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A statistical comparison was made between the results of the statutory neurohistopathological method for the post mortem diagnosis of bovine spongiform encephalopathy (BSE) and the detection of abnormal brain fibrils (SAF). A total of 773 suspect cases was examined by both methods; it comprised 531 animals born before the feeding of ruminant-derived protein to ruminant species was prohibited and 242 born after the ban. The relative sensitivities and specificities of the methods were calculated for the diagnosis of clinically suspected BSE. The agreement between the results of the methods was excellent for 331 of the cases born before the ban and for all the cases born after it. In these cases the samples were not autolysed. For the 200 cases in which autolysis was recorded there was poor agreement between the diagnostic methods and this was attributed to an apparently reduced specificity of the histopathological diagnosis in the autolysed material. Despite the potentially greater specificity of fibril detection in the diagnosis of scrapie-like disease, this study indicates that a reliance on fibril detection alone may result in some false negative diagnoses, probably owing to the inadequate sampling of the tissues.

The effect of autolysis on the electron microscopic detection of the characteristic abnormal fibrils, originally called ‘scrapie-associated fibrils’, was investigated in four different areas of the central nervous system ( cns ) from 10 clinically suspect bse cattle after postmortem delay and compared with the histopathological diagnosis. The tissues for fibril detection were subjected to controlled incubations to simulate autolysis. Fibril detection in all areas sampled from nine animals in which bse was confirmed by histopathology was not affected by combined post mortem delays and specific controlled treatments. Detection of fibrils from the cervical spinal cord was no less sensitive than from brain areas. Fibrils were not detected in the one suspect case in which histopathology did not reveal lesions of bse . The study confirms that fibril detection is of diagnostic value in bse when post mortem autolysis renders cns material unsuitable for histopathology.