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MCD diagnostics > diagnostic virology > Flashcards

diagnostic virology Flashcards

1
Q

what are we able to detect using diagnostic virology ?

A
  • infectious virus
  • Protein Components
  • Genetic Components of the virus (DNA or RNA)
  • The Host Response
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2
Q

what used to be the main diagnostic method?

what is the main diagnostic method now?

A

Cell culture and electron microscopy have been replaced

  • PCR - a sensitive method used to detect specific sequences of nucleic acids
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3
Q

what does the antibody detection test for?

A

This detects antibodies or antigens

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4
Q

what does sensitivity mean?

A

the test’s ability to correctly identify positive samples

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5
Q

what does specificity mean?

A

the test’s ability to correctly identify negative samples

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6
Q

what does a low rate of false negatives mean?

A

SENSITIVE

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7
Q

what does a low rate of false positives mean?

A

SPECIFIC

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8
Q

what are the other main diagnostic measures used?

A
  • serotyping
  • quantification of genomes
  • genome sequencing
  • quantification of the antibody or antigen
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9
Q

what is Quantification of genomes important for?

A
  • looking at the viral load
  • This is essential for diagnosis and monitoring of HIV, HBV and HCV, and also for CMV and EBV in the immunocompromised
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10
Q

what are the typical samples used?

A
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11
Q

what is serology ?

A

the scientific study or diagnostic examination of blood serum, especially with regard to the response of the immune system to pathogens or introduced substances.

looking at viruses including :

HIV, Hep A.HBV, HCV, CMV, VZV, Measles mumps, rubella,

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12
Q

how is HIV serology testing carried out?

A
  • we are on the 4th generation EIA and p24 antigen detection
  • if a positive result is found then we undergo confirmatory testing in a second assay to exclude false positives
  • the confirmed positives will undergo typing for either t 1 or t2
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13
Q

what are antibody avidity testings for?

A
  • this allows a means for confirmation a positive IgM result
  • Avidity - strength with which antibodies bind to a specific antigen
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14
Q

how does avidity change ?

A
  • early on the avidity is low
  • so avidity gradually increases over a period of 3-6 months
  • If you have high antibody avidity then it makes it unlikely that the infection occurred in the last 3 months
  • so can tell us when the infection came on
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15
Q

what is Immunofluorescence for ?

A
  • useful for direct detection of viral antigens in clincial settings
  • Can be used for typing and cell culture confirmation
  • rapid and inexpensive
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16
Q

analyse this Immunofluorescence: insert pic

A

The lungs are hyperinflated

  • Normally you should only be able to count 6 ribs but here you see 7 anteriorly so it is hyperinflated
  • This is bronchiolitis
  • inflammation of the small airways in the lungs (bronchioles) due to viral infection,
17
Q

what samples do we take for resp tract infections

A

we use PCR for all

the samples we take our the following

throat swab

nasopharyngeal swab

nasopharyngeal aspirate

bronchoalveolar lavage

endotracheal tube secretions

18
Q

what is multiplex PCR?

A

rather than using a single test tube for each virus, you test for several viruses in one tube do 3 /4

19
Q

how do we sample for CNS disease like meningitis or encephalitis?

A
  • Cerebrospinal Fluid for PCR
  • Stools and Throat Swab for enterovirus detection (PCR)
  • Blood for serology and/or PCR for west Nile or Japanese Encephalitis virus infection
20
Q

what do we sample for Diarrhoea and Vomiting?

A
  • stool (preferred!)
  • vomit - has a lower yield
  • PCR or antigen detection assays
21
Q

enteric viruses vs enteroviruses?

A

these are two different things

enteric viruses are transmitted through fecal-oral routes

enteroviruses a group of single-stranded sense RNA viruses especially in kids

22
Q

what is PCR?

A
  • polymerase chain reaction
  • is a method for amplifying specific RNA or DNA sequences
  • a normal PCR cycle lasts 30 rounds
23
Q

what are the stages of PCR?

A
  • denaturing
  • primer annealing
  • chain elongation
24
Q

what substances are required in PCR?

and what for?

A
  • the starting block for PCR is dsDNA
  • to make a dsDNA copy reverse transcriptase is needed
  • the dsDNA is then denatured by heating

- the most important enzyme is Taq polymerase which is needed to polymerase the DNA

25
Q

what is the nature of expansion after PCR?

A

exponential increase

26
Q

what is antiviral resistance testing used for?

A

This is vital for selecting the correct antiretroviral drugs

27
Q

what is Phylogenetic Analysis for?

A

tool for investigating outbreaks

28
Q

what tests should billy undergo?

A

EBV and CMV might cause a lot of the symptoms so should be tested for

  • HIV should also be checked just in case
  • Viral Hepatitis can account for the odd liver function tests

the results show :

CMV and EBV serology shows that he has had past infection with EBV and CMV

MCD diagnostics (5 decks)

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