Evaluation of a rapid western immunoblotting procedure for the diagnosis of bovine spongiform encephalopathy (BSE) in the UK

Bovine brain tissue samples from 625 UK cattle, clinically suspected as bov ine spongiform encephalopathy (BSE) cases, were used in a blind analysis to assess a rapid Western immunoblotting technique (Prionics Check; Prionics AG, Zurich), which detects bovine disease-specific protease-resistant prion protein (PrPSc). By means of statutory histopathological examination, 599 of the 625 cattle were confirmed as BSE cases by the demonstration of spong iform encephalopathy, the remaining 26 being classified as negative. Duplic ate samples from the same animals were also examined by electron microscopy for the presence of abnormal brain fibrils (scrapie-associated fibrils; SA Fs). The Prionics technique showed a high sensitivity, particularly when co mpared with the fibril detection test; the detection rates were 99.3% and 9 2.0% respectively, with histopathology being used as the "gold standard". T he false negative results by the Prionics test were possibly related to the sampling procedure. Analysis of 50 BSE-positive samples revealed similar g lycoprofiles, the majority of PrPSc isoforms being di-glycosylated protein. The Prionics test also detected PrPSc in the four brain samples from the 2 6 histopathologically negative animals, apparently reducing the specificity of the test to 84.6% however, confirmatory positive results in these sampl es were obtained by demonstrating SAF or by immunohistochemical examination , or both. It was concluded that the Prionics test detected PrPSc in a smal l percentage (0.64%) of clinically suspected BSE cases showing no spongifor m change. Since January 2000, the Prionics Western blot test has been intro duced as one of the statutory tests for the diagnosis of clinically suspect ed BSE and scrapie cases in the UK.