A prion disease of cervids: chronic wasting disease

Norwegian moose CWD induces clinical disease and neuroinvasion in gene-targeted mice expressing cervid S138N prion protein

Chronic wasting disease (CWD) is a prion disease affecting deer, elk and moose in North America and reindeer, moose and red deer in Northern Europe. Pathogenesis is driven by the accumulation of PrPSc, a pathological form of the host's cellular prion protein (PrPC), in the brain. CWD is contagious among North American cervids and Norwegian reindeer, with prions commonly found in lymphatic tissue. In Nordic moose and red deer CWD appears exclusively in older animals, and prions are confined to the CNS and undetectable in lymphatic tissues, indicating a sporadic origin. We aimed to determine transmissibility, neuroinvasion and lymphotropism of Nordic CWD isolates using gene-targeted mice expressing either wild-type (138SS/226QQ) or S138N (138NN/226QQ) deer PrP. When challenged with North American CWD strains, mice expressing S138N PrP did not develop clinical disease but harbored prion seeding activity in brain and spleen. Here, we infected these models intracerebrally or intraperitoneally with Norwegian moose, red deer and reindeer CWD isolates. The moose isolate was the first CWD type to cause full-blown disease in the 138NN/226QQ model in the first passage, with 100% attack rate and shortened survival times upon second passage. Furthermore, we detected prion seeding activity or PrPSc in brains and spinal cords, but not spleens, of 138NN/226QQ mice inoculated intraperitoneally with the moose isolate, providing evidence of prion neuroinvasion. We also demonstrate, for the first time, that transmissibility of the red deer CWD isolate was restricted to transgenic mice overexpressing elk PrPC (138SS/226EE), identical to the PrP primary structure of the inoculum. Our findings highlight that susceptibility to clinical disease is determined by the conformational compatibility between prion inoculum and host PrP primary structure. Our study indicates that neuroinvasion of Norwegian moose prions can occur without, or only very limited, replication in the spleen, an unprecedented finding for CWD.

Large-scale assessment of genetic structure to assess risk of populations of a large herbivore to disease

Chronic wasting disease (CWD) can spread among cervids by direct and indirect transmission, the former being more likely in emerging areas. Identifying subpopulations allows the delineation of focal areas to target for intervention. We aimed to assess the population structure of white-tailed deer (Odocoileus virginianus) in the northeastern United States at a regional scale to inform managers regarding gene flow throughout the region. We genotyped 10 microsatellites in 5701 wild deer samples from Maryland, New York, Ohio, Pennsylvania, and Virginia. We evaluated the distribution of genetic variability through spatial principal component analysis and inferred genetic structure using non-spatial and spatial Bayesian clustering algorithms (BCAs). We simulated populations representing each inferred wild cluster, wild deer in each state and each physiographic province, total wild population, and a captive population. We conducted genetic assignment tests using these potential sources, calculating the probability of samples being correctly assigned to their origin. Non-spatial BCA identified two clusters across the region, while spatial BCA suggested a maximum of nine clusters. Assignment tests correctly placed deer into captive or wild origin in most cases (94%), as previously reported, but performance varied when assigning wild deer to more specific origins. Assignments to clusters inferred via non-spatial BCA performed well, but efficiency was greatly reduced when assigning samples to clusters inferred via spatial BCA. Differences between spatial BCA clusters are not strong enough to make assignment tests a reliable method for inferring the geographic origin of deer using 10 microsatellites. However, the genetic distinction between clusters may indicate natural and anthropogenic barriers of interest for management.

Habitat alteration or climate: What drives the densities of an invading ungulate?

Anthropogenic habitat alteration and climate change are two well-known contributors to biodiversity loss through changes to species distribution and abundance; yet, disentangling the effects of these two factors is often hindered by their inherent confound across both space and time. We leveraged a contrast in habitat alteration associated with the jurisdictional boundary between two Canadian provinces to evaluate the relative effects of spatial variation in habitat alteration and climate on white-tailed deer (Odocoileus virginianus) densities. White-tailed deer are an invading ungulate across much of North America, whose expansion into Canada's boreal forest is implicated in the decline of boreal caribou (Rangifer tarandus caribou), a species listed as Threatened in Canada. We estimated white-tailed deer densities using 300 remote cameras across 12 replicated 50 km2 landscapes over 5 years. White-tailed deer densities were significantly lower in areas where winter severity was higher. For example, predicted deer densities declined from 1.83 to 0.35 deer/km2 when winter severity increased from the lowest value to the median value. There was a tendency for densities to increase with increasing habitat alteration; however, the magnitude of this effect was approximately half that of climate. Our findings suggest that climate is the primary driver of white-tailed deer populations; however, understanding the mechanisms underpinning this relationship requires further study of over-winter survival and fecundity. Long-term monitoring at the invasion front is needed to evaluate the drivers of abundance over time, particularly given the unpredictability of climate change and increasing prevalence of extreme weather events.

Are rapid tests and confirmatory western blot used for cattle and small ruminants TSEs reliable tools for the diagnosis of Chronic Wasting Disease in Europe?

The first case of CWD in Europe was detected in a Norwegian reindeer in 2016, followed later by two CWD cases in Norwegian moose. To prevent the potential spread of CWD to the EU, the European Commission (Regulation EU 2017_1972) implemented a CWD surveillance programme in cervids in the six countries having reindeer and or moose (Estonia, Finland, Latvia, Lithuania, Poland, and Sweden). Each country had to test a minimum of 3000 cervids for CWD using diagnostic rapid tests approved by the EC Regulation. Experimental transmission studies in rodents have demonstrated that the CWD strains found in Norwegian reindeer are different from those found in moose and that these European strains are all different from the North American ones. Data on the performances of authorised rapid tests are limited for CWD (from North America) and are currently minimal for CWD from Europe, due to the paucity of positive material. The aim of this study was to evaluate the diagnostic performances of three of the so-called "rapid" tests, commercially available and approved for TSE diagnosis in cattle and small ruminants, to detect the CWD strains circulating in Europe. The performances of these three tests were also compared to two different confirmatory western blot methods. Using parallel testing on the same panel of available samples, we evaluated here the analytical sensitivity of these methods for TSE diagnosis of CWD in Norwegian cervids tissues. Our results show that all the methods applied were able to detect the CWD positive samples even if differences in analytical sensitivity were clearly observed. Although this study could not assess the test accuracy, due to the small number of samples available, it is conceivable that the rapid and confirmatory diagnostic systems applied for CWD surveillance in Northern Europe are reliable tools.

