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Demographic risk factors for classical and atypical scrapie in Great Britain

Darren M. Green^1,

Istvan Z. Kiss^1,

Rowland R. Kao^1,

¹ Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK
² Veterinary Laboratories Agency, New Haw, Addlestone, Surrey KT15 3NB, UK
³ School of Biological Sciences, The University of Auckland, Private Bag 92019, Auckland, New Zealand

Correspondence
Rowland R. Kao
r.kao{at}vet.gla.ac.uk

Following the bovine spongiform encephalopathy (BSE) crisis, the European Union has introduced policies for eradicating transmissible spongiform encephalopathies (TSEs), including scrapie, from large ruminants. However, recent European Union surveillance has identified a novel prion disease, ‘atypical’ scrapie, substantially different from classical scrapie. It is unknown whether atypical scrapie is naturally transmissible or zoonotic, like BSE. Furthermore, cases have occurred in scrapie-resistant genotypes that are targets for selection in legislated selective breeding programmes. Here, the first epidemiological study of British cases of atypical scrapie is described, focusing on the demographics and trading patterns of farms and using databases of recorded livestock movements. Triplet comparisons found that farms with atypical scrapie stock more sheep than those of the general, non-affected population. They also move larger numbers of animals than control farms, but similar numbers to farms reporting classical scrapie. Whilst there is weak evidence of association through sheep trading of farms reporting classical scrapie, atypical scrapie shows no such evidence, being well-distributed across regions of Great Britain and through the sheep-trading network. Thus, although cases are few in number so far, our study suggests that, should natural transmission of atypical scrapie be occurring at all, it is doing so slowly.

Present address: Institute of Aquaculture, University of Stirling, Stirling, FK9 4LA, UK.

Present address: Department of Mathematics, Mantell Building, University of Sussex, Falmer, Brighton, BN1 9RF, UK.

Present address: Institute of Comparative Medicine, Faculty of Veterinary Medicine, University of Glasgow, Glasgow G61 1QH, UK.

Supplementary methods, including Supplementary Tables S1 and S2 and Supplementary Fig. S1, are available with the online version of this paper.