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Pathology - Y5 > Mycobacterial diseases > Flashcards

Mycobacterial diseases Flashcards

1
Q

What are the two main types of Mycobacteria?

A

Non-Tuberculous Mycobacteria (NTM)

M. tuberculosis (MTB)

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2
Q

What are slow growing Mycobacteria?

A

M. avium complex

  • M. avium
  • M. intracellulare

MTB complex

  • M. bovis BCG
  • M. tuberculosis
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3
Q

What are rapid growing Mycobacteria?

A

M. abscessus complex

  • M.abscessus
  • M.massiliense
  • M.bolletii
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4
Q

Which Mycobacteria spp. is ungrouped?

A

M. leprae

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5
Q

What is the microbiology of Mycobacteria?

A

Non-motile rod-shaped bacteria

Relatively slow-growing compared to other bacteria

Long-chain fatty (mycolic) acids, complex waxes & glycolipids in cell wall:

  • Structural rigidity
  • Staining characteristics

Acid alcohol fast

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6
Q

What are tests for acid alcohol fast bacilli (AAFBs)?

A

Auramine

Ziehl-Neelsen

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7
Q

What is this?

A

Auramine staining

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8
Q

What is this?

A

Ziehl-Neelson staining

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9
Q

Where are non-tuberculous mycobacteria found?

A

Water

Soil

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10
Q

Explain the aetiology/pathophysiology of non-tuberculous mycobacteria.

A

AKA Environmental or Atypical Mycobacteria

Ubiquitous in nature. Varying spectrum of pathogenicity.

Little risk of person-to-person transmission. Commonly resistant to classical anti-TB Rx. May be found colonizing humans.

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11
Q

What are features of slow-growing non-tuberculous mycobacteria?

A

Mycobacterium avium complex:

  • Immunocompetent
  • May invade bronchial tree
  • Pre-existing bronchiectasis or cavities
  • Immunosuppressed
  • Disseminated infection

Mycobacterium chimera: Associated to cardiothoracic procedures

M. marinum: Swimming pool granuloma

M. ulcerans: Skin lesions e.g. Bairnsdale ulcer, Buruli ulcer
Chronic progressive painless ulcer

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12
Q

What are features of fast-growing non-tuberculous mycobacteria?

A

M. abscessus, M. chelonae, M. fortuitum:

  • Skin & soft tissue infections: Tattoo assaociated outbreaks
  • In hospital settings, isolated from BCs: Vascular catheters & other devices, Plastic surgery complications
  • CF and bronchiectasis
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13
Q

Explain the epidemiology/risk factors of NTM.

A

Pulmonary is increasing, extrapulmonary is not as common.

Age range: 56-78

Risk factors:

  • COPD
  • Asthma
  • Previous MTB
  • Bronchiectasis
  • Previous ATB
  • CFA
  • Lung cancer
  • Cystic fibrosis
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14
Q

What is the diagnostic criteria for Mycobacterial diseases?

A

Clinical: Pulmonary symptoms, nodular/cavitary opacities, multifocal bronchiectasis with multiple small nodules.

Exclusion of other diagnoses.

Microbiologic:

  • Positive culture >1 sputum samples
  • OR +ve BAL
  • OR +ve biopsy with granulomata
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15
Q

What is the treatment of Mycobacterial diseases?

A

MAC:

  • Clarithromycin/azithromycin
  • Rifampicin
  • Ethambutol
  • +/- Amikacin/streptomycin

Rapid-growing NTM:

Based on susceptibility testing, usually macrolide-based

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16
Q

What can Mycobacterium leprae cause?

A

Leprosy

Systemic disease

Contracted via inhalation of the Bacilli

17
Q

What are two extremes of Mycobacterium leprae?

A

Paucibacillary tuberculoid

  • Lower number of bacterial cells present
  • Milder immune response
  • Less destruction of structures such as skin, nerves, bones

Multibacillary Lepromatous

  • Characterised by high number of bacterial cells
  • Highly disfiguring
  • Can eventually kill patient
18
Q

What is Mycobacterium tuberculosis? Summarise the epidemiology of TB.

A

Multisystem disease.

Epidemiology:

  • Common worldwide
  • Most common cause of death by infectious agent – pre COVID-19
  • ~2 million deaths each year
  • Increasing incidence since 1980s
  • Most common opportunistic infection in HIV
19
Q

A 23 year old male is a close contact of a person with smear positive pulmonary TB. What is his lifetime risk of developing TB?

A

10% for immunocompetent hosts

20
Q

What are the TB Disease states?

A

Once you get TB, it does not mean that you will progress to have clinical manifestation of TB.

Possible outcomes after exposure to TB:

  • Nothing
  • Mild febrile disease
  • Straight progression to clinical TB

Majority of people manage to control first exposure to TB.

