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Y2 MCD Diagnostics > Virology lab > Flashcards

Virology lab Flashcards

1
Q

What is it called if a rash has some areas that are raised and some that are flat?

A

Maculopapular

Macular = flat lesions

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2
Q

What is a blotchy appearance rash typical of?

A

Measles

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3
Q

If the distribution of a rash is dermatomal, what is this typical of?

A

Shingles

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4
Q

What can virologists detect?

A

Infectious virus- virus isolation and EM
Protein components- antigens on the virus (p24 antigen in HIV, surface antigen in HBV, etc)
Genetic components of the virus (DNA or RNA)- quantitative/qualitative tests available
Host response- antibody or cell response

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5
Q

Why are cell culture and electron microscopy not used much anymore?

A

They have been replaced by PCR (genome detection)

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6
Q

What is sensitivity?

A

A test’s ability to correctly identify positive samples –> affects the rate of false negatives

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7
Q

What is specificity ?

A

A test’s ability to correctly identify negative samples –> affects the rat eof false-positives

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8
Q

What is a marker of recent infection?

A

IgM - IgG comes later on

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9
Q

What is essential for diagnosis and monitoring of HIV, HBV and HCV and also for CMV and EBV in immunocompromised?

A

Viral load- quantification of genomes

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10
Q

What typical sort of samples are used by virologists?

A

Throat swab, nasopharyngeal aspirate, bronchoaveolar lavage- detection of respiratory viruses by PCR
Stools- For rotavirus, adenovirus and norovirus antigen detection or PCR
Urine- for BK virus and 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 and or PCR

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11
Q

What is positive IgG with absent IgM consistent with?

A

Past infection or immunisation

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12
Q

What is antibody avidity testing used for?

A

Confirming a positive IgM result

A sample of serum is taken a few weeks apart and you detect which one binds more strongly to the sample.

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13
Q

What does antibody avidity mean?

A

The strength with which antibodies bind to a specific antigen

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14
Q

How does antibody avidity change throughout infection?

A

Early on in course of infection, avidity is low
Then you get maturation of antibody response so avidity gradually increases over a period of 3-6 months
If you have high antibody avidity then it makes it unlikely that infection occured in last 3 months

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15
Q

What is virus isolation in cell culture still useful for despite being slow and time consuming?

A

Phenotypic antiretroviral susceptibility testing (HSV)

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16
Q

What is immunofluorescence still useful for? What are its pros and cons?

A

DIRECT detection of viral antigen in clinical samples DIF (e.g. respiratory viruses),

Rapid and inexpensive but subjective and dependent on skill of technician and quality of sample

17
Q

What are the recommended sample types used for investigation of respiratory tract infections?

A 
Throat swab and nose swab
Nasopharyngeal swab
Nasopharyngeal aspirate
Bronchoaveolar lavage
Endotracheal tube secretion

SENT AWAY FOR PCR

18
Q

What is multiplex PCR? How does it work?

A

Where you test for several viruses in one tube rather than single tube for each virus (makes it faster) - although you can only do 3/4 at a time

METHOD: markers of genes of different viruses are added. Bands are compared on PCR

19
Q

What are the recommended sample types for CNS disease- meningitis and encephalitis?

A
  • CSF for PCR (HSV, VZV, enterovirus etc)
  • Stools and throat swab for enterovirus detection (PCR)
  • Blood for serology and or PCR for west nile or japanese encephalitis virus infection and other arboviruses
20
Q

What is PCR?

A

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

30 cycles of denaturing, primer annealing and chain elongation

21
Q

What is the starting block for PCR?

A

If you are looking for an RNA virus e.g. influenza then you first need to make a dsDNA copy of the RNA using REVERSE TRANSCRIPTASE
You then denature the dsDNA into two separate strands - achieved by heating

22
Q

What is the most important enzyme in PCR?

A

Taq polymerase

23
Q

What is phylogenetic analysis used for?

A

Investigating outbreaks

24
Q

List some different diagnostic methods available for viruses.

A 
Cell culture and EM
Genome detection by PCR
Genome sequencing - genotyping, antiviral resistance testing 
Antibody detection (serology - EIA)
Antigen detection (Immunofluorescence, enzyme immunoassay EIA)
Quantification of antibody/antigens 
Serotyping e.g. HIV
Quantification of genomes - "viral load"
25
Q

What is serology used for?

A

Testing for a specific antibody or viral antigen e.g. in serum (salive, CSF)

26
Q

Compare the duration of IgM and IgG.

A

IgM ~3months (rapid increase, peak, levels offwithin 3 months)
IgG = lifelong (rises slowly on graph and remains high)

27
Q

What can a 4th generation EIA of HIV detect?

A

Antibody and p24 antigen(at the core of the virus)

28
Q

Describe serology tests for HIV.

A
  1. 4th gen EIA - detects both Ab and p24 antigen (if this is positive then a second assay is done for confirmatory testing to exclude false positives)
  2. Confirmed positives –> typing (HIV 1 or 2?)
  3. Blood sample released and EDTA blood taken to assess viral load, genotype and for baseline resistance testing.
29
Q

What is electron microscopy useful for? What types of samples?

A

For viruses which are too small to be seen under microscope
Sample types: stool, vesicle fluids.

BUT rarely used now,

30
Q

Describe the appearance of these viruses under EM:
Herpes
Rabies
Ebola

A

Herpes - core with 20 faces, enveloped virus.
Rabies - bullet shaped
Ebola - filamentous virus

31
Q

What temperatures does PCR operate at?

A

Denature - 95oC
Annealing - ~50oC
Extension - 72oC (Taq polymerase and nucleotides)

32
Q

What does Taq polymerase come from?

A

Thermophilus aquaticus

33
Q

List 2 applications of sequencing viruses.

A

Antiviral resistance testing - vital for selecting the correct antiretroviral drugs
Phylogenetic analysis - tool for investigating outbreaks

Y2 MCD Diagnostics (5 decks)

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