Viral Diagnostics

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Viral Diagnostics
2010-03-22 00:27:58
virology midterm subbiah

Viral Diagnostics
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  1. Validity
    • Degree to which the measurements correspond to the true state of the phenomenon being measured
    • Normally compared to a gold standard
  2. Reliability
    The extent to which repeated measurements of a relatively stable phenomenon fall close to each other
  3. Accuracy (Gold Standard)
    The proportion of all test results (true positive (a) + false positive (b) + true negative (c) + false negative (d)) that are correct (a + c)
  4. Sensitivity
    • Measure of proportion of animals that are positive to the test for that disease
    • + test w/disease/all animals with disease
  5. Specificity
    • Measure of proportion of animals w/o a disease that are negative to the test for that disease
    • true neg/total neg
  6. Positive Predictive Value
    • probability of disease in an animal with a positive or abnormal test result
    • true positive/all positives
  7. Negative predicted value
    • probability of not having the disease when the test result is negative or normal
    • true negatives/all negatives
  8. Direct Examination
    looking for virus or viral proteins
  9. Indirect examination
    effects of virus on substrate
  10. Serology
    antibody tests
  11. Direct Examination: 4 types
    • 1. Electron Microscopy
    • -morphology of virus particles
    • -immune electron microscopy
    • 2. Antigen Detection
    • -immunofluorescence, ELISA, etc
    • 3. Light Microscopy
    • -histological appearance
    • -inclusion bodies
    • 4. Viral Genome Detection
  12. Indirect Examination: Virus Isolation in... (3)
    • 1. Cell culture
    • -cytopathic effects, hemadsorption
    • 2. Embryonating chicken eggs
    • -embryo death, lesions on embryos, pocks on chorioallantoic membrane
    • 3. Susceptible animals
    • -clinical signs and lesions
    • -virological and serological identification methods
  13. Serology
    • Antigen detection: direct detection of antigen
    • Antibody detection: four-fold increase in antibody titers between acute and convalescent stages of infection, or the detection of IgM in primary infection
  14. Viral Antigen Detection
    • Unlabeled antibodies: agglutination, precipitation, complement fixation
    • Labeled antibodies: enzyme, radioactive compound, fluorescent dye
    • ELISA: semi or fully quantitative; direct (antivirus Ab labeled) or indirect (anti-Ig Ab labeled)
    • Radioimmunoassay: radiolabeled antigen or antibody
  15. Immunofluorescence Assay (IFA)
    direct or indirect
  16. Immunohistochemistry
  17. ELISA
    • Antibody binds to antigen
    • enzyme labeled anti IgG binds to antibody
    • direct or indirect
  18. Complement Fixation Test
  19. Radioimmunoassay
    • Antibody binds to antigen
    • Radiolabeled anti-IgG binds to antibody and free and bound radiolabel can be quantitated
  20. Immunochromatography (lateral flow)
    indirect or direct
  21. Western Blot
  22. Hemadsorption (HAd), -/Inhibition (HAdI)