L6 Diagnostic Virology Flashcards
What can be used as a rapid point-of-care test for the detection of viral antigen?
Immunofluorescence (IF)
What are the differences between direct and indirect assay in IF? Why indirect assay is preferred sometimes?
Direct assay: detection of virus Ag with a single primary antibody, chemically linked to fluorophore
Indirect assay: detection of virus Ag with 2 antibodies: primary binds to the target antigen and secondary with a fluorphore and binds to primary > signal amplification by an increase in the number of fluorophore per antigen
What is the Latex agglutination test?
Microbeads of latex are coated on pathogen-specific Ab/Antigens + patient’s fluid (if containing Ab/antigen) > agglutination
What does a low sensitivity of using electron microscopy indicate?
A high concentration of viruses is needed for successful visualization
Electron microscopy is used to detect virus in what samples? Give examples of viruses in each sample (4)
Stool - rotavirus, norovirus
Skin - herpesviruses, poxviruses
EM can observe virus and recognize a virus up till _________ level of the virus.
Family
Histology and cytology can be used to detect viral inclusion bodies, which are?
Example: Owl’s eye in CMV
collections of replicating virus particles either in cytoplasm/ nucleus
Which of the following about molecular methods to detect viral genome is incorrect?
A. It can be applied to solution (blood, body fluid) or sollid (tissue)
B. It is dependent on the viability of the virus
C. Nuclei acid hybridization can directly detect viral nucleic acid
D. Nucleic acid probles are DNA/RNA segments with probes for detection in nucleic acid hybridization
B
It is not dependent on the viability
Polymerase chain reaction (PCR) can be used to ampliify viral nucleic acid. What are the advantages and disadvantages of PCR?
Adv:
- fast
- specific
- extremely sensitive (but prone to contamination)
Disadv:
- have to guess the virus beforehand for appropriate primer
- difficult to interpret +ve result in latent viruses e.g. CMV may have false positive (seropositive but no disease)
What is the advantage of real-time PCR compared to conventional PCR in detection of viral genome?
- Quantification (Threshold cycle)
- smaller CT value = less cycles to reach threshold value = higher level of viral DNA/RNA - Does not require that much need expertise
Virus culture: inoculated and cultured in cell lines (animal, tissue, embryonated egg)
- Conventional culture: 1-2 weeks, and based on _______effect? What does it mean? example?
Cytopathic effect (CPE)
- structural changes in host cells caused by viral invasion
e. g. syncytia: cell clumping + multinucleated cells in respiratory synctial virus // shrinkage of cells.
Rapid culture require only 2 days, using low-speed cetrifugation of specimen that enhances _________ of certain viruses? e.g. CMV-DEAFF test (Detection of early infection)
enhances infectivity of certain viruses
What is serology of virus?
It can either be class-specific or function-specific.
Detection of Ab against virus Ag (except HBV- HbsAg)
Which of the following about class-specific serology is correct?
A. Enzyme-immunoassay can be done (EIA)
B. Radioimmunoassay can be done (RIA)
C. IF can be done
D. IgM present indicates immunity
E. one blood sample is needed after more than a week after illness onset
F. Result is either +/-
Except D
IgM is for acute infection: not all infections, may not increase until 4 days after symptoms onset
IgG is for immunity, persists for life
Give 3 examples of function-specific serology tests.
- Hemagglutination inhibition test (HAI)
- Complement fixation test (CFT)
- Neutralization test (NT)
- 2 serum samples, one with specific neutralizing Ab, one without, with specific neutralizing Ab > no CPE; without Ab > CPE
How many samples are needed in function-specific serology tests? (e.f. NT, HAI…)
2 samples to compare Ab levels in acute and convalescent phases (healed) (10-14 days apart)
For sensitivity, which is higher in class-specific or function-specific serology tests ?
Class-specific > function-specific
- EIA > RIA > IFA > NT > HAI >CFT
Which method is the most sensitive in virus detection?
PRC > virus culture > others
