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Y2 MCD Laboratory Diagnostic Methods > virology > Flashcards

virology Flashcards

virology: explain the role of virology tests in the diagnosis of infectious disease, list the types of specimen that are commonly sent for virological diagnosis, and list laboratory procedures that may be used

1
Q

diagnostic pathway to virological laboratory tests

A

history -> physical examination -> “non-specific” laboratory tests -> virological laboratory tests (make list of possible causes then determine which tests to request)

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2
Q

what is a common virological symptom in physical examination

A

rash

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3
Q

what 4 things can be detected, and how to detect it

A

infectious virus (isolation and electron microscopy), protein components (antigens e.g. in CSF, serum), genetic components (DNA or RNA), host response (antibody/cell)

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4
Q

5 diagnostic methods

A

cell culture (very rare - use PCR), electron microscopy (very rare - use PCR), antibody and antigen detection and quantification, genome detection

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5
Q

outcome of limitations of laboratory test assays for cell culture and electron microscopy

A

give rise to false negatives and false positives

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6
Q

define sensitivity

A

test’s ability to correctly identify positive samples

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7
Q

define specificity

A

test’s ability to correctly identify negative samples

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8
Q

methods of diagnostics for antibodies and antigens

A

quantification, serotyping (e.g. HIV)

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9
Q

what does quantification of genomes provide, and what is it essential for

A

viral load, essential for HIV and other blood viruses in immunocompromised

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10
Q

2 types of genome sequencing

A

genotyping, antiviral resistance testing

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11
Q

7 samples used for testing

A

throat (and maybe nose) swab, nasopharyngeal aspirate, bronchoalveolar lavage, endotracheal secretions; stools; urine; CSF; blood (clotted); blood (EDTA); saliva

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12
Q

what are throat (and maybe nose) swab, nasopharyngeal aspirate, bronchoalveolar lavage, ET secretions used for and how

A

detection of respiratory viruses by PCR

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13
Q

what are stools used for and how

A

rotavirus, adenovirus, norovirus antigen detection or PCR

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14
Q

what is urine used for and how

A

BK virus and adenovirus or PCR

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15
Q

what is CSF used for and how

A

herpes viruses and enteroviruses or PCR

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16
Q

what is blood (clotted) used for and how

A

serology (antibody detection)

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17
Q

what is blood (EDTA) used for

A

PCR/viral load testing

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18
Q

what is saliva used for

A

serology and/or PCR (e.g. measles)

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19
Q

serology prevalence

A

most common test

20
Q

serology investigations

A

HBV surface Ag/Ab, eAg/eAb, core Ab, core IgM

21
Q

serology: IgM vs IgG - when present and duration

A

both acute phase of disease, but IgM approx 3 months whilst IgG is lifelong

22
Q

antibody avidity testing: when used

A

IgM is very non-specific (sensitive), so often false positives; use avidity test to determine strength of antibody binding (mix with denaturisation agent to wash away binding; only if non-specific will it wash away and poorly bind)

23
Q

HIV serology technique

A

4th generation EIA: Ab + p24 Ag detection

24
Q

HIV serology: what must all samples undergo to excluse non-specific reactivity (false positives)

A

confirmatory testing in second essay

25
Q

HIV serology: what do confirmed positives undergo

A

typing (HIV 1 vs 2)

26
Q

HIV serology: what is required from all new positives

A

repeat blood sample and EDTA blood for HIV viral load

27
Q

automated serology equipment

A

multidisciplinary automated laboratory

28
Q

what is point-of-care testing, and disadvantages

A

virology test kit (e.g. influenza PCR test kit) at point-of-care to detect virus; not as sensitive or specific

29
Q

when is virus isolation in cell culture used

A

rarely - only in reference lab

30
Q

disadvantages of virus isolation in cell culture

A

slow, time consuming, expensive

31
Q

when is virus isolation in cell culture useful

A

phenotypic antiviral susceptibility testing, but low sensitivity and specificity

32
Q

what is (rarely) used to visualise viruses

A

electron microscope

33
Q

sample types for electron microscopy

A

stool, vesicle fluids

34
Q

when is immunofluorescence used

A

occasionally for direct detection of viral antigens in clinical samples e.g. respiratory virus

35
Q

advantages of immunofluorescence

A

rapid, inexpensive

36
Q

disadvantages of immunofluorescence

A

subjective, very dependent on skill of technician and quality of sample

37
Q

what technique is used in testing respiratory tract infections

A

multiplex PCR

38
Q

what does multiplex PCR allow you to do

A

look for multiple pathogens, simultaneously, in same sample; amplify viral DNA/RNA to detect if virus using electrophoresis

39
Q

what samples are taken for testing CNS disease e.g. meningitis, encephalitis, and techniques used

A

CSF for PCR, stools and throat swab for PCR, blood for serology and/or PCR

40
Q

clinical history vs CNS disease

A

travel, age, immunocompromised; always history and symptoms to be matched up with most relevant diagnostic test

41
Q

what samples are taken if diarrohoea and vomiting

A

stool (preferred), vomit (lower yield)

42
Q

what techniques are used in investigating diarrohoea and vomiting

A

PCR or antigen detection assays

43
Q

purpose of PCR

A

polymerase chain reaction: amplifies specific RNA or DNA sequences

44
Q

PCR method

A

cycle of: denature (hot) -> primer annealing (cool) -> chain elongation with Taq polymerase using dsDNA (RNA with reverse transcriptase)

45
Q

PCR machines

A

“real time” PCR, “real time” PCR melt curve analysis (PCR samples melt at different temperatures, so can determine which virus); automated system, viral load system

46
Q

sequencing applications

A

genotyping, antiviral resistance testing, phylogenetic analysis (determine if transmission between patients)

Y2 MCD Laboratory Diagnostic Methods (5 decks)

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