County-wide assessments of Illinois white-tailed deer (Odocoileus virginianus) prion protein gene variation using improved primers and potential implications for management

Chronic wasting disease (CWD) is a fatal, highly infectious prion disease that affects captive and wild cervids. Chronic wasting disease is the only known transmissible spongiform encephalopathy affecting free-ranging wildlife. In CWD-positive deer, some haplotypes of the prion protein gene PRNP are detected at lower frequencies as compared to CWD-negative deer, as are some variants of the prion protein PrP. Here, we examined wild, hunter-harvested CWD-negative white-tailed deer (Odocoileus virginianus) to determine whether there were geographical or temporal differences in the PRNP haplotypes, PRNP diplotypes, PrP proteoforms, and in the proportion of deer with at least one protective haplotype. We sampled 96-100 hunter-harvested deer per county at two time points in the Illinois counties of Jo Daviess, LaSalle, and Winnebago, chosen based on their geographic locations and known occurrence of CWD. The entire coding region of PRNP was sequenced, with haplotypes, diplotypes, and PrP proteoforms inferred. Across time, in Winnebago there was a significant increase in PrP proteoform F (p = 0.034), which is associated with a lower vulnerability to CWD. In every county, there was an increase over time in the frequency of deer carrying at least one protective haplotype to CWD, with a significant increase (p = 0.02) in the Jo Daviess County CWD infected region. We also found that primer combination was important as there was an 18.7% difference in the number of the deer identified as homozygous depending on primer usage. Current Illinois state management practices continue to remove CWD infected deer from locally infected areas helping to keep CWD prevalence low. Nonetheless, continued research on spatial and temporal changes in PRNP haplotypes, PrP proteoforms, and levels of deer vulnerability among Illinois deer will be important for the management of CWD within the state of Illinois and beyond.

Sensitive detection of chronic wasting disease prions recovered from environmentally relevant surfaces

Chronic wasting disease (CWD) has been identified in 30 states in the United States, four provinces in Canada, and recently emerged in Scandinavia. The association of CWD prions with environmental materials such as soil, plants, and surfaces may enhance the persistence of CWD prion infectivity in the environment exacerbating disease transmission. Identifying and quantifying CWD prions in the environment is significant for prion monitoring and disease transmission control. A systematic method for CWD prion quantification from associated environmental materials, however, does not exist. In this study, we developed an innovative method for extracting prions from swabs and recovering CWD prions swabbed from different types of surfaces including glass, stainless steel, and wood. We found that samples dried on swabs were unfavorable for prion extraction, with the greatest prion recovery from wet swabs. Using this swabbing technique, the recovery of CWD prions dried to glass or stainless steel was approximately 30% in most cases, whereas that from wood was undetectable by conventional prion immunodetection techniques. Real-time quake-induced conversion (RT-QuIC) analysis of these same samples resulted in an increase of the detection limit of CWD prions from stainless steel by 4 orders of magnitude. More importantly, the RT-QuIC detection of CWD prions recovered from stainless steel surfaces using this method was similar to the original CWD prion load applied to the surface. This combined surface swabbing and RT-QuIC detection method provides an ultrasensitive means for prion detection across many settings and applications.

Cervid Prion Protein Polymorphisms: Role in Chronic Wasting Disease Pathogenesis

Chronic wasting disease (CWD) is a prion disease found in both free-ranging and farmed cervids. Susceptibility of these animals to CWD is governed by various exogenous and endogenous factors. Past studies have demonstrated that polymorphisms within the prion protein (PrP) sequence itself affect an animal's susceptibility to CWD. PrP polymorphisms can modulate CWD pathogenesis in two ways: the ability of the endogenous prion protein (PrP^C) to convert into infectious prions (PrP^Sc) or it can give rise to novel prion strains. In vivo studies in susceptible cervids, complemented by studies in transgenic mice expressing the corresponding cervid PrP sequence, show that each polymorphism has distinct effects on both PrP^C and PrP^Sc. It is not entirely clear how these polymorphisms are responsible for these effects, but in vitro studies suggest they play a role in modifying PrP epitopes crucial for PrP^C to PrP^Sc conversion and determining PrP^C stability. PrP polymorphisms are unique to one or two cervid species and most confer a certain degree of reduced susceptibility to CWD. However, to date, there are no reports of polymorphic cervid PrP alleles providing absolute resistance to CWD. Studies on polymorphisms have focused on those found in CWD-endemic areas, with the hope that understanding the role of an animal's genetics in CWD can help to predict, contain, or prevent transmission of CWD.

Methionine oxidation within the prion protein

Prion diseases are characterized by the self-templated misfolding of the cellular prion protein (PrPC) into infectious aggregates (PrPSc). The detailed molecular basis of the misfolding and aggregation of PrPC remains incompletely understood. It is believed that the transient misfolding of PrPC into partially structured intermediates precedes the formation of insoluble protein aggregates and is a critical component of the prion misfolding pathway. A number of environmental factors have been shown to induce the destabilization of PrPC and promote its initial misfolding. Recently, oxidative stress and reactive oxygen species (ROS) have emerged as one possible mechanism by which the destabilization of PrPC can be induced under physiological conditions. Methionine residues are uniquely vulnerable to oxidation by ROS and the formation of methionine sulfoxides leads to the misfolding and subsequent aggregation of PrPC. Here, we provide a review of the evidence for the oxidation of methionine residues in PrPC and its potential role in the formation of pathogenic prion aggregates.

Shedding and stability of CWD prion seeding activity in cervid feces

CWD is an emergent prion disease that now affects cervid species on three continents. CWD is efficiently spread in wild and captive populations, likely through both direct animal contact and environmental contamination. Here, by longitudinally assaying in feces of CWD-exposed white-tailed deer by RT-QuIC, we demonstrate fecal shedding of prion seeding activity months before onset of clinical symptoms and continuing throughout the disease course. We also examine the impact of simulated environmental conditions such as repeated freeze-thaw cycles and desiccation on fecal prion seeding activity. We found that while multiple (n = 7) freeze-thaw cycles substantially decreased fecal seeding activity, desiccation had little to no effect on seeding activity. Finally, we examined whether RT-QuIC testing of landscape fecal deposits could distinguish two premises with substantial known CWD prevalence from one in which no CWD-infected animals had been detected. In the above pilot study, this distinction was possible. We conclude that fecal shedding of CWD prions occurs over much of the disease course, that environmental factors influence prion seeding activity, and that it is feasible to detect fecal prion contamination using RT-QuIC.

Use of different RT-QuIC substrates for detecting CWD prions in the brain of Norwegian cervids

Chronic wasting disease (CWD) is a highly contagious prion disease affecting captive and free-ranging cervid populations. CWD has been detected in United States, Canada, South Korea and, most recently, in Europe (Norway, Finland and Sweden). Animals with CWD release infectious prions in the environment through saliva, urine and feces sustaining disease spreading between cervids but also potentially to other non-cervids ruminants (e.g. sheep, goats and cattle). In the light of these considerations and due to CWD unknown zoonotic potential, it is of utmost importance to follow specific surveillance programs useful to minimize disease spreading and transmission. The European community has already in place specific surveillance measures, but the traditional diagnostic tests performed on nervous or lymphoid tissues lack sensitivity. We have optimized a Real-Time Quaking-Induced Conversion (RT-QuIC) assay for detecting CWD prions with high sensitivity and specificity to try to overcome this problem. In this work, we show that bank vole prion protein (PrP) is an excellent substrate for RT-QuIC reactions, enabling the detection of trace-amounts of CWD prions, regardless of prion strain and cervid species. Beside supporting the traditional diagnostic tests, this technology could be exploited for detecting prions in peripheral tissues from live animals, possibly even at preclinical stages of the disease.

