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Y3 Medical Micro > L9 Lab diagnosis > Flashcards

L9 Lab diagnosis Flashcards

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USMLE® Step 1 flashcards
1
Q

What is the direct approach to viral diagnosis

A

Demonstration of virus in material from patient approach

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2
Q

What is the indirect approach to viral diagnosis

A

Demonstration of an immune response to virus (serology)

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3
Q

How are viruses isolated

A

In tissue culture as need to grow in cells

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4
Q

How is tissue culture grown

A

In flask lying flat down
Cells stick to plastic until confluence growth and scrap cells off surface
Red liquid - cells

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5
Q

What do uninflected human embryonic lung fibroblasts look like under light microscope

A

Long thin shape of cells

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6
Q

What do rhinovirus infected lung fibroblasts look like

A

Round and shrivelled typical of rhinovirus

Cytopathic effect CPE

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7
Q

What do cytomegalovirus infected fibroblasts look like

A

Causes rounded and swollen cells for CPE effect

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8
Q

What is important when trying to isolate many viruses

A

Not all cells have a receptive for every virus - need to provide a range of different cell types if trying to isolate many viruses

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9
Q

What are Hep2 cells infected with respiratory syncytial virus like

A

Huge gaps in cell sheet
Large multi nucleated giant cells
Virus caused these cells to fuse together - syncytia

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10
Q

How is a genital ulceration tested

A

Scrap cells off swab

Break swab into transport medium as need cells alive not dried

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11
Q

What is in transport medium

A

Antibiotics to stop overgrowth

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12
Q

Where are viral antigens expressed

A

In cells as viruses replicate in cells

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13
Q

What is early antigen fluorescent foci

A

Antigen expressed early in cell cycle

Make antibody for this and tag with fluorescent marker

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14
Q

What is virus isolation like

A

Can be slow

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15
Q

Why is detection of early antigen fluorescent foci good

A

Can do within 24 hrs rather than waiting for CPEs which take long

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16
Q

What are the pros of virus isolation in tissue culture

A

Positive result unequivocal

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17
Q

What are the cons of virus isolation in tissue culture

A

May be slow

Can’t be universal (can be hard to grow in cell culture)

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18
Q

How is virus isolation sped up

A

Haemaosdrption

Detection of early antigen fluorescent foci

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19
Q

What is DEAFF

A

Detection of Early Antigen Fluorescent Foci

20
Q

What happens if the virus can’t be grown to isolate

A

Try use electron microscopes

Virus isolation in tissue culture

21
Q

What is the con with electron microscopy

A

Some viruses look the same e.g. all herpes viruses look the same so doesn’t know which one it is

22
Q

What are the pros of electron microscopy

A

Rapid technique when positive

Independent of variability

23
Q

What are the cons of electron microscopy

A

Insensitive- need a lot of virus to see it

Semi specific- can’t tell which herpesvirus it is

24
Q

If you can’t grow or see the virus what can be done to workout the virus

A

Need to find the viral proteins (antigens) and viral genetic material (genome)

25
Q

What is the principle of immunofluorescence

A

Antigen within of on virus
Cells from patient onto slide add monoclonal AB that are fluorescent
Wash unbound AB
Dry slide

26
Q

What is the immunofluorescence technique like

A

Very adaptable technique

27
Q

What happens if the cells are infected in principle of immunofluorescence

A

Cell fluorescent under UV

28
Q

What happens if the cells are uninfected in the principle of immunofluorescence

A

No binding of AB and no fluorescence

29
Q

What are the pros of antigen detection

A

Rapid technique

Widely applicable

30
Q

What are the cons of antigen detection

A

Some subjectivity needs a lot of training

Cell debris fluorescent

31
Q

Where are cells taken from for antigen detection

A

Throat swab

Nasopharynx swab

32
Q

What detection is used for respiratory virus diagnosis

A

Antigen detection

33
Q

What does genome detection involve

A

Genome amplification e.g. PCR assay

34
Q

How can genome detection be quantitative

A

E.g. monitoring of HIV viral load in response to therapy - how much virus there is, can monitor the response to the treatment

35
Q

What is the problem with antibody testing

A

Incubation period there is no AB to detect

36
Q

How can diagnosis of recent infection be tested

A

Demons of antigen specific IgM

Demonstration of rise in AB titre

37
Q

What antibodies appear and when in infection

A

IgM appear first

Followed quickly by IgG

38
Q

What antibody remains for potentially life

A

IgG

39
Q

What does it mean if IgM detected

A

Patient recently infected

40
Q

What is important to watch about antibody titre

A

Rise in AB
Goes from undetectable to high
Only in response to infection

41
Q

What is an ELISA

A

Enzyme linked immunisorbent assay

42
Q

What is good about ELISA

A

Optical density reading

Straightforward interpretation

43
Q

What is adaptable with enzyme immunoassay

A

Adapt to detect virus specific IgM response

44
Q

Pros of ELISA

A

Quick diagnosis

Very flexible technique

45
Q

Other than infection why is the window period important

A

Blood donation - check no HIV infection

46
Q

What are the ways to demonstrate virus in patient material

A

Virus isolation in tissue culture
Electron microscopy
Antigen detection
Genome detection

Y3 Medical Micro (16 decks)

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