8.1 - mycobacterium tuberculosis

Question 1

mycobacterium tuberculosis

Answer 1

acid fast bacterium

major pathogenic species within mycobacterium

Question 2

tuberculosis strains

Answer 2

§ MDR-TB - multi drug resistant TB

§ XDR-TB - extensively drug resistant TB

Question 3

TB acquired by

Answer 3

§ Disease of overcrowding and poor social conditions
§ Usually acquired by inhalation from another person with active pulmonary TB
§ Bacteria may persist in the air in the room for some time

Question 4

TB aerosol particles

Answer 4

□ Aerosol particles
□ 0.5 to 5 micrometres
□ Size gives these particles the ability to be inspired directly to the level of the alveoli without being filtered out at higher levels of the airways
§ Infection may be acquired by inhaling as few as ten tubercle bacilli

Question 5

bodily spreads of TB

Answer 5

§ In the alveoli mycobacteria are ingested by alveolar macrophages
□ They able to survive and multiply within macrophages
□ Innate immune system, cannot control the infection, but adaptive immune system can control but not eradicate the infection in the lung

Question 6

infectivity of TB

Answer 6

§ Majority of people who become infected with M tuberculosis remain asymptomatic
§ About 20% of people with develop symptoms, 10% within 2 years (1° TB) and 10% some years later (2° TB) as a result of reactivation of latent TB

Question 7

location of TB

Answer 7

§ TB is typically a pulmonary disease but 10-25% of cases are extrapulmonary

Question 8

§ Ghon focus

Answer 8

□ Granulomatous inflammation
® 1-1.5cm in diameter
® Mid lung, unilateral
® Becomes fibrosed and walled off, later calcifies
® Majority of infected patients remain asymptomatic with viable bacteria walled off in fibrotic tubercles in lung or other tissues

Question 9

hon focus may develop into

Answer 9

ghon complex

Question 10

Ghon complex

Answer 10

when ghon focus progresses to involve peribronchial and hilar lymph nodes

Question 11

primary TB

Answer 11

◊ In 10% of infected people the Ghon complex will progress and the infection disseminates through the lungs
} Tuberculosis pneumonia
} Patchy or dense consolidation
} Cavitation
◊ Primary TB usually seen in infants and children

Question 12

if the goon complex progresses and disseminates through the lungs this is

Answer 12

primary TB

Question 13

second degree TB happens when

Answer 13

◊ If cell mediated immunity diminishes then lesions may reactivate and patient becomes symptomatic

Question 14

second degree TB happens in which people

Answer 14

} Old age 
							} Steroids 
							} Diabetes
							} Immunosuppressive drugs 
							} HIV infection

Question 15

why do many people remain asymptomatic

Answer 15

Majority of infected patients remain asymptomatic with viable bacteria walled off

Question 16

clinical features of TB

Answer 16

□ Gradual, non-specific onset 
				□ Fever
				□ Night sweats 
				□ Tiredness
				□ Weight loss
				□ Persistent cough with possible blood stained sputum

Question 17

in untreated TB

Answer 17

□ Progressive involvement of the lungs may occur , resulting in cavity formation and scarring usually involving the upper lobes
□ Untreated pulmonary tuberculosis is highly infectious, particularly where there is a cavitating lesion opening into an airway

Question 18

4 methods of detecting TB

Answer 18

Mantoux
interferon gamma release assay
chest X ray
sputum testing

Question 19

Mantoux involves

Answer 19

□ Mantoux (tuberculin) skin test
® This involves the intradermal injection of a bleb purified preparation of M tuberculosis antigen (PPD - purified protein derivative)

Question 20

positive Mantoux test

Answer 20

® People who have been infected with MTB will develop a local skin reaction which is measured after 48 hours

Question 21

problem with Mantoux test

Answer 21

◊ A positive test does not differentiate between latent infection and active infection

Question 22

□ Interferon gamma release assay

Answer 22

® This test detects interferon gamma release from the patient’s T lymphocytes after being incubated, in vitro, with M tuberculosis synthetic peptides

Question 23

positive IFN gamma release assay

Answer 23

® T lymphocytes previously exposed to the organism will release high levels of interferon gamma

Question 24

problem with IFN gamma release assay

Answer 24

® A positive test dies not differentiate between latent infection and active infection

Question 25

□ Chest X ray

Answer 25

® This may demonstrate pulmonary lesions in those with a positive mantoux or interferon gamma release assay

Question 26

□ Sputum testing

Answer 26

® Demonstration of AFBs in sputum (‘smear positive’) and subsequent culture of the organism are used to make a definitive diagnosis of active disease

Question 27

problem with sputum testing

Answer 27

not useful in those not producing sputum

Question 28

detecting extrapulmonary TB

Answer 28

® Extrapulmonary TB, depending on it’s site may be diagnosed with a fine needle biopsy (eg. Lymph nodes) or microscopy and culture of urine of CSF

Question 29

4 drugs mycobacterium tuberculosis is susceptible to

Answer 29

® Isonaizid
® Rifampicin
® Pyrazinamide
® Ethambutol

Question 30

standard course of treatment

Answer 30

6 months

Question 31

treatment becoming more difficult because

Answer 31

resistance

Question 32

multi drug resistant TB

Answer 32

□ MDR TB - multidrug resistance

® resistant to isoniazid and rifampicin

Question 33

extensively drug resistant TB

Answer 33

□ XDR TB - extensive drug resistance

® Resistant to all frst line drugs and some others

Question 34

tuberculosis caused by

Answer 34

mycobacterium tuberculosis