Chronic Wasting Disease In Cervids: Prevalence, Impact And Management Strategies

Chronic wasting disease (CWD) is a transmissible spongiform encephalopathy (TSE) that affects members of the cervidae family. The infectious agent is a misfolded isoform (PrPSC) of the host prion protein (PrPC). The replication of PrPSC initiates a cascade of developmental changes that spread from cell to cell, individual to individual, and that for some TSEs, has crossed the species barrier. CWD can be transmitted horizontally and vertically, and it is the only TSE that affects free-ranging wildlife. While other TSEs are under control and even declining, infection rates of CWD continue to grow and the disease distribution continues to expand in North America and around the world. Since the first reported case in 1967, CWD has spread infecting captive and free-ranging cervids in 26 states in the US, 3 Canadian provinces, 3 European countries and has been found in captive cervids in South Korea. CWD causes considerable ecologic, economic and sociologic impact, as this is a 100% fatal highly contagious infectious disease, with no treatment or cure available. Because some TSEs have crossed the species barrier, the zoonotic potential of CWD is a concern for human health and continues to be investigated. Here we review the characteristics of the CWD prion protein, mechanisms of transmission and the role of genetics. We discuss the characteristics that contribute to prevalence and distribution. We also discuss the impact of CWD and review the management strategies that have been used to prevent and control the spread of CWD.

Estimating the amount of Chronic Wasting Disease infectivity passing through abattoirs and field slaughter

Chronic Wasting Disease (CWD) is a highly infectious, naturally occurring, transmissible spongiform encephalopathy (TSE, or prion disease) affecting many cervid species. CWD has been widely circulating in North America since it was first reported in 1967. In 2016, the first European case of prion disease in deer was reported and confirmed in Norway. There have since been several confirmed several cases in reindeer and moose and in one red deer in Norway, and recently in a moose in Finland. There is concern over the susceptibility of certain species, especially domestic livestock, to CWD. Recently, a study was presented showing transmission to cynomolgus macaques. Although preliminary, these results raise concerns that CWD may be transmissible to humans. This quantitative risk assessment estimates, by stochastic simulation, the titre of infectivity (herein referred to as "infectivity"), that would pass into the human food chain and environment (in the UK) as a result of a single CWD positive red deer passing through an abattoir, or being field dressed. The model estimated that around 11,000 mouse i.c. log ID₅₀ units would enter the human food chain through the farmed route or wild route. The model estimated that there are around 83,000 mouse i.c. log ID₅₀ units in a deer carcase, compared to around 22,000 in a sheep carcase infected with scrapie, mainly due to the size difference between a red deer and a sheep. For farmed deer, the model estimated that 87% of total carcase infectivity would become animal by-product category 3 material, with only 13% going to the food chain and a small amount to wastewater via the abattoir floor. For wild deer, the model estimated that on average, 85% of total carcase infectivity would be buried in the environment, with 13% going to the food chain and 2% to category 3 material which may be used as a protein source in other industries. Results indicate that if CWD was found in the UK there would be a risk of prions entering the human food chain and the environment. However, it is unclear if humans would be susceptible to CWD following consumption of contaminated meat, or what the environmental impact would be. This risk assessment highlights the need for further research in order to quantify the infectivity in all tissue types, in particular blood, gastrointestinal (GI) tract and skeletal muscle.

Mineral licks as environmental reservoirs of chronic wasting disease prions

Chronic wasting disease (CWD) is a fatal neurodegenerative disease of deer, elk, moose, and reindeer (cervids) caused by misfolded prion proteins. The disease has been reported across North America and recently discovered in northern Europe. Transmission of CWD in wild cervid populations can occur through environmental routes, but limited ability to detect prions in environmental samples has prevented the identification of potential transmission "hot spots". We establish widespread CWD prion contamination of mineral licks used by free-ranging cervids in an enzootic area in Wisconsin, USA. We show mineral licks can serve as reservoirs of CWD prions and thus facilitate disease transmission. Furthermore, mineral licks attract livestock and other wildlife that also obtain mineral nutrients via soil and water consumption. Exposure to CWD prions at mineral licks provides potential for cross-species transmission to wildlife, domestic animals, and humans. Managing deer use of mineral licks warrants further consideration to help control outbreaks of CWD.

Deterministic and stochastic analysis of an eco-epidemiological model

Chronic wasting disease (CWD) is a contagious prion disease among the deer family that has the potential to disrupt the ecosystems where deer occur in abundance. To understand the dynamics of this emerging infectious disease, we consider a simple eco-epidemic model where the host population is infected by CWD. Boundedness of the system is established. The structure of equilibria and their linearized stability are investigated. The persistence condition is discussed. By constructing a suitable Lyapunov function, we discuss the global stability of the endemic equilibrium. Local bifurcation (transcritical) around the boundary equilibria is developed. Sufficient conditions for the existence of Hopf-bifurcation are derived. Further, we have also introduced white type of noise into the system to investigate stochastic stability. This suggests that the deterministic model is robust with respect to stochastic perturbation. Some numerical simulations are performed to validate our results.

Vaccination strategies

Currently all prion diseases are without effective treatment and are universally fatal. It is increasingly being recognized that the pathogenesis of many neurodegenerative diseases, such as Alzheimer disease (AD), includes "prion-like" properties. Hence, any effective therapeutic intervention for prion disease could have significant implications for other neurodegenerative diseases. Conversely, therapies that are effective in AD might also be therapeutically beneficial for prion disease. AD-like prion disease has no effective therapy. However, various vaccine and immunomodulatory approaches have shown great success in animal models of AD, with numerous ongoing clinical trials of these potential immunotherapies. More limited evidence suggests that immunotherapies may be effective in prion models and in naturally occurring prion disease. In particular, experimental data suggest that mucosal vaccination against prions can be effective for protection against orally acquired prion infection. Many prion diseases, including natural sheep scrapie, bovine spongiform encephalopathy, chronic wasting disease, and variant Creutzfeldt-Jakob disease, are thought to be acquired peripherally, mainly by oral exposure. Mucosal vaccination would be most applicable to this form of transmission. In this chapter we review various immunologically based strategies which are under development for prion infection.

