Virology Lab

Question 1

Describe the ideal virological test

Answer 1

High specificity 
Sensitive
Rapid
Non-invasive
Cost-effective

Question 2

What can the virology lab be useful in detecting

Answer 2

Infectious virus
Protein components/antigens of the virus
Genetic components of the virus
The host response

Question 3

Give some examples of diagnostic methods

Answer 3

Cells culture
Electron microscopy 
Antibody detection (serology, EIA)
Antigen detection (IF, EIA)
Genome detection (PCR)

Question 4

What are the limitations of diagnostic methods such as assays

Answer 4

All assays give rise to false negative and false positive results

Question 5

What is sensitivity

Answer 5

The test’s ability to correctly identify positive samples

Question 6

What is specificity

Answer 6

The test’s ability to correctly identify negative samples

Question 7

Give examples of other diagnostic methods

Answer 7

Quantification of antibody or antigens
Serotyping (eg HIV)
Quantification of genomes – “viral load”
Genome sequencing
Genotyping
Antiviral resistance testing

Question 8

What is quantification of genomes useful for

Answer 8

Essential for diagnosis and monitoring of HIV, HBV and HCV, and also for CMV and EBV in the immunocompromised)

Question 9

What samples are used for detection of respiratory viruses

Answer 9

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

Question 10

Give examples of typical samples used

Answer 10

Stools
Urine
CSF
Blood (clotted)
Blood (EDTA)
Saliva

Question 11

What can stool and urine samples be used for

Answer 11

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

Urine - BK virus and adenovirus PCR

Question 12

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

Answer 12

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

Blood (EDTA) - for PCR / viral load testing

Question 13

What can saliva samples be used for

Answer 13

Serology and PCR e.g. measles

Question 14

Compare IgM and IgG

Answer 14

Both present in acute phase of disease
IgM- 3 months
IgG - lifelong
IgM often gives false positives - avidity testing used to test strength of antibody binding

Question 15

Describe serology testing

Answer 15

HIV - antibody + p24 antigen
Hep A - IgM and IgG
HBV - surface Ag/Ab, eAg/eAb, core Ab, core IgM
HCV - antibody, core antigen 
CMV/EBV - IgM and IgG
VZV - IgG
MMR - IgM, IgG
Parvovirus - B19 - IgM, IgG

Question 16

Describe HIV serology

Answer 16

All reactive samples undergo confirmatory testing in a second assay to exclude specific reactivity (false +ve)
Confirmed positive -> typing
Repeat blood sample + EDTA blood for HIV viral load

Question 17

Describe virus isolation in cell culture

Answer 17

Slow and time consuming and therefor expensive

Useful for phenotypic antiviral susceptibility testing (HSV)

Question 18

Describe electron microscopy

Answer 18

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

Question 19

Describe immunofluorescence

Answer 19

Still occasionally used for the direct detection of viral antigens in clinical samples (DIF) (e.g. respiratory viruses)
Rapid and inexpensive but subjective and very dependent on the skill of the technician and the quality of the sample