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YEAR 5: MICRO > MI: Mycobacterial Diseases > Flashcards

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

What are the types of mycobacteria which cause TB?

A

Mycobacterium Tubercolosis
Mycobacterium Africanum

Mycobacterium bovis - causes TB in cows not humans - hence don’t dirink unpasteurisaed milk

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4
Q

What are non-TB mycobacteria and what disease do they cause

A

Not all acid-fast bacilli cause TB

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5
Q

How is TB transmitted

A

Droplets through air

Transmission when another person inhales those droplets

Hence infected should wear masks

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6
Q

In who is the BCG vaccine most effective?

A

Protects Infants from TB infection
<5 from severe extra pulmonary TB

Mixed efficacy in adults for protecting against pulmonary TB

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7
Q

What is the distribution between pulmonary and extra pulmonary disease?

A

80% lung

20% extra-pulmonary:
lymph nodes - most common
brain
bone
kidney skin

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8
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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9
Q

What is used as a screening test for mycobacterial infections?

A

Auramine stain

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10
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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11
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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12
Q

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

A
  • Mycobacterium abscessus
  • Mycobacterium chelonae
  • Mycobacterium fortuitum
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13
Q

List some risk factors for NTM.

A

Age

Underlying lung disease

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14
Q

How is Mycobacterium avium intracellulare treated?

A
  • Clarthromycin/azithromycin
  • Rifampicin
  • Ethambutol
  • +/- streptomycin/amikacin
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15
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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16
Q

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

A
  • 1 = HIV
  • 2 = TB
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17
Q

How many species are part of the Mycobacterium tuberculosis complex?

A

7 (including Mycobacterium tuberculosis, bovix and africanum)

18
Q

What are the tests for latent TB?

What do you do if +ve?

A

Mantoux

Gamma interferon assay

If +ve offered chemoprophylaxis –> to eradicate disease and prevent patient from getting active TB

19
Q

What is the generation time of Mycobacterium tuberculosis?

A

15-20 hours

20
Q

What is the infectious dose of Mycobacterium tuberculosis?

A

1-10 bacilli

21
Q

Describe the natural history of primary TB.

A
  • Usually asymptomatic
  • Ghon focus (granuloma in the lungs)
  • Controlled by cell-mediated immunity
  • Occasionally causes diseeminated/military TB
22
Q

What is post-primary TB?

A

Reactivation or exogenous re-infection

Happens > 5 years after primary infection

23
Q

Likelihood of getting latent TB

24
Q

List some risk factors for reactivation of TB.

A
  • Immunosuppression
  • Chronic alcohol excess
  • Malnutrition
  • Ageing
25
List some types of extra-pulmonary TB.
* 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
26
Why is it important to take 3 sputum samples when investigating suspected TB?
Increases the sensitivity of the smear microscopy
27
What investigation may be done in children with suspected TB?
Gastric aspirate
28
What is the turnaround time for smear microscopy and PCR?
2 hours
29
What is the issue with culturing TB?
It takes up to 6 weeks But it is very sensitive --> can detect 1-10 TB mycobacteria, infectious dose is 3
30
What is the histological hallmark of TB?
Caseating granulomas
31
What is NAAT and why is it useful?
* Nucleic acid amplification test * Allows speciation and the detection of drug resistance mutations * Rapid
32
What is the tuberculin skin test?
A sample of tuberculin is injected intradermally and left for 48-72 hours to observe the response
33
What are the disadvantages of the tuberculin skin test?
* Cross-reacts with BCG * Cannot distinguish between active and latent TB
34
What is an IGRA assay?
* Detection of antigen-specific IFN-gamma production * Does NOT cross-react with BCG * However, it cannot distinguish between latent and active TB
35
List some side-effects of: 1. Rifampicin 2. Isoniazid 3. Pyrazinamide 4. Ethambutol
1. **Rifampicin** * Raised transaminases * CYP450 induction * Orange secretions 2. **Isoniazid** * Peripheral neuropathy (give with pyridoxine) * Hepatotoxicity 3. **Pyrazinamide** * Hepatotoxicity 4. **Ethambutol** * Visual disturbance
36
Describe the treatment regimen for TB.
* RIPE for 2 months * Followed by rifampicin and isoniazid for 4 more months
37
What is DOT?
Direct observation therapy
38
What is multi-drug resistant TB?
Resistant to rifampicin and isoniazid
39
What is extremely drug resistant TB?
Resistant to rifampicin, isoniazid, fluoroquinolones and at least 1 injectable
40
What are the diagnostic challenges of HIV and TB coinfection?
* 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
41
What are the treatment challenges of HIV and TB coinfection?
* Timing of treatment * Drug interactions * Overlapping toxicities * Duration of treatment

YEAR 5: MICRO (24 decks)

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