Chronic Wasting Disease CWD TSE Prion Strains and Potential Zoonotic Ramifications

 Chronic Wasting Disease CWD TSE Prion Strains and Potential Zoonotic Ramifications   

PLoS Pathog. 2026 Jun 4;22(6):e1014303. doi: 10.1371/journal.ppat.1014303

Distinct prion conformers from brain and peripheral tissues of gene-targeted mice produce convergent CWD strain properties

Joseph P DeFranco 1, Zoe N Atkinson 1, Jenna Crowell 1, Xutong Shi 1,2, Sehun Kim 1, Julianna L Sun 1,2,¤a, Sarah J Kane 1,¤b, Glenn C Telling 1,2,* Editor: Suzette A Priola3

Author information Article notes Copyright and License information PMCID: PMC13252839 PMID: 42241459

Abstract

Prions are unique infectious agents because different conformational properties of their constituent proteins are responsible for the manifestation of distinct strains. While prion replication in humans with sporadic Creutzfeldt-Jakob disease and cattle with bovine spongiform encephalopathy is primarily limited to the central nervous system (CNS), a seminal feature of chronic wasting disease (CWD) in cervids is high infectious titers in peripheral tissues, including skeletal muscles and the lymphoreticular system. Although extensive studies have assessed prion properties in the CNS, our understanding of prions in peripheral tissues remains limited. Here, we compared the strain properties of CWD prions in peripheral and CNS tissues of gene-targeted (Gt) mice. Our studies reveal differences in the biochemical and conformational properties of CWD prions, as well as the prion levels, between peripheral and CNS tissues. While this finding suggested that these tissues harbored distinct CWD prions, transmissions of muscle, spleen, and brain homogenates to Gt mice by the intraperitoneal route produced convergent strain properties. Importantly, transmission of these tissues by the intracerebral route resulted in different disease phenotypes than intraperitoneal inoculations. Additionally, while prion infection of CWD-susceptible cells revealed different titers in muscle, spleen, and brain tissues, the conformational properties of the resulting de novo prions were indistinguishable. While our findings support a role for tissue-specific cofactors that affect the biochemical and conformational properties of prions, they also show that these parameters do not solely dictate disease outcomes and that additional factors, particularly the route of inoculation, exert a more pronounced influence on strain outcomes.

Author summary

The contamination of the food chain by bovine spongiform encephalopathy prions, which caused disease in animals and humans, exemplifies the lethal consequences of interspecies prion transmissions. Because prion diseases also threaten wildlife ecology, it is essential to understand prion replication within the host organism and how strain differences influence the likelihood of transmission within and between species. Chronic wasting disease (CWD), a burgeoning prion epidemic of cervids, presents with high prion titers in peripheral tissues and bodily fluids, which most likely explains its irrevocable spread across North America. Here, we investigated CWD prions in the brains, spleens, and skeletal muscles of gene-targeted mice expressing the cervid prion protein. While we found that the biochemical and conformational properties, as well as the levels of CWD prions, in the brain and peripheral tissues were distinct, transmissions to gene-targeted mice produced convergent strain outcomes. These findings further validate the use of gene-targeted mice for modeling prion diseases and provide insights into the biological processes underlying strain evolution.

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Because the study reported here was successful in understanding the properties of North American CWD prions, it warrants further investigation of other prion strains in peripheral tissues. Because of the diversity and instability of CWD strains in Northern Europe [45,74,75], determining the replicative capacity of these prions in the LRS, skeletal muscle, and other peripheral tissues could inform the risk of handling or consuming tissues from diseased cervids. Furthermore, whether these “islands” of prion conformers across various tissues yield divergent outcomes following interspecies transmission requires investigation in additional Gt mice encoding for human and other mammalian prion proteins [76]. Because the zoonotic potential of CWD has primarily been evaluated following ic transmission of brain tissue, this study provides proof of concept to model natural transmission scenarios. For example, feeding Gt mice expressing human PrP with muscle from native CWD prions, or CWD prions that have adapted following transmission in GtE and GtQ mice [45], is of high priority.

https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1014303

Historical and contemporary chronic wasting disease prions from the western United States demonstrate similar strain properties

Open Access Katie Williams1​ 1​, Chase Baune1​ 1​,2​, Daniel Shoup1​ 1​, Tina Thomas3​ 3​, James F. Striebel1​ 1​,4​, Suzette A. Priola1​ 1​, Karen A. Griffin5​, Michael W. Miller5​, Kent Barbian6​ 6​, Kaitlyn Wagner7​, Mark D. Zabel8​ and Brent Race1​ 1​,View Affiliations Published: 25 June 2026 https://doi.org/10.1099/jgv.0.002265

ABSTRACT

Chronic wasting disease (CWD) is a uniformly fatal prion disease of cervids including deer, elk, reindeer and moose. CWD has been detected in cervids of North America (NA), South Korea and Scandinavia. CWD in NA continues to increase in prevalence in multiple locations and is relatively widespread in both wild and captive cervid populations. Consequently, the potential for CWD cross-species exposure to humans or animals that consume or cohabitate with infected cervids continues to increase. Fortunately, CWD infection in humans has not been detected to date, and both laboratory models and epidemiological studies suggest that a strong species barrier exists between cervids and humans. In recent years, several different strains of CWD have been identified and characterized. Unfortunately, new strains of CWD prions may harbour different abilities to cross species barriers, presenting a situation where the risks to humans and animals may also vary. To gain a better understanding of the variation in CWD strains circulating in NA, we performed strain characterization of ten CWD isolates obtained over the past 4–30 years from white-tailed deer, mule deer and elk representing infections from several geographical regions in the western United States. Our results showed that all the cervid isolates we tested had similar prion strain characteristics, suggesting that the CWD prions circulating in the western United States have remained very similar across multiple locations and stable over time.

Keywords chronic wasting disease, CWD, prion, strain, transgenic mice Author Notes One supplementary figure and three supplementary tables are available with the online version of this article. Abbreviations CSA, conformational stability assay; CWD, chronic wasting disease; ECL, enhanced chemiluminescence; GdnHCl, guanidine hydrochloride; IHC, immunohistochemistry; MD, mule deer; NA, North America; NW MT, northwest Montana; PK, proteinase K; PRNP, prion protein gene; PVDF, polyvinylidene difluoride; RML, Rocky Mountain Laboratory; RPLN, retropharyngeal lymph node; SD50, seeding dose 50; SD ELK, elk originating in South Dakota; SSBP/1, scrapie subpassaged brain pool; ThT, thioflavin T; WTD, white-tailed deer.

Data Availability The data supporting the conclusions of this article are included within the article. The brain tissue homogenates from these experiments are available from the corresponding author on request.

Data Summary Toggle display: Open fullscreen CWD isolate

GenBank accession no.

Texas 1

PX682255

SD ELK

PX682256

CO/WY 1996

PX682257

NW MT WTD1

PX682258

N MT MD

PX682259

S MT WTD

PX682260

N MT WTD

PX682261

S MT MD

PX682262

NW MT WTD2

PX682263

CO MD 2021

PX682264

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Our data from ten CWD isolates showed that each isolate carried similar CWD prions. This finding is consistent with two recent reports from the Telling laboratory that also reported that the North American CWD isolates tested were all very similar [21, 22]. However, determining the extent that strains identified by individual groups overlap each other would be difficult, as separate groups often use different rodent models that can confound direct comparisons of the resulting data [6]. Our tg33mouse model and inoculation methods differ from the gene-targeted mice currently used by the Telling laboratory, so a direct comparison between their most recent data suggesting a dominant North American strain and ours can be difficult. Fortunately, previous characterizations of several CWD strains performed by the McKenzie laboratory used the same tg33 mice as our group [15, 18]. As part of their work, they extensively characterized Wisc-1, a strain of CWD collected originally from Wisconsin. In 2015, they reported that Wisc-1 shared similarities to CWD1, a strain characterized in tg1536mice by Angers et al. in 2010 [15, 20]. When we compared the phenotype of our ten CWD isolates to the published data for Wisc-1 in tg33 mice, we see overlap in clinical signs, incubation periods, neuropathology and conformational stability following treatment with GdnHCl. The collective phenotypic similarity between Wisc-1 and our isolates suggests that they, and perhaps CWD1, may all harbour the same dominant CWD strain.

All CWD isolate characterization studies performed to date, including ours, have been limited by time and resources, so sample sizes have remained small and cannot begin to represent focal areas of CWD infection in NA. Our study attempted to represent areas where CWD had existed for many years and compare them to newer foci of infection with clear geographic separation. Unfortunately, but not surprisingly, none of the CWD isolates we had available to characterize carried polymorphisms in the host PRNP gene. Most polymorphisms in the PRNP gene are underrepresented in cervid populations, and although we did sequence all our isolates, we did not identify any unique polymorphisms for this study. Of the other CWD strains reportedly characterized to date, most appear to be a result of CWD-prion replication in deer or elk that carry unique PRNP polymorphisms [14–19]. Discovering unique prion strains in these individuals is logical, as variation in the amino acid sequence can allow and promote different conformations of mis-folded PrPSc. The frequency of PRNP polymorphisms in cervids will undoubtably increase in the future as a result of both natural genetic pressure in wild cervids [36] and selective breeding of captive cervids carrying more CWD-resistant genotypes. Understanding the variation and zoonotic potential of CWD prions propagated in these animals will be important.

In our study, we tested two historical samples that were collected from the mid-1990s: a pool of six captive elk originating in South Dakota (SD ELK) and a pool of seven WTD brains collected from Colorado and Wyoming (CO/WY 1996). The other eight samples were collected from 2019 to 2021 and were not pooled (Table 1). We hypothesized that we might see strain differences between our archived CWD samples (SD ELK and CO/WY 1996) and our contemporary isolates if CWD was evolving over time, as distinct CWD strains have been reported previously in two separate populations of captive elk [37]. Our bioassay and strain characterization data suggested that this was not the case among the ten CWD isolates we characterized. Evidence from our isolates showed that CWD prions appear to be very similar, with no evidence for substantive change over three decades despite significant geographic separation between CWD endemic areas.

The fact that the isolates that we tested were both biochemically similar and neuropathologically stable after serial passage in tg33 mice is consistent with there being a single, predominant strain of CWD in NA. However, there are some caveats to this interpretation. First, prion transmission into a new host can result in changes that are controlled more by the new host, rather than the original input prion strain [15, 38, 39]. We cannot exclude the possibility that factors within our tg33 mice did not alter strain properties by preferentially amplifying and propagating prions that were the most conformationally stable for the new recipient. If the host was influencing the strain characteristics toward a more stable, amplification competent prion for the mouse, then any subtle differences or sub-strains present in the original isolates might be difficult to resolve [40–42].

Additional factors that may influence our results are the type of genetically engineered mice we used, the route of prion inoculation, and the tissue source of the prions we used. The tg33 mice we used expressed deer prion protein via a transgene insertion rather than using a gene-targeted mouse. At the time our project was initiated, we used what was considered the gold standard for strain characterization, intracerebral inoculation of prions into a common susceptible recipient. However, recent studies by Bian et al. [17] and DeFranco et al. [21] used mice engineered to have gene-targeted cellular expression of either deer or elk prion protein and found that route of transmission (intracerebral vs. peripheral) affected the resulting CWD prion strain characteristics. Peripheral inoculation appeared to allow propagation of the natural CWD prions in brain tissue whereas direct intracerebral inoculation resulted in CWD prions divergent from the input material from deer or elk. Alternatively, comparing the outcome of brain derived CWD prions to that of lymphoid derived prions could also influence the resulting prion replication since prions that replicate in non-neuronal tissues can have unique conformers with variable abilities to adapt and propagate in a new tissue [21, 43]. However, we observed no evidence for divergent strains or unique conformers in any of the isolates we tested.

