Pathogenesis of TB Flashcards
What is tuberculosis?
a contagious, debilitating (consuming) bacterial disease
spread by airborne droplet nucleii from an infected person
What bacterium causes TB?
mycobacterium tuberculosis
What are symptoms of tuberculosis?
- A cough that will not go away
- Feeling tired all the time
- Weight loss
- Loss of appetite
- Fever – low grade
- Night sweats
- dyspnoea
- Multi-organ dysfunction or adrenal insufficiency
How does the cough in tuberculosis progress?
Initially mild non-productive
later is productive
haemoptysis
What are the symptoms like in latent TB infection compared to active TB disease?
-Latent TB has no symptoms
-Active TB has symptoms
How infectious is TB when comparing between latent TB infection and active TB disease?
-In latent TB infection, you cannot spread TB to others
-In active TB disease, it my spread TB to others
What is the comparison between in tests between latent TB infection and active TB disease?
-Latent TB infection usually has a positive skin test for quantiFeton-TB gold test
-Active TB disease usually has a positive skin test
What is the comparison between x-ray in latent TB infection and active TB disease?
-Latent TB has a normal chest x-ray and negative sputum test
-Active TB has an abnormal chest x-ray, or positive sputum smear or culture
What are BCG’s ineffective for in latent TB?
BCG largely ineffective for adult pulmonary disease
What are the risk factors for reactivation of TB?
- Malnutrition
- Poverty
- Immunosuppression
- Diabetes
- Old age
- Poor health
- HIV
What does an initial infection with mycobacterium tuberculosis produce?
Initial infection with Mycobacterium tuberculosis in an
immunocompetent individual usually occurs in an
upper region of lower lobe of the lung producing a lesion called
a Ghon focus
Why is granulomatous involvement of peribronchial and/or hilar lymph nodes frequent in primary tuberculosis?
Granulomatous involvement of peribronchial and/or hilar lymph
nodes is frequent in primary tuberculosis due to lymphangitic
spread from the Ghon focus.
What constitutes the Ghon complex?
The early Ghon focus together with the lymph node lesion
constitute the Ghon complex.
What do the lesions in the Ghon complex undergo over time and what does this lead to?
These lesions undergo healing and over time usually evolve to
fibro-calcific nodules.
What may follow primary infection of TB or reactivated TB?
Miliary TB
What is seen in miliary TB?
Lung, enlarged lymph nodes
(part of original Ghon complex)
are seen, plus miliary tubercles in lung parenchyma
When does miliary TB typically occur?
Miliary tuberculosis, as seen here, typically occurs when resistance to mycobacterial infection
is poor and often in children as consequence of primary disease
What object is typically present in miliary tuberculosis?
The small millet seed sized granulomas in this lung are typical for miliary tuberculosis
When can cause second degree intestinal TB?
Intestinal tuberculosis can be
2º to pulmonary TB from
swallowed infected sputum
What causes first degree intestinal TB?
1º intestinal TB develops in
people who drink milk
infected with M. bovis
How does TB in brain and meninges present?
- Thickened and opaque meninges
-Small tubercles are present within the brain
In what category were the characteristic of TB in brain and meninges common and in whom are they rarely seen?
This used to be a common complication in children with post-1 ̊ miliary
TB. It is rarely seen in people who have had BCG vaccination
What is potts disease?
A form of musculoskeletal tuberculosis
What is scrofula?
TB of the neck leading to swollen lymph node
What is the food in immune response against TB?
*Innate immunity: alveolar macrophages kill ingested
bacilli
*Th1 adaptive immune response: CD8 and CD4 T cells,
IFN-gamma: essential for controlling infection
What is the bad in immune response against TB?
Excessive immune response leads to overproduction of
TNF-alpha and healthy tissue damage by macrophages
(immunopathology of TB - granuloma).
How does TB live inside of a host macrophage?
- Phagocytosis of mycobacteria
- Mycobacteria escapes into cytoplasm
- Mycobacteria inhibits phagosome-lysosome(PL) fusion and maintains early endosome. Also blocks acidification
What does mycobacteria control and stop?
-Controls antigen presentation
–This stops recruitment of CTL’s and blocks macrophage activation
In TB granuloma, what does containment of infection lead to?
Tissue damage
What do TB granuloma consist of?
spherical collection of lymphocytes,
macrophages and epithelioid cells
with a small area of central
caseation necrosis
What does the centre of a granuloma undergo and what does this to produce and why is this important?
The centre of the granuloma undergoes a combination of
liquefaction and coagulative necrosis producing caseous necrosis,
which is unique to TB and causes considerable tissue destruction to the host
What is the mantoux test?
Method of determining whether an individual is infected with mycobacterium tuberculosis
What does a positive mantoux test mean?
If there is a bump of a certain size at site of injection, it means there probably is mycobacterium tuberculosis present
What is the blood diagnosis of pulmonary TB?
Interferon (IFN)-gamma blood test.
- T-cell response to Mtb proteins
What is the sputum diagnosis of pulmonary TB?
cough or induced
- smear, culture,
- GeneXpert - PCR
Bronchoscopy - BAL
Biospy
