Viral Diagnostics

• Degree to which the measurements correspond to the true state of the phenomenon being measured
• Normally compared to a gold standard

The extent to which repeated measurements of a relatively stable phenomenon fall close to each other

The proportion of all test results (true positive (a) + false positive (b) + true negative (c) + false negative (d)) that are correct (a + c)

• Measure of proportion of animals that are positive to the test for that disease
• + test w/disease/all animals with disease

• Measure of proportion of animals w/o a disease that are negative to the test for that disease
• true neg/total neg

• probability of disease in an animal with a positive or abnormal test result
• true positive/all positives

• probability of not having the disease when the test result is negative or normal
• true negatives/all negatives

looking for virus or viral proteins

effects of virus on substrate

antibody tests

• 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

• 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

• 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

• 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

direct or indirect

indirect

• Antibody binds to antigen
• enzyme labeled anti IgG binds to antibody
• direct or indirect

indirect

• Antibody binds to antigen
• Radiolabeled anti-IgG binds to antibody and free and bound radiolabel can be quantitated

indirect or direct

indirect