Research Project: Elucidating the Pathobiology and Transmission of Transmissible Spongiform Encephalopathies
Location: Virus and Prion Research
2025 Annual Report
Objectives
Objective 1: Develop highly sensitive detection tools to determine the distribution of CWD and scrapie prions in natural hosts (sheep, goats, cervids) and their environment.
Objective 2: Investigate the pathobiology of CWD, scrapie prion strains, and atypical TSEs in natural hosts including potential cross species transmission events.
Objective 3: Investigate the genetics of CWD susceptibility and resistance in white-tailed deer.
Objective 4: Evaluate the presence of and determine the appropriate methodology for CWD strain determination.
Approach
Eradication or control of a family of diseases is unlikely or impossible when an understanding of the basic mechanisms and influences on transmission are unknown and for which methods to evaluate disease status are lacking. Scrapie and BSE represent the most thoroughly studied TSEs; however, significant knowledge gaps persist with regard to the atypical variants of these diseases. Further, much of the research emphasis to date on genetics of prion disease has focused on the recipient genotype rather than the source. Since both atypical BSE and atypical scrapie have been suggested to occur spontaneously, eradication of these diseases may not be possible unless we expand our understanding of the disease at both the source and recipient level. A better understanding of the tissue distribution and potential transmission of these atypical isolates is critical to understanding what risk these disease variants may pose to ongoing control and eradication efforts. The European epizootic of BSE is waning and efforts to eradicate scrapie in the U.S. and abroad have progressed but are not complete. In the U.S., chronic wasting disease (CWD) presents the most serious challenge to regulatory efforts. CWD appears to be spreading unchecked in both free-ranging and farmed cervids. Methods for antemortem detection of TSEs in general and CWD in particular are needed to fulfill the goal of eradicating scrapie and controlling CWD. Performing these studies will allow us to address critical knowledge gaps that are relevant to developing measures to restrict further disease expansion beyond current, affected populations. Understanding prion disease persistence in animal populations is challenging due to lack of tools for study and a less than complete understanding of transmission among animals within a flock or herd or in naturally occurring reservoirs. In addition to transmission between hosts of like species, free-ranging cervids may come in contact with numerous other species including cattle, sheep, and other susceptible hosts. Transmission of CWD to other species has been studied but limited with regard to the source genotype used. The four primary objectives are inherently linked. Our focus is on developing tools needed for control and research, and using those tools to advance our understanding the complex disease process with the overall goal of eradication and control of disease in livestock, wildlife of economic importance, and potential wildlife reservoirs.
Progress Report
The goals of the project plan for fiscal year (FY) 2025 consisted of 12 milestones, 11 of which were either fully or substantially met. The only milestone in this plan that was not met was due to insufficient animal availability and space constraints. Previous studies utilizing this space are not complete due to longer than anticipated incubation periods and cannot be initiated until those studies are complete. In work toward addressing
Objective 1, “Develop highly sensitive detection tools to determine the distribution of chronic wasting disease (CWD) and scrapie prions in natural hosts (sheep, goats, cervids) and their environment”, we have worked closely with ARS researchers in Pullman, Washington, Animal and Plant Health Inspection Service (APHIS), and university partners. The tools under development are directly utilized by state diagnostic labs and have been shared with the appropriate end users for evaluation. We have also assessed alternative dyes that have do not induce amyloid formation in the amplification based diagnostic assay known as RT-QuIC. While no increase in sensitivity was observed, differences between strains were found offering an additional means to differentiate strains for some TSEs.
Objective 2, “Investigate the pathobiology of CWD, scrapie prion strains, and atypical TSEs in natural hosts including potential cross species transmission events”, the studies in question have been initiated with the goal of furthering the understanding of these TSEs in agriculturally relevant species including the natural host species and other that may be exposed to these TSEs in an agricultural environment. The studies are ongoing and anticipated to last upwards of 5 year and observation of the animals is ongoing. No anticipated signs of disease or relevant reportable information have been seen nor are they expected until near the onset of clinical signs, but if they are observed they will be reported.
Objective 3, “Investigate the genetics of CWD susceptibility and resistance in white-tailed deer”, consists of two subobjectives:
A) Investigate the susceptibility of white-tailed deer to CWD modeling direct contact exposure with infected deer, and
B) Investigate the susceptibility of white-tailed deer to CWD after direct inoculation.
The first of these has been initiated on schedule while the second has been delayed considerably (greater than 3 years at this point) due to insufficient animal space.Upon completion these two studies will aid in understanding the disease and disease progression.
Objective 4, “Evaluate the presence of and determine the appropriate methodology for CWD strain determination”, is dependent upon obtaining a diverse set of CWD isolates. We are continuing the acquisition of these samples. . Strains are one of the least understood aspects of TSEs as a whole and of importance in understanding the risks of CWD. We have initiated studies that will address the biochemical nature of prion strains and how these strains are maintained in a host which will aid in addressing features and differentiation of strains as additional samples become available.
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.