Scrapie, CWD, and Transmissible Mink Encephalopathy

Transmissible spongiform encephalopathies (TSEs), or prions, are neurodegenerative diseases that affect a variety of animal species, including humans. Cruetzfeldt-Jakob disease (CJD) in humans, sheep and goat scrapie, chronic wasting disease (CWD) of cervids, and transmissible mink encephalopathy (TME) of mink are classified as TSEs. According to the "protein-only" hypothesis (Prusiner, 1982),¹ prions are devoid of nucleic acids and consist of assemblies of misfolded host-encoded normal protein, the prion protein (PrP^C). Prion propagation is thought to occur by a templating mechanism during which PrP^C is recruited, converted to a disease-associated isoform (PrP^D), and assembled onto the growing amyloid fibril. This fibular assembly is infectious, with ability to initiate disease processes similar to other pathogenic agents. Evidence indicates that scrapie, CWD, and TME disease processes follow this rule.

Protein Misfolding Cyclic Amplification of Infectious Prions

Transmissible spongiform encephalopathies, or prion diseases, are a group of incurable disorders caused by the accumulation of an abnormally folded prion protein (PrP^Sc) in the brain. According to the "protein-only" hypothesis, PrP^Sc is the infectious agent able to propagate the disease by acting as a template for the conversion of the correctly folded prion protein (PrP^C) into the pathological isoform. Recently, the mechanism of PrP^C conversion has been mimicked in vitro using an innovative technique named protein misfolding cyclic amplification (PMCA). This technology represents a great tool for studying diverse aspects of prion biology in the field of basic research and diagnosis. Moreover, PMCA can be expanded for the study of the misfolding process associated to other neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and frontotemporal lobar degeneration.

Temporal patterns of chronic wasting disease prion excretion in three cervid species

Chronic wasting disease (CWD) is the only naturally occurring transmissible spongiform encephalopathy affecting free-ranging wildlife populations. Transmission of CWD occurs by direct contact or through contaminated environments; however, little is known about the temporal patterns of CWD prion excretion and shedding in wild cervids. We tested the urine and faeces of three species of captive cervids (elk, mule and white-tailed deer) at 6, 12, 18 and 24 months after oral inoculation to evaluate the temporal, species- and genotype-specific factors affecting the excretion of CWD prions. Although none of the animals exhibited clinical signs of CWD during the study, we determined that all three cervid species were excreting CWD prions by 6 months post-inoculation. Faecal samples were consistently positive for CWD prions for all three cervid species (88 %), and were more likely to be positive than urine samples (28 %). Cervids with genotypes encoding for the prion protein (PRNP) that were considered to be more susceptible to CWD were more likely to excrete CWD prions (94 %) than cervids with genotypes considered to be less susceptible (64 %). All cervids with CWD prions in their urine also had positive faeces (n=5), but the converse was not true. Our study is the first to demonstrate CWD prion excretion in urine by asymptomatic elk and mule deer. Our results indicate that the excretion of CWD prions in faeces and, to a lesser extent, urine may provide an important avenue for depositing prions in the environment.

Detection of chronic wasting disease prion seeding activity in deer and elk feces by real-time quaking-induced conversion

Chronic wasting disease (CWD) is an emergent prion disease affecting cervid species in North America, Canada, South Korea, and recently, Norway. Detection of CWD has been advanced by techniques that rely on amplification of low levels of prion amyloid to a detectable level. However, the increased sensitivity of amplification assays is often compromised by inhibitors and/or activators in complex biologic samples including body fluids, excreta, or the environment. Here, we adapt real-time quaking-induced conversion conditions to specifically detect CWD prions in fecal samples from both experimentally infected deer and naturally infected elk and estimate environmental contamination. The results have application to detection, surveillance and management of CWD, and potentially to other protein-misfolding diseases.

Chronic wasting disease (CWD) in cervids

In April and May of 2016, Norway confirmed two cases of chronic wasting disease (CWD) in a wild reindeer and a wild moose, respectively. In the light of this emerging issue, the European Commission requested EFSA to recommend surveillance activities and, if necessary, additional animal health risk-based measures to prevent the introduction of the disease and the spread into/within the EU, specifically Estonia, Finland, Iceland, Latvia, Lithuania, Norway, Poland and Sweden, and considering seven wild, semidomesticated and farmed cervid species (Eurasian tundra reindeer, Finnish (Eurasian) forest reindeer, moose, roe deer, white-tailed deer, red deer and fallow deer). It was also asked to assess any new evidence on possible public health risks related to CWD. A 3-year surveillance system is proposed, differing for farmed and wild or semidomesticated cervids, with a two-stage sampling programme at the farm/geographically based population unit level (random sampling) and individual level (convenience sampling targeting high-risk animals). The current derogations of Commission Implementing Decision (EU) 2016/1918 present a risk of introduction of CWD into the EU. Measures to prevent the spread of CWD within the EU are dependent upon the assumption that the disease is already present; this is currently unknown. The measures listed are intended to contain (limit the geographic extent of a focus) and/or to control (actively stabilise/reduce infection rates in an affected herd or population) the disease where it occurs. With regard to the zoonotic potential, the human species barrier for CWD prions does not appear to be absolute. These prions are present in the skeletal muscle and other edible tissues, so humans may consume infected material in enzootic areas. Epidemiological investigations carried out to date make no association between the occurrence of sporadic Creutzfeldt-Jakob disease in humans and exposure to CWD prions.

The Priority position paper: Protecting Europe's food chain from prions

Bovine spongiform encephalopathy (BSE) created a global European crisis in the 1980s and 90s, with very serious health and economic implications. Classical BSE now appears to be under control, to a great extent as a result of a global research effort that identified the sources of prions in meat and bone meal (MBM) and developed new animal-testing tools that guided policy. Priority ( www.prionpriority.eu ) was a European Union (EU) Framework Program 7 (FP7)-funded project through which 21 European research institutions and small and medium enterprises (SMEs) joined efforts between 2009 and 2014, to conduct coordinated basic and applied research on prions and prion diseases. At the end of the project, the Priority consortium drafted a position paper ( www.prionpriority.eu/Priority position paper) with its main conclusions. In the present opinion paper, we summarize these conclusions. With respect to the issue of re-introducing ruminant protein into the feed-chain, our opinion is that sustaining an absolute ban on feeding ruminant protein to ruminants is essential. In particular, the spread and impact of non-classical forms of scrapie and BSE in ruminants is not fully understood and the risks cannot be estimated. Atypical prion agents will probably continue to represent the dominant form of prion diseases in the near future in Europe. Atypical L-type BSE has clear zoonotic potential, as demonstrated in experimental models. Similarly, there are now data indicating that the atypical scrapie agent can cross various species barriers. More epidemiological data from large cohorts are necessary to reach any conclusion on the impact of its transmissibility on public health. Re-evaluations of safety precautions may become necessary depending on the outcome of these studies. Intensified searching for molecular determinants of the species barrier is recommended, since this barrier is key for important policy areas and risk assessment. Understanding the structural basis for strains and the basis for adaptation of a strain to a new host will require continued fundamental research, also needed to understand mechanisms of prion transmission, replication and how they cause nervous system dysfunction and death. Early detection of prion infection, ideally at a preclinical stage, also remains crucial for development of effective treatment strategies.

