What are the characteristics of requesting a virology report?
Virology test are very unspecific unless looking for special viruses so:
- Take history
- Physical examination
- Send suspcions up to lab
- •Make a list of possible causes
•Determine which tests to request
How can a viral infection can be detected by tests?
- Isolation of virus (now rarely done)
- Protein components (Antigens) of a virus
- Viral DNA/RNA –> Genetic material (via PCR)
- Host response against virus—> Antibodeies
Which qualitative testing for viral infections are now commonly done?
- •Antibody detection (serology - EIA)
- •Antigen detection:
- (Immunofluorescence - IF;
- enzyme immunoassay - EIA)
- •Genome detection (polymerase chain reaction - PCR) (mainly)
- Genome sequencing (genotyping + restistances)
- Serotyping (eg HIV)
Which quntitative measurements of viral infections are done?
Why are they important?
- Quantification of antibody or antigens
- Quantification of genomes –
“viral load” –> essential for monitoring HIV, or viruses in immunosupressed people
What is a serotype?
to determine the sub group of a virus by its surface proteins + markings
the same virus can have several serotypes
What are typical samples used in testing for viral infections?
- Throat swab, Nasopharyngeal aspirate (NPA), bronchoalveolar lavage (BAL), ET secretions – for detection of respiratory viruses by (IF or) PCR
- Stools - for rotavirus, adenovirus & norovirus antigen detection (EIA) or PCR
- Urine – for BK virus & 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 &/or PCR (eg measles)
What is serology?
When is serology done?
Antibody testing in serum
done in (no need to learn in detail)
- •HIV serology (antibody + p24 antigen)
- •Hepatitis A IgM and IgG
- •HBV surface Ag/Ab, eAg/eAb, core Ab, core IgM
- •HCV serology (antibody +/- core antigen)
- •CMV and EBV IgM & IgG
- •VZV IgG
- •Measles, mumps, rubella IgM & IgG
- •Parvovirus B19 IgM & IgG
When can you detect different antibodies in a viral serology test?
IgM–> detected in first 3 Month of infection
IgG–> lifelong detection
What is antibody avidity?
combined effect of all affinities participating in the biomolecular interaction
–> Antibodies mature in the first 4 month and show a higher avidtiy –> the more specific, the longer the virus is there
not just binding of one antigen (affinity)
When is virus isolation done today?
Slow, time consuming and expencive
only done for anitviral suspectibility testing
What is immunoflourescence?
When is it used in viral diagnosis?
Flourescent labelled antibodies are injected /inhaled etc, and then imagining performed
Antibodies bind to virus and stick to place –> can be seen on imaging
–> rapdi, fast but subjective interpretation
Which tests can be done using PCR in viral diagnostics?
–Reverse transcription PCR
–Real Time PCR
–Multiplex PCR
–Viral load testing
–Sequencing (antiviral drug resistance testing)