It has long been recognized that multiple prion strains can be present in prion-infected tissues, even if there is only a single PrP genotype being expressed. This is particularly true of scrapie, where biological cloning of scrapie from SSBP/1 sheep led to the isolation of multiple well-defined prion strains with different rodent tropisms [44]. By some accounts, CWD appears to also be a mixture of prion strains [6, 7]. Thus, even though our results suggest that there is a dominant CWD strain circulating in the western US, it is possible that other sub-strains or minority conformations are present in the field isolates that we inoculated, especially in the two samples that consisted of pooled tissues. If minority strains were present, and these strains replicated less efficiently they would likely not be detected in our bioassay, where the relatively high titres used for inoculation would favour the more abundant strain. However, less abundant strains might be detectable if more diluted inoculum were inoculated over several passages [40]. If CWD in cervids does represent a less heterogeneous prion strain population than scrapie in sheep, it may be because CWD has been circulating for less time than sheep scrapie (<60 years for CWD compared to >300 years for sheep scrapie), with less time to spread and adapt to different environments and hosts. The possibilities suggested above are not mutually exclusive and together might account for the relatively limited number of CWD prion strains identified so far. While we did not detect different strains in the ten CWD samples characterized in this study, it remains prudent to continue monitoring affected cervid populations for strain variation, as emergent new strain properties could affect transmission potential within and across species.

https://www.microbiologyresearch.org/content/jgv/10.1099/jgv.0.002265.IT1?fmt=ahah&fullscreen=true

Overview of North American Isolates of Chronic Wasting Disease Used for Strain Research

by W. David Walter 1, Allen Herbst 2, Chia-Hua Lue 3, Jason C. Bartz 4 and M. Camille Hopkins 5 U.S. Geological Survey, Pennsylvania Cooperative Fish and Wildlife Research Unit, The Pennsylvania State University, University Park, PA 16802, USA 2 U.S. Geological Survey, National Wildlife Health Center, Madison, WI 53711, USA 3 Pennsylvania Cooperative Fish and Wildlife Research Unit, The Pennsylvania State University, University Park, PA 16802, USA 4 Department of Medical Microbiology and Immunology, Creighton University, Omaha, NE 68178, USA 5 U.S. Geological Survey, Ecosystems Mission Area, Reston, VA 20192, USA * Author to whom correspondence should be addressed. Pathogens 2025, 14(3), 250; https://doi.org/10.3390/pathogens14030250

Submission received: 10 January 2025 / Revised: 24 February 2025 /Accepted: 28 February 2025 / Published: 4 March 2025 (This article belongs to the Special Issue Advances in Chronic Wasting Disease)

Abstract

Chronic Wasting Disease (CWD) is a prion disease that affects Cervidae species, and is the only known prion disease transmitted among wildlife species. The key pathological feature is the conversion of the normal prion protein (PrPC) misfolding into abnormal forms (PrPSc), triggering the onset of CWD infections. The misfolding can generate distinct PrPSc conformations (strains) giving rise to diverse disease phenotypes encompassing pathology, incubation period, and clinical signs. These phenotypes operationally define distinct prion strains, a pivotal element in monitoring CWD spread and zoonotic potential—a complex endeavor compounded by defining and tracking CWD strains. This review pursues a tripartite objective: 1. to address the intricate challenges inherent in ongoing CWD strain classification; 2. to provide an overview of the known CWD-infected isolates, the strains they represent and their passage history; and 3. to describe the spatial diversity of CWD strains in North America, enriching our understanding of CWD strain dynamics. By delving into these dimensions, this review sheds light on the intricate interplay among polymorphisms, biochemical properties, and clinical expressions of CWD. This endeavor aims to elevate the trajectory of CWD research, advancing our insight into prion disease. Keywords: chronic wasting disease; prion strains; tissue; infected isolates; transmission

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Currently, the conformation of PrPSc responsible for CWD (hereafter referred to as PrPCWD) is the most common animal prion disease [4,5]. We counted more than 17,000 positive cases of CWD that were reported by state and provincial wildlife agencies in 2022 in North America.

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Identifying isolates used and potential availability of these isolates may provide samples that are available for a reassessment of strains previously identified to confirm there are five distinct strains in North America.

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1.3. Strain Mixtures in Nature Current evidence indicates that some CWD natural infections can involve mixtures of strains, such as CWD1/CWD2 and 116AG long/short [43,45]. This phenomenon is not unique to CWD. It has also been observed in humans with sporadic Creutzfeldt–Jakob disease [73,74,75] and in sheep and goats infected with scrapie (Reviewed in [16]). The specific properties of a strain mixture, and how CWD strain diversity is encoded by PrPSc, however, are still unclear. It is uncertain whether the strain mixtures arise from co-existing prion conformers, or if a novel strain evolves under specific conditions by replication of a single conformation species [16,42,75,76,77].

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3. Results

3.1. North America CWD Strains

To date, eleven potential CWD strains have been described. Here, our focus will be on the five CWD strains documented in free-ranging cervid species in North America, including their infected isolates (Table 1). More information on CWD strains from Nordic countries and captive cervids can be found in a recent review [47].

3.1.1. CWD1 and CWD2 Infected isolates of CWD1 and CWD2 strains: Ref. [43] documented CWD1 and CWD2, and their strain mixtures in tg1536 mice. These strains were identified by passage of infected isolates from elk (Cervus elaphus) and deer that originated from Colorado, Wyoming, Alberta, and Saskatchewan. These isolates have also served as valuable resources for other research (Table 1).

Noteworthy information regarding CWD1: The infected isolate derived from white-tailed deer (Odocoileus virginianus), as described by [43], was sourced from Wisconsin and was one of the isolates, which did not result in the CWD2 phenotype during serial passage. This isolate shared similar strain phenotypic features (widespread symmetric neuropathology) with the wt/wt (Wisc-1) infected isolate from Wisconsin described in the work conducted by [48]. Establishing whether Wisc-1 and CWD1 are indeed identical strains remains a challenge, primarily because these prion agents were passaged in different transgenic mice.

Strain summary: CWD1 and CWD2 are the strains that were defined from CWD infected isolates from North American cervids [43]. In this study, CWD isolates from elk, mule deer (Odocoileus hemionus), and white-tailed deer were inoculated into transgenic mice overexpressing deer PrPC (tg1536mice). The two strains resulted in different disease phenotypes: CWD1 has a shorter incubation time, higher vacuolation score in hippocampus, and a widespread, symmetrical PrPSc deposition compared to CWD2, which is characterized by longer incubation periods and asymmetrical neuropathology. Transmission of elk isolates typically resulted in either CWD1 or CWD2 with a few contrasting isolates resulting in both phenotypes after first passage (IDs: 12389 and 001-4030022). Of particular interest for comparative studies of CWD strains are the isolates that did not generate mixed phenotypes among the inoculated mouse cohorts (Elk isolate 012-22012 was consistently CWD1 during serial passage). Other isolates with interesting strain instability are those that, upon first passage, generated a single strain phenotype, but in second passage shifted to the other strain phenotype (Isolate 04-0306 was first CWD2 and turned into CWD1 following second passage). This phenotypic shift in strain properties contrasts with isolates that elicited a single phenotype at first passage but during second passage produced the opposite phenotype in a small proportion of the inoculated mouse cohort (i.e., 001-44720).

Serial transmission of mule deer isolates more often resulted in propagation of CWD1 and CWD2 “mixtures” leading to mice with either pathological phenotype [43]. However, various isolates are particularly interesting because their stability during serial passage, including isolate V92 which was consistently the CWD2 strain, and isolates that were mostly CWD1, but which resulted in breakthrough of the CWD2 strain in a small proportion of the inoculated mouse cohorts (IDs: 8481, 978-24384, D10 and Db99 and 001-39647).

The primary structures of mule-deer and elk PrPC differ at codon 226 (Q and E; [84]. Despite this difference, the biochemical properties of PrPCWD such as electrophoretic mobility, conformational stability, and glycoform ratio from both strains were indistinguishable when compared within tg1536(deer PrPC) mice. However, CWD prions propagated in tg1536 mice had different conformation stability than those passaged in tg5037 (elk PrPC) after first passage [43].

Perhaps unexpectedly, the CWD1 and CWD2 classification is not phenotypically consistent when the isolates classified by [43] were transmitted in novel gene-targeted transgenic mice expressing deer PrPC [53]. Strain properties can be highly dependent on host factors such as transgene expression level [85]. For example, the Elk isolate 001-44720 was strain-typed as CWD1 (short incubation period in tg1536 [43]) and produced the longest incubation period in GtQ226 mice [53]. In contrast, the transmission of elk isolate 04-0306, which was classified as CWD2 (long incubation period in tg1536), produced relatively shorter incubation periods in GtQ226 mice. These contrasting results may indicate a disconnect between strain specific titers in the cervid isolates and the strain selection by the PrPC expressed in the Gt mice.

Similarly, the PrPSc deposition pattern, another defining phenotypic feature of CWD1 (symmetric) and CWD2 (asymmetric) is inconsistent when passaged in GtQ226 mice. Transmission of deer or elk isolates classified by [43] as CWD1 (12389) or strain mixtures (D10 and Db99) in GtQ226 produced the asymmetric PrPCWD deposition pattern characteristic of CWD2. In contrast, passage of elk isolates 04-0306 and 12389 (i.e., CWD1) in GtE226 produced symmetric prion aggregates characteristic of CWD1 strain, suggesting the pathology observed arises from strain and host interactions.

3.1.2. Wisc-1/H95+

Infected isolates of Wisc-1 and H95+ strain: The Wisc-1 and H95+ strains were characterized from orally inoculated experimental deer [62] and by passage in transgenic mice [48]. These experimental white-tailed deer were comprised of four different groups depending on the PrPCamino acid polymorphisms expressed at codon 95 and 96 (Q95H and G96S). Each deer was inoculated with a brain homogenate pool composed of two CWD positive deer brains (Animal IDs 54344 and 74792). Both animals were hunted in T7N R6E of State Forest section in Iowa County, Wisconsin, where CWD was first identified during the early stage of the outbreak in this state. One deer was a two-year-old female, and the other was a three-year-old female that contained a high abundance of CWD prions in their brain tissue. The Wisc-1 isolates were harvested during November and December 2002. By contrast, the H95+ strain is an experimentally derived CWD strain in white-tailed deer and has not been detected in free-ranging deer to date.

The four deer genotypes used to investigate the effect of polymorphisms on incubation time [62] include the following:

Q95G96/Q95G96 (wt/wt): Deer expressing Prnp genes encoding Q95G96-PrPC, also known as wt-PrPC, which is canonically the most abundant PrPC molecule in white-tailed deer and mule deer. Deer homozygous for wt-PrPC developed CWD first. Animal IDs: 1293, 1291, 1289, 1277, 1295, and 1287 (preclinical; died of intercurrent gut infection 416 days post-exposure).

Q95S96/Q95G96 (S96/wt): Second deer genotype that developed CWD consisted of heterozygous animals expressing wt-PrPC and S96-PrPC. Animal IDs: 1281, 1275, and 1285.

H95G96/Q95G96 (H95/wt): Third genotype to developed CWD comprised a single heterozygous individual expressing wt-PrPC and H95-PrPC. Animal ID: 1279.

