Atypical scrapie cases in Germany and France are identified by discrepant reaction patterns in BSE rapid tests

The intensified surveillance of scrapie in small ruminants in the European Union (EU) has resulted in a substantial increase of the number of diagnosed cases. Four rapid tests which have passed the EU evaluation for BSE testing of cattle are also recommended currently and used for the testing of small ruminants by the EU authorities. These tests include an indirect ELISA (cELISA), a colorimetric sandwich ELISA (sELISA I), a chemiluminescent sandwich ELISA (sELISA II), and a Western blot (WB). To this point, the majority of samples have been screened by using either sELISA I (predominantly in Germany) or WB (predominantly in France). In this study, it is shown that a number of the German and French scrapie cases show inconsistent results using rapid and confirmatory test methods. Forty-eight German sheep, 209 French sheep and 19 French goat transmissible spongiform encephalopathy (TSE) cases were tested. All cases were recognised by the sELISA I and either one of the confirmatory methods (scrapie-associated fibrils (SAF)-immunoblot or immunohistochemistry). Surprisingly, three rapid tests failed to detect a significant number of scrapie cases (29 in France and 24 in Germany). The possible reasons for these inconsistent reaction patterns of scrapie cases are discussed. Similar discrepancies have not been observed during rapid testing of cattle for BSE, the disease for which all diagnostic methods applied have been evaluated.