Virology Lab

Question 1

What is a maculopapular rash?

Answer 1

Some areas are raised and some areas are flat

Question 2

What is a dermatomal distribution of a rash indicative of?

Answer 2

Shingles

Question 3

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

Answer 3

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

Question 4

What is the main method of virus detection?

Answer 4

PCR

Question 5

What technique is used for antibody detection?

Answer 5

Enzyme immunoassay – detects antibodies and antigens

Question 6

Define sensitivity

Answer 6

Test’s ability to correctly identify positive samples

Low rate of false negative

Question 7

Define specificity

Answer 7

Test’s ability to correctly identify negative samples

Low rate of false positives

Question 8

What does quantification of the genomes allow assessment of

Answer 8

Viral load (amount of viral nucleic acid present in bloods/fluids)

Diagnosis and monitoring of HIV, HBV and HCV + CMV and EBV in immunocompromised

Question 9

Compare IgM and IgG

Answer 9

Both present in acute phase of disease
IgM- 3 months (recent infection)
IgG - lifelong (rises later)

IgM often gives false positives - avidity testing used to test strength of antibody binding

Question 10

What does positive IgG and absent IgM indicate

Answer 10

Past infection or immunisation

Question 11

Describe the process of HIV testing

Answer 11

4th generation EIA
Antibodies and p24 antigen

All reactive samples undergo confirmatory testing in a second assay to exclude non-specific reactivity (false positives)

Question 12

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

Answer 12

Typing (HIV 1 or HIV2)

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

Question 13

What test is used to confirm a positive IgM result

Answer 13

Antibody avidity testing

Question 14

Describe how antibody avidity changes in infection.

Answer 14

Early on in the infection, avidity is LOW
Then you get maturation of the antibody response so the avidity will increase over a period of 3-6 months
If you have HIGH antibody avidity, then it is unlikely that the infection occurred in the last 3 months

Question 15

What is immunofluorescence useful for

Answer 15

Direct detection of viral antigens e.g. resp

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

Question 16

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

Answer 16

Multiplex PCR

Question 17

What samples are used for detection of respiratory viruses

Answer 17

Throat swab
Nasopharyngeal aspirate (NPA)
bronchoalveolar lavage (BAL)
ET secretions

Question 18

What can stool and urine samples be used for

Answer 18

Stool - rotavirus, adenovirus, norovirus antigen detection (EIA) or PCR

Urine - BK virus and adenovirus PCR

Question 19

What can CSF and blood (clotted and EDTA) samples be used for

Answer 19

CSF - for herpes viruses and enteroviruses PCR
Blood (clotted) - for serology (antibody detection)

Blood (EDTA) - for PCR / viral load testing

Question 20

What can saliva samples be used for

Answer 20

Serology and PCR e.g. measles

Question 21

Give examples of types of virology testing

Answer 21

Cell culture
Electron microscopy (EM) -
Antibody detection e.g. anti-HIV antibody (Enzyme Immuno Assays)
Antigen detection (IF, EIA) - HBsAg in hepatitis B infection or RSV antigen in respiratory sample
Genome detection –PCR to detect viral DNA or RNA
Quantification of antigens and genomes (now essential for diagnosis and monitoring of HIV, HBV and HCV)
Genome sequencing: Genotyping, Antiviral resistance testing

Question 22

Give the advantages and disadvantages of virus isolation in cell culture

Answer 22

Useful for phenotypic antiviral susceptibility testing (HSV)

Slow and time consuming and therefor expensive

Question 23

Describe electron microscopy

Answer 23

Viruses are small but can be visualised using an electron microscope.
Sample types of stool and vesicle fluids
Rarely used

Question 24

What tests should be ordered for a suspected respiratory tract infection

Answer 24

Throat swab +/- nose swab
Nasopharyngeal swab
Nasopharyngeal aspirate (NPA)
Bronchoalveolar lavage (BAL)
Endotracheal tube (ET) secretions - all for respiratory virus multiplex PCR*

Question 25

What tests should be ordered for a CNS disease, for example meningitis and encephalitis

Answer 25

CSF for PCR (HSV, VZV, enterovirus)
Stools + throat swab for enterovirus detection (i.e. by PCR)
Blood for serology and/or PCR for West Nile and/or Japanese Encephalitis virus infection and other arboviruses

Question 26

What tests should be ordered for diarrhoea and vomiting

Answer 26

Stool (preferred) or vomit (but lower yield)
PCR or antigen detection assays (EIA)
Enteric viruses causing diarrhoea/vomiting = norovirus, rotavirus, adenovirus, sapovirus, astrovirus

Question 27

Describe the method for PCR

Answer 27

1. dsDNA or Viral RNA converted to dsDNA using reverse transcriptase from retroviruses
2. Denature at 95 degrees
3. Primer annealing
4. Chain elongation by taq polymerase
5. Cycle x30

Question 28

What are the uses for the products of OCR

Answer 28

Genotyping
Antiviral resistance testing
Phylogenetic analysis - investigate outbreaks/transmission

Question 29

What are the types of PCR

Answer 29

RT-PCR 
Real Time PCR (different to above) 
Multiplex PCR
Viral load testing
Sequencing (antiviral drug resistance testing)