Infection 7) Pathogenesis of TB

Question 1

What mycobacteria causes tuberculosis?

Answer 1

M.tuberculosis

Question 2

What mycobacteria causes bovine tuberculosis?

Answer 2

M.bovis

Question 3

What mycobacteria causes leprosy?

Answer 3

M.leprae

Question 4

What mycobacteria cause buruli ulcer?

Answer 4

M.ulcerans

Question 5

How many latent TB infections are there globally?

Answer 5

1.7 billion

Question 6

How many new TB cases occur per year?

Answer 6

10 million

Question 7

Why is TB a complex trait?

Answer 7

Pathogen, host immune response and environment all contribute to disease

Question 8

What special microscopy stains are used for mycobacterium tuberculosis?

Answer 8

Ziehl-Neelsen
Auramine fluorescence
Acid-fast bacilli

Question 9

What is the clinical presentation of pulmonary TB?

Answer 9

Cough > 3 weeks
Weight loss
Fatigue
Fever
Night sweats
Haemoptysis
Difficulty breathing
Mild, non specific malaise

Question 10

What medical evaluation is needed for suspected TB?

Answer 10

Medical / family history - household contacts
Physical exam
Tests for TB infection
Chest X-ray
Bacteriological examination

Question 11

Describe aerosol transmission of mycobacterium tuberculosis

Answer 11

Droplet nuclei containing 1-3 bacilli

Reach alveolar space, engulfed by macrophages

Question 12

What happens when a granuloma breaks down?

Answer 12

Bacteria escape and replicate leading to active TB disease

Question 13

Give examples of sites of TB disease

Answer 13

Larynx
Bone
Kidney
Brain
Lymph node
Pleura
Lung
Spine (Pott's disease)

Question 14

What may be seen on a chest X-ray with MTB?

Answer 14

Infiltrates
Cavities
Ghon complex

Question 15

What might be seen in a CT scan with MTB?

Answer 15

Tree in bud pattern
Bronchial wall thickening
Decreased volume in right lobe

Question 16

Describe a latent TB infection

Answer 16

Inactive
Contained tubercle bacilli in body
TST or blood test results usually positive
Chest X-ray usually normal
Sputum smears and cultures negative
No symptoms
Not infectious

Question 17

Describe active TB disease

Answer 17

Active
Multiplying tubercle bacilli in body
TST or blood test results usually positive
Chest X-ray abnormal
Sputum smear and cultures may be positive
Symptoms such as cough, fever, weight loss
Often infectious before treatment
Case of TB

Question 18

What drugs are given for pulmonary and extra-pulmonary TB?

Answer 18

4 drugs for 2 months
 - Rifampicin
 - isoniazid
 - ethabutol
 - pyrazinamide
4 months of: 
 - isoniazide
 - rifampicin

Question 19

What are some ongoing problems of TB?

Answer 19

Difficult to diagnose
BCG vaccination efficacy (0-80%)
Long treatment
Poor patient compliance
Drug resistance
Latent infection
Funding / profile / press

Question 20

Why is non-tuberculosis mycobacteria increasing?

Answer 20

Increased identification
Better clinical recognition
Improvement in other treatments unmasking infection
Improved laboratory techniques for isolation and identification

Question 21

Give examples of infections acquired by inhalation?

Answer 21

M.kansasii

M.avium

Question 22

Give examples of infections acquired by ingestion

Answer 22

Disseminated M.avium

Question 23

What is M.marinum?

Answer 23

Fish tank granuloma

Inhabits water