2. 02 Showed that gene-targeted mice are capable of reproducing strain specific effects typically limited to natural host species of chronic wasting disease (CWD). CWD is a highly contagious disease of deer, elk, moose, and reindeer found in North America, South Korea, and Scandinavian countries that is caused by misfolded proteins called prions. CWD prions transmit through direct contact between infected animals, or through contaminated soil, grass, or water. All prion diseases exhibit progressive neurodegeneration and ultimately death. Scientists typically study CWD by injecting prions into susceptible animals' brains in lab experiments. Intracranial prion injections are favored because they typically produce shorter incubation periods and higher disease attack rates compared to natural infection. ARS researchers in Ames, Iowa, along with university collaborators showed that this inoculation method can cause the prion strains to change in a way that does not accurately reflect how the disease spreads naturally. They found that using a combination of peripheral inoculation (injection outside the brain) in natural hosts and using novel gene-targeted mice generated in a manner that provides a more natural expression of the inserted prion gene that gives a more accurate picture of how CWD behaves in the real world. The novel mouse model provides an important strategy to precisely assess the zoonotic potential (likelihood of transmission from animals to humans) of CWD and other animal prion diseases using natural routes of transmission. This will impact the tools used and direction of future studies of CWD and other prion diseases allowing more rapid and comprehensive responses to emerging questions aiding both the researchers at the producers they support.
Review Publications
Lambert, Z.J., Bian, J., Cassmann, E.D., West Greenlee, H.M., Greenlee, J.J. 2024. Scrapie versus chronic wasting disease in white-tailed deer. Emerging Infectious Diseases. https://doi.org/10.3201/eid3008.240007.
Joseph, D.P., Bian, J., Sehun, K., Jenna, C., Tomas, B., Bailey, W.K., Zoe, A.N., Glenn, T.C. 2024. Propagation of distinct CWD prion strains during peripheral and intracerebral challenges of gene-targeted mice. Proceedings of the National Academy of Sciences (PNAS). https://doi.org/10.1073/pnas.2402726121.
Hyun Joo, S., Joseph, D.P., Hoo-Chang, P., Je Park, K., Bian, J., Crowell, J., Kim, S., Webster, B.K., Hae-Eun, K., Telling, G.C. 2025. The strain properties of Korean and North American chronic wasting disease prions are indistinguishable. Journal of Infectious Diseases. https://doi.org/10.1093/infdis/jiaf210.
Hay, A.J., Popichak, K.A., Mumford, G., Bian, J., Payton, S., Wolfrath, L., Eggers, M., Nicholson, E.M., Tjalkens, R.B., Zabel, M.D., Moreno, J.A. 2025. Microglia-specific NF-kB signaling is a critical regulator of prion-induced glial inflammation and neuronal loss. PLoS Pathogens. 21(6). Article 1012582. https://doi.org/10.1371/journal.ppat.1012582.
Silva, C.J., Erickson-Beltran, M.L., Cassmann, E.D., Greenlee, J.J. 2024. Quantifying the molecular properties of the elk chronic wasting disease agent with mass spectrometry. Pathogens. 13(11). Article 1008. https://doi.org/10.3390/pathogens13111008.
Cwd, cattle, pigs, sheep, raccoons, oh my!
Price of TSE Prion Poker goes up substantially, all you cattle ranchers and such, better pay close attention here...terry
"Cattle with the E211K polymorphism are susceptible to the CWD agent after oronasal exposure of 0.2 g of infectious material."
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.
https://prion2023.org/wp-content/uploads/2023/10/Meeting-book-final-version2.pdf
Prion Conference 2023
Transmission of the chronic wasting disease agent from elk to cattle after oronasal exposure
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.
https://prion2023.org/wp-content/uploads/2023/10/Meeting-book-final-version2.pdf
Abstract for Prion 2023
Title: Transmission of atypical BSE: a possible origin of Classical BSE in cattle
Authors: Sandor Dudas1, Samuel James Sharpe1, Kristina Santiago-Mateo1, Stefanie Czub1, Waqas Tahir1,2, *
Affiliation: 1National and WOAH reference Laboratory for Bovine Spongiform Encephalopathy, Canadian Food inspection Agency, Lethbridge Laboratory, Lethbridge, Canada. 2Department of Biological Sciences, University of Lethbridge, Lethbridge, Alberta, Canada.
*Corresponding and Presenting Author: waqas.tahir@inspection.gc.ca
Background: Bovine spongiform encephalopathy (BSE) is a fatal neurodegenerative disease of cattle and is categorized into classical and atypical forms. Classical BSE (CBSE) is linked to the consumption of BSE contaminated feed whereas atypical BSE is considered to be spontaneous in origin. The potential for oral transmission of atypical BSE is yet to be clearly defined.
Aims: To assess the oral transmissibility of atypical BSE (H and L type) in cattle. Should transmission be successful, determine the biochemical characteristics and distribution of PrPSc in the challenge cattle.
Material and Methods: For oral transmission, calves were fed with 100 g of either H (n=3) or L BSE (n=3) positive brain material. Two years post challenge, 1 calf from each of the H and L BSE challenge groups exhibited behavioural signs and were euthanized. Various brain regions of both animals were tested by traditional and novel prion detection methods with inconclusive results. To detect infectivity, brain homogenates from these oral challenge animals (P1) were injected intra-cranially (IC) into steer calves. Upon clinical signs of BSE, 3/4 of IC challenged steer calves were euthanized and tested for PrPSc with ELISA, immunohistochemistry and immunoblot.
Results: After 6 years of incubation, 3/4 animals (2/2 steers IC challenged with brain from P1 L-BSE oral challenge and 1/2 steer IC challenged with brain from P1 H-BSE oral challenge) developed clinical disease. Analysis of these animals revealed high levels of PrPSc in their brains, having biochemical properties similar to that of PrPSc in C-BSE.
Conclusion: These results demonstrate the oral transmission potential of atypical BSE in cattle. Surprisingly, regardless of which atypical type of BSE was used for P1 oral challenge, PrPSc in the P2 animals acquired biochemical characteristics similar to that of PrPSc in C-BSE, suggesting atypical BSE as a possible origin of C-BSE in UK.
