PBL 6 - Tuberculosis

Question 1

How does tuberculosis normally spread? (1 mark)

Answer 1

Mainly by inhalation of infected airborne aerosol (air containing water droplets containing m.
tuberculosis). (

Question 2

Which organs are normally first infected by tuberculosis, and why is this? (1 mark)

Answer 2

The lungs (1/2 mark). M.tuberculosis prefers a high level of oxygen to grow and the lungs provide
this (1/2 mark)

Question 3

Explain carefully why tuberculosis is difficult to treat with drugs (1 mark)

Answer 3

M. tuberculosis is intracellular (1/2 mark) and has a waxy cell wall that resists penetration by drugs
(1/2 mark). Antibiotics have to penetrate both the host mammalian cell and the bacterial cell wall to
be effective .

Question 4

What is usually the first symptom of pulmonary tuberculosis? (1 mark). List four other
signs/symptoms that may present. (2 marks)

Answer 4

First symptom: Productive cough (1 mark)
Other symptoms: Night sweats, Weight loss, Loss of appetite, Haemoptysis, (coughing up blood)
Chronic fatigue, (Any four 1/2 mark each)

Question 5

Give four separate methods used for the diagnosis of tuberculosis (2 marks)

Answer 5

Four from : PCR (polymerase chain reaction) (from sputum) Skin test (Mantoux/Pirquet) Chest Xray
Histological examination of biopsy Microbiological culture (sputum) Any four (1/2 mark each)

Question 6

What four drugs make up the normal first line treatment protocol for tuberculosis? (2 marks)

Answer 6

Rifampicin, Isoniazid, Pyrazinamide, ethambutol (1/2 each) (RIPE)

Question 7

What parts of the body can TB also infect? (2)

Answer 7

lymph
nodes, bones and joints, kidneys, brain, gut, the skin
(extra-pulmonary and non infectious)

Question 8

Why are mycobacteria named acid-fast bacilli? (1)

Answer 8

resistance to decoloration with acid washing;

Question 9

How long does it usually take to culture mycobacteria? (1)

Answer 9

2-6 weeks

Question 10

What is the pathophysiology of TB? (3)

Answer 10

o Primary infection – engulfed by macrophages, forms granulomas – asymptomatic
o Latent infection – bacteria dormant for months-years
o Secondary infection – reactivation of bacteria, usually in lung apex causing symptoms e.g immunosuppressed (APEX as most oxygenated)

Question 11

What percentage of the population have TB? (1)

Answer 11

1/3rd of population

Question 12

How do you do the Mantoux skin test? (2)

Answer 12

Inject Tuberculin intradermally, measure cell mediated response
 5mm pos in – HIV positive, old healed TB, recent TB contact
 10mm pos in – Injection drug users, high risk setting, recent arrivals
 15mm pos in – No TB risk factors

Question 13

What is the BCG vaccine? Why might this give a false positive on mantoux test? (2)

Answer 13

Vaccine prevent against TB

antibodies to TB still present.

Question 14

What are features of a chest X-ray you would see in someone with TB? (2)

Answer 14

Apical consolidation, bilateral opacities/calcification/cavitation
Hilar shadowing

Question 15

What would you detect in a sputum test? (1)

Answer 15

Detect bacteria

or fungi

Question 16

Why would you take a histological examination of biopsy specimens in TB (2)

Answer 16

Multinucleate Langerhans giant cells, AFBs inside macrophages
takes a long time for microbiology
In extra-pulmonary TB - Culture can be negative

Question 17

Risk factors for TB (2)

Answer 17

Close contact
Ethnic minorities
Alcoholics
HIV positive
Young and elderly 
Homeless

Question 18

What drug must you not take if you are taking rifampicin? (1)

Answer 18

Oral contraceptives

as acts on liver, may not work

Question 19

What are possible side effects of the TB treatment (3)

Answer 19

Rifampicin = Liver enzymes, orange secretions, hepatotoxicity in pregnancy
Isoniazid = Peripheral neuropathy, hepatotoxic
Ethambutol = Optic neuritis leading to red-green colour blindness
(Liver problems, vision changes, neuropathy)

Question 20

What is MDR-TB? (2)

Answer 20

Multi-drug resistant TB

• Resistant to isoniazid and rifampicin- MDR-TB
• Must take streptomycin, amikacin, levofloxacin

Question 21

What is the relationship between TB and HIV? (2)

Answer 21

TB and HIV infection act synergistically, each
condition exacerbating the other
Reactivation is higher if you have TB

Question 22

How is TB prevented in the UK (3)

Answer 22

o Contact tracing and screening
= Detect source of infection, vaccinate, offer mantoux test to people close to those with TB
BCG Vaccine – given to schoolchildren at around 12/13 years of age + High risk groups
Identifying and treating all those with TB

Question 23

What is CCDC? (1)

Answer 23

Consultant in Communicable Disease Control

Question 24

What is Sputum

Answer 24

Sputum is a thick fluid produced in the lungs and in

the adjacent airways

Question 25

What is miliary TB

Answer 25

When the body fails to control the initial infection which invades the blood stream

Question 26

What stain do you use in mycobacteria tuberculosis

Answer 26

Ziehl-Neelson (red)

Auramine (orange)

Question 27

MoA rifampicin

Answer 27

RNA polymerase inhibitor

6months

Question 28

MoA Isoniazid

Answer 28

Inhibits mycoloic acids in cell wall

6 months

Question 29

MoA pyrazinamide

Answer 29

Inhibits FA synthesis,

2 months

Question 30

MoA ethambutol

Answer 30

Inhibits cell wall synthesis

Question 31

What would you take in multi-drug resistant TB

Answer 31

Streptomycin
Amikacin
Levofloxacin
(instead of rifampicin or isoniazid)

Question 32

How long do you need to incubate bacteria

Answer 32

2-8 wks

Question 33

How much tuberculin in mantoux test

Answer 33

0.1 ml of 5 tuberculin units

Question 34

What is tuberculin

Answer 34

o purified protein derivative (PPD) extracts of

Mycobacterium tuberculosis, M. bovis, or M. avium th

Question 35

Which drug is not given to children

Answer 35

Ethambutol