Viral Identification Flashcards
Direct examination for detecting viruses (4)
- Electron microscopy (incl immune electron microscopy)
- Light microscopy
- Antigen detection (immunofluorescece, ELISA)
- PCR
Types of immune electron microscopy (2)
- Classical (IEM)
- sample treated with anti-sera. Viral particles present will agglutinate - Solid phase (SPIEM)
- grid coated with anti-sera. Virus particles present will be absorbed on grid by antibody
What is sensitivity of electron microscope
2nm
Advantages and disadvantages of antigen detection (immunoflourescence and ELISA)
Advantages:
- Quick results
Disadvantages:
- Reduced sensitivity
- Reduced specificity due to CROSS-REACTIVITY
- Tedious, time consuming
Advantages of PCR
Extremely sensitive
Easy to set up
Fast results
Disadvantages of PCR
Need specific primers
Contamination
Need to set up quantitative curve
Latent viruses can be difficult to interpret
T/F - if the virus is RNA, you cant run a straight PCR
True - need to do RT-PCR
Primers for PCR
- Random
- Oligo-DT (good for viruses with Poly-A tail)
- Sequence specific virus
Virus isolation can be done in which 3 types of cell culture? What are pros/cons of each
- Primary cells
- Pro: very similar to host, viruses like
- Con: obtaining tissue from animal, cells dont last as long - Semi-continuous cells
- Cells last longer than primary and appear similar to host - Continuous: (immortalized cells)
- Pros: commercially available
- Cons: dont resemble host as well, not all viruses grow on them
Disadvantages of cell culture
- Takes a long time
- Sensitivity depends on condition of specimen
- Susceptible to bacterial contamination
- Susceptible to toxic substances that may be present on specimen
- Many viruses wont grow on cell culture
What type of eggs are used for viral culture
EMBRYONATED!
Why are neonates used for viral cultures
Immune systems are weak
How do you use IgG and IgM to differentiate primary and secondary infections
Primary:
IgG: 4 fold increased between acute and convalescent infection.
Presence of IgM
Secondary:
IgG: 1-fold increase
IgM: not present!
What do western blots detect
Antigen/antibody
What is hemagglutination inhibition
Virus specific antibodies interfering with the capacity of the virus to agglutinate RBCs
Which viruses hemagglutinate RBCs?
Pox Parvo Toga Flavi Orthomyxo Paramyxo Corona Bunya Rhabdo Reo Rota
Virus neutralization assay. Do the results mean you are protected?
Identifies and quantifies neutralizing antibodies. You arent necessarily protected - a virus can induce an immune response but that doesnt mean youre protected
Pros/cons of serology
Pros:
- Onset of c/s occurs with development of antibodies
- Viruses that produce clnical disease a while after antibodies (retroviruses)
Cons:
- Long period of time required for dx between acute and convalescent sera
- Mild local infections may not produce a detectable immune response
- Cross reactivity (false positives) **
- Immunocompromised patients gie reduced/absent humoral response **
- Blood recipients: false pos due to antibody transfer **
- Cant be used in unculturable viruses
What is TCID50
Tissue culture infective dose 50 - measures virulence of virus in-vitro (only within same group)