Presentation Type: Oral Presentation
Funded by: CFIA, Health Canada, Alberta Livestock and Meat Agency, Alberta Prion
Research Institute
Grant Number: ALMA/APRI: 201400006, HC 414250
Abstract for Prion 2023
Acknowledgement: TSE unit NCAD, Lethbridge (Jianmin Yang, Sarah Bogart, Rachana Muley, Yuanmu Fang, Keri Colwell, Renee Anderson, John Gray, Rakhi Katoch) (CFIA, Canada), Dr. Catherine Graham (NSDA, Canada), Dr. Michel Levy (UCVM, Canada), Dr. Martin Groschup (FLI, Germany), Dr. Christine Fast (FLI, Germany), Dr. Bob Hills (Health Canada, Canada)
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
Volume 31, Number 1—January 2025
Detection of Prions in Wild Pigs (Sus scrofa) from Areas with Reported Chronic Wasting Disease Cases, United States
Abstract
Using a prion amplification assay, we identified prions in tissues from wild pigs (Sus scrofa) living in areas of the United States with variable chronic wasting disease (CWD) epidemiology. Our findings indicate that scavenging swine could play a role in disseminating CWD and could therefore influence its epidemiology, geographic distribution, and interspecies spread.
Conclusions
In summary, results from this study showed that wild pigs are exposed to cervid prions, although the pigs seem to display some resistance to infection via natural exposure. Future studies should address the susceptibility of this invasive animal species to the multiple prion strains circulating in the environment. Nonetheless, identification of CWD prions in wild pig tissues indicated the potential for pigs to move prions across the landscape, which may, in turn, influence the epidemiology and geographic spread of CWD.
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.
The successful transmission of pig-passaged CWD to Tg40 mice reported here suggests that passage of the CWD agent through pigs results in a change of the transmission characteristics which reduces the transmission barrier of Tg40 mice to the CWD agent. If this biological behavior is recapitulated in the original host species, passage of the CWD agent through pigs could potentially lead to increased pathogenicity of the CWD agent in humans. Interestingly, bioassay of material from the longest surviving >6 month orally challenged pig (72 mpc), which was negative for PrPcwd by all other tests, produced a positive bioassay result. Bioassay of material from additional animals is currently underway. This study demonstrates that pigs can serve as potential hosts for CWD, although with low attack rates and scant PrPcwd accumulation. Detection of infectivity in orally challenged pigs using mouse bioassay raises the possibility that naturally exposed pigs act as a reservoir of CWD infectivity, even though affected pigs do not develop overt clinical signs or readily detectable PrPcwd.
cwd scrapie pigs oral routes
***> However, at 51 months of incubation or greater, 5 animals were positive by one or more diagnostic methods. Furthermore, positive bioassay results were obtained from all inoculated groups (oral and intracranial; market weight and end of study) suggesting that swine are potential hosts for the agent of scrapie. <***
*** Although the current U.S. feed ban is based on keeping tissues from TSE infected cattle from contaminating animal feed, swine rations in the U.S. could contain animal derived components including materials from scrapie infected sheep and goats. These results indicating the susceptibility of pigs to sheep scrapie, 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. <***
***> Results: PrPSc was not detected by EIA and IHC in any RPLNs. All tonsils and MLNs were negative by IHC, though the MLN from one pig in the oral <6 month group was positive by EIA. PrPSc was detected by QuIC in at least one of the lymphoid tissues examined in 5/6 pigs in the intracranial <6 months group, 6/7 intracranial >6 months group, 5/6 pigs in the oral <6 months group, and 4/6 oral >6 months group. Overall, the MLN was positive in 14/19 (74%) of samples examined, the RPLN in 8/18 (44%), and the tonsil in 10/25 (40%).
***> Conclusions: This study demonstrates that PrPSc accumulates in lymphoid tissues from pigs challenged intracranially or orally with the CWD agent, and can be detected as early as 4 months after challenge. CWD-infected pigs rarely develop clinical disease and if they do, they do so after a long incubation period. This raises the possibility that CWD-infected pigs could shed prions into their environment long before they develop clinical disease. Furthermore, lymphoid tissues from CWD-infected pigs could present a potential source of CWD infectivity in the animal and human food chains.
Conclusions: This study demonstrates that PrPSc accumulates in lymphoid tissues from pigs challenged intracranially or orally with the CWD agent, and can be detected as early as 4 months after challenge. CWD-infected pigs rarely develop clinical disease and if they do, they do so after a long incubation period. This raises the possibility that CWD-infected pigs could shed prions into their environment long before they develop clinical disease. Furthermore, lymphoid tissues from CWD-infected pigs could present a potential source of CWD infectivity in the animal and human food chains.
Component 6: Transmissible Spongiform Encephalopathies
Sheep scrapie agent can infect white-tailed deer after oronasal exposure.
