Diagnosis of Viral Infections Flashcards
possible test types used nowadays?
Electron Microscopy
Virus isolation (cell culture)
Antigen detection
Antibody detection by serology
Nucleic acid amplification tests (NAATs e.g. PCR)
Sequencing for genotype and detection of antiviral resistance
Visualisation of Microbes - how can they be seen?
bacteria, protozoa, fungi and helminths can all be seen with light microscopy
viruses are much smaller, can be viewed with an electron microscope
how does electron microscopy work?
Specimens dried on a grid and stained with heavy metal e.g. uranyl acetate
Can be concentrated with application of antibody
Beams of electrons are used to produce images
Wavelength of electron beam is much shorter than light, resulting in much higher resolution than light microscopy
electron micropyle is useful in what?
characterising emerging pathogens
advantages of electron microscopy?
Rapid
Detects viruses that cannot be grown in culture
Can visualise many different viruses
limitations of electron microscopy?
low sensitivity - may be enough in vesicle secretion/stool (needs high conc of virus)
Requires maintenance and skilled operators
Expensive
Cannot differentiate between viruses of the same virus family.
which virus has a wheel shape?
rotavirus
shape of adenovirus (gastroenteritis)?
glycosohedral shape
coronavirus shape?
respiratory tract infection
crown like structure around a dumbell shape
Astrovirus shape?
star
Poxvirus - different types and what is the shape?
ball of wool
Smallpox
Monkeypox
Orf
Cowpox
what are 2 herpes viruses that cause vesicles?
Herpes simplex (cold sores or genital herpes which can cause little blisters) Varicella zoster virus (chickenpox or shingles)
they both look like a virion inside an envelope – the envelope has come from a human cell which the virus infected.
given they both look the same, distinguishing which viral infection the patient has is based on clinical context.
- if the patient has a fever and an itchy white rash all over the body, it will probably be varicella zoster virus
- if there are vesicles in just one area of the body, would be zoster/shingles
- cold sore would be Herpes Simplex
Virus isolation in cell culture
Viruses require cells to grow so we can’t grow them on an agar plate like we can with bacteria
- if you can provide a virus with cells in a test tube, viruses will be able to grow inside those cells (patient sample containing a virus is incubated with a cell layer)
- when viruses grow inside these cells, it produces a Cytopathic effect (CPE), and we see morphological changes in those cells
slow process (several days to get a results) but occasionally useful in anti-viral sensitivity testing - we now have other methods which are used more regularly
different cell lines may…
support growth of different viruses
-this is because different viruses have affinities for different cells
uses of viral neutralisation cultures?
set up a neutralisation culture, add antibodies against the suspected virus in the culture - cytopathic effect will be inhibited, then you can work out what virus it is
Important uses:
- test out anti-viral drugs by adding them and seeing if the cytopathic effect is inhibited - if it is inhibited, you know the drug will work
- you can see if a virus has developed anti-viral resistance