TB and mycobacterial infection Flashcards
how is TB related to poverty
increased rates where poverty is
TB causes poverty for individual and family - because long term illness when cant make money
what are the mycobacteria that cause TB
M. tuberculosis (effects humans)
M. bovis (1% of human TB is caused by M bovis – look for it in cattle/badgers)
M. africanum
M. microti
M. canetti
how is TB transmitted
Classic TB presentation is in chest – can get it everywhere in the body.
Cant pass on if in bones for e.g.
Can pass in cough, sneeze, speaks, sings (laryngeal TB)
Aerosol transmission – droplet size small so hangs like fog in the air.
transmission happens when inhale droplet nuclei
Stain the red organisms – sputum smear positive mycobacterium
But don’t know whether its actually TB
what are some non TB mycobacteria
M chelonae (in fish) (right)
M abscessus and CF (hard to eradicate, would stop transplant for CF)
M avium eg HIV
M chimaera-vascular bypass device
NOT ALL AFB are TB!
what changes the probability that TB will be transmitted
Infectiousness of person with TB disease
Environment in which exposure occurred
Length of exposure
Virulence (strength) of the tubercle bacilli
how to prevent TB transmission
Isolate infectious persons
Provide effective treatment to infectious persons as soon as possible
summarise latent TB
1/4-1/3 of world’s population have latent TB
-> risk of developing active disease
Post TB infection, 10% lifetime risk for active TB =dogma; 30-50% active TB if HIV positive
Latent infection: prevent active TB = diagnosis +chemoprophylaxis
Fever+Wt loss+Night sweats+cough (2-3 wks)
Disease can occur decades later but rare
TB grows very slow – about once a day (every 18hr) – so always interval between being infected and having active TB
Don’t always have all of the symptoms
summarise latent TB
1/4-1/3 of world’s population have latent TB
-> risk of developing active disease
Post TB infection, 10% lifetime risk for active TB =dogma; 30-50% active TB if HIV positive
Latent infection: prevent active TB = diagnosis +chemoprophylaxis
Fever+Wt loss+Night sweats+cough (2-3 wks)
Disease can occur decades later but rare
TB grows very slow – about once a day (every 18hr) – so always interval between being infected and having active TB
Don’t always have all of the symptoms
how do you diagnose latent TB
Mantoux with PPD or
gamma interferon release assays (IGRA) - count gamma releasing T cells – a lot of spots = likely to be affected
what is the incubation period for TB
3-9 months and almost always under two years
why are rates of ltent TB overestimated
reflects immunoreactivity to either past or present infection.
Does not indicate the presence of live bacteria, as reactivity can persist after infection has been cleared
do you need rx for latent TB
If its getting towards 3yrs since had infective contact – probably don’t need treatment – but let people know if going to be immunosuppressed
what is the treatment of drug sensitive TB
2mo:
* Isoniazid
* Rifampicin
* Pyrazinamide
* Ethambutol
For 4 months
* Rifampicin and Isoniazid
daily, PO (or 3x/wk)
total 6mo
12mo for TB meningitis
Baseline checks incl CXR, LFT, FBC, UandE, CRP,
What are the limits of TB detection of different methods?
Microscopy ZN stain – smear – know infectious
Flurescnet based microscopy – bit more sensitivity
Solid culture – takes 4-6wks
Liquid culture 2wks
Molecylar tech – a daY
how do you analyse resistance to TB meds
phenotypically ie microbiologically – TB grow in liquid, if grow with Abx - then resistant
Amplify DNA:
molecular line probe assays - PCR amplification of genes associated with resistance -> hybridisation with DNA probes on membranes -> development, reading adn interpretation of results
PCR based: Line probe assays (TB, RIF, INH from sputum eg
Genotype MTBDRplus
GenXpert (TB, RIF from sputum)
LAMP, WGS
DIAGNOSTIC TARGET PRODUCT PROFILES
use of whole genome sequencing in TB
what is (next generation sequencing) NGS and WGS
WGS and NGS are used synonymously but are not the same
WGS – is sequencing the genetic material
Next gen sequencing is the method
Take out DNA – smash into pieces – sequence them – stick along reference