The origin of chronic wasting disease (CWD) is not known, but it has many similarities to the sheep prion disease called scrapie. It has long been hypothesized that CWD arose through transmission of sheep scrapie to deer. ARS researchers in Ames, Iowa, conducted research to determine if scrapie derived from sheep could be transmitted to white-tailed deer. The deer inoculated with sheep scrapie developed clinical signs and the abnormal prion protein could be detected in a wide range of tissues. These results indicate that deer may be susceptible to sheep scrapie if exposed to the disease in natural or agricultural settings. In addition, several strong similarities between CWD in white-tailed deer and the experimental cases of scrapie in white-tailed deer suggests that it would be difficult to distinguish scrapie from CWD in deer or identify scrapie if a case occurs. This information should be considered by deer farmers for keeping their herds free from prion diseases.
https://www.ars.usda.gov/ARSUserFiles/np103/AnnualReports/NP103%20FY2023%20Annual%20Report_Final.pdf
The chronic wasting disease agent from white-tailed deer is highly infectious to humanized mice after passage through raccoons
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 , and Juan María Torres
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
Significance
Classical bovine spongiform encephalopathy (c-BSE) is a fatal cattle prion disease transmissible to humans as variant Creutzfeldt–Jakob Disease (vCJD). Understanding how c-BSE emerges is crucial for preventing future outbreaks and protecting public health. Two main hypotheses explain prion adaptation during cross-species transmission: “conformational shift or deformed templating,” where the species barrier forces a change to a different pathological prion protein, and “conformational selection,” where the species barrier filters preexisting conformers. Our results demonstrate that the conformational shift mechanism explains the emergence of c-BSE when Nor98/atypical scrapie (AS) is transmitted to cattle. This is significant because AS, found in sheep and goats worldwide, can convert to c-BSE. Preventing AS from entering the food chain is crucial to reduce c-BSE/vCJD risks.
Abstract
Prion diseases can manifest with distinct phenotypes in a single species, a phenomenon known as prion strains. Upon cross-species transmission, alterations in the disease phenotype can occur, interpreted as the emergence of a new strain. Two main and non–mutually exclusive evolutionary hypotheses have been proposed to explain this phenomenon: the “conformational shift” or “deformed templating” and the “conformational selection.” The conformational shift hypothesis proposes that the introduction of a new host prion protein (PrPC) forces a change in the conformation of the pathological prion protein (PrPSc), causing the new prion strain emergence. On the contrary, the conformational selection model postulates that prion isolates are a conglomerate of PrPSc conformations with relative distribution frequencies, wherein the species barrier acts as a filter selecting the one fittest for the new species environment. Previous studies reported the emergence of the classical bovine spongiform encephalopathy agent (c-BSE) upon transmission of Nor98/atypical scrapie (AS) onto a bovine PrP. This study investigates the evolutionary dichotomy of this c-BSE emergence by using prion strain thermostability combined with protein misfolding cyclic amplification to distinguish between both strains. 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.
Published: 04 October 2023
Detection of classical BSE prions in asymptomatic cows after inoculation with atypical/Nor98 scrapie
Marina Betancor, Belén Marín, Alicia Otero, Carlos Hedman, Antonio Romero, Tomás Barrio, Eloisa Sevilla, Jean-Yves Douet, Alvina Huor, Juan José Badiola, Olivier Andréoletti & Rosa Bolea Veterinary Research volume 54, Article number: 89 (2023) Cite this article
Abstract
The emergence of bovine spongiform encephalopathy (BSE) prions from atypical scrapie has been recently observed upon experimental transmission to rodent and swine models. This study aimed to assess whether the inoculation of atypical scrapie could induce BSE-like disease in cattle. Four calves were intracerebrally challenged with atypical scrapie. Animals were euthanized without clinical signs of prion disease and tested negative for PrPSc accumulation by immunohistochemistry and western blotting. However, an emergence of BSE-like prion seeding activity was detected during in vitro propagation of brain samples from the inoculated animals. These findings suggest that atypical scrapie may represent a potential source of BSE infection in cattle.
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Discussion
Previous studies have demonstrated that C-BSE prions can be present as a minor variant in ovine atypical scrapie isolates and that C-BSE can emerge during the passage of these isolates to pigs and bovine PrP mice [7, 8]. These results pointed to atypical scrapie as a possible origin of C-BSE. Therefore, this study was meant to assess the link between atypical scrapie and C-BSE in the natural host of C-BSE, cattle. Although the intracerebral challenge has some limitations and does not reflect the natural transmission process of prions, bioassays using experimental prion inoculation have allowed to identify and describe the transmission mechanisms of these pathogens. Therefore, we decided to challenge cattle with an atypical scrapie isolate.
It is important to note that none of the animals in this study showed any clinical signs of TSE after inoculation with atypical scrapie, according to the results previously obtained in pigs [8]. In addition, the absence of spongiform changes in brain sections, as well as the absence of PrPSc accumulation by conventional techniques in brain areas from the atypical scrapie-inoculated cows, further highlights the need for highly sensitive techniques such as PMCA to detect low levels of prions. After the in vitro propagation of brain samples from the cows included in this study, seeding activity was detected in reactions seeded with brain material from three out of the four cows, in the areas of frontal cortex, thalamus, and/or cerebellum. Interestingly, none of the samples from the obex, which is one of the most affected areas in prion diseases [14], showed seeding activity. Importantly, the observed glycosylation pattern of the positive PMCA reactions was indistinguishable from that of C-BSE prions and PMCA products from reactions seeded with C-BSE prions. To check whether C-BSE-like prions were present in the original atypical scrapie isolate or if they emerged in the brain of the cows after the inoculation, we performed PMCA of the original inoculum in TgBov substrate, following the same conditions described above. The in vitro amplification of the atypical scrapie inoculum resulted in the propagation of BSE-like seeding activity, biochemically indistinguishable from C-BSE or positive PMCA reactions seeded with brain samples from the inoculated cows, suggesting that, as described before, certain atypical scrapie isolates contain low levels of C-BSE prions [9].
Moreover, in order to rule out a spontaneous in vitro misfolding of bovine PrP during PMCA, we included, as a control for the technique, brain samples from non-inoculated age-matching cows that were also subjected to serial in vitro propagation in TgBov substrate. No positivity was observed in PMCA reactions seeded with samples from these animals, suggesting a true C-BSE-like prion seeding activity and not a spontaneous in vitro misfolding of PrP.
