NR ATKR
AU Spiropoulos,J.; Bellworthy,S.J.; Hawkins,S.A.C.; Tongue,S.C.; Simmons,M.M.
TI False negative results can arise through reliance on rapid tests to detect potentially scrapie-infected sheep
QU International Conference - Prion 2005: Between fundamentals and society's needs - 19.10.-21.10.2005, Congress Center Düsseldorf - Poster Session: Diagnosis DIA-29
PT Konferenz-Poster
AB
During a TSE surveillance programme a large number of samples are initially screened with EU approved 'rapid tests'. Positive samples are subsequently confirmed using approved confirmatory tests. Samples negative on rapid test are not investigated further due to the logistic and financial issues emerging if such an approach is adopted. Therefore there is a realistic possibility that false negative results may remain undetected. This has always been acknowledged irrespective of the rapid test used, simply because of dependence on the timing of entry to the CNS of abnormal prions. Nevertheless, while debate has surrounded "atypical scrapie", and the difficulties presented in confirming initial rapid test positive results, the reverse scenario is rarely discussed.
The Ripley Flock at VLA is endemically infected with scrapie, and is used to study various aspects of scrapie pathogenesis. A number of samples derived from sheep at different stages of incubation have been routinely screened with the Bio-Rad TeSeE rapid test and confirmed by neuropathological examination using H&E and IHC.
Of the 73 cases which were negative on Bio-Rad TeSeE, eight (11%) were subsequently confirmed as positive. These cases were timed kills (absence of clinical signs) suggesting that they were pre-clinical cases similar to those targeted by active surveillance in a healthy population. On histopathology these samples were either inconclusive or negative. By IHC, the PrPsc deposits in the obex samples were distributed mainly in the ventral aspect of DMNV providing additional evidence that these cases reflect preclinical stage of classical scrapie. The PrP genotype of these cases was ARQ/VRQ.
Our findings confirm that rapid screening test used for active surveillance may still fail to detect a proportion of CNS positive cases.
Funded by DEFRA projects TS 5300 and TS 5990
IN In der VLA gibt es eine sogenannte Ripley-Herde, in welcher sich Scrapie seit langem horizontal ausbreiten konnte und in der deshalb zumindest viele Schafe Scrapie-infiziert sind. Wenn Tiere dieser Herde sterben oder getötet werden, dann führt man einen BioRad-Schnelltest durch, untersucht die Tiere aber auch immunohistochemisch. In 73 Fällen war das Ergebnis des BioRad-Schnelltests negativ, aber in 8 von diesen 73 Fällen erwies sich das Tier immunhistochemisch als doch Scrapie-infiziert. All diese Schafe waren noch nicht klinisch erkrankt und besaßen den Genotyp ARQ/VRQ.
AD J.Spiropoulos, S.J.Bellworthy, S.A.Hawkins, S.Tongue, M.M.Simmons, VLA, UK
SP englisch
PO Deutschland