PBL 6 - Tuberculosis Flashcards
How does tuberculosis normally spread? (1 mark)
Mainly by inhalation of infected airborne aerosol (air containing water droplets containing m.
tuberculosis). (
Which organs are normally first infected by tuberculosis, and why is this? (1 mark)
The lungs (1/2 mark). M.tuberculosis prefers a high level of oxygen to grow and the lungs provide this (1/2 mark)
Explain carefully why tuberculosis is difficult to treat with drugs (1 mark)
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 .
What is usually the first symptom of pulmonary tuberculosis? (1 mark). List four other
signs/symptoms that may present. (2 marks)
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)
Give four separate methods used for the diagnosis of tuberculosis (2 marks)
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)
What four drugs make up the normal first line treatment protocol for tuberculosis? (2 marks)
Rifampicin, Isoniazid, Pyrazinamide, ethambutol (1/2 each) (RIPE)
What parts of the body can TB also infect? (2)
lymph
nodes, bones and joints, kidneys, brain, gut, the skin
(extra-pulmonary and non infectious)
Why are mycobacteria named acid-fast bacilli? (1)
resistance to decoloration with acid washing;
How long does it usually take to culture mycobacteria? (1)
2-6 weeks
What is the pathophysiology of TB? (3)
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)
What percentage of the population have TB? (1)
1/3rd of population
How do you do the Mantoux skin test? (2)
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
What is the BCG vaccine? Why might this give a false positive on mantoux test? (2)
Vaccine prevent against TB
antibodies to TB still present.
What are features of a chest X-ray you would see in someone with TB? (2)
Apical consolidation, bilateral opacities/calcification/cavitation
Hilar shadowing
What would you detect in a sputum test? (1)
Detect bacteria
or fungi