H95G96/Q95S96 (H95/S96): Last genotype that developed CWD had no wt-PrPC and expressed H95-PrPC and S96-PrPC. Animal ID: 1297. Strain Summary: Wisc-1 and 95H+ are two strains that demonstrate the impact of Prnppolymorphisms on CWD strain diversification and host range expansion [26,48,63]. To investigate the effect of polymorphisms on incubation time, the above four deer genotypes were used. The data indicate that wt/wt deer exhibited shorter incubation time compared to polymorphic deer and a different protease-resistant was observed in H95/S96 deer (Animal ID 1297; [62].

Transmission studies [48,63] of the CWD proteotypes (Animal IDs 1277, 1293, 1281, 1279 and 1297) described above were conducted in transgenic mice expressing wildtype G96-PrPC(tg33) and S96-PrPC (tg60; [86]). Serial passage in tg33 mice resulted in similar neuropathological, PrP-res profiles and conformational stability indicating a common CWD strain, Wisc-1, was selected. However, most CWD proteotypes failed to produce clinical disease when passed in tg60 mice, except for CWD allotypes (Animal IDs 1279 and 1297), which had H95-PrPCWD and resulted in the identification of a novel CWD strain (H95+). The differential strain selection that occurred for CWD allotypes 1279 and 1297, indicates PrPC heterozygous deer accumulated a strain mixture (Wisc-1 and H95+), and the strain selection was dependent on PrPCof the inoculated tg mouse line, with tg33 selecting the Wisc-1 strain while tg60 selected H95+. Importantly, passage of tg60-CWD-H95+ into tg33 mice resulted in some mice displaying the Wisc-1 phenotype while others displayed the H95+ phenotype, demonstrating the H95+ strain can also be propagated in host expressing wt-PrPC [48]. Likewise, the transmission of tg33 prions into tg60 mice resulted in H95+ selection when the donor tg33 mice received the 1297 or 1279 CWD allotypes [63]. These results indicate that H95+ strain emerged in deer expressing H95-PrPC as a result of conformational diversification as opposed to selection from the original CWD pool used to infect the polymorphic deer.

To further investigate host range of the two strains, ref. [26] inoculated non-transgenic C57BI6 mice with isolates (Animal IDs 1293, 1281, 1279 and 1297). Surprisingly, the results showed that only mice infected with isolates from animal IDs 1279 and 1297 (containing the H95+strain) produced clinical disease in C57BI6 mice. This finding also suggests the unique transmission properties of the H95+ strain, as it can propagate in a wider range of host species.

The experimental CWD isolates also exhibited PrPSc biochemical and structural differences when heterozygous CWD isolates were compared to wt/wt homozygous deer prions [63]. The PrPCWD of the H95+ strain has greater structural stability than the Wisc-1 strain and tg33 mice exposed to H95/S96 CWD prions (i.e.,1297) contain sub-populations of PrPCWD that were also more stable than those from tg33 mice exposed to 1293 [63]. Moreover, despite isolates from animal IDs 1293, 1277 and 1281 not causing prion disease in tg60 mice, they managed to establish a subclinical infection in mice after more than 600 days post infection with correspondingly low levels of PrP-res in their brains. Subclinically infected mice contained approximately 1/10 of the PrP-res accumulated in tg60 that succumbed to H95+ [63]. Analysis of the allelotype composition of PrPCWD in wt/wt and S96/wt isolates demonstrated that wt-PrPC is more susceptible to CWD prion misfolding than S96-PrPC and converted with different efficiencies in S96/wt deer [87]. Findings from serial in vitro protein misfolding cyclic amplification (PMCA) experiments also demonstrated that S96-PrPC leads to inefficient in vitro propagation of PrPCWD for most tested strains, with H95+ being able to propagate continually [59].

3.1.3. 116AG

Infected isolate of 116AG strain: The infected isolate 116AG originated from a five-year-old male white-tailed deer with original animal ID W14-70036. The deer was free-ranging and found as roadkill in Saskatchewan province. Since it was a wild animal, there is no available information about the passage history of the isolate. The deer appeared emaciated, and it tested positive for CWD using immunohistochemistry. The infected isolate was from a deer heterozygous for PrPs [45].

Strain Summary: The strain 116AG is an example of how polymorphisms at codon 116 (A to G) in PrPC of white-tailed deer can impact the stability, pathogenesis and prion properties of CWD [45]. The PrPSc from infected isolate of heterozygous PrPC deer (116AG) was conformationally less stable than PrPSc from the experimental Wisc-1 isolate (Animal ID: 1277) from PrPC wt/wt deer [64]. As compared to Wisc-1, PrPSc from isolate 116AG shows lower seeding activity in real-time quaking-induced conversion (RT-QuIC), slower disease propagation, longer incubation time in different rodent models and reduced infectivity in vitro [45,88]. Serial transmission in tg(CerPrP)1536+/− revealed the infected isolate, W14-70036 contained two strains, 116AG-long and 116AG-short. In the third passage, 116AG-long displayed a prolonged two-month clinical phase delay, prolonged survival and disease progression. The proteinase K-resistant banding patterns of PrPSc from the two strains also displayed distinctive electrophoretic mobility in both tg(CerPrP)1536+/− mice and Syrian golden hamsters [45].

3.1.4. 132LL Elk CWD

Elk are polymorphic at residue 132 of the prion protein and the presence of a leucine or methionine has significant disease modifying effects that suggest novel strain emergence [89,90]. The incubation period of CWD was extended in elk with 132LL > 132ML > 132MM. PrPCWD was less abundant in clinically affected 132LL elk as compared to clinically affected 132MM elk. 132LL elk CWD prions were differentially cleaved by proteinase-K to a lower molecular weight and had increased structural stability as compared to 132MM CWD prions. These biochemical alterations indicate novel strain emergence in isolates from 132LL elk. Subsequent experimental transmission of 132LL CWD Prions into Tg12 (132MM) transgenic mice [91] supports strain emergence [92]. When the 132LL CWD prions were passaged, they maintained their distinctive biochemical phenotypes including increased conformational stability and low molecular weight proteinase-K cleave PrP-res isoforms.

3.1.5. Other Isolates of CWD in North America

The data demonstrating that an isolate is composed of a novel strain of CWD typically include biochemical, transmission and pathology data that show a heritable phenotype upon passage. Other isolates of CWD that are likely composed of novel strains include CWD in mule deer with the 225FF polymorphism [93,94] as well as moose (Alces alces) CWD [24,95].

3.2. Spatial Representation of North American CWD Strains

Two paths can conceivably contribute to the geographic distribution of CWD; one is from captive cervids, and the other is spread among free-ranging cervids. Before 2000, the distribution of CWD in free-ranging cervids has only been reported in Colorado and Wyoming. Subsequently, CWD was concentrated in four main enzootic zones: 1. northeastern Colorado and southeastern Wyoming, 2. Saskatchewan, Canada, 3. Wisconsin, and 4. Mid-Atlantic [20]. The spread of CWD to neighboring states/regions could have originated from these, with subsequent jumps leading to the establishment of new foci. Regardless of how CWD spreads remains controversial, with limited documented evidence necessitating further research [96].

To advance our understanding of CWD strains, having well-documented records of infected isolates is imperative. Historical records of infected isolates (Table 1) suggest that several enzootic zones of CWD appear to represent the spatial distribution of known strains in North America based on a few animals that have had strain explored (Figure 3). A potential distribution of CWD 1 and CWD2 could be found in mule deer and elk in Colorado and Wyoming, United States, and Saskatchewan, Canada, while Wisc-1 was detected in white-tailed deer in Wisconsin, United States. The 116AG was isolated from Saskatchewan, Canada, although this is likely a rare event. The spatial distribution of cervid species may also play an essential role in the distribution of CWD strains. Interaction between cervid species and horizontal transmission may promote strain mixing. Importantly, whether the enzootic zones are the extension of the origin strain region, a secondary region, or a separate, spontaneous emergence of the CWD strain is difficult to identify. The emergence of novel CWD strains is transmitted through animal populations. Given that geographic variation in Prnp can impact susceptibility to prion disease, this can also result in the development of distinct strain characteristics. For instance, an investigation on human Prnp from major continental groups affected by CJD found significant geographic variation in susceptibility based on allele frequency [97]. Notably, the 129V allele is highly represented in certain populations in the United States, which predicted that Native Americans would be less susceptible to prion infection than other populations due to a higher rate of heterozygotes M/V. Heterozygotes are associated with a lower probability of contracting CJD whereas the protective 219K allele, which lowers the risk of CJD, was constantly linked with 129M and primarily confined to Asian and Pacific populations but less so in the Native American population. The counteracting susceptibility at codon 129 may lower the CJD contracting rate in those regions [97]. Therefore, polymorphism of Prnp gene among geographically varied cervid populations should be considered when modeling the epidemiological properties of CWD, as the generation of new CWD strain can be transmitted through a population and result in novel disease characteristics [47].

The origin of CWD and the most prevalent CWD strain present in nature remains elusive, and information about the epidemiology of the CWD strain is often limited. In scrapie, multiple transmission experiments in laboratories, from sheep to mice, have resulted in the same strain, ME7 [98,99,100]. Furthermore, natural scrapie transmission to mice from 26 geographic resources around the United Kingdom found that over half of the mice developed clinical signs similar to the ME7 strain [100]. If we could obtain CWD-infected isolates from free-ranging cervids from diverse geographic regions and compare their strain properties when transmitted to a panel of transgenic mice, more reliable evidence regarding the distribution of CWD strains would be available. Additionally, by comparing the properties of CWD strains between newly emergent and endemic locations, we may identify the epidemiological origin of CWD in new locations [41]. Comparable work with sheep and goats has been useful to define the temporal and geographical distribution of scrapie [98,99,101,102,103]. 4. Discussion

In our current effort, we have attempted to address some current challenges facing CWD strain research. While decades of prion research have provided a much deeper understanding of the mechanical framework of prion strains, many questions remain unanswered and unexplored in CWD. For example, little is known about the origin of strains and the mechanisms that drive the diversification and expansion of CWD strains into different host species. Additionally, we are unsure how host species manage to coexist with a mixture of strains and support multiple strains simultaneously. An extensive collection of infected isolates from across geographic regions appears warranted to answer these vital and unrequited questions. In recent years, there has been an increased focus on CWD surveillance, and the infected isolates used for CWD testing that could be made available for genotyping, strain typing, and transmission studies [44]. In 2019, a large contingent of researchers studying chronic wasting disease was formed, prioritizing establishing a tissue repository to increase the accessibility of CWD isolates [104].

Recent studies have shown that Nordic cervids carry a variety of strain profiles, contrasting with a relatively constant strain profile in North American cervids [22]. Arguments can be made, however, that the diversity of North American CWD strains is still underestimated. A more connected research network would enable tracking of CWD strains and genotypes. As CWD strains evolve [48,63], new CWD strains can emerge with unpredictable disease phenotypes and host ranges [26,42,80]. Because of the increasing prevalence of CWD, and therefore, increased exposure to CWD, there is a growing concern about transmission to humans and other species [4,46,51,105].

