Pathology of Tuberculosis (TB): Part 1 - aetiology, risks and diagnosis & Signs and symptoms Flashcards
aetiology
what bacterium causes TB in majority of cases
- Mycobacterium tuberculosis
what does mycobacterium tuberculosis being an obligate aerobe mean and what does this means for the lungs?
- means it likes oxygen rich environments
- lungs is ideal place for growth for this bacterium
What are the 2 MAIN ways can Mycobacterium tuberulosis be spread
- airborne droplets
- dust microbe particles
what are 5 features of Mycobacterium tuberculosis
- acid fast
- slow rate of growth
- sensitive to heat and UV radiation
- non-motile
- likes highly oxygenated tissue (obligate aerobe)
what was mycobacterium tuberculosis first identified?
first identified in 1882
why does M. Tuberculosis have a slow rate of growth and what does this mean for diagnosis?
- Slow rate of growth due to lipid coat
- makes diagnosis by culturing difficult
risk factors
what are 2 categories for people who are at high risk for developing TB
- people who have been recently infected with TB bacteria
- people with medical conditions that weaken the immune system
what are 5 ways higher incident rates can occur due to people who were recently infected with TB bacteria
- close contact with people with TB disease
- people who migrated from areas of the world with high TB rates
- children less than 5 years of age who have a positive TB test
- groups with high rates of TB like homeless persons and persons with HIV infection
- persons who work or reside with people who are at high risk of TB in facilities like hospitals and homeless shelters.
outline 9 medical conditions/diseases that cause a weakened immune system which can increase incidence of TB
- Substance abuse
- Silicosis
- Diabetes mellitus
- Severe kidney disease
- Low body weight
- Medical treatments such as corticosteroids or organ transplant
- Infection with HIV
- Head or neck cancer, leukaemia, or
Hodgkin’s due to it being metastising - being a baby or young as they have weaker immune systems usually
what are 2 other bacteriums that can cause TB disease
- M. bovis (from unpasteurised cow milk)
- M. africanum
write out 5 characteristics of latent TB infection
- no signs or symptoms
- host defences prevent growth of bacteria
- not infectious and cannot pass infection on
- skin or blood test might be postive for the bacteria
- normal chest X-ray
Outline out 6 characteristics of TB disease (Active TB)
- primary infection/activation of latent TB
- signs and symptoms/patient feels sick
- CAN spread infection
- skin or blood test positive
- may have abnormal chest X-ray or sputum sample
- requires treatment to resolve
diagnosis
what are 5 ways you can test and diagnosis TB?
- skin test
- microbiological sampling
- blood test
- molecular testing
- imaging
outline 3 steps for how the tuberculin skin test works
- 0.1ml of tuberculin derived protein is injected into skin of forearm
- wait 72 hours
- measure diameter of palpable, raised hardened area/swelling (Not an erythema)
what are the 2 names for the TB skin test
- tuberculin skin test
OR - Mantoux test
what is the drawback of the Tuberculin skin test
- a positive test could mean a person has latent TB infection, not necessarily TB disease/ active TB
what signifies a positive test in the Tuberculin skin test
- 5mm or larger palpable raised hardened area on skin
2 steps for microbiological sampling for diagnosing TB?
- 3 sputum analyses are taken and are stained using ziehl Neelsen techniques.
- the stain stains the acid lipid coats around TB to reveal their slender rod shape
what are 2 types of microbiological sampling methods for diagnosis of TB
- Ziehl Neelson stain
- flurescence labelling
IGRAs
outline how the Interferon-Gamma release assays work for diagnosing TB
- blood is taken from patient
- ELISA is run
- white blood cells from infected persons release IFN-𝛄 upon M. tuberculosis antigen exposure
- Increased IFN-𝛄 in the blood sample will determine if someone has TB disease
what is the drawback of the Interferon-Gamma release Assays (blood test)
it is expensive
what is the name of the interferon-gamma release assay diagnostic test for TB
QuantiFERON-TB Gold In-Tube test
what are the nice guidelines on molecular testing (NAAT) for if someone has TB
Only request if there is clincial suspicion of Pulmonary TB,
AND:
- the person has HIV
OR
- rapid information about mycobacterial species would alter the person’s care
OR
- the need for a large contact-tracing initiative is being explored
outline the 2 steps of how molecular testing (NAAT) works for diagnosing TB?
- nucleic acid from mycobacterium in patient’s blood or sputum is amplified.
- amplified so much to the point that nucleic acid from mycobacterium causing TB should be detectable
what does the type of diagnostic imaging for TB depend on
depends on where specifically the site of investigation is in the person’s body
what is the main type of diagnostic imaging for TB and why
MAIN TYPE:
- Chest X-ray/ Thoracic CT scan
- this is because pulmonary TB is the main type of TB infection
what are 3 examples of diagnostic imaging techniques for TB other than Chest/thoracic X-Ray/CT and state the type of TB infection they would be used for
chest X-ray/bronchoscopy:
- used for Pleural TB
Ultrasound/CT/MRI:
- used for lymph node TB
CT/MRI:
- used for CNS TB
what out 7 symptoms of active TB infection
- persistent cough
- constant fatigue
- weight loss
- loss of appetite
- fever
- coughing up blood
- night sweats
what symptoms (non-specific) would a patient in the primary stage of TB infection have?
may be asymptomatic or have mild flu symptoms
what 4 symptoms (specific) would someone have if they have a reactivated TB infection?
- gradual onset of anorexia
- weight loss
- fever (low grade)
- night sweats
if someone has active TB infection of the lung what 3 symptoms are they likely to see
- cough lasting longer than 3 weeks
- sputum (purulent) potentially containing bacilli
- haemoptysis
if someone has active systemic TB infection, what 3 symptoms are they likely to see
- many-local infection (multiple infection sites)
- swelling in neck
- headache and neurological deficit form brain metastasis
