Diagnostic Virology Flashcards
What is a maculopapular rash?
Some areas are raised and some areas are flat. This blotchy appearance is typical of measles rash
What is a dermatomal distribution of a rash indicative of?
Shingles
What components of the virus can be used in virus detection?
Infectious Virus
- Virus isolation and electron microscopy
Protein Components (antigens) on the virus
- E.g. p24 antigen in HIV, surface antigen in HBV etc
Genetic Componentsof the virus (DNA or RNA)
- Quantitative or qualitative tests are available
The Host Response
- E.g. antibody or cell responses
What is the main method of virus detection?
PCR
PCR is a sensitive method used to detect specific sequences of nucleic acids
What technique is used for antibody detection?
Enzyme immunoassay – detects antibodies and antigens
Define sensitivity.
Low rate of false negatives.
Sensitivity= the test’s ability to correctly identify positive samples
Define specificity.
Low rate of false positives.
Specificity= the test’s ability to correctly identify negative samples
What does quantification of the genomes allow assessment of?
Viral load
- This is essential for diagnosis and monitoring of HIV, HBV and HCV, and also for CMV and EBV in the immunocompromised
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 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 in clinical samples (e.g. respiratory viruses)
- Can be used for typing and cell culture confirmation
- Rapid and inexpensive but subjective and very dependent on the skill of the technician and the quality of the sample
- oThe lungs are hyperinflated oNormally you should only be able to count 6 ribs but here you see 7 anteriorly so it is hyperinflated , bronchitis
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 (HSV, VZV, enterovirus etc.)
- Stools and 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
- NOTE: if there is some travel history you would also look for more exotic viruses
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?
We can also sequence viral genomes •In addition to genotyping we can do antiviral resistance testing•This is vital for selecting the correct antiretroviral drugs •Phylogenetic Analysis-‐this is a tool for investigating outbreaks
