Sheep prions with molecular properties intermediate between classical scrapie, BSE and CH1641-scrapie

Efforts to differentiate bovine spongiform encephalopathy (BSE) from scrapie in prion infected sheep have resulted
in effective methods to decide about the absence of BSE. In rare instances uncertainties remain due to assumptions
that BSE, classical scrapie and CH1641–a rare scrapie variant–could occur as mixtures. In field samples including those
from fallen stock, triplex Western blotting analyses of variations in the molecular properties of the proteinase K resistant
part of the disease‑associated form of prion protein (PrPres) represents a powerful tool for quick discrimination
purposes. In this study we examined 7 deviant ovine field cases of scrapie for some typical molecular aspects of PrPres
found in CH1641‑scrapie, classical scrapie and BSE. One case was most close to scrapie with respect to molecular mass
of its non-glycosylated fraction and N-terminally located 12B2‑epitope content. Two cases were unlike classical scrapie
but too weak to differentiate between BSE or CH1641. The other 4 cases appeared intermediate between scrapie and
CH1641 with a reduced molecular mass and 12B2‑epitope content, together with the characteristic presence of a
second PrPres population. The existence of these 2 PrPres populations was further confirmed through deglycosylation by
PNGaseF. The findings indicate that discriminatory diagnosis between classical scrapie, CH1641 and BSE can remain
inconclusive with current biochemical methods. Whether such intermediate cases represent mixtures of TSE strains
should be further investigated e.g. in bioassays with rodent lines that are varying in their susceptibility or other
techniques suitable for strain typing.