Session 9: Tuberculosis Flashcards
what causes tuberculosis
mycobacterium tuberculosis
properties of MTB
acid fast
aerobic
how long does the treatment have to last for pulmonary TB
6 months
risk factors for tb
close contacts of infectious TB
countries with high rates of TB
immunosuppressed people
people with weak immune systems
homeles
undernorished
prison
drug misuse
how is TB transmitted
humans with active disease release MTB into the sputum; MTB is transmitted from person to person by infected droplets formed from this sputum being released into the air through coughing, sneezing, speaking etc
what are the possible outcomes of MTB in the lungs
- immediate clearance in the body
- compleye clearance of infection via innate immunity
- complete clearnace via innate and adaptive immunity
- primary infection contained to latent infetion: dormant bacteria present in body but no symptoms
- primary active disease- immediate onset of disease
- post primary Tb - the onset of an active disease years after a period of latent infection
active vs latent disease
if the infection is symptomatic then this is active disease if it is not symptomatic but there are MTB organisms in the body then it is latent infection
how can reactivation of TB occur
In a normal healthy individual whne they get infectied by primary TB they may be symtomatic but the viable organisms remain dormamy in a lesion in the lungs. If the persons immune system is comprimised the infection may be re-actiated
how is infection by MTB preceeded
macrophages are infected
alveolar macrophages phagocytose MTB but cant kill them
T helper cells CD4+ activate macrophages enabling them to be come bacteriacidal with enhanced ability to kill MTB
this takes 4-6 weeks to develop
what is the characteristic lesion of TB fomed by
spherica granuloma which is central caseaous necrosis surrounded by epitheliod macrophages, langhans multinucleated giant cells and lymphocytes
what is the Ghon’s fcus
subpleural focus of tubercles formed due to the deposition of Tb bacilli in the alveoli
ususally in any lung zone
what is the Gohn complex
the primary gohn focus and the draining lymph nodes together
how is latent infection characterised
positive quantiferon test
positive tuberculin skin test
what is the skin test
tuberculin which is a protein derived from mycobacteria is injected intra-dermally
the prescence of a skin reaction 48-72 hours later at the site indicates previous exposure to TB
it occurs due to type 4 hypersensitivity
what is cavity formation and when does it occur
post primary TB
softening and liquefaction of the caseous material whicb us discharged into a bronchus resulting in a cavity formation
what can you get with post-primary TB
haemorrage
spread to rest of lung
pleural effusion
cavity formation
which types of TB lead to miliary pulmonary TB
primary or post primary
how does miliary pulmonary TB occur
when the MT bacteria draining through the lymphatic system enter venous blood and circulate back to the lung
small foci of infection are visible throughout the lungs
what sites does extra-pulmonary Tb occur at
bones CNS joints GI tract urinary tract adrnal glands lymph nodes
how do you diagnose tb in patients with ACTIVE lumg disease
acid-fast smear
culture of sputum
how do you diagnise TB in LATENT infectio
manoux
skin test
IFN-gamma assay
what is diadvantage of skin test/IGRA
doesnt differentiate between latent infecyion and peple who have had the BCG vaccine or infection with atypical mycobacterium
people with dysfunctional or suppressed immune systems or peiple with active TB may have falsely negative tests
what would a CXR show in TB
pulmonary shadowing
- patch lesions
- caviated solid lesion
- streaky fibrosis with flecks of calcification
- hilar adenopathy
what comnination f antibiotics are used to treat TB
rifampicin
isoniazid
pyrazinamide
ethambutol
