van-esch阿尔泽特.ppt

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
What has to be detected?
Antigen
Different types
Different strains
Antibodies
Different classes
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 inated animals?
Discrimination between types / strains?
Detection limits?
Required sensitivity and specificity?
Regulations (national, OIE)?
……
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
ine control
ess of ination
Diagnostics, definitions
Infected
Yes
No
Test
Result
Positive
a
b
a+b
Negative
c
d
c+d
a+c
b+d
a+b+c+d
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
Diagnostics, false positives and false negatives
Selection of materials
ELISA  antigen
Whole virus vs binants
PCR  primers
Type specific? General?
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