Dr. Behr -- Tuberculosis Flashcards Preview

Block G -- Infection > Dr. Behr -- Tuberculosis > Flashcards

Flashcards in Dr. Behr -- Tuberculosis Deck (43)
1

Define tuberculosis

The diseased state:

  • Actively replicating bacteria
  • Contagious, culture positive

2

Define tuberculous infection

The carrier state

  • Clinically latent (latent TB infection/LTBI)
  • Non-infectious, tuberculin positive

3

Bacteria responsible for tuberculosis and tuberculous infection

Mycobacterium tuberculosis

4

Cause of avian TB

Mycobacterium avium

5

Hypothesized cause of Crohn's disease

M. avium paratuberculosis

6

Environmental bacterium that causes TB-like disease in miners with silicosis

M. kansasil

7

Cause of leprosy

M. leprae

8

Place of origin of M. tuberculosis and its geographic journey (4)

  1. Africa
  2. Paleo-migration --> Europe (by foot)
  3. Colonization of Americas (by ship)
  4. Fur trade = All across Canada (by canoe)

9

What kind of organism is M. tuberculosis (i.e. its behavior with humans)

  • Pathogen
  • Symbiont

10

How is M. tb an educated pathogen?

  • Localized, chronic pathology = ambulatory host and transmission
  • (As opposed to organisms such as Legionella pneumonia, which is a diffuse, fast disease with a very sick host and no transmission)

11

3 potential outcomes after TB exposure and their respective frequencies

  1. No infection
    • `(?; 2/3 don't test +)
  2. Infection, no disease 
    • (90% if immune status OK)
  3. Infection, disease +/- death
    • 5% in 2 years
    • 5% in rest of life

12

3 reasons why a few progress to TB

  • Age (infants)
  • Acquired immune deficiency
    • HIV+, steroids, Anti-TNF
  • Natural immunity
    • Genetics: people who progressed 1st time and are cured = 5x higher rate of TB than community

13

Where M. tuberculosis ends up in the human body

Alveoli of lungs (in alveolar macrophages)

14

2 options for the outcome of M. tb in alveolar macrophages

  1. Kill bacteria on contact --> no infection, tuberculin -
  2. Permit bacterial infectoin (Ghon focus)
    • Infection
    • TB positive
    • Attraction of other cells to aggregate --> granuloma

15

3 components of a granuloma

  1. Macrophages
  2. Lymphocytes
  3. Fibrous ring

16

How does M. tb end up in hilar lymph nodes?

Dendritic cells via lymphatics

17

2 options for the outcome of M. tb in hilar lymph nodes

  1. Chronic localized lymphadenitis
  2. Further spread

18

2 ways that TB can further spread if in hilar lymph nodes

  1. Up lymphatics via thoracic ducts --> hematogenous seeding
  2. Through lymphatics, within lungs --> areas of lowest vacular perfusion (apex)

19

Non-transmissible TB

TB meningitis

20

M. tb reservoir host

Human (rarely from animals)

21

% of world's population infected by M. tb

1/3

22

Cause of death in ~25% of AIDS

TB

23

Strongest risk factor for progression of TB infection to disease

HIV infection

24

4 general clinical manifestations of TB

  1. Fever
  2. Sweats
  3. Weight loss
  4. "Consumption"

25

2 contagious organ specific clinical manifestations of TB

Pulmonary

  • Cough
  • Sputum +/- blood

26

5 organ-specific non-contagious clinical manifestations of TB

  1. Scrofula = swollen lymph nodes
  2. Genitourinary = sterile pyuria
  3. Bone = back pain, fracture, "hump-back"
  4. Meningitis = headache, obtundation
  5. Miliary TB (no obvious site)

27

Number of sputum specimens for smear exam and culture

3

28

3 things to do if patient is unable to cough up sputum

  • Induce sputum (kids too)
  • Bronchoscopy
  • Gastric aspiration

29

Positive AFB smear

Red rods = tubercle bacilli

30

Purpose of cultures in TB diagnosis and how long results take

  • Confirmation
  • 2 - 3 weeks

31

Compare PCR sensitivity to other forms of TB diagnosis

  • Better than microscopy
  • Not as good as culture

32

2 situations where PCR use is appropriate in TB diagnosis

  1. AFB smear + and want quick answer to what bacteria is present
  2. New, rapid test by Cepheid for developing world (including Nunavik)

33

2 situations where PCR has limited utility in TB diagnosis

  1. AFB smear negative
  2. Non-pulmonary sample

34

Length of short course treatment for TB

24 weeks

35

3 points for prioritizing TB control

  1. Identify and treat active TB to reduce # of contagious persons
  2. Identify contacts of cases, test for infection, provide chemoprophylaxis
  3. Identify people with patent infection as potential candidates for chemoRx

36

2 possible causes of a false-positive PPD

  1. Nontuberculous mycobacteria
  2. BCG vaccination

37

5 possible causes of false-negative PPD

  1. Anergy
  2. Recent TB infection
  3. Very young age (<6 months old)
  4. Live-virus vaccination
  5. Overwhelming TB disease

38

New test for TB detection

IFN-gamma release assays

39

Platform of IFN-gamma release assays

From skin to lab ELISA

40

Advantage of IFN-gamma release assays

Specificity in face of BCG vaccination

41

Disadvantage of IFN-gamma release assays

Poor reproducibility

42

LTBI treatment

Isoniazid for 9 months

43

Efficacy of BCG vaccination against peditric TB

80%