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Medical Microbiology > 10 Laboratory diagnosis of virus infections > Flashcards

10 Laboratory diagnosis of virus infections Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

what are the approaches to viral diagnosis

A
  • demonstration of virus in material derived from the patient
  • demonstration of immune response to virus (serology) (only immune response if been infected)
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2
Q

how is virus grown to test

A

virus isolation in tissue culture (very difficult to isolate viruses as don’t grow in inanimate surface – has to grow in tissue culture)
Tissue culture flask incubate laying down, cells grow until surface completely covered, then can scrap the cells off and inoculate glass tubes, lay them on side and cells will settle around base of tube

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3
Q

what is the light microscope used for in virus growth

A

Observation for cytopathic effects
Inspect growth using light microscope
If can see effects of the virus growing

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4
Q

how is a sample of genital ulceration done

A
  • swab ulcer, place in viral transport medium (isotonic solution with some AB to stop overgrowing – and so does not die)
  • virus in cells
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5
Q

what is virus isolation like

A

may be slow

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6
Q

where do viruses replicate

A

in cells

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7
Q

what is made in viral replication

A

viral antigens will be expressed within the cells some viruses express a haemagglutinin molecules

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8
Q

what is haemadsorption

A

adherence of red blood cells to the surface of something (as a virus or cell)

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9
Q

how can viral antigens be detected

A

Detection of early antigen fluorescent foci
Look under UV light
Can see that there is a nucleus infected

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10
Q

what are the advantages of virus isolation

A
  • sensitive
  • ‘catch all’ (don’t need to know in advance which virus it is)
  • generates isolates for further study
  • detects viable virus
  • adaptation for rapid result
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11
Q

what are the disadvantages of virus isolation

A
  • slow
  • labour-intensive
  • multiple cell lines required
  • not applicable to all viruses
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12
Q

what are the methods in demonstration of virus in patient-derived material

A
  • Virus isolation in tissue culture
  • Electron microscopy
  • Genome detection
  • Antigen detection
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13
Q

what are the pros of electron microscopy

A

> Rapid technique when positive

> Independent of viability

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14
Q

what are the cons of electron microscopy

A

> Insensitive

> Semi-specific (e.g. can tell you it is a herpesvirus but not which one)

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15
Q

what is electron microscopy used for

A

viral gastroenteritis, vesicle fluid

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16
Q

what happens in the principle of immunofluorescence

A

Principle of antigen detection
virus is replicating in the cell, viral proteins being expressed
Make monoclonal antibody against viral antigens tag with a fluorescent label
Need patient cells – put down on the slide
Spot the cells on slide then dry them
Add monoclonal AB (wait 30mins)
Wash unbound
Look under fluorescent microscope
(one spot should shine – where the virus is)

17
Q

what are the pros of antigen detection by immunofluorescence

A

> Rapid technique

> Widely applicable

18
Q

what are the cons of antigen detection by immunofluorescence

A

Some subjectivity (know what is the debri and what is the cell fluorescence)

19
Q

what is antigen detection by immunofluorescence used for

A

respiratory virus diagnosis

20
Q

what does genome detection usually involve

A

genome amplification e.g. polymerase chain reaction assay

- Highly sensitive assays

21
Q

Genome detection

Advantages

A
  • speed
  • high sensitivity
  • wide range of applications
  • wide range of utility
  • detection of un-cultivable viruses
22
Q

Genome detection Disadvantages

A
  • expensive
  • high set-up costs
  • rigorous QC systems required
  • target sequence must be known and highly conserved
23
Q

what are the approaches to viral diagnosis

A
  • Demonstration of virus in material derived from the patient
  • Demonstration of an immune response to virus (serology)
24
Q

demonstration of immune response to virus (serology)

A
  1. Demonstration of antigen-specific IgM

2. Demonstration of rise in antibody titre

25
Q

what are enzyme immunoassays adapted to detect

A

adapt to detect virus-specific IgM response

26
Q

what is the benefit of ELISA

A

diagnosis is rapid ie on day of presentation – by the time patient is ill IgM should be present

27
Q

what is the significance of window period

A
  • Diagnosis of HIV infection is by detection of anti-HIV
  • In window period, patient is anti-HIV negative, but HIV positive
  • Blood donation would be infectious
28
Q

what is the approach to viral diagnosis

A

nucleic acid detection (RNA or DNA) techniques usually used now

Medical Microbiology (13 decks)

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