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MCD Lab diagnostics > Virology > Flashcards

Virology Flashcards

1
Q

what features can we detect in suspected viral infection

A
  • infectious virus itself (by isolation or electron microscopy)
  • protein components (antigens)
  • genetic components (RNA or DNA)
  • host response (antibody or cellular response)
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2
Q

what are the main methods of diagnosing viral infections?

A

o Cell culture and electron microscopy (replaced by PCR)
o Antibody detection – serology (EIA = Enzyme Immunoassay).
o PCR – Polymerase chain reaction detects specific sequences of DNA (genome detection)
o Antigen detection – serology (EIA, IF = Immunofluorescence).
o Quantification of antibody or antigen.
o Serotyping – i.e. in HIV.
o Quantification of genomes – viral load.
o Genome sequencing – genotyping and antiviral resistance testing.

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3
Q

what viruses is genome quantification used for?

A

diagnosis and monitoring of HIV, HBV, HCV and CMV/EBV in the immunocompromised.

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4
Q

what are the limitations of lab tests?

A
  • false negatives due to sensitivity

- false positives due to specificity

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5
Q

what is sensitivity

A

ability to correctly identify positive samples

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6
Q

what is specificity

A

ability to correctly identify negative samples

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7
Q

what types of samples can be taken when investigating viral pathology?

A

o Throat swab, nasopharyngeal aspirate (NPA), Bronchoalveolar lavage (BAL), ET (Endotracheal tube) secretions for PCR.

o Stools – rotavirus, adenovirus, norovirus for antigen detection (EIA) or PCR.

o Urine – BK virus and adenovirus for PCR.

oCSF – herpes viruses and enteroviruses for PCR.

o Blood (clotted) for serology (antibody detection)

o Blood (EDTA) for PCR / 
viral load testing.

o Saliva for serology and/or PCR (e.g. measles).

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8
Q

what biochemical markers are looked out for in HIV?

A

antibody

p24 antigen

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9
Q

what type of antibodies are looked out for in Hep B?

A

IgM and IgG

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10
Q

what is looked out for in HBV?

A

surface Ab, Ag, eAg, eAb, core Ab

core IGM

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11
Q

what is looked for in HCV?

A

antibody with or without core antigen

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12
Q

what is looked for in CMV,EBV, MMR and parvovirus B19?

A

IgM and IgG

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13
Q

what is look for in VZV?

A

IgM

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14
Q

what is IgM a marker of in terms of infection timing?

A

recent infection

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15
Q

what is IgG a marker of?

A

as it is created later in host response it lasts longer and indicated an earlier infection

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16
Q

when are IgM and IgG created?

A

both created in acute phase of disease. IgM peaks early and drops off after a few weeks while IgG only get higher and plateau

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17
Q

what is the process of HIV serology testing?

A
  • 4th gen. currently detects antibody and p24 antigen
  • positive result goes into confirmatory test to reduce false positives in an assay
  • confirmed positives undergo typing for HIV 1 or 2
  • samples repeated and EDTA blood for viral load (for genotyping and resistance testing)
18
Q

what can confirm a positive IgM result?

A

antibody avidity test

19
Q

what is avidity?

A

strength at which antibodies bind to a specific antigen

20
Q

how does avidity change throughout an infection?

A

early on it is low but as the ABs mature it increases

avidity= stability of the overall complex of antibody and antigen

21
Q

what is viral isolation used for despite being time consuming and expensive?

A

phenotypic antiretroviral susceptibility test

22
Q

what is immunofluorescence used for?

A

direct detection of viral antigens
typing and cell culture

rapid and inexpensive but produces subjective results dependent on the skill of the technician

23
Q

what samples are collected in resp tract infection?

A 
Throat swab, nasopharyngeal aspirate (NPA)
Bronchoalveolar lavage (BAL), ET (Endotracheal tube)

then do multiplex PCR with multiple viruses in one tube

24
Q

what is tested for CNS disease?

A
  • Meningitis or encephalitis – HSV, VZV and enterovirus.
  • Young child with febrile fits – Add HHV-6 + parechovirus.
  • Immunocompromised (HIV) – Add CMV, EBV, JC virus.
  • Recent exotic travel – Japanese encephalitis, West Nile virus, equine encephalitides, tick borne encephalitis.
  • Outbreaks – mumps.
25
Q

what sample is taken for diarrhoea and vomiting?

A

stool (preferred)

vomit (low yield)

26
Q

which viruses can be detected in vomit by PCR or EIA?

A 
norovirus
rotavirus
adenovirus
sapovirus
astrovirus
27
Q

what is the process of PCR to amplify RNA (RT-PCR for RNA) or DNA?

A
  • Carry out 30 cycles usually.
  • Starting block is dsDNA ( if the initial virus has RNA, use RT-PCR to form dsDNA).
  • Denaturing the dsDNA into strands by heating.
  • Taq polymerase elongates the chain.
  • Cycles induce exponential expansion.
  • “Real-time” PCR produces a read-out of results.
28
Q

how can outbreaks be investigated?

A

phylogenetic analysis

29
Q

what needs to be done to select the correct antiretroviral drugs?

A

antiretroviral resistance testing

with genotyping

30
Q

what do you need to investigate in a history when diagnosing viral illness?

A
  • vaccination history
  • travel (last 3 weeks)
  • animals/pets
  • contact with infected persons
  • occupation
31
Q

what are the ideal qualities of a virological test?

A
  • high specificity (low level cross reactivity)
  • sensitive (detect virus/antibody at very low levels)
  • rapid
  • non-invasive (reduced risks and easier to repeat)
  • cost effective
32
Q

throat swab

A

virus isolation

enteroviruses and resp viruses

33
Q

stools

A

rotavirus
enteroviruses
diarrhoea causing e.g. adenovirus

34
Q

CSF

A
  • PCR for herpes and enteroviruses

- viruses causing meningitis or encephalitis e.g. VZV

35
Q

nasopharyngeal aspirate

A

resp viruses using immunofluoresence or PCR

e.g. influenza

36
Q

urine

A

virus isolation or PCR

37
Q

blood

A

antibody detection

38
Q

blood with EDTA

A

PCR

- detection and quantification of HIV, HBV, HCV

39
Q

what are the methods of detection?

A
  • electron microscopy (visualise)
  • immunofluorescence (antigens)
  • enzyme immuno assays (antibody and antigen detection e.g. western blot)
  • EIA for HIV antibody
  • PCR
40
Q

what are some advantages of real time PCR?

A
  • quantification during linear phase gives better reproducibility and precision
  • multi-plexing (multiple viruses detected)
  • closed tube eliminates contamination

MCD Lab diagnostics (5 decks)

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