As the emergence of novel strains increases the zoonotic potential, developing and standardizing methods to efficiently identify new strains and their transmission is warranted to document CWD spread [41]. New approaches include amplification-based assays such as PMCA are offering the possibility to distinguish CWD strains. Forty-five CWD+ retropharyngeal lymph node samples from Texas were screened and identified a single PMCA amplified isolate (64420) migrated faster on Western blot [106]. In another example, PMCA was used with five different substrates to amplify CWD+ isolates from six cervid species [23]. One of the isolates, DB99 (Table 1), was previously identified as a mixture of CWD1 and CWD2. Further characterization of isolates by PMCA may enhance confidence in their distinctiveness or similarity. Other exciting work for understanding CWD strains includes the first cryo-EM images and structural analysis of CWD [107]. It seems likely that structures for other CWD strains will soon be completed. Understanding the structures that encode the different strains of CWD is particularly important to explain the disease modifying properties of different polymorphisms. It is unclear how the G96S polymorphism can extend incubation period in Wisc-1/CWD1 infected deer or how the Q95H can drive the emergence of H95+. Structural information that explains this would increase our understanding of prion replication.

https://www.mdpi.com/2076-0817/14/3/250

Emergence of CWD strains

Review Open access Published: 06 October 2022 Volume 392, pages 135–148 (2023) Cite this article You have full access to this open access article Download PDF Save article View saved research Cell and Tissue Research Aims and scope Submit manuscript Alicia Otero, Camilo Duque Velasquez, Debbie McKenzie & Judd Aiken 8982 Accesses 28 Citations 2 Altmetric Explore all metrics

Abstract

Chronic wasting disease (CWD) strains present a novel challenge to defining and mitigating this contagious prion disease of deer, elk, moose, and reindeer. Similar to strains of other prion diseases (bovine spongiform encephalopathy, sheep scrapie), CWD strains can affect biochemical and neuropathological properties of the infectious agent, and importantly interspecies transmission. To date, ten CWD strains have been characterized. The expanding range of CWD in North America and its presence in South Korea as well as Scandinavian countries will potentially result in millions of cervids infected with CWD; thus, novel strains will continue to emerge. In this review, we will summarize the characteristics of known CWD strains and describe the impact of prion protein gene polymorphisms on the generation of strains. We will also discuss the evidence that individual cervids can harbor more than one CWD strain, complicating strain analysis, and affecting selection and adaptation of strains in new hosts.

snip…

Interspecies transmission

One of the more important characteristics that can define a strain is interspecies transmission. Success of an interspecies transmission is dependent on the interactions of the PrPSc with the PrPC of the new host; these parameters are not, however, readily predictable. The species barrier effect and interspecies transmission have not been thoroughly investigated at the level of CWD strains. Although CWD has been successfully transmitted to several other species (Table 1 and reviewed in Otero et al. 2021a), individual strains have not been extensively analyzed.

Evidence for interspecies transmission resulting in emergent CWD strains was observed upon adaptation of CWD into ferrets (Mustela putorius furo). Mule deer CWD passaged through ferrets causes clinical disease in Syrian hamsters (Mesocricetus auratus), while the initial mule deer CWD inocula did not (Bartz et al. 1998). Passage of CWD through transgenic mice expressing hamster PRNP followed by passage in hamsters resulted in the isolation of two distinct phenotypes based on incubation periods and clinical signs (Crowell et al. 2015). These two observed phenotypes, termed cheeky (CKY) for the development of incessant hiccips and wasted (WST) for the dramatic weight loss upon onset of clinical disease, were subsequently determined to be two distinct strains, demonstrating that cross-species CWD transmission can result in new strains (Crowell et al. 2015).

An expanded host range was also observed with the H95+ strain. When C57Bl/6 mice and Syrian golden hamsters were intracerebrally infected with the Wisc-1 and H95+ strains, differential transmission patterns were observed. We, and others, have demonstrated that C57Bl/6 mice are not susceptible to infection with common CWD strains (Herbst et al. 2017). H95+, however, resulted in clinical infection of this mouse line. Conversely, hamsters were susceptible to the Wisc-1 strain but had limited susceptibility to H95+.

In another study testing interspecies transmission of CWD, challenge of a transgenic mouse line expressing beaver PRNP with a range of CWD strains showed no species barrier. There were, however, strain-specific differences in incubation periods and in the biochemical properties of the CWD prions generated in the transgenic beaver mice (Herbst et al. 2022).

Strain adaptation, selection, and evolution The concept of strain adaptation, selection, and evolution was first described in mice infected with sheep scrapie isolates, prior to the discovery of the prion protein (reviewed by Dickinson and Meikle 1970; Bruce and Dickinson 1979; Kimberlin 1982). Several different types of biological stability were described, based on the “visible” properties of the disease (incubation periods, neuropathology, clinical signs). In general, upon serial passage of a specific isolate in a new host, the incubation period, clinical signs, and neuropathology stabilize, this is considered adaptation to a new host. Passage of some isolates into a new host resulted in different strain properties (i.e., different incubation periods, neuropathology, and clinical signs following adaptation to the new host) suggesting selection or mutation of the original strain.

With the discovery of the prion protein, these observations can be linked to changes in prion conformation/structure. Upon primary passage into a new host, the PrPSc:PrPC interaction varies depending on the homology between the two. With serial passage, the selection for the most favorable conformation for conversion is selected, with a resulting decrease in incubation period, stabilization of neuropathology (i.e., deposition of PrPd and lesion profiles), and clinical signs. This stabilization of strain properties can also result in changes in the biochemical properties of PrPSc (guanidine stability, sensitivity to proteinase K, migration patterns on SDS-Page).

Field isolates of scrapie can contain more than one strain, i.e., more than one conformation that can be converted to PrPSc. These conformers can then compete for PrPC, resulting in variable incubation periods. Subsequent passages, particularly with low titers of PrPSc, will lead for the selection of one strain or the other. This was nicely demonstrated by Bartz et al. (2000) with transmission of mink transmissible encephalopathy into hamsters. On the initial passage, the incubation period was long and western blot analysis showed two different sized PrPSc migration patterns. Low titer passage then resulted in the adaptation and selection of two different strains (hyperactive, HY; and drowsy, DY) with significantly different incubation periods and two different PrPSc structures (Bartz et al. 2000; Caughey et al. 1998; Safar et al. 1998; Cortez et al. 2021).

Several models have been proposed to explain the process of strain selection. Prion strains have been proposed to exist as quasispecies or clouds of conformational variants that “mutate” and are selected based on compatibility with the host PrPC (Li et al. 2010; Collinge 2010). Different host PrPC molecules would be compatible with only a subset of the PrPSc conformers, resulting in the selection and adaptation of the infectious agent. Another model, deformed templating mechanism suggests that inaccurate matching of the host PrPC and incoming PrPSc results in the generation of novel conformers (Baskakov 2014). Despite all the evidence for the link between PrPSc conformation and strain, there is, to date, no data directly measuring the conformational diversity, frequency, and mutation rate of conformers in an infectious prion preparation.

As described for scrapie strains, CWD strains undergo adaptation, selection, and evolution in a strain-specific manner. Transmission of CWD prions into white-tailed deer expressing amino acid polymorphisms (H95 and/or S96) resulted in the prion conformation expansion (and the formation of strain mixtures in deer heterologous for H95 (Duque Velasquez et al. 2015, 2020). Passage of these CWD lineages into the tg60 mice (expressing S96-PrPC) resulted in the selection and adaption of the H95+ strain accompanied by the reduction of conformational heterogeneity, buildup of higher infections titers, and stabilization of phenotypic characteristics. By comparison, passage in tg33mice (expressing G96-PrPC) resulted in selection of Wisc-1. Transmission of CWD lineages from deer that do not express H95+ did not result in clinical disease but amplified non-adaptive S96 conformers. None of these lineages (Wisc-1, etc.), upon passage in tg60 mice, contained H95+ conformers based on both serial PMCA in S96-PrPC substrate and bioassay in tg60 mice (Otero et al. 2021b; Duque Velasquez et al. 2020). Together, these experiments suggest that the H95+ conformers efficiently convert S96-PrPC, while the Wisc-1 conformer loses the ability to convert S96-PrPC with passage.

Another excellent system for characterization of strain evolution is the gene-targeted mice generated by the Telling lab. As described above, different strains/sources of CWD agent are more readily transmitted in either the GtE or the GtQ mice. Of interest is the serial passage of moose strains from Norway in these mice (Bian et al. 2019, 2021). The Scandinavian moose strains have very different properties than North American moose strains, with no apparent involvement of the lymph system. Serial passage of these agents in GtQ mice, however, results in the selection/adaptation of prion conformers such that the isolates more resemble North American CWD lineages. These data suggest that the North American CWD strains (i.e., Wisc-1) have also evolved, through numerous passages, to a few dominant strains.

Understanding strain selection and adaptation in cervids is complicated by the presence of more than one strain/conformer in free-ranging CWD-positive deer. In many areas where CWD is endemic, an individual animal may be exposed to CWD from either different cervid species or the same species expressing different PrPC molecules. The passage history is unknown for naturally infected animals so it is difficult to assess the strain composition in a given animal. Characterization of isolates from CWD-infected cervids suggests that many are comprised of strain mixtures. Passage into a specific host results in the selection of the most favored conformation. Subsequent serial passages in the same host result in host adaptation (seen as a reduction in incubation periods). In our experience, these mixtures complicate strain characterization as passage through a panel of rodent hosts results in selection of a myriad of conformations, some of which stabilize becoming distinct strains, while others are temporary. Temporary conformations appear to revert to common strains (i.e., Wisc-1).

Conclusions and perspective

The generation of new variants as a CWD strain is transmitted through a population is not uncommon and can result in variants with novel characteristics. CWD is no exception. To date, 10 CWD strains have been identified, strains that can impact incubation period, distribution of the agent in the brain, biochemistry of PrPCWD, shedding of infectivity (and environmental contamination), and, most importantly, the species barrier. A few strains currently predominate the CWD landscape but experimental data suggests these strains can evolve (Duque Velasquez et al. 2015, 2020; Hannaoui et al. 2021; Crowell et al. 2015; Telling 2022). There is little evidence the disease has spilled over into non-cervid species; however, CWD strains represent a changing dynamic, potentially affecting interspecies transmission. The diversity of strains identified, to date, and the likelihood of novel strains emerging and being selected (due to PrPC polymorphisms and/or interspecies transmission) means that the biological properties of CWD need to be constantly monitored and assessed.

https://link.springer.com/10.1007/s00441-022-03688-9

Volume 26, Number 6—June 2020

Research

Radical Change in Zoonotic Abilities of Atypical BSE Prion Strains as Evidenced by Crossing of Sheep Species Barrier in Transgenic Mice

Atypical BSE prions showed a modification in their zoonotic ability after adaptation to sheep-PrP producing agents able to infect TgMet129 and TgVal129, bearing features that make them indistinguishable of sporadic Creutzfeldt-Jakob disease prions.

https://wwwnc.cdc.gov/eid/article/26/6/18-1790_article

Conversion of the BASE Prion Strain into the BSE Strain: The Origin of BSE?