Prions are affected by evolution at two levels

Prions, infectious proteins, can transmit diseases or be the basis of heritable traits (or both), mostly based on amyloid forms of the prion protein. A single protein sequence can be the basis for many prion strains/variants, with different biological properties based on different amyloid conformations, each rather stably propagating. Prions are unique in that evolution and selection work at both the level of the chromosomal gene encoding the protein, and on the prion itself selecting prion variants. Here, we summarize what is known about the evolution of prion proteins, both the genes and the prions themselves. We contrast the one known functional prion, [Het-s] of Podospora anserina, with the known disease prions, the yeast prions [PSI+] and [URE3] and the transmissible spongiform encephalopathies of mammals.

Seeded Amplification of Chronic Wasting Disease Prions in Nasal Brushings and Recto-anal Mucosa-Associated Lymphoid Tissues from Elk by Real-Time Quaking-Induced Conversion

Chronic wasting disease (CWD), a transmissible spongiform encephalopathy of cervids, was first documented nearly 50 years ago in Colorado and Wyoming and has since been detected across North America and the Republic of Korea. The expansion of this disease makes the development of sensitive diagnostic assays and antemortem sampling techniques crucial for the mitigation of its spread; this is especially true in cases of relocation/reintroduction or prevalence studies of large or protected herds, where depopulation may be contraindicated. This study evaluated the sensitivity of the real-time quaking-induced conversion (RT-QuIC) assay of recto-anal mucosa-associated lymphoid tissue (RAMALT) biopsy specimens and nasal brushings collected antemortem. These findings were compared to results of immunohistochemistry (IHC) analysis of ante- and postmortem samples. RAMALT samples were collected from populations of farmed and free-ranging Rocky Mountain elk (Cervus elaphus nelsoni;n= 323), and nasal brush samples were collected from a subpopulation of these animals (n= 205). We hypothesized that the sensitivity of RT-QuIC would be comparable to that of IHC analysis of RAMALT and would correspond to that of IHC analysis of postmortem tissues. We found RAMALT sensitivity (77.3%) to be highly correlative between RT-QuIC and IHC analysis. Sensitivity was lower when testing nasal brushings (34%), though both RAMALT and nasal brush test sensitivities were dependent on both thePRNPgenotype and disease progression determined by the obex score. These data suggest that RT-QuIC, like IHC analysis, is a relatively sensitive assay for detection of CWD prions in RAMALT biopsy specimens and, with further investigation, has potential for large-scale and rapid automated testing of antemortem samples for CWD.

Expert elicitation on the uncertainties associated with chronic wasting disease

A high degree of uncertainty exists for chronic wasting disease (CWD) transmission factors in farmed and wild cervids. Evaluating the factors is important as it helps to inform future risk management strategies. Expert opinion is often used to assist decision making in a number of health, science, and technology domains where data may be sparse or missing. Using the "Classical Model" of elicitation, a group of experts was asked to estimate the most likely values for several risk factors affecting CWD transmission. The formalized expert elicitation helped structure the issues and hence provide a rational basis for estimating some transmission risk factors for which evidence is lacking. Considered judgments regarding environmental transmission, latency of CWD transmission, management, and species barrier were provided by the experts. Uncertainties for many items were determined to be large, highlighting areas requiring more research. The elicited values may be used as surrogate values until research evidence becomes available.

Applications of mathematical modeling in managing the spread of chronic wasting disease (CWD) in wild deer under alternative harvesting scenarios

The application of a recently developed mathematical model for predicting the spread of chronic wasting disease (CWD) in wild deer was assessed under different scenarios where harvesting is employed in disease management. A process-based mathematical model for CWD transmission in wild deer populations was recently developed and parameterized by Al-arydah et al. (2011) to provide a scientific basis for understanding the factors that affect spread of CWD and evaluate concomitant disease-control strategies. The impact of gender on CWD transmission was shown to have a significant influence on the spread of the disease in the wild. Our model demonstrates a range of harvesting rates in which CWD is controlled and deer populations survive. However, if harvesting rates are too low, the disease remains endemic for decades. Conversely, the Canadian deer population is eradicated if harvesting rates are excessive. Future investigation includes building the model to assess the spread of CWD under different disease-management scenarios.

Using expert judgments to improve chronic wasting disease risk management in Canada

ABSTARCT Chronic wasting disease (CWD) is a neurodegenerative, protein misfolding disease affecting cervids in North America in epidemic proportions. While the existence of CWD has been known for more than 40 years, risk management efforts to date have not been able to curtail the spread of this condition. An expert elicitation exercise was carried out in May 2011 to obtain the views of international experts on both the etiology of CWD and possible CWD risk management strategies. This study presents the results of the following three components of the elicitation exercise: (1) expert views of the most likely scenarios for the evolution of the CWD among cervid populations in Canada, (2) ranking analyses of the importance of direct and indirect transmission routes, and (3) rating analyses of CWD control measures in farmed and wild cervids. The implications of these findings for the development of CWD risk management strategies are described in a Canadian context.

Caribou consumption in northern Canadian communities

Chronic wasting disease (CWD) is a transmissible spongiform encephalopathy (TSE) found in both farmed and wild deer, elk, and moose in the United States and Canada. Surveillance efforts in North America identified the geographical distribution of the disease and mechanisms underlying distribution, although the possibility of transmission to other cervids, including caribou, and noncervids, including humans, is not well understood. Because of the documented importance of caribou (Rangifer tarandus) to human populations in the northern regions of Canada, a risk-management strategy for CWD requires an understanding of the extent of potential dietary exposure to CWD. Secondary 24-h dietary recalls conducted among Inuvialuit and Inuit in 4 communities in the Northwest Territories and Nunavut were employed in this study. Econometric demand systems were estimated to model the impacts of individual- and community-level socioeconomic characteristics on expenditures on caribou and other foods, in order to examine the households' ability to consume other foods in response to changing levels of caribou consumption. Thirty-five percent of respondents reported consuming caribou in the survey period, and caribou comprised, on average, 26% of daily dietary intake by weight, or approximately 65 g/d, across individuals in the 4 communities. Consuming caribou was also shown to exert positive impacts on dietary quality, as measured by calorie intake and dietary diversity. Communities with less access to employment, income and food stores are predicted to be constrained in their ability to obtain an adequate diet in the event of scarcity of caribou meat.

Complex folding and misfolding effects of deer-specific amino acid substitutions in the β2-α2 loop of murine prion protein

The β2-α2 loop of PrP(C) is a key modulator of disease-associated prion protein misfolding. Amino acids that differentiate mouse (Ser169, Asn173) and deer (Asn169, Thr173) PrP(C) appear to confer dramatically different structural properties in this region and it has been suggested that amino acid sequences associated with structural rigidity of the loop also confer susceptibility to prion disease. Using mouse recombinant PrP, we show that mutating residue 173 from Asn to Thr alters protein stability and misfolding only subtly, whilst changing Ser to Asn at codon 169 causes instability in the protein, promotes oligomer formation and dramatically potentiates fibril formation. The doubly mutated protein exhibits more complex folding and misfolding behaviour than either single mutant, suggestive of differential effects of the β2-α2 loop sequence on both protein stability and on specific misfolding pathways. Molecular dynamics simulation of protein structure suggests a key role for the solvent accessibility of Tyr168 in promoting molecular interactions that may lead to prion protein misfolding. Thus, we conclude that 'rigidity' in the β2-α2 loop region of the normal conformer of PrP has less effect on misfolding than other sequence-related effects in this region.