All these results suggest the amplification of C-BSE-like prions during the transmission of ovine atypical scrapie to cows. It is true that, in order to confirm the presence of infectious BSE prions in the challenged cows, strain typing experiments of the PMCA products should be carried out in established mouse lines. Therefore, studies involving a bioassay in bovine and ovine PrP-expressing mice have been started.
Interestingly, the time after inoculation and the BSE-like prion seeding activity were not correlated. As previously stated, the emergence of C-BSE from atypical scrapie has been associated with the presence of low levels of C-BSE prions in the atypical scrapie isolates and our results after the in vitro amplification of the PS152 inoculum support this theory. Therefore, the number of C-BSE conformers contained in the used atypical scrapie isolates may be reduced and not homogeneously distributed, making cows receiving different amounts of C-BSE-like prions. It is true that the emergence of C-BSE-like PMCA seeding activity from the brains of cows could be related to the persistence of prions from the original atypical scrapie inoculum. Previous studies, in which prion seeding activity was detected in the brain of intracerebrally inoculated PrP0/0 mice have highlighted the capacity of prions to persist in non-replicative environments [15]. Nevertheless, cows were intracerebrally challenged in the frontal cortex, and seeding activity was detected in caudal regions of their brains but not in more rostral areas such as the frontal cortex. If these positive PMCA reactions were not a bona fide propagation of C-BSE-like prions but associated to inoculum persistence, it would be expected to detect such amplification in the most rostral areas of the brain. Although all these results support a bona fide propagation of C-BSE-like prions, the possibility of PMCA detecting remaining prions of the inoculum, would be definitely ruled out after in vivo bioassays in mouse lines, which are currently being carried out.
The lack of clinical signs of prion disease in cows after inoculation with atypical scrapie contrasts with results from a previous study in which bovine PrP mice (TgBov) were challenged with atypical scrapie isolates and displayed signs of clinical prion disease, developing neuropathological characteristics of C-BSE [7]. In addition, in the mentioned study, after the first passage, signs of clinical prion disease were only observed in a low proportion of the inoculated mice, and several of the inoculated isolates did not lead to PrPSc accumulation. Three serial passages of atypical scrapie were needed to observe complete attack rates in TgBov mice. Moreover, mice from the first passage that developed clinical signs showed long incubation periods considering the lifespan of a mouse. The cows in this study were also euthanized after a long post-inoculation period (between ~7 and ~11 years). However, the number of C-BSE-like prions present in the original atypical scrapie inoculum was probably too low to produce disease in the cows upon first passage. We also need to consider that TgBov mice overexpress ~8 times bovine PrPC, making them more susceptible to develop disease after the inoculation of C-BSE prions.
Further in vivo experiments challenging different mouse lines have been started in order to confirm the infectivity of the PMCA products obtained in this study. However, in conclusion, our findings show that the propagation of atypical scrapie in cattle leads to the emergence of BSE-like seeding activity. This is a concerning issue with far-reaching implications for public health and food safety. The possibility of interspecies transmission of prion diseases and the emergence of new prion strains highlight the critical need for continued surveillance and monitoring of these diseases in both animal and human populations. Early detection of prion diseases is crucial, and highly sensitive detection techniques such as PMCA can play an important role in this regard.
Classical BSE prions emerge from asymptomatic pigs challenged with atypical/Nor98 scrapie
Belén Marín, Alicia Otero, Séverine Lugan, Juan Carlos Espinosa, Alba Marín-Moreno, Enric Vidal, Carlos Hedman, Antonio Romero, Martí Pumarola, Juan J. Badiola, Juan María Torres, Olivier Andréoletti & Rosa Bolea
Scientific Reports volume 11, Article number: 17428 (2021) Cite this article
Abstract
Pigs are susceptible to infection with the classical bovine spongiform encephalopathy (C-BSE) agent following experimental inoculation, and PrPSc accumulation was detected in porcine tissues after the inoculation of certain scrapie and chronic wasting disease isolates. However, a robust transmission barrier has been described in this species and, although they were exposed to C-BSE agent in many European countries, no cases of natural transmissible spongiform encephalopathies (TSE) infections have been reported in pigs. Transmission of atypical scrapie to bovinized mice resulted in the emergence of C-BSE prions. Here, we conducted a study to determine if pigs are susceptible to atypical scrapie. To this end, 12, 8–9-month-old minipigs were intracerebrally inoculated with two atypical scrapie sources. Animals were euthanized between 22- and 72-months post inoculation without clinical signs of TSE. All pigs tested negative for PrPSc accumulation by enzyme immunoassay, immunohistochemistry, western blotting and bioassay in porcine PrP mice. Surprisingly, in vitro protein misfolding cyclic amplification demonstrated the presence of C-BSE prions in different brain areas from seven pigs inoculated with both atypical scrapie isolates. Our results suggest that pigs exposed to atypical scrapie prions could become a reservoir for C-BSE and corroborate that C-BSE prions emerge during interspecies passage of atypical scrapie.
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Discussion The outbreak of C-BSE was followed by the appearance of TSE in species that had never been diagnosed with prion diseases and the emergence in humans of vCJD16,17,18. However, no natural prion disease has been described in pigs, even though they were exposed to C-BSE contaminated feed12. Posterior experimental challenges in pigs and mice expressing porcine PrP have demonstrated that, although they are not completely resistant, pigs present a robust transmission barrier for C-BSE prions4,14,19.
