Diagnostic Virology Flashcards
What components of the virus can be used in virus detection?
Virus isolation + electron microscopy to visualise the virus itself Protein components (antigens) Genetic components (RNA or DNA) Host response (antibody or cell responses)
What is the main method of virus detection?
PCR
What technique is used for antibody detection?
Enzyme immunoassay: detects antibodies + antigens
Define sensitivity.
Test’s ability to correctly identify positive samples
Define specificity.
Tests ability to correctly identify negative samples
What does quantification of the genomes allow assessment of?
Viral load
What is the difference between IgM and IgG in terms of when their levels rise following infection?
IgM is a marker of RECENT infection
IgG rises later on
What does positive IgG and absent IgM indicate?
Past infection or immunisation
What is targeted in the detection of HIV?
Antibody + p24 antigen
What other investigations are performed on people who are identified as HIV positive?
Confirmatory testing
Typing (HIV 1 or HIV2)
Repeat blood sample + EDTA blood for HIV viral load (for genotyping + baseline resistance testing)
What test is used to confirm a positive IgM result?
Antibody avidity testing
Describe how antibody avidity changes in infection.
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
What is immunofluorescence useful for? Why is it rarely used?
Direct detection of viral antigens
Subjective + dependent on skill of technician
What is the term given to the method of PCR that allows testing for more than one virus using a single test tube?
Multiplex PCR
What is sampled when testing for meningitis/encephalitis?
CSF (for PCR)
Stools + throat swab (for enterovirus detection)
Blood (for serology)
What is sampled when testing for causes of diarrhoea/vomiting?
Stool
Vomit
What must happen first before PCR is performed to identify the genome of an RNA virus?
RNA must be reverse transcribed by reverse transcriptase to dsDNA
dsDNA is the start point of PCR
Describe the process of PCR.
dsDNA is denatured by heating it
Primers bind to the single stranded DNA
Taq polymerase joins complementary nucleotides to the template strand
What are the applications of sequencing viral genomes?
Genotyping
Antiviral resistance testing
Phylogenetic analysis
When is virus isolation in cell culture useful? Why is it no longer commonly used?
Phenotypic antiviral susceptibility testing (HSV)
Slow + time consuming
List 6 sample sites
Throat swab Stools CSF Nasopharyngeal aspirate Urine Blood (clotted or EDTA)
