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

Abstract

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 (PrP^res) 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 PrP^res 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 PrP^res population. The existence of these 2 PrP^res 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.

Keywords:

• CH1641
• prion
• sheep
• typing
• Western blot

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Acknowledgments

We thank Dr. Jim Foster from Roslin institutes (UEDIN, Edinburgh, UK) for supply of CH1641 challenge material used for generating the different experimental CH1641 tissues at CVI and AHVLA. Dr. Jacques Grassi (CEA, Saclay, France) and Dr. Martin Groschup (FLI, Riems-Greifswald, Germany) provided kindly an initial batch of respectively antibodies SAF84 and L42. We thank Dr. Human Rezaei (INRA, Jouy-en-Jozas, France) for kind gift of rec-ovine PrP_ARQ.

Funding

This work was largely supported by the Dutch Ministry of Economic Affairs (grant WOT-01-002-01). Part of this work was also possible thanks to Department for Environment, Food and Rural Affairs (Defra, UK; project SE1700/CSA 7335), European Commission funded STREP project GoatBSE, FOOD-CT-2006-36353 and EMIDA ERA-NET project GOAT-TSE-FREE.