However, the possible transmission of a TSE to swine is a public health concern due to the wide use of pork as a source of human food, and the increasing use of pigs as tissue donors, being reported a case of vCJD in a human patient receiving a swine dura mater graft20. Although pigs are apparently non-susceptible to C-BSE after oral challenge4,5,21, infectivity has been detected in tissues from pigs orally inoculated with classical scrapie or CWD10,11. In addition, these positive orally inoculated pigs are often subclinical, what could represent a public health concern, considering that these animals could reach the slaughterhouse without showing signs suggestive of prion disease.
In the present study, we evaluated the transmissibility of atypical scrapie to pigs. Pigs were euthanized between 22- and 72-months post inoculation (mpi), and their tissues tested for PrPSc accumulation and infectivity. We did not find evidence of transmission of atypical scrapie to any of the animals by EIA (Table 2), western blotting, or mouse bioassay (Table 3). PrPSc accumulation can be detected in BSE-challenged pigs at 34 mpi4, and at 22 mpi when inoculated with SBSE7. Although scrapie or CWD-inoculated pigs do not show clinical signs, PrPSc presence can be found in scrapie-challenged animals at 51 mpi11 and as early as 6 mpi in the case of CWD10.
Our main goal was to test the ability of atypical scrapie/Nor98 strain to propagate in swine, given that mice expressing porcine PrP (PoPrP-Tg001/tgPo mice) showed to be susceptible to atypical scrapie inoculation. One atypical scrapie isolate adapted to this transgenic line, reaching a 100% attack rate and rapid incubation periods in serial passages13, a similar adaptation to that observed with the C-BSE agent19. However, when this atypical scrapie isolate was tested for propagation in tgPo mice again, together with other atypical scrapie isolates, no positive results were obtained, in vitro nor in vivo14. These results, together with the negative transmissions showed in the present study, reinforce the conclusion that porcine species is highly resistant to atypical scrapie. However, we only performed one passage in tgPo mice, and further passages in this line and/or PMCA analysis of tgPo brains to detect any possible prion replication would be of interest.
However, it was demonstrated that C-BSE prions can be present as a minor variant in ovine atypical scrapie isolates and that C-BSE can emerge during the passage of these isolates to bovine PrP mice15. Considering that the aforementioned atypical scrapie isolate also acquired BSE-like properties when transmitted to tgPo mice13, and that C-BSE is the only prion that efficiently propagates in swine PrP4,7,14, we decided to investigate whether C-BSE prions could emerge from atypical scrapie during the ovine-porcine interspecies transmission.
Interestingly, PMCA reactions seeded with brain material from 7 pigs propagated in tgBov substrate showing PrPres with identical biochemical characteristics to those of C-BSE (Fig. 1). Positive C-BSE amplification was detected in the brain of pigs inoculated with either the PS152 or TOA3 atypical scrapie isolates, at minimum incubation periods of 28- and 35-months post inoculation, respectively. From each animal, positive reactions were not obtained from all brain areas tested (Supplementary table 1). Although PrPres amplified from the pigs showed C-BSE biochemical characteristics, further bioassays in tgBov mice are required to know whether these prions replicate the neuropathological features of C-BSE.
Altogether, our results and data obtained from transmission studies of prions to pigs, tgPo mice and in vitro studies using porcine substrate have shown that pig PrP has a very limited ability to sustain prion replication. No significant polymorphisms have been described for pig PRNP22, and it has been suggested that the conformational flexibility of pig PrP sequence is very low, limiting the number of PrPSc conformations able to produce misfolding14. No differences have been found between pig and minipig PrP sequences either23, suggesting that the conclusions obtained here could be extrapolated to domestic, non-experimental pigs. However, using tgBov substrate, we have demonstrated in vitro the presence of C-BSE seeding activity in some pig brain areas, suggesting that C-BSE prions emerged during the transmission of ovine atypical scrapie prions to pigs. Interestingly, C-BSE prions did not emerge from brain material of all the pigs, and, of those from which it did emerge, it was not detected in all brarsain areas tested. No correlation between time after inoculation and BSE emergence was found either. When the emergence of C-BSE from atypical scrapie in PMCA was described, it was associated to low levels of C-BSE prions that were present in the original atypical scrapie isolates15. It is possible that this result is related to the great resistance that pigs present to prion diseases, making the penetrance of the BSE prions that could be present in the original inoculum incomplete. In addition, considering that the amount of C-BSE conformers in the atypical scrapie inocula is probably very reduced and perhaps not homogeneously distributed throughout the isolate, it is also possible that not all the pigs received a sufficient amount of C-BSE conformers capable of being detected by PMCA. Finally, we should consider that PMCA amplification of prions is sometimes a stochastic phenomenon, which could explain why no C-BSE propagation was obtained from some of the pigs. It could be also discussed that C-BSE emergence from the pig brains could be related to persistence of the original atypical scrapie inoculum. However, C-BSE amplification was not obtained from all of the pigs and, in some of them (i.e. P-1217 and P-1231) C-BSE propagation was detected in caudal regions of the brain (cerebellum or occipital cortex) but not in more rostral areas (such as parietal cortex). If C-BSE amplification from pig brain samples were associated to inoculum persistence and not bona fide propagation of C-BSE prions it would be expected that such amplification would be detected mainly in the most rostral areas of the brain. Finally, even though the titer generated was not enough to produce disease in the pigs, these results evidence again the issue that pigs could act as subclinical reservoirs for prion diseases as observed with scrapie and CWD, and that the presence of prions can be detected in pigs short after exposure to prions7,10,11.