X-ray structural and molecular dynamical studies of the globular domains of cow, deer, elk and Syrian hamster prion proteins

Misfolded prion proteins are the cause of neurodegenerative diseases that affect many mammalian species, including humans. Transmission of the prion diseases poses a considerable public-health risk as a specific prion disease such as bovine spongiform encephalopathy can be transferred to humans and other mammalian species upon contaminant exposure. The underlying mechanism of prion propagation and the species barriers that control cross species transmission has been investigated quite extensively. So far a number of prion strains have been characterized and those have been intimately linked to species-specific infectivity and other pathophysiological manifestations. These strains are encoded by a protein-only agent, and have a high degree of sequence identity across mammalian species. The molecular events that lead to strain differentiation remain elusive. In order to contribute to the understanding of strain differentiation, we have determined the crystal structures of the globular, folded domains of four prion proteins (cow, deer, elk and Syrian hamster) bound to the POM1 antibody fragment Fab. Although the overall structural folds of the mammalian prion proteins remains extremely similar, there are several local structural variations observed in the misfolding-initiator motifs. In additional molecular dynamics simulation studies on these several prion proteins reveal differences in the local fluctuations and imply that these differences have possible roles in the unfolding of the globular domains. These local variations in the structured domains perpetuate diverse patterns of prion misfolding and possibly facilitate the strain selection and adaptation.

AGE AND REPEATED BIOPSY INFLUENCE ANTEMORTEM PRP(CWD) TESTING IN MULE DEER (ODOCOILEUS HEMIONUS) IN COLORADO, USA

Biopsy of rectal mucosa-associated lymphoid tissue provides a useful, but imperfect, live-animal test for chronic wasting disease (CWD) in mule deer (Odocoileus hemionus). It is difficult and expensive to complete these tests on free-ranging animals, and wildlife health managers will benefit from methods that can accommodate test results of varying quality. To this end, we developed a hierarchical Bayesian model to estimate the probability that an individual is infected based on test results. Our model was estimated with the use of data on 210 adult female mule deer repeatedly tested during 2010-14. The ability to identify infected individuals correctly declined with age and may have been influenced by repeated biopsy. Fewer isolated lymphoid follicles (where PrP(CWD) accumulates) were obtained in biopsies of older deer and the proportion of follicles showing PrP(CWD) was reduced. A deer's genotype in the prion gene (PRNP) also influenced detection. At least five follicles were needed in a biopsy to assure a 95% accurate test in PRNP genotype 225SS deer.

Longitudinal Detection of Prion Shedding in Saliva and Urine by Chronic Wasting Disease-Infected Deer by Real-Time Quaking-Induced Conversion

Chronic wasting disease (CWD) is an emergent, rapidly spreading prion disease of cervids. Shedding of infectious prions in saliva and urine is thought to be an important factor in CWD transmission. To help to elucidate this issue, we applied an in vitro amplification assay to determine the onset, duration, and magnitude of prion shedding in longitudinally collected saliva and urine samples from CWD-exposed white-tailed deer. We detected prion shedding as early as 3 months after CWD exposure and sustained shedding throughout the disease course. We estimated that the 50% lethal dose (LD50) for cervidized transgenic mice would be contained in 1 ml of infected deer saliva or 10 ml of urine. Given the average course of infection and daily production of these body fluids, an infected deer would shed thousands of prion infectious doses over the course of CWD infection. The direct and indirect environmental impacts of this magnitude of prion shedding on cervid and noncervid species are surely significant.

IMPORTANCE

Chronic wasting disease (CWD) is an emerging and uniformly fatal prion disease affecting free-ranging deer and elk and is now recognized in 22 U.S. states and 2 Canadian provinces. It is unique among prion diseases in that it is transmitted naturally through wild populations. A major hypothesis to explain CWD's florid spread is that prions are shed in excreta and transmitted via direct or indirect environmental contact. Here we use a rapid in vitro assay to show that infectious doses of CWD prions are in fact shed throughout the multiyear disease course in deer. This finding is an important advance in assessing the risks posed by shed CWD prions to animals as well as humans.

Safety, specificity and immunogenicity of a PrP(Sc)-specific prion vaccine based on the YYR disease specific epitope

Prions are a novel form of infectivity based on the misfolding of a self-protein (PrP(C)) into a pathological, infectious isomer (PrP(Sc)). The current uncontrolled spread of chronic wasting disease in cervids, coupled with the demonstrated zoonotic nature of select livestock prion diseases, highlights the urgent need for disease management tools. While there is proof-of-principle evidence for a prion vaccine, these efforts are complicated by the challenges and risks associated with induction of immune responses to a self-protein. Our priority is to develop a PrP(Sc)-specific prion vaccine based on epitopes that are uniquely exposed upon misfolding. These disease specific epitopes (DSEs) have the potential to enable specific targeting of the pathological species through immunotherapy. Here we review outcomes of the translation of a prion DSE into a PrP(Sc)-specific vaccine based on the criteria of immunogenicity, safety and specificity.

Emerging infectious diseases of wildlife: a critical perspective

We review the literature to distinguish reports of vertebrate wildlife disease emergence with sufficient evidence, enabling a robust assessment of emergence drivers. For potentially emerging agents that cannot be confirmed, sufficient data on prior absence (or a prior difference in disease dynamics) are frequently lacking. Improved surveillance, particularly for neglected host taxa, geographical regions and infectious agents, would enable more effective management should emergence occur. Exposure to domestic sources of infection and human-assisted exposure to wild sources were identified as the two main drivers of emergence across host taxa; the domestic source was primary for fish while the wild source was primary for other taxa. There was generally insufficient evidence for major roles of other hypothesized drivers of emergence.

Prion and prion-like diseases in animals

Transmissible spongiform encephalopaties (TSEs) are fatal neurodegenerative diseases characterized by the aggregation and accumulation of the misfolded prion protein in the brain. Other proteins such as β-amyloid, tau or Serum Amyloid-A (SAA) seem to share with prions some aspects of their pathogenic mechanism; causing a variety of so called prion-like diseases in humans and/or animals such as Alzheimer's, Parkinson's, Huntington's, Type II diabetes mellitus or amyloidosis. The question remains whether these misfolding proteins have the ability to self-propagate and transmit in a similar manner to prions. In this review, we describe the prion and prion-like diseases affecting animals as well as the recent findings suggesting the prion-like transmissibility of certain non-prion proteins.

