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Lab > Diagnostic virology > Flashcards

Diagnostic virology Flashcards

1
Q

Example of a flat and a raised rash

A 
Flat= macular rash 
Raised= vesicular (=blister)
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2
Q

What kind of rash would be found in measles and herpes

A

Measles= macular

also macular: rubella, parvovirus, EBV, CMV

Herpes= vesicular, but a discrete distribution across just a couple of dermatomes (shingles is a infection of just a couple of dermatomal nerves)

also vesicular: VZV/entero

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3
Q

What can be detected for viruses

A

Infectious virus (virus isolation & EM)

Protein components (antigens) of the virus (p24 antigen in HIV, surface antigen in HBV, etc)

Genetic components of the virus (DNA or RNA) - quantitative or qualitative tests are available

The host response (e.g. antibody or cell responses)

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4
Q

What does old vs current virus detection involved

A

OLD: cell culture and electron microscopy

CURRENT:

Antibody detected for the antigen in the blood (serology enzyme immunoassay= EIA)

Antigen can be detected by immunoflorescence (IF) or enzyme immunoassay (EIA)

PCR

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5
Q

Differentiate sensitivity and specificity

A

Sensitivity: the test’s ability to correctly identify positive samples
Specificity: the test’s ability to correctly identify negative samples

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6
Q

As well as detecting antibodies/viruses/DNA/protein components,

what else in virology testing is useful and why

A
  1. Quantity of antibody found (antibody is much higher in vaccinated people than people with infection, so helps to distinguish)
  2. Serotyping (=classification based on cell surface antigens) i.e. with HIV
  3. Quantification of genomes= VIRAL LOAD (essential for diagnosis and monitoring of HIV, HBV, HCV, CMV, EBV in immunocompromised)
  4. Genome sequencing —genotyping as different virus types have different prognosis
    - antivrial resistance testing (to find out what treatment will work)
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7
Q

Wat could following samples test

Throat swab, Nasopharyngeal aspirate (NPA), bronchoalveolar lavage (BAL), ET secretions –

Stools

Urine

CSF

Blood (clotted)

Blood (EDTA)

Saliva

A

Throat swab, Nasopharyngeal aspirate (NPA), bronchoalveolar lavage (BAL), ET secretions – for detection of respiratory viruses by (IF or) PCR

Stools - for rotavirus, adenovirus & norovirus antigen detection (EIA) or PCR

Urine – for BK virus & adenovirus PCR

CSF - for herpes viruses and enteroviruses PCR

Blood (clotted) - for serology (antibody detection)

Blood (EDTA) - for PCR / viral load testing

Saliva – for serology &/or PCR (eg measles)

SUMMARY: we do PCR on all apart from clotted blood, which is used for antibody detection against the virus, not to identify the virus

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8
Q

Which antibody is shown at which time

A 
IgM iMmediate (acute infection)
IgG after infection (chronic infection for life)
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9
Q

What is serology and outline HBV serology

A

Serology is looking at human response to infection, looking at antigens etc.

Hep B… surface antigen present in acute or chronic HBV. Surface antibody present in recovery/immunity for HBV (incl. vaccinated).

Core antibody persists throughout life…. if the core antobody is IgM it indicated HIV within last 6 months

https://epi.publichealth.nc.gov/cd/lhds/manuals/hepB/docs/hbv_serology.pdf

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10
Q

Which serology for HIV

A

4th generation (test for AB and anitgen)… so looks for Ab + p24 (which is in the protein capsid)

confirm testing for to exlude non-specific reactivity (false positive)

Typing- HIV 1 or 2

Repeat and measure HIV viral load

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11
Q

Which type of sample can be used for viral load testing

A

Blood (EDTA) i.e. anticoagulated blood

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12
Q

When is IgM and IgG observed

A

IgM–> around 3 months

IgG –> lifelong

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13
Q

What is antibody avitdity testing

A

Over time, the antibodies produced against an antigen increases affinity….
you can test the strenght of antibody binidng 4 weeks apart… if the affinity increases this is consistent with an old infection

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14
Q

When is virus isolation in cell culture used

A

Rarely
phenotypic antiviral susceptibility testing (HSV)

i.e. to test which antivirals work on a virus

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15
Q

Electron microscope rarely used, but which samples if it was

A

stool and vesicle fluids

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16
Q

Enveloped virus with 20 faces

A

Herpes

17
Q

Bullet shaped viruses

A

Rabies

18
Q

Filamentous virus… long and windey

A

Ebola

19
Q

How is IF still used

A

Still occasionally used for the direct detection of viral antigens in clinical samples (DIF) …. inexpensive but subjective

20
Q

Cause of respiratory distress due to bronchiolitis

A

RSV

21
Q

How can respiratory viruses be identified

A

respiratory virus PCR

22
Q

How does multiplex PCR work

A

You put in primers for lots of different genes for many viruses…. if the gene is present then that DNA will be replicated lots of times and will be detected

23
Q

What is PCR

A

Method for amplifying specific RNA (RT-PCR) or DNA sequences

24
Q

What is required for RNA identification

A

reverse transcription (hence RT-PCR)

25
Q

3 stages PCR

A

Denature, primer annealing, chain elongation

26
Q

What can be used in CNS disease for virus testing

A

PCR:

CSF (for HSV, VZV, enterovirus)

Stools and throat swap for enterovirus

Blood for serology and/or PCR (west nile, japanese encephalitis virus and other arbovirus)

27
Q

Which virus are you testing for meningitis and encephalitis

A

HSV, VZV and enterovirus

28
Q

What can you do for D&V for virus testing

A

Stool sample…. PCR or EIA for norovirus, rotavirus,adenovirus, sapovirus, astrovirus

29
Q

How many cycles in PCR

A

around 30

30
Q

How was PCR interpreted previously vs now

A

In past: with gel

Now: real time PCR melt curve analtysis

31
Q

Why is sequencing helpful

A

Genotyping virus

Antiviral resistance testing

Phyogenetic analysis… to see how related viruses are and see if the same virus in different people!

32
Q

What is CMV

A

CMV, cytomegalovirus, is similar to the herpes virus that causes cold sores and chickenpox.

Once you have the virus, it stays in your body for the rest of your life

Can get flu like symptoms first time you catch it, after that only dnagerous if past onto new born

33
Q

Viral cause of fever and rash

A

HIV (important), EBV, CMV

Lab (5 decks)

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