Diagnostic Virology

Question 1

What is a maculopapular rash?

Answer 1

Some areas are raised and some areas are flat

Question 2

What is a macular rash

Answer 2

Essentially the rash is flat

Question 3

What does quantification of viral genomes allow assessment of?

Answer 3

Viral load

Question 4

In viral serology what does positive IgG and absent IgM indicate?

Answer 4

Past infection or immunisation

Question 5

What is targeted in the detection of HIV?

Answer 5

Antibody and p24 antigen (viral protein that makes up the capsid)

Question 6

What other investigations are performed on people who are identified as HIV positive?

Answer 6

Typing (HIV 1 or HIV2)

Repeat blood sample and EDTA blood for HIV viral load (for genotyping and baseline resistance testing)

Question 7

What test is used to confirm a positive IgM result?

Answer 7

Antibody avidity testing

Question 8

What must happen first before PCR is performed to identify the genome of an RNA virus?

Answer 8

The RNA must be reverse transcribed by reverse transcriptase to dsDNA dsDNA is the start point of PCR

Question 9

What are the applications of sequencing viral genomes?

Answer 9

Antiviral resistance testing Phylogenetic analysis

Question 10

With shingles what patterns of rash is observed?

Answer 10

Dematomal

Question 11

How can we isolate viral particles?

Answer 11

Traditionally use cell culture + electron microscopy (slow + expensive)
Now can use PCR

Question 12

How can we detect viral antigens?

Answer 12

Immunofluorescence (ELISA etc…) or serotype

Question 13

How do we define the sensitivity of an assay?

Answer 13

Sensitivity is the tests ability to correctly identify true positives
in other words it is the fraction of detected positives that are truly positive from the total pool of true positives
Mathematically we would express this as:

Sensitivity = TP / TP + FN

Question 14

How do we define the specificity of an assay?

Answer 14

Specificity is the tests ability to correctly identify true negatives

With both sensitivity and specificity it is easiest to define them mathematically

Specificity = TN / FP + TN

Question 15

What is the precision of positive predictive values and negative predictive value?

Answer 15

These simply describe the true predictive power based on the total predicted of that nature e.g.

PPV = TP / Total positives

Question 16

Identify samples we can use for abstracting biological material? What do we use these for?

Answer 16

Throat swab/nasopharyngeal aspirate/bronchoalveolar lavage (respiratory viruses/microorganisms)
Stools (e.g. norovirus)

Urine (adenovirus)

CSF (herpes simplex virus)

Clotted blood for serology, whilst EDTA blood for PCR/viral load testing

Saliva for serology and/or PCR

Question 17

What exactly do we look at in serology examinations? And what kind of things can we tell?

Answer 17

Serology is essentially examining the individuals immune response, that is the antibodies present in their blood. IgM would predict a recent infection, whilst IgG suggests a more long-term infection.

Question 18

How could you distinguish between chronic and acute infections?

Answer 18

Do an avidity test. Avidity is high in chronic infection because there is an accumulated strength of multiple affinities of receptor to their molecule. Relates to maturation of the antibody. Avidity specifically involves non-covalent interactions.

Question 19

How can you define avidity mathematically?

Answer 19

Avidity index (AI) = OD(8M urea)/OD(0.85% NaCl) x 100 (%)

Question 20

With respect to virology what is the advantage of multiplex PCR?

Answer 20

Rather than using a single test tube for each virus, you test for several viruses in one tube - much faster + cheaper