Raffaella Capobianco, Cristina Casalone, Silvia Suardi, Michela Mangieri, Claudia Miccolo, Lucia Limido, Marcella Catania, Giacomina Rossi, Giuseppe Di Fede, Giorgio Giaccone, Maria Grazia Bruzzone, Ludovico Minati, Cristiano Corona, [ ... ], Fabrizio Tagliavini [ view all ]

Published: March 9, 2007

https://doi.org/10.1371/journal.ppat.0030031

In this study, we show that an atypical form of spongiform encephalopathy of cattle, termed BASE, is caused by a prion strain distinct from that of classical BSE. ***> Noteworthy, this newly characterized prion strain has the ability to convert into the classical BSE strain upon serial transmission to inbred mouse lines.

https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.0030031

Classical BSE emergence from Nor98/atypical scrapie: Unraveling the shift vs. selection dichotomy in the prion field

Sara Canoyra https://orcid.org/0000-0001-6371-8122, Alba Marín-Moreno https://orcid.org/0000-0002-4023-6398, Juan Carlos Espinosa https://orcid.org/0000-0002-6719-9902, +5 , and Juan María Torres https://orcid.org/0000-0003-0443-9232jmtorres@inia.csic.es

Authors Info & Affiliations Edited by Byron Caughey, National Institute of Allergy and Infectious Diseases (National Institutes of Health), Hamilton, MT; received January 17, 2025; accepted June 7, 2025 by Editorial Board Member Lila M. Gierasch July 15, 2025 122 (29) e2501104122 https://doi.org/10.1073/pnas.2501104122

Our results suggest that the conformational shift could be the principal mechanism responsible for the c-BSE emergence. Furthermore, the selection model was dismissed as the key mechanism based on the analysis of an artificial c-BSE and AS mixture. The ability of the AS conformers to shift conformation to a c-BSE one supports the hypothesis that the epidemic c-BSE prion may have originated from the transmission of AS in cattle.

https://www.pnas.org/doi/10.1073/pnas.2501104122

Assessment of the Zoonotic Potential of Atypical Scrapie Prions in Humanized Mice Reveals Rare Phenotypic Convergence but Not Identity With Sporadic Creutzfeldt-Jakob Disease Prions

Alba Marín-Moreno , Fabienne Reine , Laetitia Herzog , Naima Aron , Florence Jaffrézic , Jean-Luc Vilotte , Human Rezaei , Olivier Andréoletti , Davy Martin , Vincent Béringue Author Notes

The Journal of Infectious Diseases, Volume 230, Issue 1, 15 July 2024, Pages 161–171, https://doi.org/10.1093/infdis/jiae093

Published: 24 February 2024

Conclusions The results obtained suggest a low zoonotic potential for AS. Rare adaptation may allow the emergence of prions phenotypically resembling those spontaneously forming in humans.

https://academic.oup.com/jid/article/230/1/161/7613915

PROBLEM STATEMENT 6B: REVEAL GENETICS OF PRION DISEASE SUSCEPTIBILITY.

Greater frequency of chronic wasting disease in free-ranging elk genetically tolerant to disease progression raises concerns related to prion transmission and strain evolution.

Animal Disease Research Unit, Pullman, Washington

Genetic variations in the prion protein gene of Rocky Mountain elk do not confer complete resistance to fatal infection by chronic wasting disease. However, elk carrying one or two copies of the amino acid leucine (L) variant at position 132 of the prion protein (132L*, where * is either M for methionine or L) survive much longer than 132MM elk. An ARS researcher in Pullman, Washington, in collaboration with researchers at the University of Wyoming, the University of California at Davis, the National Park Service, and the Animal and Plant Health Inspection Service, found a higher frequency of 132L* elk in areas of Wyoming with high infection rates, consistent with the expected positive effect of prolonged survival on reproduction. However, the frequency of chronic wasting disease infection in 132L* elk was also higher than previous estimates. To improve the long-term management of native elk populations, these findings underscore the importance of determining the effects of prolonged infection on disease transmission from 132L* elk and the potential for driving prion strain diversification.

https://www.ars.usda.gov/ARSUserFiles/np103/AnnualReports/Final%20NP103%20FY2024%20Annual%20Report.updated%205.30.25.pdf

Research Project: Elucidating the Pathobiology and Transmission of Transmissible Spongiform Encephalopathies

Location: Virus and Prion Research

Title: Update: CWD genetic resistance project at NADC

Author item Cassmann, Eric item Greenlee, Justin Submitted to: North American Deer Farmer Publication Type: Trade Journal Publication Acceptance Date: 11/5/2023 Publication Date: 11/15/2023 Citation: Cassmann, E.D., Greenlee, J.J. 2023.

Update: CWD genetic resistance project at NADC. North American Deer Farmer. P. 83. Interpretive Summary: Technical Abstract: In March of 2020, we began a study to examine the susceptibility of whitetail deer with rare prion protein genotypes to chronic wasting disease (CWD). In the sequence of amino acids that make up the deer prion protein, there are several locations that are variable. These variations are sometimes called polymorphisms. In the data collected from depopulations, whitetail deer with certain prion gene polymorphisms were not positive for CWD. In 2019, Dr. Nick Haley published a paper that showed H95/S96, HH95, and S96/K226 deer from depopulated herds in the US were not CWD positive. Based on the overall low number of deer with these genotypes () we’re unable to determine if they were resistant to CWD or if there were too few deer with these genotypes to be statistically represented in the positive cases. It’s also possible that they could be partially susceptible with longer incubation times than deer with generic (wild type) prion genotypes. Samples gathered at depopulation represent a snapshot of the herd. It is possible these rare genotypes were exposed, but had not yet accumulated abnormal prion protein to a level detectable by the detection methods used. The NADC susceptibility study was initiated to help answer these questions.

We studied deer with polymorphisms at 3 amino acid locations (codons): 95, 96, and 226. Wild type deer are QQ95GG96QQ226. Whitetail deer with wild type prion genotypes were inoculated with CWD and co-housed with other whitetail deer (contact deer) that had rare prion protein genotypes. The genotypes of contact deer included QH95GS96QQ226, QH95GG96QK226, QQ95GS96QQ226, QQ95SS96QQ226, Q95GS96QK226, and QQ95GG96KK226 (bolded text indicates a prion gene polymorphism).

During the first year, we collected feces, saliva, nasal swabs, skin, blood, and rectal biopsies from the inoculated and contact deer to determine if deer are CWD positive and the period of CWD shedding. After the first year, we started collecting rectal biopsies annually on the contact deer, but all other samples are still collected every three months.

Eight out of ten (8/10) inoculated deer developed clinical signs for CWD and tested positive after necropsy (Figure 1). The average time from inoculation to euthanasia of these eight inoculated deer was 23 months.

Two inoculated deer are still on-study; one of these deer has tested positive for CWD on rectal biopsy IHC.

To date, two deer from the contact group have developed CWD clinical signs and tested positive (Figure 2). The positive deer from the contact group had the GS96QK226 and KK226 genotypes.

We have detected CWD prions in rectal biopsies with IHC in three other contact deer as of October 2023. Their prion genotypes are GS96, QH95GS96, and GS96QK226.

As the experiment continues, we hope to answer 2 main questions. (1) Are there any prion protein polymorphisms that make deer resistant to CWD, and (2) what are the CWD shedding dynamics in deer with detectable CWD. One potential outcome of the study would be identifying genotypes with very long incubation periods that, while susceptible to CWD, still could be used to manage CWD.

https://www.ars.usda.gov/research/publications/publication/?seqNo115=410188

Update: CWD genetic resistance project at NADC 1) Are there any prion protein polymorphisms that make deer resistant to CWD, and (2) what are the CWD shedding dynamics in deer with detectable CWD. One potential outcome of the study would be identifying genotypes with very long incubation periods that, while susceptible to CWD, still could be used to manage CWD.

https://www.ars.usda.gov/research/publications/publication/?seqNo115=410188

Another potential and likely outcome of this study, imo, is that genotypes developed with very long incubation, could therefore, if released into the wild, could help spread cwd even further, exposing even more wild species, and surrounding environments, for even longer periods of time, due to the longer incubation, a terrible potential outcome, one that must be avoided at all cost, imo…terry

SATURDAY, APRIL 11, 2026

Chronic Wasting Disease CWD TSE PrP, Cervid, Genetic Manipulation, Unforeseen Circumstances

https://chronic-wasting-disease.blogspot.com/2026/04/chronic-wasting-disease-cwd-tse-prp.html

MONDAY, JUNE 09, 2025

Genetic Approaches and Tools to Prevent, Control, and Eradicate Transmissible Spongiform Encephalopathies 2024 Annual Report ARS Research

https://chronic-wasting-disease.blogspot.com/2025/06/genetic-approaches-and-tools-to-prevent.html

***> cwd, tse, prion, cattle, pigs, sheep, primates, oh my! 

***> Very low oral exposure to prions of brain or saliva origin can transmit chronic wasting disease

Nathaniel D. Denkers , Clare E. Hoover , Kristen A. Davenport, Davin M. Henderson, Erin E. McNulty, Amy V. Nalls, Candace K. Mathiason, Edward A. Hoover

Published: August 20, 2020

https://doi.org/10.1371/journal.pone.0237410

Abstract

The minimum infectious dose required to induce CWD infection in cervids remains unknown, as does whether peripherally shed prions and/or multiple low dose exposures are important factors in CWD transmission. With the goal of better understand CWD infection in nature, we studied oral exposures of deer to very low doses of CWD prions and also examined whether the frequency of exposure or prion source may influence infection and pathogenesis. We orally inoculated white-tailed deer with either single or multiple divided doses of prions of brain or saliva origin and monitored infection by serial longitudinal tissue biopsies spanning over two years. We report that oral exposure to as little as 300 nanograms (ng) of CWD-positive brain or to saliva containing seeding activity equivalent to 300 ng of CWD-positive brain, were sufficient to transmit CWD disease. This was true whether the inoculum was administered as a single bolus or divided as three weekly 100 ng exposures. However, when the 300 ng total dose was apportioned as 10, 30 ng doses delivered over 12 weeks, no infection occurred. While low-dose exposures to prions of brain or saliva origin prolonged the time from inoculation to first detection of infection, once infection was established, we observed no differences in disease pathogenesis. These studies suggest that the CWD minimum infectious dose approximates 100 to 300 ng CWD-positive brain (or saliva equivalent), and that CWD infection appears to conform more with a threshold than a cumulative dose dynamic.

https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0237410

Prion Conference 2023

***> Transmission of the chronic wasting disease agent from elk to cattle after oronasal exposure

Justin Greenlee, Jifeng Bian, Zoe Lambert, Alexis Frese, and Eric Cassmann Virus and Prion Research Unit, National Animal Disease Center, USDA-ARS, Ames, IA, USA

Aims: The purpose of this study was to determine the susceptibility of cattle to chronic wasting disease agent from elk.

Materials and Methods: Initial studies were conducted in bovinized mice using inoculum derived from elk with various genotypes at codon 132 (MM, LM, LL). Based upon attack rates, inoculum (10% w/v brain homogenate) from an LM132 elk was selected for transmission studies in cattle. At approximately 2 weeks of age, one wild type steer (EE211) and one steer with the E211K polymorphism (EK211) were fed 1 mL of brain homogenate in a quart of milk replacer while another 1 mL was instilled intranasally. The cattle were examined daily for clinical signs for the duration of the experiment. One steer is still under observation at 71 months post-inoculation (mpi).

Results: Inoculum derived from MM132 elk resulted in similar attack rates and incubation periods in mice expressing wild type or K211 bovine PRNP, 35% at 531 days post inoculation (dpi) and 27% at 448 dpi, respectively. Inoculum from LM132 elk had a slightly higher attack rates in mice: 45% (693 dpi) in wild type cattle PRNP and 33% (468) in K211 mice. Inoculum from LL132 elk resulted in the highest attack rate in wild type bovinized mice (53% at 625 dpi), but no K211 mice were affected at >700 days. At approximately 70 mpi, the EK211 genotype steer developed clinical signs suggestive of prion disease, depression, low head carriage, hypersalivation, and ataxia, and was necropsied. Enzyme immunoassay (IDEXX) was positive in brainstem (OD=4.00, but non-detect in retropharyngeal lymph nodes and palatine tonsil. Immunoreactivity was largely limited to the brainstem, midbrain, and cervical spinal cord with a pattern that was primarily glia-associated.

“Conclusions: Cattle with the E211K polymorphism are susceptible to the CWD agent after oronasal exposure of 0.2 g of infectious material.”

