Chronic wasting disease in Europe: new strains on the horizon

Abstract

Prion diseases are fatal neurodegenerative disorders with known natural occurrence in humans and a few other mammalian species. The diseases are experimentally transmissible, and the agent is derived from the host-encoded cellular prion protein (PrPC), which is misfolded into a pathogenic conformer, designated PrPSc (scrapie). Aggregates of PrPSc molecules, constitute proteinaceous infectious particles, known as prions. Classical scrapie in sheep and goats and chronic wasting disease (CWD) in cervids are known to be infectious under natural conditions. In CWD, infected animals can shed prions via bodily excretions, allowing direct host-to-host transmission or indirectly via prion-contaminated environments. The robustness of prions means that transmission via the latter route can be highly successful and has meant that limiting the spread of CWD has proven difficult. In 2016, CWD was diagnosed for the first time in Europe, in reindeer (Rangifer tarandus) and European moose (Alces alces). Both were diagnosed in Norway, and, subsequently, more cases were detected in a semi-isolated wild reindeer population in the Nordfjella area, in which the first case was identified. This population was culled, and all reindeer (approximately 2400) were tested for CWD; 18 positive animals, in addition to the first diagnosed case, were found. After two years and around 25,900 negative tests from reindeer (about 6500 from wild and 19,400 from semi-domesticated) in Norway, a new case was diagnosed in a wild reindeer buck on Hardangervidda, south of the Nordfjella area, in 2020. Further cases of CWD were also identified in moose, with a total of eight in Norway, four in Sweden, and two cases in Finland. The mean age of these cases is 14.7 years, and the pathological features are different from North American CWD and from the Norwegian reindeer cases, resembling atypical prion diseases such as Nor98/atypical scrapie and H- and L-forms of BSE. In this review, these moose cases are referred to as atypical CWD. In addition, two cases were diagnosed in red deer (Cervus elaphus) in Norway. The emergence of CWD in Europe is a threat to European cervid populations, and, potentially, a food-safety challenge, calling for a swift, evidence-based response. Here, we review data on surveillance, epidemiology, and disease characteristics, including prion strain features of the newly identified European CWD agents.

A single amino acid residue in bank vole prion protein drives permissiveness to Nor98/atypical scrapie and the emergence of multiple strain variants

“…Animal TSEs present largely as acquired diseases: classical scrapie (CS) in small ruminants, bovine spongiform encephalopathy (BSE) in cattle, chronic wasting disease (CWD) in cervids, and, likely, the recently discovered prion disease of dromedary camels [2,3]. However, the existence of sporadic or idiopathic forms in animals is increasingly recognized: H-and L-BSE in cattle [4,5], Nor98/atypical scrapie (AS) in small ruminants [6] and, possibly, the newly discovered forms of CWD in some European cervid species [7][8][9][10][11] do not show an obvious infectious origin and are often supposed to be spontaneous.…”

Characteristic distribution and molecular properties of normal cellular prion protein in human endocrine and exocrine tissues

“…There have been no reports of PrP expression in the ductal epithelium of animals or humans. CWD is a fatal neurodegenerative prion disease that affects species of the Cervidae family and is now a widespread global problem in the United States, Canada, and Europe 12 , 28 , 29 . Saliva and feces containing PrP Sc are likely sources of infection 28 , 29 .…”

“…In particular, PrP is related to endocrine tissues (e.g., the pituitary and adrenal glands and the pancreas) and endocrine pathway crinophagy [6][7][8][9][10] . In addition, chronic wasting disease (CWD), a prion disease of deer and elk, has become an issue in the United States, Canada, and Europe 11,12 . Transmission routes are thought to be prion-contaminated environments derived from saliva 13,14 , urine 15 , and feces 16 .In humans, information about the relationship between prion proteins and endocrine and exocrine organs remains limited, even regarding their histological localization.…”

Transport of Prions in the Peripheral Nervous System: Pathways, Cell Types, and Mechanisms

“…Recently, CWD cases have been identified in Norway, Sweden, and Finland. Compared to North American CWD, the Scandinavian CWD cases have PrP Sc and transmission properties suggesting that it is a unique strain of CWD [ 24 , 62 , 63 , 64 , 65 , 66 , 67 ]. Notably, CWD prions persist in the environment and are highly contagious resulting in horizontal transmission in both captive and free-ranging cervid populations [ 24 , 25 , 68 ].…”