Diagnosis of Viral Infections Flashcards
why is it harder to diagnose viruses than bacterial (generally)
viruses can’t be seen under a light microscope (can’t see them)
viruses need living cells to replicate in (can’t culture them)
what techniques are closest to visualising/culturing bacteria for viruses- but can’t be used in labs with high throughput due to it taking too long?
EM- electron microscopy (black and white)
CPE- cytopathic effect: grow the virus in cells and look at the effect it has on them (2-4 weeks)
We can look for viruses in swabs, blood, tissue however by?
there are traces of DNA/RNA from the virus in them
therefore can detect them by nucleic acid amplification techniques (NAATs) - like PCR
serology
What is PCR and how does it work?
polymerase chain reaction
creates logarithmic increases the copies of DNA/RNA to allow them to be detected
enzymes unzip the DNA/RNA, matching primer binds to single strand. polymerase enzyme then produces complimentary copy. (therefore there is double the amount of DNA)
the matching nucleotides are tagged with fluorescence, and will fluoresce when bound in a chain, so increase in fluorescence can be quantified
advantages and disadvantages of PCR
very sensitive
very quick
quite cheap
because very sensitive, very vulnerable to contamination, may give false positive
only detects sequences which you have the primer for: therefore wont find one you’re not suspecting, can be esp difficult in novel viruses
what is serology?
the study or detection of antibodies in the serum (esp IgG and IgM)
explain the trend in levels of IgM and IgG after initial infection?
IgM appears after infection (within one week on onset)
and remains positive up to 12 weeks after the acute infection
IgG appears later but has a greater affinity to the antigen and can last for many years or even whole life and is responsible for giving immunity
what colour are the different swabs for bacteria and viruses?
black swab= bacteria
green swab= viruses
what is the varicella zoster virus?
3rd of the 8 herpes viruses
responsible for chickenpox in young people, and shingles in the older population
what is EBV? + what initial differential diagnosis is important to consider in the diagnosis of this?
epstein barr virus (herpes virus 4)
causes glandular fever aka infective mononucleosis
must make sure it is not strep throat (similar symptoms)
what is found in the purple blood tube and what does it do?
EDTA- stops clotting
what is CMV, what family does it belong to, and who is likely to become infected?
Cytomegalovirus - 5th of the 8 herpes virus
A lot of people are already infected with the virus, but does not become a problem until they are immunocompromised (suppressant drugs or HIV)
if a HIV test comes back positive, what should you do?
retest later if you think you might be in the window period/if comes back positive again do confirmatory testing
if CSF is infected with viral meningitis, what would you expect the results of CSF to look like?
normal glucose and protein,
lymphocytic
