diagnostic virology Flashcards
what are we able to detect using diagnostic virology ?
- infectious virus
- Protein Components
- Genetic Components of the virus (DNA or RNA)
- The Host Response
what used to be the main diagnostic method?
what is the main diagnostic method now?
Cell culture and electron microscopy have been replaced
- PCR - a sensitive method used to detect specific sequences of nucleic acids
what does the antibody detection test for?
This detects antibodies or antigens
what does sensitivity mean?
the test’s ability to correctly identify positive samples
what does specificity mean?
the test’s ability to correctly identify negative samples
what does a low rate of false negatives mean?
SENSITIVE
what does a low rate of false positives mean?
SPECIFIC
what are the other main diagnostic measures used?
- serotyping
- quantification of genomes
- genome sequencing
- quantification of the antibody or antigen
what is Quantification of genomes important for?
- looking at the viral load
- This is essential for diagnosis and monitoring of HIV, HBV and HCV, and also for CMV and EBV in the immunocompromised
what are the typical samples used?
what is serology ?
the scientific study or diagnostic examination of blood serum, especially with regard to the response of the immune system to pathogens or introduced substances.
looking at viruses including :
HIV, Hep A.HBV, HCV, CMV, VZV, Measles mumps, rubella,
how is HIV serology testing carried out?
- we are on the 4th generation EIA and p24 antigen detection
- if a positive result is found then we undergo confirmatory testing in a second assay to exclude false positives
- the confirmed positives will undergo typing for either t 1 or t2
what are antibody avidity testings for?
- this allows a means for confirmation a positive IgM result
- Avidity - strength with which antibodies bind to a specific antigen
how does avidity change ?
- early on the avidity is low
- so avidity gradually increases over a period of 3-6 months
- If you have high antibody avidity then it makes it unlikely that the infection occurred in the last 3 months
- so can tell us when the infection came on
what is Immunofluorescence for ?
- useful for direct detection of viral antigens in clincial settings
- Can be used for typing and cell culture confirmation
- rapid and inexpensive
analyse this Immunofluorescence: insert pic
The lungs are hyperinflated
- Normally you should only be able to count 6 ribs but here you see 7 anteriorly so it is hyperinflated
- This is bronchiolitis
- inflammation of the small airways in the lungs (bronchioles) due to viral infection,
what samples do we take for resp tract infections
we use PCR for all
the samples we take our the following
throat swab
nasopharyngeal swab
nasopharyngeal aspirate
bronchoalveolar lavage
endotracheal tube secretions
what is multiplex PCR?
rather than using a single test tube for each virus, you test for several viruses in one tube do 3 /4
how do we sample for CNS disease like meningitis or encephalitis?
- Cerebrospinal Fluid for PCR
- Stools and Throat Swab for enterovirus detection (PCR)
- Blood for serology and/or PCR for west Nile or Japanese Encephalitis virus infection
what do we sample for Diarrhoea and Vomiting?
- stool (preferred!)
- vomit - has a lower yield
- PCR or antigen detection assays
enteric viruses vs enteroviruses?
these are two different things
enteric viruses are transmitted through fecal-oral routes
enteroviruses a group of single-stranded sense RNA viruses especially in kids
what is PCR?
- polymerase chain reaction
- is a method for amplifying specific RNA or DNA sequences
- a normal PCR cycle lasts 30 rounds
what are the stages of PCR?
- denaturing
- primer annealing
- chain elongation
what substances are required in PCR?
and what for?
- the starting block for PCR is dsDNA
- to make a dsDNA copy reverse transcriptase is needed
- the dsDNA is then denatured by heating
- the most important enzyme is Taq polymerase which is needed to polymerase the DNA
