Chronic wasting disease (CWD) is a fatal contagious prion disease in cervids that is enzootic in some areas in North America. The disease has been found in deer, elk and moose in the USA and Canada, and in South Korea following the importation of infected animals. Here we report the first case of CWD in Europe, in a Norwegian free-ranging reindeer in Southern Norway. The origin of the disease is unknown. Until now a low number of cervids, and among them a few reindeer, have been tested for CWD in Norway. Therefore the prevalence of CWD is unknown.

Prions are proteinaceous infectious particles that replicate by structural conversion of the host-encoded cellular prion protein (PrP ^C ), causing fatal neurodegenerative diseases in mammals. Species-specific amino acid substitutions (AAS) arising from single nucleotide polymorphisms within the prion protein gene ( Prnp ) modulate prion disease pathogenesis, and, in several instances, reduce susceptibility of homo- or heterozygous AAS carriers to prion infection. However, a mechanistic understanding of their protective effects against clinical disease is missing. We generated gene-targeted mouse infection models of chronic wasting disease (CWD), a highly contagious prion disease of cervids. These mice express wild-type deer or PrP ^C harboring the S138N substitution homo- or heterozygously, a polymorphism found exclusively in reindeer ( Rangifer tarandus spp. ) and fallow deer ( Dama dama ). The wild-type deer PrP-expressing model recapitulated CWD pathogenesis including fecal shedding. Encoding at least one 138N allele prevented clinical CWD, accumulation of protease-resistant PrP (PrP ^res ) and abnormal PrP deposits in the brain tissue. However, prion seeding activity was detected in spleens, brains, and feces of these mice, suggesting subclinical infection accompanied by prion shedding. 138N-PrP ^C was less efficiently converted to PrP ^res in vitro than wild-type deer (138SS) PrP ^C . Heterozygous coexpression of wild-type deer and 138N-PrP ^C resulted in dominant-negative inhibition and progressively diminished prion conversion over serial rounds of protein misfolding cyclic amplification. Our study indicates that heterozygosity at a polymorphic Prnp codon can confer the highest protection against clinical CWD and highlights the potential role of subclinical carriers in CWD transmission.

A clear association of amino acid variation in the prion protein gene (PRNP) with susceptibility and resistance to classical scrapie exists in sheep, but not in goats. In this study we examined DNA sequence variation in the PRNP of 149 animals from two scrapie-infected herds of Saanen dairy goats, and identified 6 non-synonymous variants in the coding region. In the larger herd, all of the 54 scrapie-affected goats tested had at least one allele with the arginine (R) codon at position 211, with 52 being homozygous for that variant. No animal homozygous for the glutamine (Q) codon at 211 were affected and only two heterozygotes (R/Q) were affected. A weak association was found at position 146 and no significant associations were found with amino acid variation at the remaining four variant positions (142, 143, 222 and 240), however, the allelic variation was low. Similar patterns were observed in the second scrapie-affected herd. We also evaluated previous studies on goat herds affected with scrapie and this relationship of R susceptibility and Q resistance at 211 was present independent of the genotypes at the other positions including 222. The fact that glutamine at 211 provides a significant protective property to scrapie irrespective of the other positions could be important for breeding strategies aimed at improving herd resistance to scrapie, while maintaining important productivity traits.

Real-time quaking-induced conversion (RT-QuIC) assays have become a common tool to detect chronic wasting disease (CWD) and are very sensitive provided the assay duration is sufficient. However, a prolonged assay duration may lead to non-specific signal amplification. The wide range of pre-defined assay durations in current RT-QuIC applications presents a need for methods to optimize the RT-QuIC assay. In this study, receiver operating characteristic (ROC) analysis was applied to optimize the assay duration for CWD screening in obex and retropharyngeal lymph node (RLN) tissue specimens. Two different fluorescence thresholds were used: a fixed threshold based on background fluorescence (T_stdev) and a max-point ratio (maximum/background fluorescence) threshold (T_MPR) to determine CWD positivity. The optimal assay duration was 33 h for obex and 30 h for RLN based on T_stdev, and 29 h for obex and 32 h for RLN based on T_MPR. The optimized assay durations were then evaluated for screening CWD in white-tailed deer from an affected farm. At a replicate level, using the optimized assay durations with T_Stdev and T_MPR, the level of agreement with enzyme-linked immunosorbent assay (ELISA) was significantly higher (p < 0.05) than that when using a 40 h assay duration. These findings demonstrate that the optimization of assay duration via a ROC analysis can improve RT-QuIC assays for screening CWD in white-tailed deer.

Prion transmission into rodents is essential for understanding prion strains. However, it is often limited by a “species barrier” that makes transmission challenging and complicates the study of animal and human prion diseases. Here, we report that North American deer mice (Peromyscus maniculatus) are susceptible to infection with both human sporadic Creutzfeldt–Jakob disease (sCJD) and chronic wasting disease (CWD). Experimental transmission of both sCJD and CWD in deer mice resulted in 100% attack rates, albeit with differing incubation times, with CWD-inoculated mice taking nearly three times longer than sCJD-inoculated mice to succumb. We observed distinct patterns of spongiform vacuolation and prion-protein deposition in the brain, as well as distinct protein-glycosylation profiles and seeding kinetics in RT-QuIC for each strain. Adaptation on the second passage led to reduced incubation periods and marked strain-specific pathology, as seen predominantly in the cortex in sCJD and the thalamus in CWD. Notably, primary transmission of CWD resulted in infrequent vacuoles and widespread punctate deposits of prion protein in the brain, while diffuse staining and remarkable vacuolation of the thalamus were seen on passage. Prion seeding kinetics for sCJD and CWD were indistinguishable in the second passage; however, the distinct glycosylation patterns seen on immunoblot of the prion protein were maintained. Adaptation also resulted in extraneural dissemination of prion seeding activity distinct to CWD infection. Overall, the ability to transmit both CWD and sCJD to this model, resulting in clear differences in incubation period, biochemical properties, clinical signs, pathology and seeding kinetics, indicates that the model has the potential for use as a tool to investigate atypical cases of sCJD that may indicate CWD spillover to humans.

Chronic wasting disease (CWD), a transmissible spongiform encephalopathy that targets cervids, has become a significant threat to both free-ranging and captive populations of Canadian white-tailed deer. In an effort to mitigate its spread, research in the past 20 years has demonstrated that the genetic background of deer may influence the pathogenesis of CWD. Specifically, variants located on the 95-, 96-, 116- and 226-codon of the prion protein gene seem to attenuate disease progression in white-tailed deer. The influence of these alleles on the likelihood of being found CWD-positive on Saskatchewan and Albertan farms was assessed using a Bayesian logistic regression model. To assess the presence of selection for favourable prion protein gene alleles, shifts in variant genotype frequencies were examined over the last seventeen years. Our results show that deer harboring the G96S allele have significantly lowered odds of infection within Canadian herds. Furthermore, the prevalence of this allele has increased significantly in farmed deer over the past seventeen years. Establishing the dynamic genetic background of Canadian deer populations will inform future disease management initiatives.