Tuberculosis

Question 1

Properties of tubercolosis (TB)

Answer 1

Slow growing
Infects lungs but can become extrapulmonary

Acid fast bacteria, is lipid rich
V. hydrophobic therefore resistant to drying and weak disinfectant

Question 2

1st stage of TB

Answer 2

Just a few needed to be inhaled

Settles in alveoli and begins growing

Engulfed by phagocytes however not killed in this process

Asymptomatic

Question 3

2nd stage of TB

Answer 3

TB multiplies in phagocyte

Phagocyte bursts and releases TB which are engulfed by other phagocytes

This continues for 3-4 weeks

Still asymptomatic

Question 4

3rd stage of TB

Answer 4

Cell mediated response started

Tubercules form (growths of the TB in the lung)

Symptoms start appearing

Question 5

Percentage of people that progress infection after 3rd stage?

Answer 5

5-10% progress

Around 45-50% clear infection while 45-50% just have a latent infection

Question 6

4th stage of TB

Answer 6

TB continues multiplying and uncontrolled lysis occurs and the TB spreads around the lungs

Enzymes released destroys tissue causing lesions

Question 7

TB symptoms

Answer 7

Cough
Afternoon fever 
Weight loss (hence the name 'consumption)
Blood in sputum 
Night sweats

Question 8

How might you diagnose TB?

Answer 8

Chest x-ray will reveal the lesions that have caused scarring

Sputum test/cultures will reveal the TB

Molecular assays (MTB/RIF assay)

Question 9

How might yo diagnose latent TB?

Answer 9

There are no lesions because infection has not progressed past 3rd stage hence chest x ray not useful

Tuberculin is given SC and a +ve test gives a lesion on skin >10mm afer 2-3days

Molecular assay (IGRA)

Question 10

TB prevention

Answer 10

BCG vaccine given to high risk groups

Question 11

How many 1st line drugs for TB are there and how are they used?

Answer 11

4 first line drugs and they’re used in combo

They include:
Rifampicin
Isoniazid
Pyrazinamide 
Ethambutol

Question 12

Rifampicin effect on TB

Answer 12

Bactericidal via inhibition of RNA polymerase
Absorption reduced by food

Can cause liver damage
hypersensitivity
reduces activity of other drugs
body fluids can turn red/orange

Question 13

Isoniazid effect on TB

Answer 13

A prodrug

Acts bactericidal if TB growing but bacteriostatic if there is little growth via the inhibition of the synthesis of mycolic acid

Metabolised by liver and excreted by kidneys

Can cause hypersensitivity, peripheral neuropathy, hepatoxicity and decreases effects of birth control pills

Question 14

Pyrnzinamide effect on TB

Answer 14

Prodrug that is bactericidal via inhibition of mycolic acid synthesis and damage of bacterial membrane

Metabolised by liver, excreted by kidneys

Can cause joint pain, liver damage and hypersensitivity

Question 15

Ethambutol effect on TB

Answer 15

Bacteriostatic against growing TB via increasing permeability by affecting cell wall synthesis

Half of it excreted unchanged in urine

Can cause reversible optic neuritis and joint pain

Question 16

Treating active TB (RIPE)

Answer 16

Rifampicin and isoniazid for 6-9months

PYrazinamide and ethambutol for the first 2 months

Question 17

Treatment of latent TB

Answer 17

Isoniazid for 6 months
or
Rifampicin and isoniazid for 3 months

Question 18

2nd drugs for TB

Answer 18

Streptomycin 
Capreomycin
Cycloserine 
Ciprofloxacin 
Azithromycin

Question 19

MDR-TB is defined as….

Answer 19

Multi-drug resistant TB

Res to >2 1st line drugs

Question 20

XDR-TB is defined as…

Answer 20

Extra (extreme?) drug resistant TB

Res to >2 1st line drugs + 3> of 6 2nd line drugs

XXDR-TB and TDR-TB (totally resistant) also exist but not recognised by WHO yet