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YR5 Microbiology > Mycobacterial diseases > Flashcards

Mycobacterial diseases Flashcards

(65 cards)

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1
Q

What species causes the most TB cases?

A

M. tuberculosis (MTB)

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2
Q

List 5 Mycobacteria that can cause TB

A

M. tuberculosis

M. bovis

M. africanum

M. microti

M. canetti

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3
Q

Name 4 non-TB Mycobacteria and which populations are most susceptible

A

M. avium complex: untreated HIV

M chelonae: Salmon farmers

M abscessus: CF

M chimaera: vascular bypass device

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4
Q

How is TB transmitted?

A

Aerosol

Infectious expulsion on: coughing, sneezing, speaking, singing

Droplet nuclei suspended in air for up to 30min

Inhalation of droplet nuclei, reach lower airway macrophages

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5
Q

What percentage of the world’s population have latent TB infection? How many go on to develop active TB?

A

¼ to ⅓

~10% lifetime risk of progression to active TB

~30-50% if HIV +ve

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6
Q

What can be used to diagnose latent TB infection?

A

Mantoux with PPD

Gamma Interferon Release Assays (IGRA)

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7
Q

What is the normal incubation period of active TB? What may have happened if active TB occurs later?

A

3-9m

Almost always <2y

Most are endogenously reinfected with TB (not TB activation)

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8
Q

What drugs are used in treatment of TB?

A

Rifampicin: 6m

Isoniazid: 6m

Pyrazinamide: 2m

Ethambutol: 2m

Directly observed therapy (DOTs)

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9
Q

Name the side effects of each TB drug

A

Rifampicin: orange secretions, raised transaminases, induces CYP450

Isoniazid: peripheral neuropathy, hepatoxicity

Pyrazinamide: hepatotoxic

Ethambutol: optic neuritis

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10
Q

What drug can be given to prevent the peripheral neuropathy caused by Isoniazid?

A

Pyridoxine

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11
Q

What is the natural clinical course of TB?

A

Infection usually asymptomatic, controlled by cell mediated immunity: becomes latent in Gohn focus/ caeseating granuloma

Upon reactivation (e.g. immunosuppression) becomes symptomatic

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12
Q

Which baseline investigations must be made before commencing anti-TB treatment?

A

FBC, LFT, U+Es, CRP

CXR

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13
Q

What is the duration of treatment for TB meningitis?

A

12m

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14
Q

What is the microbiology of Mycobacteria?

A

Non-motile rod-shaped bacteria

Relatively slow-growing cf. other bacteria

Long-chain fatty (mycolic) acids, complex waxes + glycolipids in cell wall giving structural rigidity

Acid alcohol fast

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15
Q

What are tests for acid alcohol fast bacilli (AAFBs)? What is the turn around time? Which is more sensitive?

A

Auramine 20-30m (more sensitive)

Ziehl-Neelsen 30m

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16
Q

What is this?

A

Auramine staining

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17
Q

What is this?

A

Ziehl-Neelson staining

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18
Q

Name 3 slow growing non tuberculous mycobacterium

A

Mycobacterium avium-intracellulare complex (MAC)

Mycobacterium marinarum

Mycobacterium ulcerans

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19
Q

Describe the pathology of mycobacterium avium intracellulare complex

A

RF: pre-existing lung disease, heavy smoking/ drinking, HIV

Immunocompetent: invades bronchial tree

Immunocompromised: disseminated infection

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20
Q

Describe the pathology of mycobacterium marinarum

A

“Fish tank/ Swimming pool granuloma”

Swimmers/ Aquarium owners

Plaques/ papules- granulomatous ulcers

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21
Q

Describe the pathology of mycobacterium ulcerans

A

aka. Buruli ulcer

Tropical: S America, Australia, Africa

Painless nodule/ induration/ swelling progressing to ulceration, scarring + contractures

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22
Q

Where are non-tuberculous mycobacteria found?

A

Water

Soil

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23
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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24
Q

