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Flashcards in Mycobacteria and Tuberculosis Deck (28)
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1

TB prevalence?

2nd most infectious killer worldwide

2

Mycobacterium tuberculosis features?

2-4 μ by 0.2-0.5 μ
Obligate aerobe
well-aerated upper lobes
Facultative intracellular parasite
usually macrophages
Slow generation time
15-20 h

3

Where does tuberculosis most commonly affect? Where else can it effect?

Lungs - Pulmonary TB
Lymph nodes, bones, joints, kidneys and can cause meningitis

4

How do people catch TB?

Droplets from coughs or sneezes
Close/frequent prolonged contact with an infected person

5

Who is most at risk to TB?
Who else is at risk?

People with weakened immune systems

HIV infec
Steroids, chemotherapy, transplants, elderly
Unhealthy, overcrowded conditions
High rate country - S.E Asia
Exposed to TB in youth
Prisoners, drug addicts, alcoholics
Malnourished

6

How does primary TB occur?

Droplet nuclei inhaled = taken up by alveolar macrophages - not activated
Droplet nuclei reaches alveoli = infec begins
Granuloma in lung = Ghon focus
Enlarged lymph nodes + GF = primary complex

7

What causes secondary TB?

Reactivation of dormant mycobacteria - impaired immune func
Reinfec in a person previously sensitised to mycobacterial antigens
- occurs in months, yrs, decades after 1 infec

8

Where is reactivation of TB most common?

Apex of lungs - highly oxygenated

9

What occurs in secondary TB?

Caseous centres of tubercles liquefy = organisms grow very rapidly here
Large Ag load:
- Bronchi walls become necrotic and rupture
- Cavity formation
- Organisms spill into airways and spread to other areas of lung
Primary lesions heal - Ghon complex, Simon foci

10

How do TB infection and TB lung disease differ?

Infec TB:
Chest x-ray normal
Sputum smears negative
putum culture negative
No symptoms
Not infectious
Not defined as a case of TB

Lung disease TB
Lesion on chest x-ray
Sputum smear positive
Sputum culture positive
Symptoms
Infectious
Defined as TB case

11

What do TB infec and TB lung disease have in common?

Organism present
Tuberculin skin test positive

12

Most common symptoms of TB?

Cytokines causing:
Persistent cough, +/- sputum
Anorexia
Weight loss
Swollen glands
Fever
Night sweats
Sense of tiredness
Coughing blood

13

How to treat TB?

Isoniazid, rifampicin, pyrazinamide and ethambutol
for two months followed by isoniazid and rifampicin for four months
Non-infec after 2 weeks
Begin to feel better after 2-4 weeks
Treatment for 6+ months (prevent resistance)
Longer treatment for TB meningitis or if TB is resistant

14

How to prevent spread of MDR-TB? (multi-drug resistant)

Standardised drug regimens
Directly observed treatment
Good supply of high quality drugs
Isolation of infectious pts

15

What does vitamin D do?

Activates macrophages to destroy macrobacteria

16

TB fatality rates?

Untreated = 40-60%
Treated = 5-50%, depending on nutrition; quality and availability of med care, HIV status

17

Name the vaccine for TB?

Bacille Calmette Guerin (BCG)

18

Features of BCG?

Protection restricted to childhood TB = rarely infectious
No impact on HIV related TB
Does not prevent infec - only disease
= Targeted vaccination, effective for 15yrs

19

How are HIV and TB linked?

HIV increases risk of TB - destroys immune system
TB makes HIV worse - increases replication rate of HIV
TB treatment slows down HIV and keeps pt alive to get HIV drugs

20

How are TB and animals linked?

TB common in cattle and humans infected with M.bovis

21

What are the obstacles of controlling TB?

Lack of money
Social instability
HIV epidemic
Drug resistance
Stigma

22

How to diagnose TB?

Suspicion
Chest x-ray
Tuberculin tests:
- Heaf, tine, mantoux
- May be negative in severe TB or concomitant HIV, malnutrition, steroids
- May be positive with BCG or after exposure to mycobacteria

T-SPOT TB and QuantiFeron Gold:
- Blood tests to replace tuberculin tests
- Detect reactive T cells
Specific for Mtb, not BCG

Microscopy:
- Ziehl-Neelsen stain
- 1/3 of pulmonary TB undiagnosed by microscopy

Sputum Culture:
- Homogenise
- Decontaminate
- Concentrate
- 4-6 weeks for visible colonies

23

Types of Multi/extensive drug resistance?

MDR TB - rifampicin and isoniazid
XDR TB - as above and aminoglucosides

24

Risk factors of MDR/XDR?

Previous treatment
Current failure
Contact with MDR TB
HIV+
London resident
Male 25-44yrs

25

MDR/EDR mortality?

25% MDR TB, 50% XDR TB

26

How does automated culture work?

MGIT 960:
Fluorescent reaction quenched by O2
Growth of mycobacteria lifts quenching and tubes fluoresce
10 days

27

Nucleic acid detection tests?

RFLP IS6110
Strand displacement – BD ProbeTec
Amplified Mycobacterium tuberculosis Direct Test - Gen-Probe (rRNA)
Enhanced Amplified Mycobacterium tuberculosis Direct Test - Gen-Probe
AMPLICOR Mycobacterium tuberculosis Test – Roche (DNA PCR)
Multiplex PCR assay for 23S rDNA

28

Typing?

Spoligotyping
Variable Number of Tandem Repeats
Mycobacterial Interspersed Repetitive Units - VNTR-MIRU