Infection 7: Pathogenesis of TB Flashcards

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1
Q

Describe 3 features of M. tb

A
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)
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2
Q

What symptoms would a TB patient present with clinically?

A
Cough (>3wks)
Weight loss
Fatigue
Fever
Night sweats
Hemoptysis (1/3rd)
Difficulty breathing
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3
Q

Describe some tests we would do to diagnose TB (3)

A

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

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4
Q

How is TB spread?

A

Droplet nuclei containing 1-3 bacilli

Reach alveolar space

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5
Q

How does TB evade the immune system?

A

M.tb able to survive within macrophages, which engulf and destroy most other bacteria

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6
Q

List some other sites of TB (8)

A
brain 
larynx 
LN
pleura 
lung 
bone 
kidney 
spine
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7
Q

Describe 2 radiological findings you may expect on a CXR with TB

A

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)

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8
Q

what sign do you see on CT for TB

A

tree in bud pattern

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9
Q

how do you get GI TB

A

Primary infection due to unpasteurized milk

Secondary infection:

- 1° complex elsewhere with reinfection

 - ingestion of expectorated, infected sputum 
 - contiguous spread from organs
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10
Q

Compare latent TB and Active TB Disease (7)

A
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
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11
Q

treatment of TB

A
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
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12
Q

List some barriers to TB eradication

A

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

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13
Q

what is M.marinum

A

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

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14
Q

Name 2 NTM and the disease they cause

A

leprosy from m.leprae

buruli ulcer from m.ulcerans

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