Texas Chronic Wasting Disease management rules headed for change
Texas' chronic wasting disease management rules headed for change
Matt Wyatt
Staff writer
Sep. 16, 2021
Texas is modifying its CWD management rules in the wake of an outbreak of the disease at seven breeding facilities.The Texas Parks and Wildlife Commission held a special work session this week, focusing its efforts on chronic wasting disease management. A slate of regulations was proposed that could potentially be adopted at the next commission meeting in early November.
Many of the proposals are geared toward regulation of the deer breeding industry. CWD, an always-deadly neurological disease in cervids, was detected in seven breeding facilities since spring. More than 30 white-tailed deer have tested positive from these facilities, which sparked a massive epidemiological investigation that has encompassed 181 trace breeding facilities and 119 release sites.
Perhaps the most significant of the proposed regulations would be to continue to make mandatory the live testing of deer prior to release, the crux of the emergency orders Texas Parks and Wildlife Department issued earlier this year in response to the outbreak. The proposal requires 100 percent of deer 12 months and older to be live tested at least eight months prior to being sent to a release site. About 30 percent of the state’s breeder herd is released annually.
“We are very proud to be the first state in the country, and still the only state in the country, that recognizes and allows for ante-mortum testing of deer,” said TPWD big game program director Mitch Lockwood, who added that “we love this tool as a herd-screening tool, but not for clearing individual deer.”
Breeders that do not adhere to testing all deer before release will essentially be shut down.
“We believe that this requirement is so important that a facility should lose movement-qualified status if deer are transferred in violation of this requirement and that the facility be required to follow up with whole-herd, ante-mortum testing of all release-eligible deer, as well as a testing plan being prescribed to the release site where those deer were liberated,” Lockwood said.
During his invited testimony, Deer Breeders Corporation chief executive officer Kevin Davis said it is no secret that he was not a fan of the emergency order’s live-testing requirement. He said that deer breeders understand the need for surveillance, and that the industry supports most of the regulations that were proposed at the session, but the ante-mortum testing requirements are too taxing.
“The wholesale practice of testing every animal is an additional financial burden on the producer and it also creates stress on the animal. It cannot be conducted without veterinarian services, sedation medication and sufficient staffing,” Davis said.
“What this means, is the burden is more significant on the smaller to medium sized breeder than on larger breeders. This will force the smaller folks out of business.”
Davis said the cost goes far beyond the $25-45 tests. Veterinarians and sedation drugs are not cheap. Davis estimates the cost of live-animal testing is about $300 a deer and said this summer’s emergency orders cost the industry $3.3 million.
“When we put the smaller producer out of business, we significantly negatively impact recruitment. The result is the industry will die, families will suffer, hunters will suffer, hunting heritage will suffer and, yes, hunter recruitment will suffer,” Davis said.
Sarah Biedenharn is the president of Texas Wildlife Association, an organization that represents hunters and private landowners, and supports the proposed live-animal testing measures.
“TWA supports the need for ante-mortum tests of all breeder deer before they are released. No matter the origination of the disease, it is without question that the greatest risk of spreading CWD comes from the unnatural movement of live animals,” Biedenharn said during her invited testimony.
“We have learned through briefings from this department and Texas Animal Health Commission that the accuracy of the live test depends heavily on the time since exposure to the disease, which we of course can’t always know. Knowing these limitations, it does not seem responsible to test anything less than 100 percent of deer to be released. We must do all we can to protect our native deer; there’s just too much at stake.”
Biedenharn also said TWA would like to see ear tags on breeder deer that have been sent to release sites to give adjacent landowners a way to identify escaped deer.
“TWA also supports the position that a permanent ID tag be clearly visible from a distance and should be required for all released deer,” she said.
“Neighboring landowners need to be notified of a positive case, so that cautionary measures can be taken before it spreads further. They also need to be able to clearly identify an escaped deer on their own property. We understand that this issue is a complex one, but we urge the commission to continue exploring ways to address these issues in order to protect our native herds as well as the private property rights of thousands of landowners that have never moved or released deer.”
Texas is spearheading live-deer testing efforts to help mitigate the risk of spreading a disease that is considered impossible to eradicate once it becomes established. CWD, which is caused by misfolded proteins called prions, can spread through bodily fluids, environmental contamination and other unknown vectors. It is difficult to detect in early stages; deer can show no symptoms for years while the disease quietly incubates. CWD currently has no cure.
Many states are struggling to arrest the spread of CWD and, in the wake of the unprecedented severity of this latest outbreak in the state, Texas officials are working to contain it before it gets out of hand and potentially causes long-term impacts to native deer populations.
“The decision we make over the coming weeks may not impact hunting in our lifetime. But they could very easily impact the next generation of hunters. I’m here today because I want to make sure that my future kids and grandkids get to experience the joys of hunting like I did. Now is the time to take action and ensure the long-term survivability of this natural resource,” Biedenharn said.
