NR AUML
AU Andrzejewski,M.
TI Untersuchungen zum Vorkommen von Scrapie-Prion-Protein in Tonsillenbioptaten genetisch hochempfänglicher Schafe in Niedersachsen (Investigations on the incidence of scrapie-prion-protein in genetically susceptible sheep from Lower Saxony by the use of tonsillar biopsies)
QU Inaugural-Dissertation zur Erlangung des Grades einer Doktorin der Veterinärmedizin (Dr. med. vet.) durch die Tierärztliche Hochschule Hannover, vorgelegt von Maike Andrzejewski aus Herne, 3.6.2005
PT Dissertation
AB Within sheep of a certain kind of PrP genotype the spread of the scrapie agent by lymphoid tissue is known. That allows an intravitale diagnostic by the use of lymphoid tissue biopsies. The practical handling of taking tonsillar biopsies and the gaining of evaluable samples were reviewed as part of this dissertation. Tonsillar biopsies and blood samples were taken from then sheep out of each of 72 flocks which were not under suspicion of being scrapie-infected. By using the blood samples, the sheep were genotyped. This genotyping gave an overview on the PrP Genotyps in the sheep population of Lower Saxony. 41% of the examined sheep showed the resistant PrP genotypes G1 or G2, which has to be considered as an advantage under the aspect of breeding for scrapie resistant animals. The tonsillar biopsie technique could be performed easily in every surrounding without exception. Out of 720 tissue samples, 462 had been examined histologically for the number of lymphoid follicles in the tissue section. The histological review of the tissue sections showed that only 67% of the samples contained the minimum of three follicles required for further examination. The incidence of scrapie prion protein in genetically susceptible sheep in Lower Saxony has been tested by examining tonsillar tissue from scrapie non suspect as well as from scrapie positive flocks of sheep. Out of 720 samples from scrapie non suspect animals, 200 samples from sheep with the PrP genotypes G3 to G5 were chosen. Out of these 200 samples one half was tested for accumulation of PrPsc in the tissue section by the use of IHC. The other half was tested by the use of PET blot. All 200 samples showed a negative result. For the research in scrapie positive flocks, four flocks of sheep were chosen (A-D) in which at least one sheep was detected positive by fallen stock survey. Within flock A to C, from all animals matching the same genotype of the fallen sheep or an even more susceptible genotype, tonsillar biopsies were taken. More scrapie positive animals were preclinically detected in each of the three flocks. In each flock the genotype of the preclinically detected sheep matched the genotype of the previously fallen sheep. In the aftermath of the tissue examinations all animals with genotypes G3 to G5 except the sheep found positive in the tonsillar tissue samples were culled. The brainstem of each culled sheep was investigated with a rapid test for PrPsc. Additional positive results were found in flock C. Within the biopsy samples of flock C in 4 out of 49 sheep PrPsc was found. Additional three sheep were found PrPsc positive after culling by rapid testing despite the tonsillar biopsy had been negative. Due to the large number of susceptible sheep in Flock D, only a part of the susceptible animals underwent tonsillar biopsies. All results of PrPsc testing were negative. In this study 17 sheep of genotype ARQ/ARQ were found PrPsc positive. There were only two PrPsc positive sheep of genotype VRQ/ARH and one VRQ/ARQ. To investigate the scrapie status of one flock tonsillar biopsies were taken and tissue samples were examined for accumulation of PrPsc from all sheep. Because of a large number of samples not containing the required number of follicles for accurate testing scrapie could not be excluded. Due to the results of this investigation taking tonsillar biopsies under field conditions is a feasible option, but the yield of evaluable samples for a reliable preclinical diagnosis of scrapie is not satisfying. Furthermore, a negative result of a PrPsc test in a tonsillar tissue section does not exclude scrapie even in a genetically susceptible sheep. To determine a scrapie status at flock level the examination of tonsillar biopsy tissue alone is not a suitable option. Nevertheless it has to be considered that immunodetection of PrPsc in lymphoid tissue biopsies is the only option for a preclinical test for prion diseases on living sheep at the moment. For pathogenetic studies investigations of naturally TSE infected living sheep would be desirable. Therefore it is recommended to examine animals of the same genotype as already fallen TSE positive sheep by taking lymphoid tissue biopsies before culling.
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