They then go into state of latent TB infection, may remain like this for many years until something affects their immune system, causing re-activation.

New evidence is going against this current paradigm.

21
Q

How is Mycobacterium tuberculosis transmitted?

A

Droplet nuclei/airborne The particles are so small (<10um) that they can be naturally suspended in air. Reach lower airway macrophages.

Infectious dose 1-10 bacilli.

3000 infectious nuclei:

  • Cough
  • Talking 5 mins

Air remains infectious for 30 mins

22
Q

How is TB prevented?

A

Detection of cases

Treatment of index case

Prevention of transmission:

  • PPE
  • Negative pressure isolation

Optimisation of susceptible contacts

Address risk factors

Bacille Calmette-Guerin (BCG): live attenuated M. bovis strain.

23
Q

What is post-primary TB and what is the risk of developing this?

A

Reactivation or exogenous re-infection: 5-10% risk per lifetime

Risk factors for reactivation:

  • Immunosuppression
  • Chronic alcohol excess
  • Malnutrition
  • Ageing

Clinical presentation: Pulmonary or extra-pulmonary

24
Q

In order of most effective to least effective immune response, what are the outcomes of TB?

A

Healthy contact (LTBI)

Lymph node

Localised Extrapulmonary

Pulmonary (localized)

Pulmonary (widespread)

Meningeal

Miliary

25
Q

What is pulmonary TB?

A

Caseating granulomata

Lung parenchyma

Mediastinal LNs

Commonly upper lobe

26
Q

What are features of extra-pulmonary TB?

A

Lymphadenitis:

  • AKA scrofula
  • Cervical LNs most commonly
  • Abscesses & sinuses

Gastrointestinal:

  • Swallowing of tubercles
  • Peritoneal
  • Ascitic or adhesive

Genitourinary:

  • Slow progression to renal disease
  • Subsequent spreading to lower urinary tract

Bone & joint:

  • Haematogenous spread
  • Spinal TB most common
  • Pott’s disease

Miliary TB:

  • Millet seeds on CXR
  • Progressive disseminated haematogenous TB
  • Increasing due to HIV

Tuberculous meningitis

27
Q

What are risk factors for TB?

A
  • Non-UK born/recent migrants
  • South Asia
  • Sub-Saharan Africa
  • HIV
  • Other immunocompromise
  • Homeless
  • Drug users, prison
  • Close contacts
  • Young adults (also higher incidence in elderly)
28
Q

What is the clinical presentation of TB?

A
  • Fever
  • Weight loss 74%
  • Night sweats 55%
  • Pulmonary symptoms
  • Cough 80%
  • Haemoptysis 6-37%
  • Malaise 68%
  • Anorexia
29
Q

What is this?

A

Milliary TB

30
Q

What is this?

A

Milliary TB

31
Q

What is this?

A

Mediastinal lymph nodes

32
Q

What are the first line treatments of TB?

A

Rifampicin (R)

Isoniazid (H)

Pyrazinamide (Z)

Ethambutol (E)

33
Q

What are second line medications for TB?

A
  • Quinolones (Levofloxacin)
  • Injectables: Capreomycin, kanamycin, amikacin
  • Ethionamide/Prothionamide
  • Cycloserine
  • PAS
  • Linezolid
  • Clofazimine
  • Beta-lactams
  • Bedaquiline
  • Delamanid
34
Q

What are side effects of RHZE?

A

Rifampicin (R)

  • Raised transaminases & induces cytochrome P450
  • Orange secretions

Isoniazid (H)

  • Peripheral neuropathy (pyridoxine 10mg od)
  • Hepatotoxicity

Pyrazinamide (Z)

  • Hepatotoxicity

Ethambutol (E)

  • Visual disturbance
35
Q

How long is the duration of therapy for TB? How can compliance be monitored?

A

Duration:

  • 3 or 4 drugs for 2/12
  • Then Rifampicin & Isoniazid 4/12
  • 12/12 if CNS TB
  • Cure rate 90%

Adherence:

  • Directly observed therapy (DOT)
  • Video observed therapy (VOT)
36
Q

What is multi-drug resistant TB?

A
  • Resistant to rifampicin & isoniazid
  • Extremely drug-resistant TB (XDR)
  • Also resistant to fluoroquinolones & at least 1 injectable

Risk factors:

  • Previous TB Rx
  • HIV+
  • Known contact of MDR TB
  • Failure to respond to conventional Rx
  • >4 months smear +ve/>5 months culture +ve
  • 4/5 drug regimen, longer duration
  • Quinolones, aminoglycosides, PAS, cycloserine, ethionamide

Pathology - Y5 (59 decks)

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