B3.025 Tuberculosis

Question 1

which bacteria causes TB?

Answer 1

mycobacterium tuberculosis

Question 2

describe the physical characteristics of m.tuberculosis

Answer 2

rod shaped
non spore forming
thin
aerobic
acid-fast bacilli

Question 3

why is m.tuberculosis acid fast?

Answer 3

high content of mycolic acids
long chain cross linked fatty acids
call wall lipids

Question 4

how is TB transmitted?

Answer 4

droplet nuclei which are aerosolized by coughing, sneezing, or speaking
TB patients with sputum that contains AFB visible by microscopy are most likely to transmit the infection

Question 5

what is one of the most important factors in transmission of TB

Answer 5

crowding in poorly ventilated rooms

Question 6

what is primary TB

Answer 6

clinical illness directly following infection
common among children and immunocompromised
not associated w high level transmissibility

Question 7

what is secondary TB

Answer 7

bacilli persist for years before reactivation
frequent cavitation
more infectious
developed in 10% of infected patients, higher in those w HIV

Question 8

how are TB bacilli able to survive during transmission?

Answer 8

small fraction reach alveoli
adhesion to macrophages
phagocytosis occurs
bacterial cell wall lipoarabinomannan inhibits phagosome-lysosome fusion and bacilli survive
bacterial factors also block host defense’s autophagy

Question 9

how is TB spread within a person?

Answer 9

bacilli replicate within a macrophage
eventually bursts, spilling contents
infect neighboring cells

Question 10

what are the two host responses to m.tuberculosis 2-4 weeks after infection?

Answer 10

macrophage activated CMI response

tissue damaging response

Question 11

describe the macrophage activating response

Answer 11

T cell mediated phenomenon resulting in the activation of macrophages that capable of killing and digesting tubercle bacilli

Question 12

describe the tissue damaging response

Answer 12

result of delayed type hypersensitivity (DTH)
destroys unactivated macrophages that contain multiple bacilli
causes caseous necrosis of involved tissues

Question 13

when do granulomatous lesions form?

Answer 13

accumulation of large numbers of activated macrophages

some can contain the spread of mycobacteria, some cannot > leads to “latency”

Question 14

what is the cellular mechanism of the TB skin test?

Answer 14

CD4+ T lymphocytes being attracted to skin-test site
proliferate and produce cytokines
DTH is associated with protective immunity BUT does not confer protection against reactivation

Question 15

what are the two classes of clinical TB?

Answer 15

pulmonary

extrapulmonary

Question 16

what are the two classes of pulmonary Tb

Answer 16

primary

secondary

Question 17

primary pulmonary TB

Answer 17

soon after initial infection
fever, pleuritic chest pain
seen in children
middle and lower lung zones

Question 18

what lesion can be formed in primary pulmonary TB?

Answer 18

Ghon focus

usually peripheral and accompanied by transient hilar or paratracheal lymphadenopathy

Question 19

pleural effusion due to primary TB

Answer 19

2/3 of cases

penetration of bacilli into pleural space

Question 20

secondary pulmonary TB

Answer 20

“adult type” TB
endogenous reactivation of distant LTBI or recent infection
apical and posterior upper lobes
satellite lesions can form due to bronchogenic spread

Question 21

symptoms and signs of TB

Answer 21

fever
night sweats
weight loss
anorexia
malaise
weakness
cough in 90% of cases
cough eventually becomes accompanied by sputum, sometimes w blood streaking

Question 22

what % of TB cases devlop hemoptysis?

Answer 22

20-30%

Question 23

extrapulmonary sites commonly involved in TB

Answer 23

lymph nodes
pleura
GU tract
bones and joints
meninges
peritoneum
pericardium

Question 24

what happens in HIV individuals w TB?

Answer 24

hematogenous dissemination

Question 25

key to diagnosis of TB

Answer 25

high index of suspicion

Question 26

describe AFB microscopy in the diagnosis of TB

Answer 26

microscopic exam of sputum or tissue
inexpensive
low sens (40-60%)
2-3 sputum samples collected in early morning

Question 27

traditional AFB microscopy method

Answer 27

light microscopy on specimens stained with Ziehl-Neelsen basic fuchsin dyes

Question 28

modern method

Answer 28

auramine-rhodamine staining and fluorescence microscopy
more sensitive
more expensive

Question 29

nucleic acid amplification technology

Answer 29

rapid confirmation of TB in persons with AFB positive specimens
Xpert MTB/RIF assay
-can detect TB and rifampin resistance in <2 h

Question 30

culture of m.tuberculosis

Answer 30

slow, 4-8 weeks

Question 31

what drugs are tested in TB for resistance?

Answer 31

isoniazid

rifampin

Question 32

what drugs are tested for when MDR-TB is found?

Answer 32

second line

fluoroquinoloes and injectables most commonly

Question 33

what are the aims of TB treatment?

Answer 33

1. prevent morbidity and death by curing TB while preventing the emergence of drug resistance
2. to interrupt transmission by rendering patients noninfectious

Question 34

what 4 drugs are considered 1st line treatment for TB?

Answer 34

isoniazid
rifampin
pyrazinamide
ethambutol

Question 35

why are these 4 drugs recommended?

Answer 35

well absorbed
bactericidal activity
sterilizing activity
low rate of drug resisitance induction

Question 36

treatment regimen of choice

Answer 36

2 month phase of all 4 drugs
4 month phase of isoniazid and rifampin
cures 90% of patients

Question 37

what are the 6 classes of second line drugs

Answer 37

1. fluoroquinolones (later generations preferred)
2. injectable aminoglycosides (kanamycin, amikacin,streptomycin)
3. injectable polypeptide capreomycin
4. ethionamide and prothionamide
5. cycloserine and terizidone
6. PAS

Question 38

how does TB become resistant?

Answer 38

spontaneous point mutations that occur at low but predictable rates
rifampin = rpoB gene
isoniazid = katG gene, inhA gene

Question 39

BCG vaccine

Answer 39

attenuated M. bovis
efficacy ranges from 0-80%
safe and rarely causes complications
available at birth in countries with high TB prevalence

Question 40

what is the most widely used screening for LTBI?

Answer 40

skin test with tuberculin PPD (purified protein derivative)

Question 41

when are IFNy release assays used?

Answer 41

in setting with low TB and HIV burdens

less cross reactivity due to BCG vaccination