TB Flashcards
What pathogen causes TB?
Mycobacterium Tuberculosis
How would you describe the pathogen that causes TB?
Acid fast bacilli
Stains Bright Red with Ziehl-Neelsen stain
How is TB contracted?
How does it spread?
by inhaling saliva droplets
via blood and lymph nodes
What is a Ghon Focus?
What is a Ghon Complex?
what does this lead to?
Lesion in the lungs, contains macrophages
macrophages frequently spread to regional lymph nodes
lung lesion + affected lymph node = Ghon Complex
leads to formation of a granuloma (containing the bacteria) to develop around the body. Granulomas have caseous necrosis at the centre.
Which inflammatory response mediates TB
Type 4 hypersensitivity
What is active TB
How does the initial lesion heal in healthy individuals
Active infection in various areas of the body
in majority of cases body is able to kill and clear infection
In healthy individuals, heals by fibrosis
What is latent TB?
What is Secondary TB?
Immune system may encapsulate sites of infection and stop the progression of disease
when latent TB reactivates (usually in the immunpcompromised)
Where does secondary (post-primary) TB develop?
generally in the apex of the lung
may spread locally or to more distant sites
What is disseminated TB
when the immune system is unable to control the infection
severe disease is called Milliary TB
What are causes of immunocompromise ?
- immunosuppresive drugs including steroids
- HIV
- malnutrition
Where may extra-pulmonary infection occur?
- lymph nodes (cold abcess)
- pleura
- pericardium
- CNS
- gastrointestinal system
- GU system
- bones and joints
- cutaneous TB affecting skin
How does TB present?
- Lethargy
- Fever +/- night sweats
- cough +/- haemoptysis
- weight loss
- lympadenopathy
- erythema nodosum
- spinal pain in spinal TB - potts disease of the spine
What does the BCG vaccine contain
live, attenuated mycobacterium bovis
What is the BCG vaccine good at protecting against?
severe and complicated TB
less effective at protecting against pulmonary TB
What must you do prior to BCG vaccination?
Do a Mantoux test
give vaccine only if this test is negative
Who should be given a BCG vaccine?
- Neonates born in areas of the UK with high rates of TB
- Neonates with relatives from countries with a high rate of TB
- Neonates with a family history of TB
- Unvaccinated older children and young adults (< 35) who have close contact with TB
- Unvaccinated children or young adults that recently arrived from a country with a high rate of TB
- Healthcare workers
What are contraindications to BCG vaccine?
- previous BCG vaccine
- previous TB
- positive tuberculin test
- HIV
- pregnancy
What investigations can you do for Latent TB? drawbacks?
Mantoux test
Interferon Gamma release assay
How does the Mantoux test work
When is it considered positive?
What must you then do?
will be positive in cases of previous exposure e.g BCG vaccine or latent TB
if induration and erythema > 10mm = positive result
if strongly positive TB is likely. response to BCG decreases over time
Need to do further Ix e.g Chest Xray
How does IGRA work
blood test
looks for latent TB
used for confirmation if positive mantoux or had a previous BCG
How do you diagnose active TB? Which is gold standard?
- CXR
- Sputum smear - stained for zeihl-neelsen
- Sputum culture gold standard
- Nucleic Acid Amplification Test (NAAT)
What is the classical finding on CXR in TB
upper lobe cavitation (usually not primary)
bilateral hilar lympadenopathy
What is the added benefit of sputum culture in TB?
how many samples are needed?
can assess drug sensitivties
3 samples need to be tested
How do you manage latent TB?
Isoniazid and Rifampicin for 3 months
or
Isoniazid for 6 months