Strain characterization of chronic wasting disease in bovine-PrP transgenic mice

Conclusions: Altogether, these results exhibit the diversity of CWD strains present in the panel of CWD isolates and the ability of at least some CWD isolates to infect bovine species. Cattle being one of the most important farming species, this ability represents a potential threat to both animal and human health, and consequently deserves further study.

Prion 2023 Congress Organizing Committee and the NeuroPrion Association, we invite you to join us for the International Conference Prion2023 from 16-20 October 2023 in Faro, Portugal.

https://prion2023.org/wp-content/uploads/2023/10/Meeting-book-final-version2.pdf

https://web.archive.org/web/20250828201533/https://prion2023.org/wp-content/uploads/2023/10/Meeting-book-final-version2.pdf

https://www.researchgate.net/profile/Syed-Zahid-Shah/publication/378314391_Meeting-book-final-version_prion_2023/links/65d44dad28b7720cecdca95f/Meeting-book-final-version-prion-2023.pdf

Department for Environment, Food and Rural Affairs

Preliminary Outbreak Assessment

Chronic wasting disease prions in cervids and wild pigs in North America

26 January 2026

Disease report

Chronic wasting disease (CWD) is a fatal neurodegenerative disease of cervids, such as deer, elk, moose and reindeer. It is caused by prions – infectious proteins that cause normal cellular prion proteins to misfold (CIDRAP, 2025). The disease is widespread in captive and free-ranging cervids in North America (Figure 1). For the first time, CWD prions have also been detected in the tissues of wild pigs (Sus scrofa) caught in CWD-affected areas of the USA (Soto et al. 2025). This discovery emerged from a study designed to investigate potential interactions between wild pigs and CWD prions, as wild pigs often coexist with cervids, which can shed prions into the environment. The following assessment discusses the epidemiology of CWD in North America and the detection of CWD prions in wild pigs. It also considers the potential implications for Great Britain.

Conclusion

CWD has continued to spread among captive and free-ranging cervids in North America since it was first detected in the 1960s. The finding of CWD prions in wild pigs in the USA suggests they could contribute towards transmission of the disease, influencing its epidemiology, geographic distribution and interspecies spread. However, further research is needed to confirm this. CWD has never been reported in Great Britain and the current risk of CWD prions being introduced into Great Britain’s wild pig or cervid population ranges from very low to negligible.

Readers are reminded to be vigilant for signs of CWD. Information on how to spot the disease can be found here. Suspected cases must be reported immediately to the Defra Rural Services Helpline on 03000 200 301. In Wales, call 0300 303 8268. In Scotland, contact your local Field Services Office. Failure to do so is an offence. We will continue to monitor the situation.

Authors • Lawrence Finn • Dr. Lauren Perrin • John Spiropoulos • Dr. Helen RobertsDepartment for Environment, Food and Rural Affairs

References

snip…see full report;

https://assets.publishing.service.gov.uk/media/697a3b013c71d838df6bd413/CWD_Prions_in_Cervids_and_Wild_Pigs_in_North_America.pdf

WEDNESDAY, JANUARY 28, 2026

Chronic wasting disease prions in cervids and wild pigs in North America Preliminary Outbreak

https://journals.asm.org/doi/10.1128/mbio.01800-25

https://media.ark.org/agri/Moore_2017_Swine_CWD.pdf

https://transmissiblespongiformencephalopathy.blogspot.com/2026/01/chronic-wasting-disease-prions-in.html

cwd to sheep

Chronic Wasting Disease CWD vs Scrapie TSE Prion

https://www.ars.usda.gov/research/publications/publication/?seqNo115=410511

Detection of infectivity in orally inoculated pigs using mouse bioassay raises the possibility that naturally exposed pigs could act as a reservoir of CWD infectivity. Currently, swine rations in the U.S. could contain animal derived components including materials from deer or elk. In addition, feral swine could be exposed to infected carcasses in areas where CWD is present in wildlife populations. The current feed ban in the U.S. is based exclusively on keeping tissues from TSE infected cattle from entering animal feeds. These results indicating the susceptibility of pigs to CWD, coupled with the limitations of the current feed ban, indicates that a revision of the feed ban may be necessary to protect swine production and potentially human health.

https://www.ars.usda.gov/research/publications/publication/?seqNo115=353091

https://www.ars.usda.gov/research/project/?accnNo=432011&fy=2017

https://www.ars.usda.gov/research/publications/publication/?seqNo115=337105

https://www.ars.usda.gov/research/publications/publication/?seqNo115=326166

Research Project: Elucidating the Pathobiology and Transmission of Transmissible Spongiform Encephalopathies

Location: Virus and Prion Research

Title: Differentiation of scrapie from chronic wasting disease in white-tailed deer

Accomplishments

1. 01 Determined that white-tailed deer (WTD) infected with scrapie from sheep can transmit the disease to other deer under conditions mimicking natural exposure. It has long been suggested that prion disease in deer (chronic wasting disease (CWD)) was caused by the prion agent from sheep. The prion disease that affects sheep, scrapie, has been recognized for hundreds of years. However, chronic wasting disease, a similar disease found in WTD, has only been recognized since the 1960s. ARS researchers in Ames, Iowa, showed that white-tailed deer sick with scrapie from sheep can infect other deer under conditions mimicking natural exposure. Furthermore, this work shows that CWD is difficult to differentiate from WTD infected with scrapie. WTD scrapie prions accumulate in the lymphoreticular system in a manner similar to CWD, meaning that environmental contamination may occur through feces, saliva, and other body fluids of scrapie affected WTD as has been shown for CWD. The presence of WTD infected with scrapie could confound mitigation efforts for chronic wasting disease. This information informs regulatory officials, the farmed cervid industry, and officials tasked with protecting animal health such as state Departments of Agriculture, Natural Resources, or Parks and Wildlife with regard to a disease similar to CWD but arising from sheep scrapie that could be present in WTD that have contact with scrapie affected sheep and/or goats.

https://www.ars.usda.gov/research/project/?accnNo=440677&fy=202

CWD TSE Prion 2026

THURSDAY, SEPTEMBER 24, 2026

***> Looming Crisis U. S. Transmissible Spongiform Encephalopathy TSE Prion, in Cattle, Cervid, Sheep, Pigs, and Humans, oh my <***

https://transmissiblespongiformencephalopathy.blogspot.com/2026/09/looming-crisis-u-s-transmissible.html

https://prpsc.proboards.com/thread/246/looming-crisis-prion-cattle-cervid

Tuesday, June 9, 2026

***> Hazard identification for the risks to terrestrial animal health from the import of hay and straw, BSE, CWD, Scrapie, TSE, Prion

https://www.gov.uk/government/publications/hazard-identification-for-the-risks-to-terrestrial-animal-health-from-the-import-of-hay-and-straw/hazard-identification-for-the-risks-to-terrestrial-animal-health-from-the-import-of-hay-and-straw

https://defrauktseprp.blogspot.com/2026/06/hazard-identification-for-risks-to.html

***> 1. 01 Determined that white-tailed deer (WTD) infected with scrapie from sheep can transmit the disease to other deer under conditions mimicking natural exposure.

https://www.ars.usda.gov/research/project/?accnNo=440677&fy=202

https://www.ars.usda.gov/research/publications/publication/?seqNo115=336834

https://wwwnc.cdc.gov/eid/article/30/8/24-0007_article

see;

https://nor-98.blogspot.com/2016/09/goat-k222-prpc-polymorphic-variant-does.html

https://transmissiblespongiformencephalopathy.blogspot.com/2026/04/us-report-scrapie-cwd-cattle-sheep-pigs.html

***> Scrapie TSE Prion, Singeltary review, October 2026

https://scrapie-usa.blogspot.com/2026/10/scrapie-tse-prion-singeltary-review.html

https://prpsc.proboards.com/thread/250/scrapie-prion-singeltary-review-2026

Chronic Wasting Disease CWD TSE Prion, Economical, Environmental, Zoonotic, Risk Factors 2026

https://transmissiblespongiformencephalopathy.blogspot.com/2026/02/chronic-wasting-disease-cwd-tse-prion.html

***> USA Report, Scrapie, CWD, BSE, TSE, Cattle, Sheep, Pigs, Cervid, Humans, Zoonotic, 2026

April 2026

https://fdabse589.blogspot.com/2026/04/usa-report-scrapie-cwd-bse-tse-cattle.html

https://www.researchgate.net/publication/403956772_USA_Report_Scrapie_CWD_BSE_TSE_Cattle_Sheep_Pigs_Cervid_Humans_Zoonotic_2026

APHIS USDA Captive CWD Herds Update by State March 2026 Update

https://prpsc.proboards.com/thread/243/aphis-captive-herd-status-september

https://chronic-wasting-disease.blogspot.com/2026/09/aphis-captive-herd-cwd-status-september.html

SATURDAY, SEPTEMBER 19, 2026

Texas 5th Captive Herd Depopulated This Year Due To Positive CWD TSE Prion

https://chronic-wasting-disease.blogspot.com/2026/09/texas-5th-captive-herd-depopulated-this.html

https://prpsc.proboards.com/thread/242/texas-captive-deer-herd-depopulated

***> Cervid CWD TSE PrP Transmission to Humans, has it already happened and being masked as sporadic CJD, What if? July 2026 Review

https://chronic-wasting-disease.blogspot.com/2026/07/cervid-cwd-tse-prp-transmission-to.html

https://prpsc.proboards.com/thread/224/cervid-transmission-humans-july-review

WEDNESDAY, SEPTEMBER 2, 2026

A new chapter for CWRU’s Prion Center

https://prionunitusaupdate.blogspot.com/2026/09/a-new-chapter-for-cwrus-prion-center.html

https://prpsc.proboards.com/thread/239/new-chapter-cwru-prion-center

Volume 26, Number 6—June 2020

Research

Radical Change in Zoonotic Abilities of Atypical BSE Prion Strains as Evidenced by Crossing of Sheep Species Barrier in Transgenic Mice

Atypical BSE prions showed a modification in their zoonotic ability after adaptation to sheep-PrP producing agents able to infect TgMet129 and TgVal129, bearing features that make them indistinguishable of sporadic Creutzfeldt-Jakob disease prions.

https://wwwnc.cdc.gov/eid/article/26/6/18-1790_article

Conversion of the BASE Prion Strain into the BSE Strain: The Origin of BSE?

Raffaella Capobianco, Cristina Casalone, Silvia Suardi, Michela Mangieri, Claudia Miccolo, Lucia Limido, Marcella Catania, Giacomina Rossi, Giuseppe Di Fede, Giorgio Giaccone, Maria Grazia Bruzzone, Ludovico Minati, Cristiano Corona, [ ... ], Fabrizio Tagliavini [ view all ]

Published: March 9, 2007

https://doi.org/10.1371/journal.ppat.0030031

In this study, we show that an atypical form of spongiform encephalopathy of cattle, termed BASE, is caused by a prion strain distinct from that of classical BSE. ***> Noteworthy, this newly characterized prion strain has the ability to convert into the classical BSE strain upon serial transmission to inbred mouse lines.

https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.0030031

Classical BSE emergence from Nor98/atypical scrapie: Unraveling the shift vs. selection dichotomy in the prion field 

Sara Canoyra, Alba Marín-Moreno, Juan Carlos Espinosa, +5 , and Juan María Torres jmtorres@inia.csic.esAuthors Info & Affiliations Edited by Byron Caughey, National Institute of Allergy and Infectious Diseases (National Institutes of Health), Hamilton, MT; received January 17, 2025; accepted June 7, 2025 by Editorial Board Member Lila M. Gierasch July 15, 2025 122 (29) e2501104122 https://doi.org/10.1073/pnas.2501104122

Our results suggest that the conformational shift could be the principal mechanism responsible for the c-BSE emergence. Furthermore, the selection model was dismissed as the key mechanism based on the analysis of an artificial c-BSE and AS mixture. The ability of the AS conformers to shift conformation to a c-BSE one supports the hypothesis that the epidemic c-BSE prion may have originated from the transmission of AS in cattle.

https://www.pnas.org/doi/10.1073/pnas.2501104122

Assessment of the Zoonotic Potential of Atypical Scrapie Prions in Humanized Mice Reveals Rare Phenotypic Convergence but Not Identity With Sporadic Creutzfeldt-Jakob Disease Prions

Alba Marín-Moreno , Fabienne Reine , Laetitia Herzog , Naima Aron , Florence Jaffrézic , Jean-Luc Vilotte , Human Rezaei , Olivier Andréoletti , Davy Martin , Vincent Béringue Author Notes

The Journal of Infectious Diseases, Volume 230, Issue 1, 15 July 2024, Pages 161–171, https://doi.org/10.1093/infdis/jiae093

Published: 24 February 2024

Conclusions The results obtained suggest a low zoonotic potential for AS. Rare adaptation may allow the emergence of prions phenotypically resembling those spontaneously forming in humans.

https://academic.oup.com/jid/article/230/1/161/7613915

PROBLEM STATEMENT 6B: REVEAL GENETICS OF PRION DISEASE SUSCEPTIBILITY.

