Cases of scrapie with unusual features in Norway and designation of a new type, Nor98

Five cases of scrapie with unusual features have been diagnosed in Norway since 1998. The affected sheep showed neurological signs dominated by ataxia, and had the PrP genotypes homozygous A 136 H 154 Q 171 / A 136 H 154 Q 171 or heterozygous A 136 H I54 Q 171 /A 136 R 154 Q 171 , which are rarely associated with scrapie. Brain histopathology revealed neuropil vacuolisation essentially in the cerebellar and cerebral cortices; vacuolation was less prominent in the brainstem, and no lesions were observed at the level of the obex. The deposits of PrP Sc were mainly in the cortex of the cerebellum and cerebrum, and no PrP Sc was detectable by immunohistochemistry and ELISA in the lymphoid tissues investigated. Western blot analysis showed that the glycotype was different from other known scrapie strains and from the BSE strain. From a diagnostic point of view, these features indicate that this type of scrapie, designated Nor98, could have been overlooked and may be of significance for sampling in scrapie surveillance programmes.