Chronic wasting disease of cervids: current knowledge and future perspectives

A naturally occurring transmissible spongiform encephalopathy (TSE) of mule deer was first reported in Colorado and Wyoming in 1967 and has since spread to other members of the cervid family in 22 states, 2 Canadian provinces, and the Republic of Korea. Chronic wasting disease (CWD), caused by exposure to an abnormally folded isoform of the cellular prion protein, is characterized by progressive neurological disease in susceptible natural and experimental hosts and is ultimately fatal. CWD is thought to be transmitted horizontally in excreta and through contaminated environments, features common to scrapie of sheep, though rare among TSEs. Evolving detection methods have revealed multiple strains of CWD and with continued development may lead to an effective antemortem test. Managing the spread of CWD, through the development of a vaccine or environmental cleanup strategies, is an active area of interest. As such, CWD represents a unique challenge in the study of prion diseases.

Prion-seeding activity in cerebrospinal fluid of deer with chronic wasting disease

Transmissible spongiform encephalopathies (TSEs), or prion diseases, are a uniformly fatal family of neurodegenerative diseases in mammals that includes chronic wasting disease (CWD) of cervids. The early and ante-mortem identification of TSE-infected individuals using conventional western blotting or immunohistochemistry (IHC) has proven difficult, as the levels of infectious prions in readily obtainable samples, including blood and bodily fluids, are typically beyond the limits of detection. The development of amplification-based seeding assays has been instrumental in the detection of low levels of infectious prions in clinical samples. In the present study, we evaluated the cerebrospinal fluid (CSF) of CWD-exposed (n=44) and naïve (n=4) deer (n=48 total) for CWD prions (PrP^d) using two amplification assays: serial protein misfolding cyclic amplification with polytetrafluoroethylene beads (sPMCAb) and real-time quaking induced conversion (RT-QuIC) employing a truncated Syrian hamster recombinant protein substrate. Samples were evaluated blindly in parallel with appropriate positive and negative controls. Results from amplification assays were compared to one another and to obex immunohistochemistry, and were correlated to available clinical histories including CWD inoculum source (e.g. saliva, blood), genotype, survival period, and duration of clinical signs. We found that both sPMCAb and RT-QuIC were capable of amplifying CWD prions from cervid CSF, and results correlated well with one another. Prion seeding activity in either assay was observed in approximately 50% of deer with PrP^d detected by IHC in the obex region of the brain. Important predictors of amplification included duration of clinical signs and time of first tonsil biopsy positive results, and ultimately the levels of PrP^d identified in the obex by IHC. Based on our findings, we expect that both sPMCAb and RT-QuIC may prove to be useful detection assays for the detection of prions in CSF.

Modeling seasonal behavior changes and disease transmission with application to chronic wasting disease

Behavior and habitat of wildlife animals change seasonally according to environmental conditions. Mathematical models need to represent this seasonality to be able to make realistic predictions about the future of a population and the effectiveness of human interventions. Managing and modeling disease in wild animal populations requires particular care in that disease transmission dynamics is a critical consideration in the etiology of both human and animal diseases, with different transmission paradigms requiring different disease risk management strategies. Since transmission of infectious diseases among wildlife depends strongly on social behavior, mechanisms of disease transmission could also change seasonally. A specific consideration in this regard confronted by modellers is whether the contact rate between individuals is density-dependent or frequency-dependent. We argue that seasonal behavior changes could lead to a seasonal shift between density and frequency dependence. This hypothesis is explored in the case of chronic wasting disease (CWD), a fatal disease that affects deer, elk and moose in many areas of North America. Specifically, we introduce a strategic CWD risk model based on direct disease transmission that accounts for the seasonal change in the transmission dynamics and habitats occupied, guided by information derived from cervid ecology. The model is composed of summer and winter susceptible-infected (SI) equations, with frequency-dependent and density-dependent transmission dynamics, respectively. The model includes impulsive birth events with density-dependent birth rate. We determine the basic reproduction number as a weighted average of two seasonal reproduction numbers. We parameterize the model from data derived from the scientific literature on CWD and deer ecology, and conduct global and local sensitivity analyses of the basic reproduction number. We explore the effectiveness of different culling strategies for the management of CWD: although summer culling seems to be an effective disease eradication strategy, the total culling rate is limited by the requirement to preserve the herd.

In vitro prion protein conversion suggests risk of bighorn sheep (Ovis canadensis) to transmissible spongiform encephalopathies

Background

Transmissible spongiform encephalopathies (TSEs) affect both domestic sheep (scrapie) and captive and free-ranging cervids (chronic wasting disease; CWD). The geographical range of bighorn sheep (Ovis canadensis; BHS) overlaps with states or provinces that have contained scrapie-positive sheep or goats and areas with present epizootics of CWD in cervids. No TSEs have been documented in BHS, but the susceptibility of this species to TSEs remains unknown.

Results

We acquired a library of BHS tissues and found no evidence of preexisting TSEs in these animals. The prion protein gene (Prnp) in all BHS in our library was identical to scrapie-susceptible domestic sheep (A¹³⁶R¹⁵⁴Q¹⁷¹ genotype). Using an in vitro prion protein conversion assay, which has been previously used to assess TSE species barriers and, in our study appears to recollect known species barriers in mice, we assessed the potential transmissibility of TSEs to BHS. As expected based upon Prnp genotype, we observed BHS prion protein conversion by classical scrapie agent and evidence for a species barrier between transmissible mink encephalopathy (TME) and BHS. Interestingly, our data suggest that the species barrier of BHS to white-tailed deer or wapiti CWD agents is likely low. We also used protein misfolding cyclic amplification to confirm that CWD, but not TME, can template prion protein misfolding in A¹³⁶R¹⁵⁴Q¹⁷¹ genotype sheep.

Conclusions

Our results indicate the in vitro conversion assay used in our study does mimic the species barrier of mice to the TSE agents that we tested. Based on Prnp genotype and results from conversion assays, BHS are likely to be susceptible to infection by classical scrapie. Despite mismatches in amino acids thought to modulate prion protein conversion, our data indicate that A¹³⁶R¹⁵⁴Q¹⁷¹ genotype sheep prion protein is misfolded by CWD agent, suggesting that these animals could be susceptible to CWD. Further investigation of TSE transmissibility to BHS, including animal studies, is warranted. The lack of reported TSEs in BHS may be attributable to other host factors or a lack of TSE surveillance in this species.

Evaluation of a combinatorial approach to prion inactivation using an oxidizing agent, SDS, and proteinase K

BACKGROUND

Prions demonstrate an unusual resistance to methods effective at inactivating conventional microorganisms. This has resulted in a very tangible and difficult infection control challenge to the medical and veterinary communities, as well as animal agriculture and related industries. Currently accepted practices of harsh chemical treatments such as prolonged exposure to sodium hydroxide or sodium hypochlorite, or autoclaving are not suitable in many situations. Less caustic and more readily applicable treatments to contaminated environments are therefore desirable. We recently demonstrated that exposure of the RML scrapie agent to a commercial product containing sodium percarbonate (SPC-P) with or without sodium dodecyl sulfate (SDS) rendered PrP(Sc) sensitive to proteinase K (PK), but did not eliminate infectivity. The current study was designed to evaluate the efficacy of a combinatorial approach to inactivating prions by exposing RML-positive brain homogenate to SPC-P and SDS followed by PK. Treated samples were evaluated for PrP(Sc)-immunoreactivity by western blot, and residual infectivity by mouse bioassay.

