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MI: Mycobacterial Diseases Flashcards

1
Q

How can mycobacteria be categorised?

A

Rapid-growing and slow-growing

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2
Q

List three types of mycobacterial complex.

A

Mycobacterium tuberculosis complex

  • Mycobacterium tuberculosis
  • Mycobacterium bovis

Mycobacterium avium complex

  • Mycobacterium avium
  • Mycobacterium intracellulare

Mycobacterium abscessus complex

  • Mycobacterium abscessus
  • Mycobacterium massiliense
  • Mycobacterium bolletii
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3
Q

Describe the morphology of mycobacteria.

A
  • Non-motile rod-shaped bacteria
  • Relatively slow-growing
  • Cell wall composed of mycolic acids, complex waxes and glycoproteins
  • Acid-alcohol fast
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4
Q

What is used as a screening test for mycobacterial infections?

A

Auramine stain

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5
Q

How are non-tuberculous mycobacterial infections transmitted?

A
  • NOT person-to-person
  • From the environment
  • May be colonising rather than infecting
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6
Q

List three examples of slow-growing non-tuberculous mycobacteria and the diseases that they cause.

A

Mycobacterium avium intracellulare

  • May invade bronchial tree or pre-existing bronchiectasis/cavaties
  • Disseminated infection in immunocompromised patients

Mycobacterium marinum

  • Swimming pool granuloma

Mycobacterium ulcerans

  • Skin lesions (e.g. Bairnsdale ulcer, Buruli ulcer)
  • Chronic progressive painless ulcer
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7
Q

List three examples of rapid-growing non-tuberculous mycobacteria.

A
  • Mycobacterium abscessus
  • Mycobacterium chelonae
  • Mycobacterium fortuitum
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8
Q

List some risk factors for NTM.

A

Age

Underlying lung disease

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9
Q

How is Mycobacterium avium intracellulare treated?

A
  • Clarthromycin/azithromycin
  • Rifampicin
  • Ethambutol
  • +/- streptomycin/amikacin
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10
Q

What are the two types of Mycobacterium leprae infection?

A
  • Paucibacillary tuberculoid - few skin lesions, robust T cell response
  • Multibacillary lepromatous - multiple skin lesions, poor T cell response
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11
Q

What is the most common cause of death by infectious agent in the world?

A
  • 1 = HIV
  • 2 = TB (10% of world infected)
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12
Q

How many species are part of the Mycobacterium tuberculosis complex?

A

7 (including Mycobacterium tuberculosis, bovix and africanum)

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13
Q

What is the generation time of Mycobacterium tuberculosis?

A

15-20 hours

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14
Q

What is the infectious dose of Mycobacterium tuberculosis?

A

1-10 bacilli

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15
Q

What are the 2 types of primary TB infection

A
  • Latent TB
    • Asymptomatic
    • Not contagious
  • Active primary TB
    • Symptomatic
    • Infectious
    • Can cause progessive disseminated disease
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16
Q

What is post-primary (secondary) TB?

A

Reactivation or exogenous re-infection

10% chance after primary infection

17
Q

List some risk factors for reactivation of TB.

A
  • Immunosuppression
  • Chronic alcohol excess
  • Malnutrition
  • Ageing
18
Q

List some types of extra-pulmonary TB.

A
  • Lymphadenitis (scrofula) - cervical lymph nodes most commonly
  • Gastrointestinal - due to swallowing of tubercle
  • Peritoneal - ascitic or adhesive
  • Genitourinary
  • Bone and joint - due to haematogenous spread (e.g. Pott’s disease)
  • Miliary TB
  • Tuberculous meningitis
19
Q

Why is it important to take 3 sputum samples when investigating suspected TB?

A

Increases the sensitivity of the smear microscopy

20
Q

What is the turnaround time for smear microscopy and PCR?

A

2 hours

21
Q

What is the issue with culturing TB?

A

It takes up to 6 weeks

22
Q

What is the histological hallmark of TB?

A

Caseating granulomas

23
Q

What is NAAT and why is it useful?

A
  • Nucleic acid amplification test
  • Allows speciation and the detection of drug resistance mutations
  • Rapid
24
Q

What are the screening tests for latent TB

A

Tuberculin skin test

Interferon gamma release assay

25
Q

What is the tuberculin skin test (Mantoux test) and how does it work?

A

A sample of tuberculin is injected intradermally and left for 48-72 hours to observe the response

Type IV hypersensitivity (T cell) response to antigen

26
Q

What are the disadvantages of the tuberculin skin test?

A
  • Cross-reacts with BCG
  • Cannot distinguish between active and latent TB
  • False negative in immunosuppressed individuals
27
Q

What is an IGRA assay?

A
  • Uses M. tuberculosis specific antigens to stimulate T cell IFN-gamma production which is then measured using ELISA
28
Q

What are the advantags and disadvantges of IGRA assay?

A

No cross reactivity with other strains

Does not distinguish between latent or active TB

29
Q

What do you do if screening tests are positive?

A

CXR (looks for active TB)

if CXR normal - treat with latent TB protocol

30
Q

What is the treatment of latent TB

A
  • 3 months of isoniazid plus rifampicin
  • Or 6 months of isoniazid
31
Q

What is the treatment of active TB

A
  • Initiation phase: rifampicin, isoniazid, pyrazinamide, ethambutol for 2 months
  • Continuation phase: rifampicin plus isoniazid for 4 months
32
Q

List some side-effects of:

  1. Rifampicin
  2. Isoniazid
  3. Pyrazinamide
  4. Ethambutol
A
  1. Rifampicin
    • Raised transaminases
    • CYP450 induction
    • Orange secretions
  2. Isoniazid
    • Peripheral neuropathy (give with pyridoxine)
    • Hepatotoxicity
  3. Pyrazinamide
    • Hepatotoxicity
  4. Ethambutol
    • Visual disturbance
33
Q

What drug is given to prevent peripheral neuropathy from isoniazid?

A

Pyridoxine

34
Q

What is DOT?

A

Direct observation therapy

35
Q

What is multi-drug resistant TB?

A

Resistant to rifampicin and isoniazid

36
Q

What is extremely drug resistant TB?

A

Resistant to rifampicin, isoniazid, fluoroquinolones and at least 1 injectable

37
Q

What are the diagnostic challenges of HIV and TB coinfection?

A
  • Clinical presentation is less likely to be classical
  • Symptoms may be absent if CD4+ count is low
  • More likely to have extra-pulmonary manifestations
  • Tuberculin skin test more likely to give false-negative
  • Low sensitivity for IGRAs
38
Q

What are the treatment challenges of HIV and TB coinfection?

A
  • Timing of treatment
  • Drug interactions
  • Overlapping toxicities
  • Duration of treatment

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