Bovine spongiform encephalopathy in Sweden: an H-type variant

Bovine spongiform encephalopathy (BSE) had never been detected in Sweden until 2006, when the active surveillance identified a case in a 12-year-old cow. The case was an unusual form, because several molecular features of the protease-resistant prion protein (PrPres) were different from classical BSE. The differences included higher susceptibility for proteinase K, higher molecular weight of the PrPres bands, affinity to the N-terminus-specific antibodies 12132 and P4, and peculiar banding pattern with antibody SAF84 showing an additional band at the 14 kDa position. The molecular characteristics were in accordance to previous descriptions of H-type BSE. This report shows that a range of Western blot techniques and antibodies can be applied to confirm H-type BSE and further describes that the ratio of the amounts of PrPres#1 and PrPres#2, after deglycosylation, depends on the antibody used during processing. Immunohistochemistry on sections of medulla at the level of the obex applying antibodies with epitopes covering a broad range of the PrP sequence showed accumulation of disease-specific PrP (PrPd) in the gray matter. Fine punctate deposition in the neuropil was the most predominant type and was more severe in BSE target nuclei. The types of PrPd deposition are described in comparison with classical BSE. PrP-gene sequencing showed 6 copy octarepeat alleles and no abnormalities. It is postulated that the disease had a spontaneous origin, rather than having had been acquired in the BSE epidemic.