR
5. TB culture (days to weeks) allows to test for antibiotic resistance

Question 9

Why are mycobacteria acid fast bacteria

Answer 9

They have a lot of fat in their cell membrane which helps them retain the carbol-fuchsin ziehl neelsen stain after its been washed off with HCL (alc), Provided its been heated up after the stain is applied)

Question 10

Compare the two ways that latent TB infection is diagnosed

Answer 10

1. Mantoux test which tests for an inflammatory lump in 72 hours after TB protein is given intradermally. (however unreliable)
   better way is
2. Interferon gamma release assay where a whole blood sample is first primed to make a positive control by adding mitogen, which causes lymphocytes to proliferate and release interferon gamma. The TB antigen is added and if sensitised lymphocytes release interferon gamma, then there has been exposure to TB in the past

Question 11

Why would you need to test for latent TB infection

Answer 11

• Starting immunosuppresive treatment
• HIV/AIDs
• Healthcare worker

Question 12

How is TB treated

Answer 12

TB treatment includes using 4 main TB antibiotics (not penicillin) and there is active prevention of transmission through isolation, respirator masks and antibiotics until non-infectious