PT1: Tuberculosis Pathophysiology, Microbiology and Treatment Flashcards
what bacteria causes TB
mycobacterium tuberculosis
what type of bacteria is mycobacterium tuberculosis
slow growing bacillus
what part of the body does mycobacterium tuberculosis infect
lungs (pulmonary TB)
can spread to other organs
what are the features of acid fast bacteria
cell wall is lipid rich
very hydrophobic, resistant to drying and weak disinfectants
what are the three types of mycobacterium tuberculosis
m. bovis, m. africanum, m. microti
which form of mycobacterium tuberculosis is not pathogenic
m. microti
what types of mycobacterium tuberculosis do not cause disease in immunocompetent people
m. bovis, m. africanum
what occurs in stage 1 progression of primary tuberculosis
bacilli inhaled in droplets, settle in alveoli in lung, start to grow
phagocytosed by macrophages which do not destroy bacilli, so it can survive outside the host
how many organisms are needed to cause infection in primary tuberculosis
<10 organisms
what occurs in stage 2 progression of primary tuberculosis
mycobacterium tuberculosis multiplies inside macrophages for 7-21 days
macrophages burst, incoming macrophages phagocytose released MTB
continues for 3-4 weeks
asymptomatic or mild fever
what happens in stage 3 of progression of primary tuberculosis
cell mediated response initiated, granulomas (tubercules) formed, symptoms appear
what percentage of tuberculosis progresses to latent infection
45-50%
what percentage of tuberculosis progresses to progressive infection
5-10%
what percentage of tubercolosis infections are cleared
45-50%
what occurs during stage 4 of tuberculosis progression
bacteria multiply inside macrophage; uncontrolled lysis means bacteria spread throughout the lungs
enzymes released destroy local tissue causing legions in the lung (pulmonary TB)
what are the symptoms of TB (appearing at stage 4)
cough, afternoon fever, weight loss, blood stained sputum, night sweats
how is active TB diagnosed
clinical examination, chest x-ray, sputum test (smears/cultures), molecular assays
what is the appearance of a chest x-ray for active TB
white lesions replace alveoli with scar tissue
what is the appearance of a sputum test for active TB
visualise bacteria in sputum using staining/microscopy, culture bacteria
what is the appearance of molecular assays for active TB
Xpert MTB/RIF assay
what are the methods of latent TB diagnosis
tuberculin skin test (Mantoux test), molecular tests (interferon-gamma assay)
how does a tuberculin skin test work
tuberculin injected subcutaneously into forearm
positive test is skin lesion >10mm diameter after 48-72 hours
how is TB screened for
chest x-ray, sputum test
when is TB screening compulsory
for people travelling to a country where TB is common if they are staying in the UK for >6 months
needed before visa applications
