Abstract
Since 2004 it become clear that atypical bovine spongiform encephalopthies (BSEs) exist in cattle. Whenever their detection has relied on active surveillance plans implemented in Europe since 2001 by rapid tests, the overall and inter-laboratory performance of these diagnostic systems in the detection of the atypical strains has not been studied thoroughly to date. To fill this gap, the present study reports on the analytical sensitivity of the EU-approved rapid tests for atypical L- and H-type and classical BSE in parallel. Each test was challenged with two dilution series, one created from a positive pool of the three BSE forms according to the EURL standard method of homogenate preparation (50% w/v) and the other as per the test kit manufacturer's instructions. Multilevel logistic models and simple logistic models with the rapid test as the only covariate were fitted for each BSE form analyzed as directed by the test manufacturer's dilution protocol. The same schemes, but excluding the BSE type, were then applied to compare test performance under the manufacturer's versus the water protocol. The IDEXX HerdChek ® BSE-scrapie short protocol test showed the highest sensitivity for all BSE forms. The IDEXX® HerdChek BSE-scrapie ultra short protocol, the Prionics® - Check WESTERN and the AJ Roboscreen® BetaPrion tests showed similar sensitivities, followed by the Roche® PrionScreen, the Bio-Rad® TeSeE™ SAP and the Prionics® - Check PrioSTRIP in descending order of analytical sensitivity. Despite these differences, the limit of detection of all seven rapid tests against the different classes of material set within a 2 log10 range of the best-performing test, thus meeting the European Food Safety Authority requirement for BSE surveillance purposes. These findings indicate that not many atypical cases would have been missed surveillance since 2001 which is important for further epidemiological interpretations of the sporadic character of atypical forms.
Highlights
Transmissible spongiform encephalopathies (TSEs) or prion diseases include a group of progressive, neurodegenerative as yet untreatable disorders affecting several mammalian species, including Creutzfeldt-Jakob disease (CJD) in humans, bovine spongiform encephalopathy (BSE) in cattle and scrapie in small ruminants
The IDEXXH HerdCheck BSE-scrapie short protocol was taken as the reference test, as it provided the highest analytical sensitivity for all BSE forms
Comparison of test performance under the two dilution protocols based on the descriptive analysis (Table 1) showed that all seven tests had a higher analytical sensitivity for the BSEpositive samples prepared under the manufacturer’s protocol than those prepared as per the water protocol for all BSE types, except for H-type BSE (H-BSE), toward which the tests performed generally better with the 50% w/v homogenates
Summary
Transmissible spongiform encephalopathies (TSEs) or prion diseases include a group of progressive, neurodegenerative as yet untreatable disorders affecting several mammalian species, including Creutzfeldt-Jakob disease (CJD) in humans, bovine spongiform encephalopathy (BSE) in cattle and scrapie in small ruminants. TSEs are characterized by the concentration of an anomalous isoform (PrPRes) of the natural prion protein (PrPc) in the central nervous system (CNS) and peripheral tissues. PrPres differs from PrPc in its aggregated state and partial protease resistance. These characteristics are exploited by the majority of the methods currently used for TSE diagnosis. The protease resistant disease related PrP entity, varies in its extent of degradation by proteinase K (PK) which is influenced by the strain-dependent conformational variations of the secondary and tertiary structure of PrPres. In different TSE strains, the pathological prion protein displays disease-specific features such as different cleavage sites after proteolytic treatment, glycosylation profile, and deposition patterns, which make strain identification possible [1]
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