Infection 7: Pathogenesis of TB Flashcards
Describe 3 features of M. tb
Bacterium Hydrophobic High lipid content of cell wall Gram stain difficult Slow-growing (generation time ~22h) Special microscopy stains Ziehl–Neelsen Auramine fluorescence “Acid-Fast Bacilli” (AFBs)
What symptoms would a TB patient present with clinically?
Cough (>3wks) Weight loss Fatigue Fever Night sweats Hemoptysis (1/3rd) Difficulty breathing
Describe some tests we would do to diagnose TB (3)
Culture is standard but lengthy
Liquid culture (MGIT) and MODS both culture based but quicker and can do resistance testing (days-weeks). Time to positivity.
Solid media (3-4 weeks)
Smear positive (AFB microscopy)
Molecular methods including PCR increasingly used (GeneXpert MTB/RIF)
Need sputum
How is TB spread?
Droplet nuclei containing 1-3 bacilli
Reach alveolar space
How does TB evade the immune system?
M.tb able to survive within macrophages, which engulf and destroy most other bacteria
List some other sites of TB (8)
brain larynx LN pleura lung bone kidney spine
Describe 2 radiological findings you may expect on a CXR with TB
When a person has pulmonary TB disease, the chest x-ray usually appears abnormal. It may show:
Infiltrates (collections of fluid and cells in lung tissue)
Cavities (hollow spaces within lung)
what sign do you see on CT for TB
tree in bud pattern
how do you get GI TB
Primary infection due to unpasteurized milk
Secondary infection:
- 1° complex elsewhere with reinfection
- ingestion of expectorated, infected sputum - contiguous spread from organs
Compare latent TB and Active TB Disease (7)
inactive vs active bacilli TST + in both CXR normal vs abnormal Sputum smears and cultures neg vs positive no sx vs sx not infectious vs infectious not a case of TB vs a case of TB
treatment of TB
RIPEis the mnemonic used to remember the treatment for TB. It involves a combination of 4 drugs used at the same time: R–Rifampicin for 6 months I–Isoniazid for 6 months P–Pyrazinamide for 2 months E–Ethambutol for 2 months
List some barriers to TB eradication
Difficult to diagnose
BCG vaccination efficacy 0%-80%
Long treatment: 4 drugs for 6 months (need healthcare systems)
Poor patient compliance, need for Directly Observed Therapy (DOT)
Drug resistance (MDR/XDR-TB)
Latent infection (10% lifetime risk of reactivation of TB disease)
Funding/profile/press
what is M.marinum
M.marinum
Fish tank granuloma:
Scratches from fish scales,
Abrasions in non-chlorinated swimming pools
Inhabits water, causes systemic disease in fish
Prognosis poor for fish, Good for humans
Name 2 NTM and the disease they cause
leprosy from m.leprae
buruli ulcer from m.ulcerans