RESULTS

Treatment of infected brain homogenate with SPC-P and SDS followed by PK exposure resulted in a 4-5 log10 reduction in infectivity when bioassayed in tga20 mice.

CONCLUSIONS

This study demonstrates that exposure of the RML scrapie agent to SPC-P and SDS followed by PK markedly reduces, but does not eliminate infectivity. The results of this study encourage further investigation into whether consecutive or concomitant exposure to sodium percarbonate, SDS, and a protease may serve as a viable and non-caustic option for prion inactivation.

Chronic wasting disease in bank voles: characterisation of the shortest incubation time model for prion diseases

In order to assess the susceptibility of bank voles to chronic wasting disease (CWD), we inoculated voles carrying isoleucine or methionine at codon 109 (Bv109I and Bv109M, respectively) with CWD isolates from elk, mule deer and white-tailed deer. Efficient transmission rate (100%) was observed with mean survival times ranging from 156 to 281 days post inoculation. Subsequent passages in Bv109I allowed us to isolate from all CWD sources the same vole-adapted CWD strain (Bv(109I)CWD), typified by unprecedented short incubation times of 25-28 days and survival times of ∼35 days. Neuropathological and molecular characterisation of Bv(109I)CWD showed that the classical features of mammalian prion diseases were all recapitulated in less than one month after intracerebral inoculation. Bv(109I)CWD was characterised by a mild and discrete distribution of spongiosis and relatively low levels of protease-resistant PrP(Sc) (PrP(res)) in the same brain regions. Despite the low PrP(res) levels and the short time lapse available for its accumulation, end-point titration revealed that brains from terminally-ill voles contained up to 10(8,4) i.c. ID50 infectious units per gram. Bv(109I)CWD was efficiently replicated by protein misfolding cyclic amplification (PMCA) and the infectivity faithfully generated in vitro, as demonstrated by the preservation of the peculiar Bv(109I)CWD strain features on re-isolation in Bv109I. Overall, we provide evidence that the same CWD strain was isolated in Bv109I from the three-cervid species. Bv(109I)CWD showed unique characteristics of "virulence", low PrP(res) accumulation and high infectivity, thus providing exceptional opportunities to improve basic knowledge of the relationship between PrP(Sc), neurodegeneration and infectivity.

Distinct morphological and electrophysiological properties of an elk prion peptide

A key event in prion diseases is the conversion of the prion protein (PrP) from its native α-helical conformation to a misfolded, β-sheet rich conformation. Thus, preventing or reversing PrP misfolding could provide a means to disrupt prion disease progression and transmission. However, determining the structure of misfolded PrP has been notoriously difficult due to its inherent heterogeneity and aggregation behavior. For these reasons, simplified peptide fragments have been used as models that recapitulate characteristics of full-length PrP, such as amyloid-like aggregation and fibril formation, and in vitro toxicity. We provide a biochemical and structural comparison of PrP(127-147) peptides from elk, bovine and hamster using electrophysiology, electron microscopy and fluorescence. Our results demonstrate that the PrP(127-147) peptides adopt distinct populations of fibril structures. In addition, the elk PrP(127-147) peptide is unique in its ability to enhance Thioflavin T fluorescence and its ability to modulate neuronal ion channel conductances.

Exposure of RML scrapie agent to a sodium percarbonate-based product and sodium dodecyl sulfate renders PrPSc protease sensitive but does not eliminate infectivity

BACKGROUND

Prions, the causative agents of the transmissible spongiform encephalopathies, are notoriously difficult to inactivate. Current decontamination recommendations by the World Health Organization include prolonged exposure to 1 N sodium hydroxide or > 20,000 ppm sodium hypochlorite, or autoclaving. For decontamination of large stainless steel surfaces and equipment as in abattoirs, for example, these methods are harsh or unsuitable. The current study was designed to evaluate the effectiveness of a commercial product containing sodium percarbonate to inactivate prions. Samples of mouse brain infected with a mouse-adapted strain of the scrapie agent (RML) were exposed to a sodium percarbonate-based product (SPC-P). Treated samples were evaluated for abnormal prion protein (PrPSc)-immunoreactivity by western blot analysis, and residual infectivity by mouse bioassay.

RESULTS

Exposure to a 21% solution of SPC-P or a solution containing either 2.1% or 21% SPC-P in combination with sodium dodecyl sulfate (SDS) resulted in increased proteinase K sensitivity of PrPSc. Limited reductions in infectivity were observed depending on treatment condition. A marginal effect on infectivity was observed with SPC-P alone, but an approximate 2-3 log10 reduction was observed with the addition of SDS, though exposure to SDS alone resulted in an approximate 2 log10 reduction.

CONCLUSIONS

This study demonstrates that exposure of a mouse-adapted scrapie strain to SPC-P does not eliminate infectivity, but does render PrPSc protease sensitive.

Chimeric elk/mouse prion proteins in transgenic mice

Chronic wasting disease (CWD) of deer and elk is a highly communicable neurodegenerative disorder caused by prions. Investigations of CWD are hampered by slow bioassays in transgenic (Tg) mice. Towards the development of Tg mice that will be more susceptible to CWD prions, we created a series of chimeric elk/mouse transgenes that encode the N terminus of elk PrP (ElkPrP) up to residue Y168 and the C terminus of mouse PrP (MoPrP) beyond residue 169 (mouse numbering), designated Elk3M(SNIVVK). Between codons 169 and 219, six residues distinguish ElkPrP from MoPrP: N169S, T173N, V183I, I202V, I214V and R219K. Using chimeric elk/mouse PrP constructs, we generated 12 Tg mouse lines and determined incubation times after intracerebral inoculation with the mouse-passaged RML scrapie or Elk1P CWD prions. Unexpectedly, one Tg mouse line expressing Elk3M(SNIVVK) exhibited incubation times of <70 days when inoculated with RML prions; a second line had incubation times of <90 days. In contrast, mice expressing full-length ElkPrP had incubation periods of >250 days for RML prions. Tg(Elk3M,SNIVVK) mice were less susceptible to CWD prions than Tg(ElkPrP) mice. Changing three C-terminal mouse residues (202, 214 and 219) to those of elk doubled the incubation time for mouse RML prions and rendered the mice resistant to Elk1P CWD prions. Mutating an additional two residues from mouse to elk at codons 169 and 173 increased the incubation times for mouse prions to >300 days, but made the mice susceptible to CWD prions. Our findings highlight the role of C-terminal residues in PrP that control the susceptibility and replication of prions.