In conclusion, our findings suggest that, although pigs present a strong transmission barrier against the propagation of atypical scrapie, they can propagate low levels of C-BSE prions. The prevalence of atypical scrapie and the presence of infectivity in tissues from atypical scrapie infected sheep are underestimated24,25. Given that pigs have demonstrated being susceptible to other prion diseases, and to propagate prions without showing signs of disease, the measures implemented to ban the inclusion of ruminant proteins in livestock feed must not be interrupted.
The prevalence of atypical scrapie and the presence of infectivity in tissues from atypical scrapie infected sheep are underestimated24,25.
Given that pigs have demonstrated being susceptible to other prion diseases, and to propagate prions without showing signs of disease, the measures implemented to ban the inclusion of ruminant proteins in livestock feed must not be interrupted.
EFSA atypical Scrapie
***> AS is considered more likely (subjective probability range 50–66%) that AS is a non-contagious, rather than a contagious, disease.
SNIP...SEE;
THURSDAY, JULY 8, 2021
EFSA Scientific report on the analysis of the 2‐year compulsory intensified monitoring of atypical scrapie
***> AS is considered more likely (subjective probability range 50–66%) that AS is a non-contagious, rather than a contagious, disease.
***> Incomplete inactivation of atypical scrapie following recommended autoclave decontamination procedures <***
John Spiropoulos Richard Lockey Katy E. Beck Chris Vickery Thomas M. Holder Leigh Thorne Mark Arnold Olivier Andreoletti Marion M Simmons Linda A. Terry First published: 21 May 2019 https://doi.org/10.1111/tbed.13247 This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1111/tbed.13247
Summary Prions are highly resistant to the decontamination procedures normally used to inactivate conventional pathogens. This is a challenging problem not only in the medical and veterinary fields for minimising the risk of transmission from potentially infective sources, but also for ensuring the safe disposal or subsequent use of animal by‐products. Specific pressure autoclaving protocols were developed for this purpose, but different strains of prions have been reported to have differing resistance patterns to established prion decontamination procedures, and as additional TSE strains are identified it is necessary to determine the effectiveness of such procedures. In this study we assessed the efficacy of sterilisation using the EU recommended autoclave procedure for prions (133o C, 3 Bar for 20 min) on the atypical or Nor98 (AS/Nor98) scrapie strain of sheep and goats. Using a highly sensitive murine mouse model (tg338) that overexpresses ovine PrPC, we determined that this method of decontamination reduced the infectivity titre by 1010. Infectivity was nonetheless still detected after applying the recommended autoclaving protocol. This shows that AS/Nor98 can survive the designated legislative decontamination conditions, albeit with a significant decrease in titre. The infectivity of a classical scrapie isolate subjected to the same decontamination conditions was reduced by 106 suggesting that the AS/Nor98 isolate is less sensitive to decontamination than the classical scrapie source. This article is protected by copyright. All rights reserved.
***> SCRAPIE TSE Prion USA RAPID RESPONSE URGENT UPDATES DECEMBER 25, 2025 <***
2026 USDA EXPLANATORY NOTES, APHIS, CWD, BSE, Scrapie, TSE, Prion
Final rule on the Importation of Sheep, Goats, and Certain Other Ruminants (APHIS-2009-0095) Scrapie, BSE, CWD, TSE Prion Singeltary Submission
APHIS USDA Captive CWD Herds Update by State December 2025 Update
SUNDAY, MAY 04, 2025
Texas Senate Bill 2651 establishment of a pilot program to breed deer resistant to CWD TSE Prion, what could go wrong?
FRIDAY, NOVEMBER 21, 2025
Chronic Wasting Disease CWD TSE Prion Herd Declines
FRIDAY, OCTOBER 31, 2025
Captive Cervid and the Economic Burden of Chronic Wasting Disease CWD TSE Prion?
The economic burden of ignoring CWD would be far greater, imo, with time, if no cervid were left, or just a select few, if the environment/property was so exposed and saturated with CWD, that you couldn’t sell it, you couldn’t grow crops because of the soil saturation of the CWD, water tables saturated with CWD, saturation of hay, grains, from crops uptake on said property, cervid meat saturated from Cervid CWD, remember, You cannot cook the TSE prion disease out of meat, In fact new data now shows that exposure to high temperatures used to cook the meat increased the availability of prions for in vitro amplification. So, what Do we do, how many humans and animals do we continue to expose, continue to saturate with the CWD TSE Prion, …
Docket No. FDA-2003-D-0432 (formerly 03D-0186) Use of Material from Deer and Elk in Animal Feed
PUBLIC SUBMISSION
Comment from Terry Singeltary Sr.
Posted by the Food and Drug Administration on May 17, 2016 Comment
Docket No. FDA-2003-D-0432 (formerly 03D-0186) Use of Material from Deer and Elk in Animal Feed Singeltary Submission
USA BSE Testing and Surveillance?
Bottom line, USA is testing so few cows for BSE (<25k tested annually)
BUT, even at those low testing figures, the USA did just confirm another case of BSE just here recently. Feed ban has failed terribly, and CWD is spreading in the USA, at an alarming rate. Recent transmission studies show oral transmission of CWD of Cervid to cattle. Studies also show links of sporadic CJD to BSE, Scrapie, and CWD. It’s a Whole new game of Prion poker now$$$
Wednesday, May 24, 2023
***> WAHIS, WOAH, OIE, United States of America Bovine spongiform encephalopathy Immediate notification
SATURDAY, MAY 20, 2023
***> Tennessee State Veterinarian Alerts Cattle Owners to Disease Detection Mad Cow atypical L-Type BSE
MAY 19, 2023
2 weeks before the announcement of this recent mad cow case in the USA, i submitted this to the APHIS et al;
***> APPRX. 2 weeks before the recent mad cow case was confirmed in the USA, in Tennessee, atypical L-Type BSE, I submitted this to the APHIS et al;
Document APHIS-2023-0027-0001 BSE Singeltary Comment Submission May 2, 2023
''said 'burden' cost, will be a heavy burden to bear, if we fail with Bovine Spongiform Encephalopathy BSE TSE Prion disease, that is why this information collection is so critical''...
