Diagnosis and Viral Infections Flashcards
Why is rapid diagnosis important?
What things aid diagnosis apart from labaratory diagnostic tests?
Give examples of lab tests?
How are different microbes visualised?
How is the use of electron microscopy in viewing viruses?
What are the steps to look at a specimen through electron microscopy?
What are the advantages of electron micrscopy?
What are the limitations of electron micrscopy?
What method to hospitals use to view viruses now instead of electron microscopy?
What is a disadvantage to using electron microscopes when viewing certain viruses?
Give examples of virus types that cant be differentiated using electro microscopy?
What are the steps in virus isolation?
What factor does virus isolation in cell culture depend on?
Virus causes cytopathic effect (CPE) - changes in cell morphology that can be detected
- diff viruses give diff cytopathic effects
What are the diff ways we can look for cytopathic effect after virus isolation in cell culture?
Apart from virus isolation in cell culture to detect cytopathic effects, what other way can be identify viruses? and why?
Direct detection of viral antigens using nucleic acid detection methods (greater sensitivity + rapid diagnosis nearby patient)
What are viral antigens?
Capside structural proteins or secreted proteins
Where can viral antigens be detected?
Cells, blood, saliva, tissues or organs
as whole virus or free antigens or cell associated virus antigens
What are the most common antigen detection metfhods?
Direct immunofluorescence for cell associated antigens
Enzyme immunoassay for free soluble antigens or whole viruses
Immunochromatographic methods (lateral flow test) for NPT rapid diagnosis
Serology
ELISA
Describe how immunofluorescence is used for antigen detection?
Antigen from infected host cells put on slide
Specific antibody (polyclonal or monoclonal) to the antigen is tagged to a fluorchrome and added to sample (only if cell is infected and has antigens antibodies bind)
Sample viewed under microscope using UV light
In which case is immunofluorescence used for antigne detection?
When we know which antigen we are looking for and have specific antibody to it
Name a few immunochromatographic methods and viruses that can be identified with it
Lateral flow tests - method
Virus - diagnose dengue
What is dengue and why is it useful to diagnose using immunochromatographic methods?
Dengue is a flavivirus carried by an arthropod vector
- useful for near patient test (NPT)
What is immunochromatography?
Lateral flow test
Why are PCR tests used over lateral flow tests (immunochromatographic methods)?
PCR is more sensitive and specific
What is ELISA?
Eznyme linked immunosorbet assay
What are the 3 forms of ELISA?
Indirect, direct, sandwich
What is the use of ELISA in diagnosing viral infections?
Antigen detection
What are the steps for detection of antigen by ELISA?
Why is serology used for antibody detection?
Good to detect stage in infection or whether it is an acute or chronic infection using class switching of antibodies principle
How does serology detect pathogens?
Indirect detection of pathogen by detecting the antibodies produced against it
How is serum produced?
What are the steps of antibody detection in serology?
Humoral response upon infection, IgM produced first then class switching to IgG, further along reaction = more IgG than IgM shows how far along disease (stage) patient is at (take test twice for this)
Give an example of a viral infection detected using serology antibody detections?
Hepatitis A
How do you know which stage of hepatitis A a patient has using serology antibody detection (specific diagnosis)?
No past / current infection and no immunisation = negative for both Hep A IgM and Hep A IgG
Acute or recent infection - Hep A IgM positive and Hep A IgG positive or negative
Resolved infection/immunisation = Hep A IgM negative and Hep A IgG positive
What is the modern labarotory detection method of antibodies/antigens in blood?
serology and use enzyme immunoassay (e.g. ELISA)
- can detect multiple diff antibodies at once from one specimen
What is NAAT? + an examples
Nucleic acid amplification - PCR is an example
What does NAAT detect?
RNA or DNA
What are the stages of NAAT?
What are the advantages of NAAT?
What is required in NAAT?
nucleic acid extraction prior to amplification
What type of molecular diagnostic test is NAAT?
Either qualitative or quantitative
What are the limitations of NAAT?
What is real time PCR
What is multiplex PCR?
Give examples of when multiplex PCR is used? (which viruses?)
Which substances inhibit PCR?
How do we avoid the problem of PCR inhibition?
What are the 2 types of genome sequencing?
Why is genome sequencing useful is diagnosis?
What methods are used to diagnose HIV?
What are the targets for antiviral resistance testing?
Give an example of a virus we can test for anti-viral resistance?
What might screening be used for in viral diagnosis?
