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Flashcards in Lec 8 TB Deck (27):

What is morphology of mycobacterium tuberculosis?

aerobic rod-shaped bacterium
acid-fast bacilli
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]
- alcoholism
- malignancy


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?

6-8 wks


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

pleura effusion

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
- culture


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]


Who gets non-TB mycobacteria?

- pts with underlying lung disease who are immune compromised
- pts with systemic immunity = AIDS

can be localized to lung and mimic TB or hematogenously disseminate in body [particuarly in AIDS]