Evaluation of CSFV Antibody ELISAs for the differentiation of infected from vacci-nated animals

Classical swine fever (CSF) is one of the most important epizootic diseases of pigs. With few exceptions the Member States of the European Union (EU) are currently considered to be free of CSF in domestic pigs. However, the disease is still endemic in the wild boar populations of several European countries and out-breaks occurred recently e.g. in Germany, France, Hungary, Romania, Bulgaria, and the Slovak Republic.

Preventive vaccination is prohibited within the EU, but emergency vaccination can be part of the strategy in case of a contingency. Using conventional vaccines, differentiation of vaccinated from infected animals (DIVA) is not possible. Newly developed modified live marker vaccines allow a DIVA strategy based on the use of enzyme linked immunosorbent assay (ELISA) tests.

The aim of this study was to evaluate CSF virus (CSFV) Antibody ELISAs, com-mercially available in Europe, for their diagnostic sensitivity as well as for their potential in differentiating between infected and marker vaccinated animals. Two newly available ELISAs were included into the tests, the Priocheck® CSFV Erns ELISA, a special DIVA test, and the LDL Pigtype® CSFV Antibody ELISA.

An inter-laboratory comparison test with four EU national CSF reference labora-tories and one EU reference laboratory participating was organized. Seven differ-ent CSFV antibody ELISA test kits, targeting distinct antibodies (against E2, Erns, NS3) were provided to the participating laboratories together with a set of 41 samples.

This set included the following, well characterized samples derived from animal experiments: CSFV antibody positive sera with low, medium and high titers, sera free of CSF antibodies, sera from pigs infected with pestiviruses other than CSFV (Bovine viral diarrhoea type I and II and Border disease virus), sera from pigs vaccinated with conventional vaccines (C-strain, GPE-), sera from pigs vaccinated with E2 subunit vaccine and recent 3rd generation marker vaccines (cp7E2Alf, cp7E2gif, pRiemsABCgif, FLc11, FLc9), as well as sera from pigs vaccinated and afterwards challenged with CSFV.

In addition each of the laboratories was asked to additionally test approximately 50 samples from their national pig herds, which were regarded to be negative and approximately 100 samples from DIVA experiments to assure a wide cover-age of different serum samples. Practicability, diagnostic sensitivity, specificity, repeatability, and reproducibility were calculated and conclusions were drawn on the feasibility of using existing Ab-ELISAs for DIVA testing.

The results will be presented at the meeting. Acknowledgement: This work was supported by the EU Network of Excellence, EPIZONE (Contract No FOOD-CT-2006-016236).