Diagnostic Virology Flashcards
What is a maculopapular rash?
Some areas are raised and some areas are flat
What is a dermatomal distribution of a rash indicative of?
Shingles or herpes
What can be used in virus detection?
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)
What is the main method of virus detection?
PCR
What technique is used for antibody detection?
Enzyme immunoassay – detects antibodies and antigens
Define sensitivity.
Low rate of false negatives
The ability of the test to identify everyone with the disease
Define specificity.
Low rate of false positives
The ability of the test to identify everyone without the disease
What does quantification of the genomes allow assessment of?
Viral load - used in HIV
What is the difference between IgM and IgG in terms of when theirlevels rise following infection?
IgM is a marker of RECENT infection IgG rises later on in the infection and some remains after the infection has passed
What does positive IgG and absent IgM indicate?
Past infection or immunisation
What is targeted in the detection of HIV?
Antibody and p24 antigen
What other investigations are performed on people who are identified as HIV positive?
Typing (HIV 1 or HIV2) Repeat blood sample and EDTA blood for HIV viral load (for genotyping and baseline resistance testing)
What test is used to confirm a positive IgM result?
Antibody avidity testing
Describe how antibody avidity changes in infection.
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
What is immunofluorescence useful for?
Direct detection of viral antigens
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 4 things are sampled when testing for meningitis/encephalitis?
- CSF
- Stools and throat swab (for enterovirus detection)
- Blood
What is sampled when testing for causes of diarrhoea/vomiting?
Stool (and vomit)
What must happen first before PCR is performed to identify the genome of an RNA virus?
The RNA must be reverse transcribed by reverse transcriptase to dsDNA dsDNA is the start point of PCR
Describe the process of PCR.
The dsDNA is denatured by heating it The primers then bind to the single stranded DNA and Taq polymerase joins complementary nucleotides to the template strand
What are the applications of sequencing viral genomes?
Antiviral resistance testing Phylogenetic analysis
