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PRRSV Diagnostics, specificity or sensitivity, that’s the question

PRRSV Diagnostics, specificity or sensitivity, that’s the question. Eric van Esch Technical director BioChek BV, Reeuwijk, Netherlands. PRRSV diagnostics. Definitions Reasons false positives or false negatives Setting cut off Conclusions. Diagnostics, definitions.

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PRRSV Diagnostics, specificity or sensitivity, that’s the question

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  1. PRRSV Diagnostics, specificity or sensitivity, that’s the question Eric van Esch Technical director BioChek BV, Reeuwijk, Netherlands.

  2. PRRSV diagnostics • Definitions • Reasons false positives or false negatives • Setting cut off • Conclusions

  3. Diagnostics, definitions • What has to be detected? • Antigen • Different types • Different strains • Antibodies • Different classes

  4. Diagnostics, definitions • Setting up an assay • Depending on what has to be detected • Antigen / Antibodies  Which technique? • Matrix (blood, tissue, oral fluids, sperm, etc) • Additional questions • Discrimination between field infected and vaccinated animals? • Discrimination between types / strains? • Detection limits? • Required sensitivity and specificity? • Regulations (national, OIE)? • ……

  5. Diagnostics, definitions • In what situation will the assay be used? • Clinical diagnosis • Antigen present on farm, clinical cases from time to time • Herd screening • Establishing herd status, clinical cases present or not • Eradication • Elimination of agens from the farm • Monitoring • Control of freedom of disease • Vaccine control • Success of vaccination

  6. Diagnostics, definitions • Prevalence = a+c/a+b+c+d • Sensitivity = a/a+c • Specificity = d/b+d • Predictive value positive = a/a+b • Predictive value negative = d/c+d

  7. Diagnostics, false positives and false negatives • Selection of materials • ELISA  antigen • Whole virus vs recombinants • PCR  primers • Type specific? General?

  8. Diagnostics, false positives and false negatives • Reasons of false negative results • Test itself • Time of sampling (too soon or too late) • (Very) low level of antibodies / antigen • Immunosuppression • Prozone, high dose Hook effect

  9. Diagnostics, false positives and false negatives • Reasons of false positive results • Test itself • Cross reaction with antibodies against related antigen • Cross reactions by other factors • Bridging, non-specific adhesion (fat)

  10. Diagnostics, setting cut off

  11. Diagnostics, setting cut off

  12. Diagnostics, setting cut off

  13. Diagnostics, setting cut off

  14. Diagnostics, setting cut off • Interpretation • Technical  experimental samples • Diagnostic  field samples • Could be different! • Baselines • Natural infected animals • Vaccinated animals

  15. Conclusions, take home messages • There is not one universal test • Parameters Specificity and Sensitivity are important, but are competing against each other • In different situation requirements are different, therefore parameters can change • Evaluation of an assay should be done in each lab with respect of the purpose of the assay

  16. Thank you for your attention!

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