Diagnostic Virology

Question 1

What components of the virus can be used in virus detection?

Answer 1

Virus isolation + electron microscopy to visualise the virus itself 
Protein components (antigens)  
Genetic components (RNA or DNA)  
Host response (antibody or cell responses)

Question 2

What is the main method of virus detection?

Answer 2

PCR

Question 3

What technique is used for antibody detection?

Answer 3

Enzyme immunoassay: detects antibodies + antigens

Question 4

Define sensitivity.

Answer 4

Test’s ability to correctly identify positive samples

Question 5

Define specificity.

Answer 5

Tests ability to correctly identify negative samples

Question 6

What does quantification of the genomes allow assessment of?

Answer 6

Viral load

Question 7

What is the difference between IgM and IgG in terms of when their levels rise following infection?

Answer 7

IgM is a marker of RECENT infection

IgG rises later on

Question 8

What does positive IgG and absent IgM indicate?

Answer 8

Past infection or immunisation

Question 9

What is targeted in the detection of HIV?

Answer 9

Antibody + p24 antigen

Question 10

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

Answer 10

Confirmatory testing
Typing (HIV 1 or HIV2)
Repeat blood sample + EDTA blood for HIV viral load (for genotyping + baseline resistance testing)

Question 11

What test is used to confirm a positive IgM result?

Answer 11

Antibody avidity testing

Question 12

Describe how antibody avidity changes in infection.

Answer 12

Early in infection, avidity is LOW
Maturation of the antibody response occurs so avidity increases over 3-6 months
HIGH antibody avidity, indicates the infection is unlikely to have occurred in the last 3 months

Question 13

What is immunofluorescence useful for? Why is it rarely used?

Answer 13

Direct detection of viral antigens

Subjective + dependent on skill of technician

Question 14

What is the term given to the method of PCR that allows testing for more than one virus using a single test tube?

Answer 14

Multiplex PCR

Question 15

What is sampled when testing for meningitis/encephalitis?

Answer 15

CSF (for PCR)
Stools + throat swab (for enterovirus detection)
Blood (for serology)

Question 16

What is sampled when testing for causes of diarrhoea/vomiting?

Answer 16

Stool

Vomit

Question 17

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

Answer 17

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

Question 18

Describe the process of PCR.

Answer 18

dsDNA is denatured by heating it
Primers bind to the single stranded DNA
Taq polymerase joins complementary nucleotides to the template strand

Question 19

What are the applications of sequencing viral genomes?

Answer 19

Genotyping
Antiviral resistance testing
Phylogenetic analysis

Question 20

When is virus isolation in cell culture useful? Why is it no longer commonly used?

Answer 20

Phenotypic antiviral susceptibility testing (HSV)

Slow + time consuming

Question 21

List 6 sample sites

Answer 21

Throat swab
Stools
CSF
Nasopharyngeal aspirate
Urine
Blood (clotted or EDTA)