List 3 fast-growing non-tuberculous mycobacteria

A

M. abscessus

M. chelonae

M. fortuitum

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25
What are fast-growing non-tuberculous mycobacteria outbreaks associated with?
Skin + soft tissue infections Tattoo assaociated outbreaks In hospital settings from BCs: Vascular catheters, Plastic surgery
26
Give 2 broad risk factors for NTM.
Age Underlying lung disease: COPD, Asthma, Bronchiectasis, CF, cancer
27
What is the diagnostic criteria for Mycobacterial diseases?
**Clinical:** Pulmonary Sx, nodular/cavitary opacities, multifocal bronchiectasis with multiple small nodules. Exclusion of other dx. **Microbiologic:** * +ve culture \>1 sputum samples * OR +ve BAL * OR +ve biopsy with granulomata
28
What is the treatment of MAC/ slow growing non tuberculous Mycobacterial diseases?
Rifampicin Clarithromycin/ azithromycin Ethambutol +/- Amikacin/streptomycin “RiCES”
29
What is the treatment for fast growing non tuberculous mycobacterial diseases?
Based on susceptibility testing, usually macrolide-based
30
What is Leprosy? What is it caused by?
aka Hansen disease Chronic infectious disease caused by prolonged exposure to Mycobacterium Leprae
31
Give 3 cardinal clinical manifestations of Leprosy
Hypopigmented skin lesions Nerve thickening Peripheral nerve palsies +/- repeated injury due to sensory loss
32
Compare the two types of Mycobacterium leprae
**Paucibacillary/ Tuberculoid** * Few bacilli * Strong Th1 response * Less destruction of structures- skin, nerves, bones **Multibacillary/ Lepromatous** * Abundance of bacilli * Th2 response * Multiple skin lesions + joint infiltration
33
What is Mycobacterium tuberculosis? Summarise the epidemiology of TB.
Multisystem disease. Obligate aerobe * Common worldwide * Most common cause of death by infectious agent, pre COVID: ~2 million deaths each year * Increasing incidence since 80s * Most common opportunistic infection in HIV
34
What vaccination is given to protect against TB?
BCG Attenuated strain of M. bovis Given to infants + high risk CI in immunosuppressed (live vaccine)
35
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?
10% for immunocompetent hosts
36
What are the 3 possible outcomes after exposure to TB?
* Nothing * Mild febrile disease * Straight progression to clinical TB Majority control 1st exposure, 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.
37
List 5 clinical investigations for TB
CXR: predilection to apices, mediastinal LNs, miliary TB Sputum x 3 EBUS TBNA (endobronchial US transbronchial needle aspiration) Bronchoscopy Early morning urine
38
What tests are performed on broncho-alveolar lavage for TB?
Check for acid fast bacilli on smear Culture on Lowenstein-Jenson medium, stain with auramine/ Ziehl-Neelson
39
How is an endobronchial ultrasound transbronchila needle aspiration utilised in diagnosis of TB?
Histology- caseating granuloma
40
What is the tuberculin skin test?
aka. Mantoux Intradermal tuberculin purified protein derivative (PPD) Examine induration 48-72h later Indicates previous exposure- BCG, active, latent
41
List 3 disadvantages of the tuberculin skin test
No differentiation of vaccination, latent or active Poor sensitivity (HIV, age, immunosuppression, overwhelming TB) Risk of delayed type hypersensitivity reaction from PPD
42
What is an IGRA test?
Interferon gamma release assay e.g. Elispot, Quantiferon Detects antigen-specific IFNg production No cross reaction with BCG
43
Give 2 disadvantages of IGRAs
Can't distinguish latent + active TB Issues with sensitivity + specificity
44
How is TB prevented?
Detection + Tx of index case **Prevention of transmission:** * PPE * -ve pressure isolation Optimisation of susceptible contacts Address RFs **Bacille Calmette-Guerin (BCG):** live attenuated M. bovis strain.
45
What is post-primary TB and how does this present?
Reactivation or exogenous re-infection: 10% risk per lifetime Clinical presentation: Pulmonary or extra-pulmonary depending on host immune response
46
List 4 risk factors for reactivation of latent TB
Immunosuppression Chronic alcohol excess Malnutrition Ageing
47
In order of most effective to least effective immune response, what are the outcomes of TB?
Healthy contact (LTBI) Lymph node Localised Extrapulmonary Pulmonary (localized) Pulmonary (widespread) Meningeal Miliary
48
What is pulmonary TB?
Caseating granulomata in lung parenchyma + mediastinal LNs Commonly upper lobe
49
Give 5 systems affected by extra-pulmonary TB. What are the features of involvement in each?
**Lymphadenitis:** aka scrofula Cervical LNs most commonly Abscesses + sinuses **GI:** May present like IBD, due to swallowing of tubercles **Peritoneal:** Ascitic or adhesive **GU:** slow progression to renal disease Subsequent spreading to lower urinary tract **Bone + joint:** Haematogenous spread Spine (Pott’s disease)
50
What is miliary TB?
Disseminated haematogenous spread Millet seeds on CXR Increasing due to HIV
51
Give 4 features of presentation of tuberculosis meningitis. How is it diagnosed?
Headaches Personality change Meningism Confusion Ix: LP- turbid
52
What are 8 risk factors for TB?
Non-UK born/recent migrants South Asia SS Africa HIV/ Other immunocompromise Homeless IVDU, prison Close contacts YA (also higher in elderly)
53
List 8 signs/ symptoms of TB
Cough 80% Weight loss 74% Night sweats 55% Fever Pulmonary Sx Haemoptysis 6-37% Malaise 68% Anorexia
54
What is this?
Milliary TB
55
What is this?
Milliary TB
56
What is this?
Mediastinal lymph nodes
57
List 7 second line medications for drug resistant TB
* Quinolones (Levofloxacin) * Bedaquiline * Linezolid * Clofazimine * Injectables: kanamycin, amikacin * Ethionamide/ Prothionamide
58
List 4 risk factors for drug resistant TB
Previous TB Rx HIV+ Known contact of MDR TB Failure to respond to conventional
59
What test can be used to determine TB drug sensitivity?
Molecular line-probe assays Whole genome sequencing on culture Next gen sequencing
60
What are the forms of resistant TB?
Multidrug resistant (MDR): resistant to Rifampicin + Isoniazid Extremely drug resistant (XDR): resistant to rifampicin, isoniazid, fluoroquinolones + at least 1 injectable
61
What is drug resistant TB though to be due to?
Spontaneous mutation Inadequate tx
62
What is the treatment for drug resistant TB?
\>,4 drugs for 9-12m Levofloxacin/ Moxifloxacin Bedaquiline Linezolid Clofazimine Pretomanid
63
List 5 diagnostic challenges of HIV and TB coinfection
1. Clinical presentation less likely to be classical, Sx + signs absent if low CD4 2. CXR may be normal (more likely extra pulmonary manifestations) 3. Smear microscopy + culture less sensitive 4. Tuberculin skin test more likely to be -ve 5. Low sensitivity of IGRAs
64
List 5 treatment challenges of HIV and TB coinfection
Timing of tx initiation Drug interactions Overalapping toxicity Duration of tx ?adherence Healthcare resources
65
What is the MTB complex? List 3 important members
Genetically related group of mycobacterium that can cause TB Mycobacterium tuberculosis Mycobacterium bovis Mycobacterium africanum

YR5 Microbiology (23 decks)

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