Mycobacterial disease Flashcards Preview

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Flashcards in Mycobacterial disease Deck (27):
1

What are the distinguishing features of mycobacteria?

- Unusual waxy cell wall:

•High lipid content

- Slow growing

•Different media requirements

- Intra - cellular pathogens

2

What are the staining characteristics of mycobacteria?

•Poor take up of standard Gram’s stains

–(Gram positive: Ghost cells)

•Retain certain stains without decolourisation by acid / alcohol:

–“acid fast bacilli” (AFBs).

•Ziehl Neelsen (ZN)

•Phenol auramine.

3

Which types of mycobacterium cause tuberculosis?

–M. tuberculosis

–M. bovis

4

What mycobacterium causes leprosy?

M. leprae

5

How does the transmission of TB occur?

Inhalation of infected respiratory droplets

6

What are the features of primary TB?

•1o acquisition / infection & body’s reaction.

•Periphery of lung midzone: most common site

•Inhaled bacilli phagocytosed by macrophages

•Hilar lymph nodes – “Ghon focus”

•Intracellular multiplication

•Dissemination via lymphatic system / bloodstream 

7

What is the body's response to mycobacterial invasion?

–Granuloma
–Cell - mediated immune response
–Central area of epithelioid cells, giant cells.
–Surrounding lymphocytic cell infiltration.
–Central area caseous necrosis.
–Fibrosis / calcification of lesions
–Bacilli slowly die / may remain viable 20 years

8

What is the clinical presentation of primary TB?

“Influenza - like” syndrome

9

What happens after the primary phase of the disease?

Dissemination or latency.

10

Why might TB reactivate?

–Lowered immunity
–Western countries : over 50 year old, men
–Malnutrition
–Alcoholism
–Debilitating illness
–HIV infection.
–Silicosis, chronic renal failure, gastrectomy..
–Anti TNFα blockade (e.g. infliximab)

11

What are the features of reactivated TB?

•Coalescing tubercles, central caseous necrosis

•Cavitation

–High organism load - risk of  transmission.

•Lung apices: highest oxygen tension.

•Symptomatic:

–Chronic productive cough

•Haemoptysis

–Weight loss, fever, night sweats.

12

What is extra-pulmonary tuberculosis?

  • Disseminated (miliary TB)
    • Very young / old; immunocompromised
    • 1o disease
    • 2o - erosion of necrotic tubercle into blood vessel
    • Widespread infection, including meningitis.

13

What are the common extr-pulmonary sites?

–Pleura
–Lymph nodes
–Kidneys , epididymis
–Bone
–Intestines
–Brain / meninges
–Pericardium

14

What are the clinical features of TB meningitis?

–Often insidious onset

–Unidentified fever

–Personality change

–Focal neurological deficit

•Basilar inflammation.

–Mild headache / meningism.

–May lack constitutional quartet

•(fever, night sweats, anorexia, weight loss)

15

What tests are used to perform the diagnosis of TB?

–Index of suspicion
–Clinical
–Radiology:  Chest X - ray.
–Histology
–Skin testing
–(Blood test: Interferon- γ release assay: IGRA)

16

What microbiological tests are performed in the diagnosis of TB?

•Confirmation of diagnosis

•Drug sensitivities.

•Molecular typing profile: “MIRUs”.

•“Fresh” samples / tissue: i.e. NOT formalin fixed

17

What is the treatment for TB?

–Lengthy

–Protocols - combined tablets

–Resistance development:

•DOTS: Directly Observed Therapy,Short - course

 

–Standard - pulmonary:

•2 months  Isoniazid, rifampicin, pyrazinamide   ethambutol / (streptomycin)

•4 months  Isoniazid, rifampicin

18

How long is drug therapy required for TB meningitis?

12 months

19

How long is drug therapy required for other sites (not meningeal)?

6 months

20

What are the second-line agents used for drug-resistant strains?

–Amikacin
–Ethionamide / prothionamide
–Cycloserine
–Fluoroquinolones: ciprofloxacin, moxifloxacin

21

What new drugs have been developed for TB?

–Bedaloquine
–Delamanid
–Pa-824

22

Is TB a notifiable disease?

Yes

23

What is the BCG vaccine?

An attenuated strain of M bovis.

24

Give an example of 'atypical' Mycobacterium.

•Mycobacterium avium Complex

–HIV infected

•Disseminated disease

–Non HIV infected -

•pulmonary: tuberculosis - like.

Young children: cervical lymphadenitis.

Treatment: Macrolide: clarithromycin

25

Leprosy is caused by which species of bacteria?

Mycobacterium leprae

26

What are the two clinical forms of leprosy?

–Tuberculoid

•Macules / plaques

•Nerve: ulnar, common peroneal

- Th1 polarised immune resoponse

 

–Lepromatous

•Subcutaneous tissue accumulation.

•Ear lobes, face - leonine facies.

- Th2 polarised immune response

27

What is the treatment for leprosy?

–Dapsone, rifampicin, clofazimine

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