Infection: Mycobacterium Tuberculosis Flashcards Preview

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Flashcards in Infection: Mycobacterium Tuberculosis Deck (15)
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1
Q

How is tuberculosis diagnosed?

A

Cant be gram stained so use acid fast staining instead - it is a bacillus
Tuberculin skin test
Chest xrays
Culture sputum

2
Q

Does mycobacterium tuberculosis grown fast or slow?

A

Very slow growing - the generation time is 15-20hrs - therefore culture can take 2 - 12 weeks

3
Q

What is the mode of transmission of mycobacterium tuberculosis?
How contagious is TB?

A

Via respiratory droplets - coughing, sneezing, speaking. Casual contact is not enough for transmission - need prolonged exposure eg family members, homeless, prisons

4
Q

Why is mycobacterium tuberculosis not phagocytosed by alveolar macrophages?

A

It has a cell wall with a high lipid content which prevents fusion of the phagosome to the lysosome.
It can even multiply inside alveolar macrophages

5
Q

What is the treatment for TB?

A

R ifampicin (makes urine orangey red)
I troniazid
P yrazinamide
E thambutol

Because TB is slow growing it is a prolonged course (6months - 2 years) therefore need to closely monitor compliance. If taken correctly 90% cure rate

6
Q

What is latent TB and how can it progress?

A

Latent infection is where there are live bacilli but they are dormant - not multiplying.
From latency 95% of cases will self cure and the other 5% will become post primary TB (the bacilli start multiplying).

7
Q

What are the main differences between latent TB infection and TB disease?

A

Latent TB is not a case of TB - there are no symptoms, normal xray, sputum negative. However there is a strong immune response.
TB disease is infectious, has abnormal xray and there are symptoms.

8
Q

What are the risk factors for latent TB being reactivated to post primary TB infection?

A
  • Infection with HIV is the highest risk (therefore all cases of TB are tested for HIV)
  • immunosuppressive therapy
  • diabetes mellitis
  • malignancy
9
Q

How can pulmonary TB spread to become miliary TB? (whole body)

A

Can spread directly, through the blood stream or via lymphatics

10
Q

What are the common symptoms for pulmonary TB?

A

Fever, weight loss, night sweats, malaise

Cough (most common) may be heamoptysis and breathlessness if pleural effusion

11
Q

What is the appearance of the chest Xray in someone with pulmonary TB?

A

ill-defined patchy consolidation
Can get cavitations
May have pleural effusion

12
Q

What is the tuberculin sensitivity test?

A

Used to diagnose latent TB
Tuberculin is injected intradermally and read 48-72 hours later - the swelling should be measured (not the redness)
Looking for a strong immune response

13
Q

TB is a notifiable disease, what does this mean?

A

The doctor making or suspecting a diagnosis of TB is legally responsible to notify public health so they can begin screening of close contacts.

14
Q

How can TB be prevented?

A

BCG vaccine - a live vaccine therefore cant be given to HIV pts.
Given to babies in high prevalence communities - 70-80% effective at preventing severe childhood TB.

15
Q

What is extra-pulmonary TB and how can this present?

A

TB affects other parts of the body eg

  • TB meningitis (chronic headache, fevers)
  • lymph node TB (abcesses, mainly affects cervical LNs)
  • orthapaedic TB (spreads to bones and joints via blood, spinal TB is most common)

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