Infection 7) Pathogenesis of TB Flashcards
What mycobacteria causes tuberculosis?
M.tuberculosis
What mycobacteria causes bovine tuberculosis?
M.bovis
What mycobacteria causes leprosy?
M.leprae
What mycobacteria cause buruli ulcer?
M.ulcerans
How many latent TB infections are there globally?
1.7 billion
How many new TB cases occur per year?
10 million
Why is TB a complex trait?
Pathogen, host immune response and environment all contribute to disease
What special microscopy stains are used for mycobacterium tuberculosis?
Ziehl-Neelsen
Auramine fluorescence
Acid-fast bacilli
What is the clinical presentation of pulmonary TB?
Cough > 3 weeks Weight loss Fatigue Fever Night sweats Haemoptysis Difficulty breathing Mild, non specific malaise
What medical evaluation is needed for suspected TB?
Medical / family history - household contacts Physical exam Tests for TB infection Chest X-ray Bacteriological examination
Describe aerosol transmission of mycobacterium tuberculosis
Droplet nuclei containing 1-3 bacilli
Reach alveolar space, engulfed by macrophages
What happens when a granuloma breaks down?
Bacteria escape and replicate leading to active TB disease
Give examples of sites of TB disease
Larynx Bone Kidney Brain Lymph node Pleura Lung Spine (Pott's disease)
What may be seen on a chest X-ray with MTB?
Infiltrates
Cavities
Ghon complex
What might be seen in a CT scan with MTB?
Tree in bud pattern
Bronchial wall thickening
Decreased volume in right lobe
Describe a latent TB infection
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
Describe active TB disease
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
What drugs are given for pulmonary and extra-pulmonary TB?
4 drugs for 2 months - Rifampicin - isoniazid - ethabutol - pyrazinamide 4 months of: - isoniazide - rifampicin
What are some ongoing problems of TB?
Difficult to diagnose BCG vaccination efficacy (0-80%) Long treatment Poor patient compliance Drug resistance Latent infection Funding / profile / press
Why is non-tuberculosis mycobacteria increasing?
Increased identification
Better clinical recognition
Improvement in other treatments unmasking infection
Improved laboratory techniques for isolation and identification
Give examples of infections acquired by inhalation?
M.kansasii
M.avium
Give examples of infections acquired by ingestion
Disseminated M.avium
What is M.marinum?
Fish tank granuloma
Inhabits water