Greater frequency of chronic wasting disease in free-ranging elk genetically tolerant to disease progression raises concerns related to prion transmission and strain evolution.

Animal Disease Research Unit, Pullman, Washington

Genetic variations in the prion protein gene of Rocky Mountain elk do not confer complete resistance to fatal infection by chronic wasting disease. However, elk carrying one or two copies of the amino acid leucine (L) variant at position 132 of the prion protein (132L*, where * is either M for methionine or L) survive much longer than 132MM elk. An ARS researcher in Pullman, Washington, in collaboration with researchers at the University of Wyoming, the University of California at Davis, the National Park Service, and the Animal and Plant Health Inspection Service, found a higher frequency of 132L* elk in areas of Wyoming with high infection rates, consistent with the expected positive effect of prolonged survival on reproduction. However, the frequency of chronic wasting disease infection in 132L* elk was also higher than previous estimates. To improve the long-term management of native elk populations, these findings underscore the importance of determining the effects of prolonged infection on disease transmission from 132L* elk and the potential for driving prion strain diversification.

https://www.ars.usda.gov/ARSUserFiles/np103/AnnualReports/Final%20NP103%20FY2024%20Annual%20Report.updated%205.30.25.pdf

Research Project: Elucidating the Pathobiology and Transmission of Transmissible Spongiform Encephalopathies

Location: Virus and Prion Research

Title: Update: CWD genetic resistance project at NADC

Author item Cassmann, Eric item Greenlee, Justin Submitted to: North American Deer Farmer Publication Type: Trade Journal Publication Acceptance Date: 11/5/2023 Publication Date: 11/15/2023 Citation: Cassmann, E.D., Greenlee, J.J. 2023.

Update: CWD genetic resistance project at NADC. North American Deer Farmer. P. 83. Interpretive 

Summary: Technical Abstract: In March of 2020, we began a study to examine the susceptibility of whitetail deer with rare prion protein genotypes to chronic wasting disease (CWD). In the sequence of amino acids that make up the deer prion protein, there are several locations that are variable. These variations are sometimes called polymorphisms. In the data collected from depopulations, whitetail deer with certain prion gene polymorphisms were not positive for CWD. In 2019, Dr. Nick Haley published a paper that showed H95/S96, HH95, and S96/K226 deer from depopulated herds in the US were not CWD positive. Based on the overall low number of deer with these genotypes () we’re unable to determine if they were resistant to CWD or if there were too few deer with these genotypes to be statistically represented in the positive cases. It’s also possible that they could be partially susceptible with longer incubation times than deer with generic (wild type) prion genotypes. Samples gathered at depopulation represent a snapshot of the herd. It is possible these rare genotypes were exposed, but had not yet accumulated abnormal prion protein to a level detectable by the detection methods used. The NADC susceptibility study was initiated to help answer these questions.

We studied deer with polymorphisms at 3 amino acid locations (codons): 95, 96, and 226. Wild type deer are QQ95GG96QQ226. Whitetail deer with wild type prion genotypes were inoculated with CWD and co-housed with other whitetail deer (contact deer) that had rare prion protein genotypes. The genotypes of contact deer included QH95GS96QQ226, QH95GG96QK226, QQ95GS96QQ226, QQ95SS96QQ226, Q95GS96QK226, and QQ95GG96KK226 (bolded text indicates a prion gene polymorphism).

During the first year, we collected feces, saliva, nasal swabs, skin, blood, and rectal biopsies from the inoculated and contact deer to determine if deer are CWD positive and the period of CWD shedding. After the first year, we started collecting rectal biopsies annually on the contact deer, but all other samples are still collected every three months.

Eight out of ten (8/10) inoculated deer developed clinical signs for CWD and tested positive after necropsy (Figure 1). The average time from inoculation to euthanasia of these eight inoculated deer was 23 months.

Two inoculated deer are still on-study; one of these deer has tested positive for CWD on rectal biopsy IHC.

To date, two deer from the contact group have developed CWD clinical signs and tested positive (Figure 2). The positive deer from the contact group had the GS96QK226 and KK226 genotypes.

We have detected CWD prions in rectal biopsies with IHC in three other contact deer as of October 2023. Their prion genotypes are GS96, QH95GS96, and GS96QK226.

As the experiment continues, we hope to answer 2 main questions. (1) Are there any prion protein polymorphisms that make deer resistant to CWD, and (2) what are the CWD shedding dynamics in deer with detectable CWD. One potential outcome of the study would be identifying genotypes with very long incubation periods that, while susceptible to CWD, still could be used to manage CWD.

https://www.ars.usda.gov/research/publications/publication/?seqNo115=410188

Update: CWD genetic resistance project at NADC 1) Are there any prion protein polymorphisms that make deer resistant to CWD, and (2) what are the CWD shedding dynamics in deer with detectable CWD. One potential outcome of the study would be identifying genotypes with very long incubation periods that, while susceptible to CWD, still could be used to manage CWD.

https://www.ars.usda.gov/research/publications/publication/?seqNo115=410188

Another potential and likely outcome of this study, imo, is that genotypes developed with very long incubation, could therefore, if released into the wild, could help spread cwd even further, exposing even more wild species, and surrounding environments, for even longer periods of time, due to the longer incubation, a terrible potential outcome, one that must be avoided at all cost, imo…terry

SATURDAY, APRIL 11, 2026

Chronic Wasting Disease CWD TSE PrP, Cervid, Genetic Manipulation, Unforeseen Circumstances

https://chronic-wasting-disease.blogspot.com/2026/04/chronic-wasting-disease-cwd-tse-prp.html

***> Transmission of prion infectivity from CWD-infected macaque tissues to rodent models demonstrates the zoonotic potential of chronic wasting disease.

Further passage to cervidized mice revealed transmission with a 100% attack rate.

Our findings demonstrate that macaques, considered the best model for the zoonotic potential of prions, were infected upon CWD challenge, including the oral one.

The disease manifested as atypical in macaques and initial transgenic mouse transmissions, but with infectivity present at all times, as unveiled in the bank vole model with an unusual tissue tropism.

Epidemiologic surveillance of prion disease among cervid hunters and people likely to have consumed venison contaminated with chronic wasting disease

=====

https://intcwdsympo.files.wordpress.com/2023/06/final-agenda-with-abstracts.pdf?force_download=true

***> Fortuitous generation of a zoonotic cervid prion strain

Aims: Whether CWD prions can infect humans remains unclear despite the very substantial scale and long history of human exposure of CWD in many states or provinces of USA and Canada. Multiple in vitro conversion experiments and in vivo animal studies indicate that the CWD-to-human transmission barrier is not unbreakable. A major long-term public health concern on CWD zoonosis is the emergence of highly zoonotic CWD strains. We aim to address the question of whether highly zoonotic CWD strains are possible.

Materials and Methods: We inoculated several sCJD brain samples into cervidized transgenic mice (Tg12), which were intended as negative controls for bioassays of brain tissues from sCJD cases who had potentially been exposed to CWD. Some of the Tg12mice became infected and their brain tissues were further examined by Western blot as well as serial passages in humanized or cervidized mice.

Results: Passage of sCJDMM1 in transgenic mice expressing elk PrP (Tg12) resulted in a “cervidized” CJD strain that we termed CJDElkPrP. We observed 100% transmission of the original CJDElkPrP in transgenic mice expressing human PrP. We passaged CJDElkPrP two more times in the Tg12mice. We found that such second and third passage CJDElkPrP prions retained 100% transmission rate in the humanized mice, despite that the natural elk CWD isolates and CJDElkPrP share the same elk PrP sequence. In contrast, we and others found zero or poor transmission of natural elk CWD isolates in humanized mice.

Conclusions: Our data indicate that highly zoonotic cervid prion strains are not only possible but also can retain zoonotic potential after serial passages in cervids, suggesting a very significant and serious long-term risk of CWD zoonosis given that the broad and continuing spread of CWD prions will provide fertile grounds for the emergence of zoonotic CWD strains over time.

https://prion2023.org/wp-content/uploads/2023/10/Meeting-book-final-version2.pdf

https://web.archive.org/web/20250828201533/https://prion2023.org/wp-content/uploads/2023/10/Meeting-book-final-version2.pdf

https://www.researchgate.net/profile/Syed-Zahid-Shah/publication/378314391_Meeting-book-final-version_prion_2023/links/65d44dad28b7720cecdca95f/Meeting-book-final-version-prion-2023.pdf

***> Transmission of cervid prions to humanized mice demonstrates the zoonotic potential of CWD

Samia Hannaoui1 · Irina Zemlyankina1 · Sheng Chun Chang1 · Maria Immaculata Arifn1 · Vincent Béringue2 · Debbie McKenzie3 · Hermann M. Schatzl1 · Sabine Gilch1

Received: 24 May 2022 / Revised: 5 August 2022 / Accepted: 7 August 2022

© The Author(s) 2022

Abstract

Prions cause infectious and fatal neurodegenerative diseases in mammals. Chronic wasting disease (CWD), a prion disease of cervids, spreads efficiently among wild and farmed animals. Potential transmission to humans of CWD is a growing concern due to its increasing prevalence. Here, we provide evidence for a zoonotic potential of CWD prions, and its probable signature using mice expressing human prion protein (PrP) as an infection model. Inoculation of these mice with deer CWD isolates resulted in atypical clinical manifestation with prion seeding activity and efficient transmissible infectivity in the brain and, remarkably, in feces, but without classical neuropathological or Western blot appearances of prion diseases. Intriguingly, the protease-resistant PrP in the brain resembled that found in a familial human prion disease and was transmissible upon second passage. Our results suggest that CWD might infect humans, although the transmission barrier is likely higher compared to zoonotic transmission of cattle prions. Notably, our data suggest a different clinical presentation, prion signature, and tissue tropism, which causes challenges for detection by current diagnostic assays. Furthermore, the presence of infectious prions in feces is concerning because if this occurs in humans, it is a source for human-to-human transmission. These findings have strong implications for public health and CWD management.

