PBL 8: Fasial Shah Flashcards
What is the cause of TB?
Mycobacterium tuberculosis (rod shaped mycobacterium)
What are the types of mycobacterium?
M. leprae (causes leprosy)
M. africaanum
M. bovis
What are some features of mycobacteria?
Strong lipid rich cell wall so:
- grow very slowly
- stain resistant
- antibody resistant
- require cell mediated immunity
- can liver inside macrophages and use them as a host
Like oxygen rich environments - e.g. the lungs
Who are the CCDC?
Consultant in Communicable Disease Control
Monitor outbreaks, epidemiological trends for tracing
How is TB transmitted?
Bacteria travel in the air via water droplets which are expelled by those infected who are coughing/speaking/sneezing/singing/laughing
Gets inhaled by someone who is not infected
If individual is healthy they can fight off the infection but if not they become ill
What does transmission of TB depend on?
Infectiousness of the individual spreading it
Virulence of the mycobacterium
Healthiness of the individual being exposed
Length of time of exposure
Environment of the exposure - i.e. if it is crowded or not
What is the pathophysiology of TB?
- Inhale mycobacterium from the air and it enters the lungs as it likes/thrives in oxygen rich environments
- recognise as foreign and so there is an acute inflammatory response (neutrophils phagocytose the bacteria and sequester it into a phagosome releasing toxic compounds)
- if individual is immunocompromised/malnourished the infected neutrophils cannot get through the thick waxy protein coat of the mycobacterium
- neutrophils release cytokines and die = caseous necrosis with the bacteria trapped inside
- macrophages and T lymphocytes come due to the cytokine signalling and accumulate in rings around the caseous necrosis to phagocytose the bacteria but some still survive
- macrophages fuse releasing cytokines which attract lymphocytes (lymphocyte collar) forming a langhan cell
- fibroblast wall forms around the langhan cell forming a granuloma = ghon focus
- fibroblasts deposit collagen and together with calcium seals off the ghon focus to stop the bacteria escaping
What is post primary TB?
Sealed ghon focus already formed in the lungs
- becomes immunocompromised/malnourished so alive bacteria trapped inside can now escape so you get symptoms
- immune system responds to contain bacteria again and kill them
What is primary progressive TB?
Sealed ghon focus already formed in the lungs
- becomes immunocompromised/malnourished so alive bacteria trapped inside can now escape so you get symptoms
- cannot mount a vigorous enough response so the bacteria escape and spread resulting in granuloma enlargement in lymph nodes
What is extra-pulmonary TB?
In primary progressive TB bacteria can spread to pleura, CNS, lymphatics, GI, bones and joints
What are the main signs of TB?
Fever, malaise, weight loss, night sweats, cough, chest pain, haemoptysis
What is night sweats a sign of?
Chronic infection
What are the main diagnostic methods?
CXR
Mantoux Test
Sputum Sample and culture
Sputum to stain
What would a chest x-ray show?
Hilar shadowing
Opaque regions in the upper zones
Nodular patchy cavitation
Calcification
How does sputum staining take place?
Cannot use normal stain as mycobacterium is resistant to it
Have to use special ziehl-neelson staining which shows mycobacteria as pink rods
Also can use fluorescent staining