Bovine Spongiform Encephalopathy BSE TSE Prion Origin USA?, what if?
Research Project: Pathobiology, Genetics, and Detection of Transmissible Spongiform Encephalopathies Location: Virus and Prion Research
Title: Sheep are susceptible to the agent of TME by intracranial inoculation and have evidence of infectivity in lymphoid tissues
Author item CASSMANN, ERIC - Oak Ridge Institute For Science And Education (ORISE) item MOORE, SARA - Oak Ridge Institute For Science And Education (ORISE) item SMITH, JODI - Iowa State University item Greenlee, Justin
Submitted to: Frontiers in Veterinary Science Publication Type: Peer Reviewed Journal Publication Acceptance Date: 11/14/2019 Publication Date: 11/29/2019 Citation: Cassmann, E.D., Moore, S.J., Smith, J.D., Greenlee, J.J. 2019.
Sheep are susceptible to the agent of TME by intracranial inoculation and have evidence of infectivity in lymphoid tissues.
Frontiers in Veterinary Science. 6:430. https://doi.org/10.3389/fvets.2019.00430. DOI: https://doi.org/10.3389/fvets.2019.00430
Interpretive Summary: Prion diseases are protein misfolding diseases that are transmissible between animals. The outcome of prion infection is irreversible brain damage and death. Transmission can occur between animals of the same or different species, however, transmission between different species is usually less efficient due to the species barrier, which results from differences in the amino acid sequence of the prion protein between the donor and recipient species. The present work evaluated whether transmissible mink encephalopathy (TME) can infect sheep. Our results demonstrate that sheep are susceptible to the TME agent and that the TME agent has similar properties to the agent of L-type atypical bovine spongiform encephalopathy (L-BSE). This work supports the ideas that L-BSE is a possible source for TME in mink and that the practice of feeding cattle with neurologic disease to mink should be avoided. This information is important to farmers who raise cattle, sheep, or mink.
Technical Abstract: Transmissible mink encephalopathy (TME) is a food borne prion disease. Epidemiological and experimental evidence suggests similarities between the agent of TME and L-BSE. This experiment demonstrates the susceptibility of four different genotypes of sheep to the agent of TME by intracranial inoculation. The four genotypes of sheep used in this experiment had polymorphisms corresponding to codons 136 and 171 of the prion gene: VV136QQ171, AV136QQ171, AA136QQ171, and AA136QR171. All intracranially inoculated sheep without comorbidities (15/15) developed clinical scrapie and had detectable PrPSc by immunohistochemistry, western blot, and enzyme immunoassay (EIA). The mean incubation periods in TME infected sheep correlated with their relative genotypic susceptibility. There was peripheral distribution of PrPSc in the trigeminal ganglion and neuromuscular spindles; however, unlike classical scrapie and C-BSE in sheep, ovine TME did not accumulate in the lymphoid tissue. To rule out the presence of infectious, but proteinase K susceptible PrPSc, the lymph nodes of two sheep genotypes, VV136QQ171 and AA136QQ171, were bioassayed in transgenic ovinized mice. None of the mice (0/32) inoculated by the intraperitoneal route had detectable PrPSc by EIA. Interestingly, mice intracranially inoculated with RPLN tissue from a VV136QQ171 sheep were EIA positive (3/17) indicating that sheep inoculated with TME harbor infectivity in their lymph nodes. Western blot analysis demonstrated similarities in the migration patterns between ovine TME and the bovine TME inoculum. Overall, these results demonstrate that sheep are susceptible to the agent of TME, and that the tissue distribution of PrPSc in TME infected sheep is distinct from classical scrapie.
Previous work has shown that the Stetsonville, WI outbreak of TME could have been precipitated by feeding mink a downer cow with atypical BSE; therefore, it very well may have originated from a cow with L-BSE. The agent of TME appears to remain stable, and it has a high transmission efficiency after a sequence of interspecies transmission events. Although C-BSE is the archetypal foodborne TSE, our findings indicate that L-BSE and bTME have greater transmission efficiencies in bovinized mice. Previous work has demonstrated that L-BSE also is more virulent than C-BSE in mice expressing the human prion protein [46, 55]. Although the documented incidence of L-BSE is low, the propensity of L-BSE and the TME agent to cross species barriers support the continued monitoring for atypical BSE.
***>This work supports the ideas that L-BSE is a possible source for TME in mink and that the practice of feeding cattle with neurologic disease to mink should be avoided. This information is important to farmers who raise cattle, sheep, or mink.<***
1985
Evidence That Transmissible Mink Encephalopathy Results from Feeding Infected Cattle Over the next 8-10 weeks, approximately 40% of all the adult mink on the farm died from TME.
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The rancher was a ''dead stock'' feeder using mostly (>95%) downer or dead dairy cattle...
FRIDAY, NOVEMBER 21, 2025
While no one was watching: Tenuous status of CDC prion unit, risk of CWD to people worry scientists
WEDNESDAY, OCTOBER 15, 2025
US NATIONAL PRION DISEASE PATHOLOGY SURVEILLANCE CENTER CJD TSE REPORT 2025
terry
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