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A species barrier limits transmission of chronic wasting disease to mink (Mustela vison)

¹ Department of Comparative Medicine, University of Washington, Seattle, WA 98195-7190, USA
² Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, WA 99164-7040, USA
³ Animal Disease Research Unit, Agricultural Research Service, US Department of Agriculture, Pullman, WA 99164-6630, USA
⁴ Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, CO 80523-1619, USA

Correspondence
Robert D. Harrington
rdhdvm{at}u.washington.edu

Transmissible mink encephalopathy (TME) occurs as sporadic outbreaks associated with ingestion of feed presumably contaminated with some type of prion disease. Mink lack a species barrier to primary oral challenge with bovine spongiform encephalopathy, whereas they have a barrier to such challenge with scrapie. We investigated whether mink have a species barrier to chronic wasting disease (CWD) by performing primary intracerebral (IC) and primary oral challenge with CWD-positive elk brain. Primary IC challenge resulted in clinical disease in two of eight mink at 31–33 months incubation. Affected mink had spongiform vacuolation and astrocytosis within the central nervous system and immunoreactivity to disease-associated prion protein (PrP^d) in brain, retina and lymph node. CWD IC recipients had significantly lower brain vacuolation and PrP^d deposition scores, significantly lower cerebrocortical astrocyte counts and significantly higher hippocampal astrocyte counts than TME IC recipients. Primary oral challenge with CWD-positive elk brain (n=22) or with CWD-negative elk brain given IC (n=7) or orally (n=23) did not result in clinical or microscopic abnormalities during 42 months observation. Novel prion gene polymorphisms were identified at codon 27 (arginine/tryptophan) and codon 232 (arginine/lysine). This study shows that, whilst CWD can cause disease when given IC to mink, the lesions are not characteristic of TME, transmission is inefficient compared with TME and oral challenge does not result in disease. The demonstration of a species barrier in cervid-to-mustelid prion transmission indicates that mink are unlikely to be involved in natural CWD transmission.