A comparison of rapid bovine spongiform encephalopathy testing methods on autolyzed bovine brain tissue

Veterinary Laboratories Agency, Newcastle Upon Tyne, NE12 9SE, KT15 3NB UK.

In 1999, the European Union (EU) approved 3 rapid methods for the testing of bovine brain samples for the presence of bovine spongiform encephalopathy (BSE). The evaluation that led to the approval did not include an analysis of autolyzed material. Member states of the EU have active surveillance programs for BSE, which target fallen stock as well as other categories of cattle. Autolysis is a common feature of fallen stock samples because there can be a considerable delay between death and collection of samples. Therefore, it is important to know whether these tests perform optimally on autolyzed samples. The Veterinary Laboratories Agency (VLA) selected 250 positive fallen stock samples. These had been detected during routine testing using the Prionics-Check Western blot and confirmed as BSE cases by immunohistochemistry or electron microscopy. Samples were graded according to the degree of autolysis and then tested by the 3 methods: Prionics-Check Western blot, Platelia test, and Enfer test. All 3 methods correctly classified the samples as positive BSE cases, therefore alleviating doubt about their ability to do so. Subsequent EU validation exercises, such as those conducted in 2002--2003, have included the testing of autolyzed material. It is important that all new methods be evaluated on autolyzed tissue before approval for official use.

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