Keywords Chronic wasting disease · CWD · Zoonotic potential · Prion strains · Zoonotic prions

HIGHLIGHTS OF THIS STUDY

================================

Our results suggest that CWD might infect humans, although the transmission barrier is likely higher compared to zoonotic transmission of cattle prions. Notably, our data suggest a different clinical presentation, prion signature, and tissue tropism, which causes challenges for detection by current diagnostic assays. Furthermore, the presence of infectious prions in feces is concerning because if this occurs in humans, it is a source for human-to-human transmission. These findings have strong implications for public health and CWD management.

In this study, we evaluated the zoonotic potential of CWD using a transgenic mouse model overexpressing human M129-PrPC (tg650 [12]). We inoculated tg650mice intracerebrally with two deer CWD isolates, Wisc-1 and 116AG [22, 23, 27, 29]. We demonstrate that this transgenic line was susceptible to infection with CWD prions and displayed a distinct leading clinical sign, an atypical PrPSc signature and unusual fecal shedding of infectious prions. Importantly, these prions generated by the human PrP transgenic mice were transmissible upon passage. Our results are the first evidence of a zoonotic risk of CWD when using one of the most common CWD strains, Wisc-1/CWD1 for infection. We demonstrated in a human transgenic mouse model that the species barrier for transmission of CWD to humans is not absolute. The fact that its signature was not typical raises the questions whether CWD would manifest in humans as a subclinical infection, whether it would arise through direct or indirect transmission including an intermediate host, or a silent to uncovered human-to-human transmission, and whether current detection techniques will be suffcient to unveil its presence.

Our findings strongly suggest that CWD should be regarded as an actual public health risk. Here, we use humanized mice to show that CWD prions can cross the species barrier to humans, and remarkably, infectious prions can be excreted in feces.

Our results indicate that if CWD crosses the species-barrier to humans, it is unlikely to resemble the most common forms of human prion diseases with respect to clinical signs, tissue tropism and PrPSc signature. For instance, PrPSc in variable protease-sensitive prionopathy (VPSPr), a sporadic form of human prion disease, and in the genetic form Gerstmann-Sträussler-Scheinker syndrome (GSS) is defined by an atypical PK-resistant PrPSc fragment that is non-glycosylated and truncated at both C- and N-termini, with a molecular weight between 6 and 8 kDa [24, 44–46]. These biochemical features are unique and distinctive from PrPSc (PrP27-30) found in most other human or animal prion disease. The atypical PrPSc signature detected in brain homogenate of tg650 mice #321 (1st passage) and #3063 (2nd passage), and the 7–8 kDa fragment (Figs. 2, 4) are very similar to that of GSS, both in terms of migration profile and the N-terminal cleavage site.

CWD in humans might remain subclinical but with PrPSc deposits in the brain with an unusual morphology that does not resemble the patterns usually seen in different prion diseases (e.g., mouse #328; Fig. 3), clinical with untraceable abnormal PrP (e.g., mouse #327) but still transmissible and uncovered upon subsequent passage (e.g., mouse #3063; Fig. 4), or prions have other reservoirs than the usual ones, hence the presence of infectivity in feces (e.g., mouse #327) suggesting a potential for human-to-human transmission and a real iatrogenic risk that might be unrecognizable.

“suggesting a potential for human-to-human transmission and a real iatrogenic risk that might be unrecognizable.”

=================================

Supplementary Information The online version contains supplementary material available at

https://doi.org/10.1007/s00401-022-02482-9

snip...see full text;

https://link.springer.com/article/10.1007/s00401-022-02482-9

https://link.springer.com/content/pdf/10.1007/s00401-022-02482-9.pdf

***> Transmission of Cervid Prions to Humanized Mice Demonstrates the Zoonotic Potential of CWD

Samia Hannaouia, Irina Zemlyankinaa, Sheng Chun Changa, Maria Immaculata Arifina, Vincent Béringueb, Debbie McKenziec, Hermann M. Schatzla, and Sabine Gilcha

Results: Here, we provide the strongest evidence supporting the zoonotic potential of CWD prions, and their possible phenotype in humans. Inoculation of mice expressing human PrPCwith deer CWD isolates (strains Wisc-1 and 116AG) resulted in atypical clinical manifestations in > 75% of the mice, with myoclonus as leading clinical sign. Most of tg650brain homogenates were positive for seeding activity in RT-QuIC. Clinical disease and presentation was transmissible to tg650mice and bank voles. Intriguingly, protease-resistant PrP in the brain of tg650 mice resembled that found in a familial human prion disease and was transmissible upon passage. Abnormal PrP aggregates upon infection with Wisc-1 were detectable in thalamus, hypothalamus, and midbrain/pons regions.

Unprecedented in human prion disease, feces of CWD-inoculated tg650 mice harbored prion seeding activity and infectious prions, as shown by inoculation of bank voles and tg650 with fecal homogenates.

Conclusions: This is the first evidence that CWD can infect humans and cause disease with a distinctive clinical presentation, signature, and tropism, which might be transmissible between humans while current diagnostic assays might fail to detect it. These findings have major implications for public health and CWD-management.

https://www.tandfonline.com/doi/full/10.1080/19336896.2022.2091286

***> why do we not want to do TSE transmission studies on chimpanzees $

snip...

5. A positive result from a chimpanzee challenged severly would likely create alarm in some circles even if the result could not be interpreted for man. I have a view that all these agents could be transmitted provided a large enough dose by appropriate routes was given and the animals kept long enough. Until the mechanisms of the species barrier are more clearly understood it might be best to retain that hypothesis.

snip...

R. BRADLEY

http://collections.europarchive.org/tna/20080102222950/http://www.bseinquiry.gov.uk/files/yb/1990/09/23001001.pdf

***> CDC CWD TSE Prion Update 2025

KEY POINTS

Chronic wasting disease affects deer, elk and similar animals in the United States and a few other countries.

The disease hasn't been shown to infect people.

However, it might be a risk to people if they have contact with or eat meat from animals infected with CWD.

https://web.archive.org/web/20240531213416/https://www.cdc.gov/chronic-wasting/about/index.html#cdc_disease_basics_prevention-reducing-risk

Prions in Muscles of Cervids with Chronic Wasting Disease, Norway

Volume 31, Number 2—February 2025

Research

Prions in Muscles of Cervids with Chronic Wasting Disease, Norway

Snip…

In summary, the results of our study indicate that prions are widely distributed in peripheral and edible tissues of cervids in Norway, including muscles. This finding highlights the risk of human exposure to small amounts of prions through handling and consuming infected cervids.

Appendix

https://wwwnc.cdc.gov/eid/article/31/2/24-0903-app1.pdf

https://wwwnc.cdc.gov/eid/article/31/2/24-0903_article

Volume 31, Number 2—February 2025

Dispatch

***> Detection of Chronic Wasting Disease Prions in Raw, Processed, and Cooked Elk Meat, Texas, USA

Snip…

Of note, our data show that exposure to high temperatures used to cook the meat increased the availability of prions for in vitro amplification. Considering the potential implications in food safety and public health, we believe that the findings described in this study warrant further research. Our results suggest that although the elk meat used in this study resisted different manipulations involved in subsequent consumption by humans, their zoonotic potential was limited. Nevertheless, even though no cases of CWD transmission to human have been reported, the potential for human infection is still unclear and continued monitoring for zoonotic potential is warranted.

https://wwwnc.cdc.gov/eid/article/31/2/24-0906_article

***> Of note, our data show that exposure to high temperatures used to cook the meat increased the availability of prions for in vitro amplification...

Detection of chronic wasting disease prions in processed meats

Results: Our results show positive prion detection in all the samples analyzed using deer and elk substrates. Surprisingly, cooked meats displayed increased seeding activities. This data suggests that CWD-prions are available to people even after meats are processed and cooked.

Conclusions: These results suggest CWD prions are accessible to humans through meats, even after processing and cooking. Considering the fact that these samples were collected from already processed specimens, the availability of CWD prions to humans is probably underestimated.

"Our results show positive prion detection in all the samples analyzed using deer and elk substrates. Surprisingly, cooked meats displayed increased seeding activities."

Meeting-book-final-version prion 2023 Prion 2023 Congress Organizing Committee and the NeuroPrion Association, we invite you to join us for the International Conference Prion2023 from 16-20 October 2023 in Faro, Portugal.

https://prion2023.org/wp-content/uploads/2023/10/Meeting-book-final-version2.pdf

https://web.archive.org/web/20250828201533/https://prion2023.org/wp-content/uploads/2023/10/Meeting-book-final-version2.pdf

https://www.researchgate.net/profile/Syed-Zahid-Shah/publication/378314391_Meeting-book-final-version_prion_2023/links/65d44dad28b7720cecdca95f/Meeting-book-final-version-prion-2023.pdf

DETECTION OF CHRONIC WASTING DISEASE PRIONS IN PROCESSED MEATS.

In this study, we analyzed different processed meats derived from a pre-clinical, CWD-positive free-ranging elk. Products tested included filets, sausages, boneless steaks, burgers, ham steaks, seasoned chili meats, and spiced meats. CWD-prion presence in these products were assessed by PMCA using deer and elk substrates. Our results show positive prion detection in all products. To confirm the resilience of CWD-prions to traditional cooking methods, we grilled and boiled the meat products and evaluated them for any remnant PMCA seeding activity. Results confirmed the presence of CWD-prions in these meat products suggesting that infectious particles may still be available to people even after cooking. Our results strongly suggest ongoing human exposure to CWD-prions and raise significant concerns of zoonotic transmission through ingestion of CWD contaminated meat products.

Products tested included filets, sausages, boneless steaks, burgers, ham steaks, seasoned chili meats, and spiced meats.

CWD-prion presence in these products were assessed by PMCA using deer and elk substrates.

Our results show positive prion detection in all products.

Results confirmed the presence of CWD-prions in these meat products suggesting that infectious particles may still be available to people even after cooking.

Our results strongly suggest ongoing human exposure to CWD-prions and raise significant concerns of zoonotic transmission through ingestion of CWD contaminated meat products.

https://intcwdsympo.files.wordpress.com/2023/06/final-agenda-with-abstracts.pdf?force_download=true

***> Our results show positive prion detection in all products. To confirm the resilience of CWD-prions to traditional cooking methods, we grilled and boiled the meat products and evaluated them for any remnant PMCA seeding activity. Results confirmed the presence of CWD-prions in these meat products suggesting that infectious particles may still be available to people even after cooking...

Transmission of prion infectivity from CWD-infected macaque tissues to rodent models demonstrates the zoonotic potential of chronic wasting disease.

Further passage to cervidized mice revealed transmission with a 100% attack rate.

Our findings demonstrate that macaques, considered the best model for the zoonotic potential of prions, were infected upon CWD challenge, including the oral one.

The disease manifested as atypical in macaques and initial transgenic mouse transmissions, but with infectivity present at all times, as unveiled in the bank vole model with an unusual tissue tropism.

Epidemiologic surveillance of prion disease among cervid hunters and people likely to have consumed venison contaminated with chronic wasting disease

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https://intcwdsympo.files.wordpress.com/2023/06/final-agenda-with-abstracts.pdf?force_download=true

CWD TSE Prion 2026

***> Cervid CWD TSE PrP Transmission to Humans, has it already happened and being masked as sporadic CJD, What if? July 2026 Review

https://chronic-wasting-disease.blogspot.com/2026/07/cervid-cwd-tse-prp-transmission-to.html

https://prpsc.proboards.com/thread/224/cervid-transmission-humans-july-review

WEDNESDAY, SEPTEMBER 2, 2026

A new chapter for CWRU’s Prion Center

https://prionunitusaupdate.blogspot.com/2026/09/a-new-chapter-for-cwrus-prion-center.html

https://prpsc.proboards.com/thread/239/new-chapter-cwru-prion-center

Terry S. Singeltary Sr.