Flashcards in Lec 8 TB Deck (27):
What is morphology of mycobacterium tuberculosis?
aerobic rod-shaped bacterium
not dyed by gram stain
What is pathogenesis of TB infection?
- primarily intracellular
- slow growth rate
- induces granulomatous response in normal host
How is TB transmitted?
small aerosol droplets w/ close contact
not transmitted by fomites [articles of clothing, eating utensils]
What happens in primary TB infection?
- droplets containing mycobacteria reach alveoli --> develop primary Ghon lesion
- alveolar macrophages are defense
- organism spreads via hilar lymph nodes via lymphatics = Ghon complex or travels via blood stream
in majority of pts, body's defense mech controls and limits primary infection
Which pts are at risk for having clinially apparent primary TB?
- medications [immunotherapy, immune suppressant]
What is delayed hypersensitivity in TB?
- develops a few wks after primary infection
- cell mediated immunity
hallmark = development of granulomas + can have caseous necrosis + multinucleated giant cells
high Ca deposition here is why it shows up
How is granuloma formed?
alveolar macrophage in contact with TB --> sends out cytokines to recuit T cells
IFN-gamma and TNF-alpha are important in development
IFN-y by T cells; TNF-a by macrophage
What is latent TB? how likely does it happen?
small number of TB organisms remain in granuloma in latent state
can develop reactivation
- over lifetime ~10% of normal immune with latent TB develop reactivation; [5% within 2 yrs; 5% after that]
- if HIV = 10% PER YEAR
When does skin test conversion develop?
What does TB skin test test? Who gets false pos/neg?
- put small amount of purified protein [PPD] from TB intradermally
- those with acquired cell immunity to TB will get swelling at injection site
- does not distinguish between active TB and previous infection
false positive if past infection with other not tuberculous mycobacteria
false negative if depressed cell immunity
What is interferon gamma release assay [IGRA]?
take blood + expose to antigens specific to TB --> cells process it and measure IFN-gamma presented by T cells
helps with false positives but not false negatives
What is definition latent tuberculous infection?
+ PPD or +IGRA but no evidence of active disease
WHat is defintion TB disease aka active TB?
presence of clinically active disease in 1 or more organ systems ideally with confirmation of diagnosis by isolation of organism
What is defintion primary TB?
disease after initial exposure
What is definition primary progressive TB?
primary diease that has not been controlled by immune defense mech --> continues to be active beyond point at which delayed hypersensitivity has developed
What is reinfection TB?
disease in previously infected person results from exposure to another source of organisms
How does TB spread in body?
- during primary infection via blood stream
- can also spread hematogenously to other parts of lung
What are characteristic location of reactivation TB?
apical regions of upper lobes b/c less perfused + high PO2 = good for survival
and less so--> superior segment of lower lobes
What are clinical feature of TB?
- consumption = weight loss, wasting, loss of appetite
- fatigue, low fever, night sweats
- scarring and loss of lung tissue but resp function generally preserved
pulm symptoms: cough, sputum, hemoptysis
usually insidious rather than acute onset
What do you see in chest radiograph from primary TB?
nonspecific infiltrate often in lower lobes
hilar lymphe node enlargement
when primary disease heals --> small calcified lesions
What do you see in reactivation TB on chest radiograph?
apical/posterior segments of upper lobes more affected
infiltrates, cavities, nodules, scarring, contraction
What is miliary TB?
progressive widely disseminated hematoenous spread of TB
can arise as result of progressive primary infection or via reactivation
How do you diagnose TB?
- stain smears from sputum
- nucleic acid amplification
What is treatment for TB?
need for ~6 months
Why do you have to test for latent TB before starting anti-TNF
to make sure you don't give anti-TNF which inhibits granuloma formation
WHat is most common organism of atypical mycobacteria?
mycaobacterium avium complex [MAC]