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Diagnostics > 2. Virology lab > Flashcards

2. Virology lab Flashcards

1
Q

Which disease is a widespread macularpapular (flat) rash typical of?

A

Measles

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2
Q

Which disease is a dermatomally distributed vesicular (raised) rash typical of?

A

Shingles (varicellar zoster)

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3
Q

What can we detect in the (virology) lab?

A
  • Infectious viruses and their components
  • Protein components of the virus (antigens)
  • Genetic components of the virus (DNA or RNA)
  • The host response e.g. antibodies and cell responses
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4
Q

What is the viral load?

A

Amount of viral nucleic acid present in the blood or other bodily fluids

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5
Q

What is sensitivity and specificity?

A
  • Sensitivity - the test’s ability to correctly identify positive sample (less false negative results)
  • Specificity - the test’s ability to correctly identify negative samples (less false positive results)
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6
Q

What samples can you use for detection of respiratory viruses?

A
  • Throat swap
  • Nasopharyngeal aspirate (NPA)
  • Bronchoalveolar lavage (BAL)

IF / PCR

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7
Q

What samples can you use for a rotavirus, adenovirus and norovirus detection?

A

• Stools

Antigen detection (EIA) / PCR

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8
Q

What samples can you use for BK virus and adenovirus detection?

A

• Urine

PCR

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9
Q

What samples can you use for herpes viruses and enteroviruses?

A

• CSF

PCR

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10
Q

What type of blood can you use for serology (antibody detection)?

A

Clotted blood

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11
Q

What samples can you use for viral load testing/PCR?

A

Blood (EDTA)

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12
Q

What does serology consist of and give examples?

A

• Testing for specific antibodies or viral antigens in serum or other body fluids (saliva, CSF)

  • HIV (antibody + p24 antigen)
  • Hepatitis A - IgM + IgG
  • CMV and EBV - IgM + IgG
  • M, M, R - IgM + IgG
  • VZV - IgG
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13
Q

What is the difference between the IgM and IgG results?

A
  • IgM - marker for recent or acute infection (duration: 3 months)
  • IgG - in absence of IgM - infection at some time in the past, or immunisation (duration: life long)
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14
Q

What is the specificity like for IgM tests and how can you determine the significance of a positive IgM result?

A
  • Low specificity
  • Therefore, more false positives

• Antibody avidity test for significance of positives

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15
Q

How does antibody avidity change over the duration of an infection?

A
  • Low avidity at acute stages of infection

* Maturation of immune response - avidity increases

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16
Q

What does a low and high antibody avidity indicate?

A
  • Low - recent/acute infection

* High - past infection

17
Q

What generation of EIA are we on?

A
  • 4th generation

* Ab + p34 Ag detection

18
Q

What does confirmatory testing in HIV serology involve?

A
  • Second assay
  • Exclude non-specific reactivity (false positives)
  • Confirmed positives undergo typing (HIV 1 vs. 2)
  • Repeat blood samples and EDTA blood is required for HIV viral load from all new positives
  • Genotyping and baseline resistance testing
19
Q

How does serology allow early treatment?

A
  • Identifies infection at slightly earlier stages
  • Before antibodies reach detectable levels
  • Highly automated - more samples tested, quickly and cheaply
  • However, more false negatives
20
Q

What is virus isolation in cell culture useful for?

A

Phenotypic antiviral susceptibility testing

21
Q

Why is virus isolation in cell culture only performed in specialised laboratories?

A

Because it’s slow and time consuming

22
Q

How can you visualise viruses and what samples would you used?

A
  • Electron microscopy
  • Limited - time consuming and costly
  • Stool and vesicle fluid samples
23
Q

How can you directly detect viral antigens in clinical samples and when is this method used?

A
  • Immunofluorescence
  • Out-of-hours respiratory virus testing
  • Rapid and inexpensive
  • Subjective and dependent on technician skill and sample quality
24
Q

What disease usually causes hyper-inflated lungs in young children and how can you detect it?

A
  • Bronchiolitis
  • RSV
  • Immunofluorescence and x-ray
25
Q

What type of PCR do you use for respiratory virus testing?

A
  • Multiplex PCR assay
  • Can test for more than one virus per tube (3 or 4)
  • Quicker and more cost effective
26
Q 
Which CNS diseases should you consider having obtained the following information:
• meningitis/encephalitis
• young child with febrile fits
• immunocompromised
• recent travel to endemic region
• SSPE (progressive brain inflammation)
A
  • Meningitis/encephalitis - HSV, VZV, enterovirus
  • Young child with febrile fits - HHV-6, parechovirus
  • Immunocompromised - CMV, EBV, JC virus
  • Recent travel to endemic region - consider Japanese Encephalitis, West Nile virus, equine encephalitides, tick borne encephalitis
  • SSPE - measles (antibody index)
27
Q

Where is it better to take a sample from during diarrhoea and vomiting?

A
  • Stool preferred

* Vomit - low yield

28
Q

What is the difference between enteric and enteroviruses?

A
  • Enteric viruses - causes diarrhoea and vomiting e.g. norovirus, rotavirus
  • Enteroviruses - genus of RNA viruses (intestinal transmission)
29
Q

How do you amplify RNA/DNA virus sequences?

A

• PCR
• Starting block is double-stranded DNA
- if you have RNA: make a ds-DNA copy of the viral RNA
- reverse transcription, using reverse transcriptase from retroviruses
• Strands denatured (95°C),
• Primers annealed (50°C)
• Chain elongation - taq polymerase (72°C)
• Sequence doubles at each completed cycle - exponential amplification

30
Q

What type of PCR detects the amplification of DNA in real time, qualitatively detecting gene expression through the creation of complementary DNA (cDNA) transcripts from RNA?

A

RT-PCR (qPCR - quantitive)

31
Q

What is phylogenetic analysis used for?

A

Investigation of outbreaks and transmission incidence

Diagnostics (5 decks)

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