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CHRONIC wasting disease (CWD) is a prion disease affecting many species of deer, which was, until recently, confined to North America. However, confirmed diagnoses in Norway in both reindeer (Rangifer tarandus) and European elk/moose (Alces alces) in two geographically widely separated regions (Defra 2016a) is particularly disturbing.
The origin of CWD in Norway is obscure. It is possible that introduction from North America in contaminated deer material occurred as a single episode and the infection has spread or there have been two independent introductions. Alternatively, abnormal prions may have been generated anew in a Norwegian deer with subsequent dissemination. Establishing the most probable route will facilitate the implementation of appropriate control strategies to limit further incursion of CWD into Europe. However, if the North American experience is anything to go by, this incursion will have far-reaching implications throughout Europe and Asia since it has severely damaged deer farming and hunting industries in affected regions of Canada and the USA.
Like all prion diseases, such as scrapie and bovine spongiform encephalopathy (BSE), CWD is a member of the transmissible spongiform encephalopathies (TSE) identified by the typical histological lesions found in the brain. As such, it is an invariably fatal neurodegenerative disease with pathological changes associated with the conversion of the normal host-encoded membrane-associated prion protein (PrPC) to abnormal disease-associated isoforms (PrPd) which accumulate, principally in nervous tissue, due to their resistance to enzymatic breakdown; it is also referred to as PrPres (Collinge 2001). In CWD, PrPd also accumulates peripherally in lymphoid tissue, similar to scrapie in sheep, and detection of PrPd is the current method of definitive diagnosis (Gavier-Widen and others 2005).⇓
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