NR ATJR
AU Tongue,S.C.; Wilesmith,J.W.; Nash,J.; Kossaibati,M.; Ryan,J.
TI Genotype-specific differences in detection rates observed between two rapid screening tests used in ovine TSE surveillance
QU International Conference - Prion 2005: Between fundamentals and society's needs - 19.10.-21.10.2005, Congress Center Düsseldorf - Poster Session: Diagnosis DIA-03
PT Konferenz-Poster
AB
The introduction of large scale targeted surveillance programmes for ovine TSEs preceded the development of appropriate rapid screening tests. Accordingly, rapid tests used in the bovine population were provisionally approved for use. In Great Britain, the first surveys (2002-2003) utilised both the BioRad Platelia Elisa (BioRad) in series with immunohistochemistry (IHC) and the Prionics Check Western Blot (Prionics) in parallel with IHC. PrP genotype was also determined for all suitable samples. Subsequent surveys to date have used the BioRad TeSeE Elisa in series with IHC and PrP genotype has been determined for positive samples only. When stratified by genotype the two original screening tests present very different distributions of genotype-specific prevalence of PrPsc. The use of indirect standardisation enables the estimation of genotype-specific numbers of positives detected, if each test had been used as the screening test for the complete survey dataset (2002-2004 inclusive). So far, further investigations have generally focussed on the 'atypical' cases, detected by the BioRad but not the Prionics. These occur in genotypes traditionally considered to be at low risk of developing clinical disease. It appears however, that the reverse situation also exists: cases in genotypes containing the VRQ allele may go undetected by the BioRad. The magnitude of this effect is in the order of 20% and has several implications. Firstly, the consequent underestimate of overall prevalence of prion disease derived from any survey using only one of these screening tests (it could be 30-100% greater if both were used); secondly, the reduction in 'classical-scrapie case finding' for eradication purposes and thirdly, the effect on comparability of results from surveys using different screening methods. It also raises the question as to what the mechanism is behind this allele-specific difference in detection.
Ovine TSE surveillance in Great Britain is funded by Defra.
IN Die Autoren stellten fest, dass sich die in Großbritannien mit den TSE-Schnelltests gefundenen und immunhistochemisch bestätigten Scrapie-Fälle hinsichtlich der Anteile der verschiedenen Prionprotein-Genotypen in Abhängigkeit vom verwendeten Schnelltest (BioRad und Prionics) stark unterscheiden. Beide Schnelltests scheinen sich für die Scrapie-Diagnose bei bestimmten Genotypen besonders, bei anderen Genotypen jedoch schlecht bis gar nicht zu eignen. Die Probleme des Prionics-Tests bei Scrapie-Fällen mit nicht sehr proteaseresistentem PrPsc waren ja schon bekannt, aber auch der BioRad-Test scheint blind gegenüber Scrapie-Fällen zu sein, bei denen das Scrapie-Schaf auf mindestens einem Chromosom den Genotyp VRQ besitzt.
AD S.C.Tongue, J.Nash, M.Kossaibati, J.Ryan, Veterinary Laboratories Agency (Weybridge), UK; J.W.Wilesmith, Animal Health and Welfare, Directorate General, Defra, UK
SP englisch
PO Deutschland