Diagnosis Of Viral Infections Flashcards
- Is it always possible to diagnose an infection clinically?
Not always possible to diagnose a infection clinically. Often require a laboratory diagnostic test
- What kind of information would the doctor need to diagnose a patient?
Aid to diagnosis - history, examination & special investigations
- Why is it important to diagnose viral infections quickly ?
Rapid diagnosis of viral infections can reduce need for unnecessary tests, inappropriate antibiotics
- Give 6 possible test mechanisms for viral infections?
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
- Which microbes can be seen using light microscopy (x400-x1000) ?
Bacteria
Fungi
Protozoa
Helminths (might be seen by naked eye)
- Can we see viruses with light microscopy? if no, what kind of microscope can we see them with?
No we cant
Viruses can be seen with electron microscopy x20,000
- What is electron microscopy useful for ?
- > Faeces and Vesicle Specimens
- >Characterising emerging pahogens
- How does electron microscopy work?
Specimens are dried on a grid
Can be stained with heavy metal e.g. uranyl acetate
Can be concentrated with application of antibody i.e. immuno-electron microscopy to concentrate the virus
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
- What are three advantages of electron microscopy?
Rapid
Detects viruses that cannot be grown in culture
Can visualise many different viruses
- What are four limitations of electron microscopy?
low sensitivity need 106 virions/millilitre. May be enough in vesicle secretion/stool
Requires maintenance
Requires skilled operators
Cannot differentiate between viruses of the same virus family.
- Explain what
Rotavirus (gastroenteritis),
Adenovirus (gastroenteritis),
Coronavirus (respiratory tract infection), Nonovirus (gastroenteritis)
Astrovirus (gastroenteritis)
all appear like on an Electron Microscope?
Rotavirus (gastroenteritis) = circular shaped , has a distinct lining
Adenovirus (gastroenteritis), = Circular, all white
Coronavirus (respiratory tract infection), =looks like a dog bone, two circles joined by a line in the middle
Nonovirus (gastroenteritis) = lots of small circles
Astrovirus (gastroenteritis) =small white circles
- Which viruses shows vesicles in an EM?
How do we differentiate between these two
Herpes Viruses:
- Herpes Simplex
- Varicella Zoster Virus
EM cant differentiate between these two viruses so we need to use clinical context, site of vesicle and symptoms to differentiate?
- Can EM differentiate between the different types of Poxvirus ( eg Smallpox, Monkeypox , Orf, Cowpox) ?
No it cant
Depends on clinical context to diagnose
- How does isolating a virus in a cell culture work?
Use different cell lines in test tubes or plates. Selection of cell types important.
Slow, but occasionally useful in anti-viral sensitivity testing
- What has viral isolation in cell culture led to the discovery of in the past 20 yrs?
Led to discovery of hMPV and Nipha virus in last 20 years
- Viral infection in cell culture is an old method and has been replaced for diagnosis but in what situations could we use this technique?
Old method, now replaced by molecular techniques, but still needed for research or for rare viruses
- Explain the process of viral isolation in cell culture?
Use different cell lines in test tubes or plates. Selection of cell types important
Different viruses viruses may give different appearances
Different cell lines may support growth of different viruses
Identify virus using antigen detection techniques or neutralisation of growth
- What is one advantage and disadvantage if using viral isolation in cell culture?
Slow, but occasionally useful in anti-viral sensitivity testing
- What would you look for if your cell culturing a virus PLUS an antiviral is present?
look for inhibition of cytopathic effect
- Can we detect the viruses by their antigens?
Viral antigens, usually proteins – either capsid structural proteins, secreted proteins can be detected. Infected cells may display viral antigens on their surfaces.
- For the following patient samples explain which viruses you would expect to find there:
- Nasopharyngeal Aspirates (NPA)
- Blood (Serum or plasma)
- Vesicle Fluid
- Faeces
Nasopharyngeal aspirates (NPA): e.g. RSV, influenza
Blood (serum or plasma): Hepatitis B Dengue Vesicle fluid: Herpes simplex, varicella zoster Faeces Rotavirus, adenovirus