***> CONGRESSIONAL ABSTRACTS PRION CONFERENCE 2018
P69 Experimental transmission of CWD from white-tailed deer to co-housed reindeer
Mitchell G (1), Walther I (1), Staskevicius A (1), Soutyrine A (1), Balachandran A (1)
(1) National & OIE Reference Laboratory for Scrapie and CWD, Canadian Food Inspection Agency, Ottawa, Ontario, Canada.
Chronic wasting disease (CWD) continues to be detected in wild and farmed cervid populations of North America, affecting predominantly white-tailed deer, mule deer and elk. Extensive herds of wild caribou exist in northern regions of Canada, although surveillance has not detected the presence of CWD in this population. Oral experimental transmission has demonstrated that reindeer, a species closely related to caribou, are susceptible to CWD. Recently, CWD was detected for the first time in Europe, in wild Norwegian reindeer, advancing the possibility that caribou in North America could also become infected. Given the potential overlap in habitat between wild CWD-infected cervids and wild caribou herds in Canada, we sought to investigate the horizontal transmissibility of CWD from white-tailed deer to reindeer.
Two white-tailed deer were orally inoculated with a brain homogenate prepared from a farmed Canadian white-tailed deer previously diagnosed with CWD. Two reindeer, with no history of exposure to CWD, were housed in the same enclosure as the white-tailed deer, 3.5 months after the deer were orally inoculated. The white-tailed deer developed clinical signs consistent with CWD beginning at 15.2 and 21 months post-inoculation (mpi), and were euthanized at 18.7 and 23.1 mpi, respectively. Confirmatory testing by immunohistochemistry (IHC) and western blot demonstrated widespread aggregates of pathological prion protein (PrPCWD) in the central nervous system and lymphoid tissues of both inoculated white-tailed deer. Both reindeer were subjected to recto-anal mucosal associated lymphoid tissue (RAMALT) biopsy at 20 months post-exposure (mpe) to the white-tailed deer. The biopsy from one reindeer contained PrPCWD confirmed by IHC. This reindeer displayed only subtle clinical evidence of disease prior to a rapid decline in condition requiring euthanasia at 22.5 mpe. Analysis of tissues from this reindeer by IHC revealed widespread PrPCWD deposition, predominantly in central nervous system and lymphoreticular tissues. Western blot molecular profiles were similar between both orally inoculated white-tailed deer and the CWD positive reindeer. Despite sharing the same enclosure, the other reindeer was RAMALT negative at 20 mpe, and PrPCWD was not detected in brainstem and lymphoid tissues following necropsy at 35 mpe. Sequencing of the prion protein gene from both reindeer revealed differences at several codons, which may have influenced susceptibility to infection.
Natural transmission of CWD occurs relatively efficiently amongst cervids, supporting the expanding geographic distribution of disease and the potential for transmission to previously naive populations. The efficient horizontal transmission of CWD from white-tailed deer to reindeer observed here highlights the potential for reindeer to become infected if exposed to other cervids or environments infected with CWD.
SOURCE REFERENCE 2018 PRION CONFERENCE ABSTRACT
Research Project: TRANSMISSION, DIFFERENTIATION, AND PATHOBIOLOGY OF TRANSMISSIBLE SPONGIFORM ENCEPHALOPATHIES Location: Virus and Prion Research
Title: Horizontal transmission of chronic wasting disease in reindeer
Author
item MOORE, SARAH - ORISE FELLOW item KUNKLE, ROBERT item WEST GREENLEE, MARY - IOWA STATE UNIVERSITY item Nicholson, Eric item RICHT, JUERGEN item HAMIR, AMIRALI item WATERS, WADE item Greenlee, Justin
Submitted to: Emerging Infectious Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/29/2016
Publication Date: 12/1/2016
Citation: Moore, S., Kunkle, R., Greenlee, M., Nicholson, E., Richt, J., Hamir, A., Waters, W., Greenlee, J. 2016. Horizontal transmission of chronic wasting disease in reindeer. Emerging Infectious Diseases. 22(12):2142-2145. doi:10.3201/eid2212.160635.
Interpretive Summary: Chronic wasting disease (CWD) is a fatal neurodegenerative disease that occurs in farmed and wild cervids (deer and elk) of North America and was recently diagnosed in a single free-ranging reindeer (Rangifer tarandus tarandus) in Norway. CWD is a transmissible spongiform encephalopathy (TSE) that is caused by infectious proteins called prions that are resistant to various methods of decontamination and environmental degradation. Little is known about the susceptibility of or potential for transmission amongst reindeer. In this experiment, we tested the susceptibility of reindeer to CWD from various sources (elk, mule deer, or white-tailed deer) after intracranial inoculation and tested the potential for infected reindeer to transmit to non-inoculated animals by co-housing or housing in adjacent pens. Reindeer were susceptible to CWD from elk, mule deer, or white-tailed deer sources after experimental inoculation. Most importantly, non-inoculated reindeer that were co-housed with infected reindeer or housed in pens adjacent to infected reindeer but without the potential for nose-to-nose contact also developed evidence of CWD infection. This is a major new finding that may have a great impact on the recently diagnosed case of CWD in the only remaining free-ranging reindeer population in Europe as our findings imply that horizontal transmission to other reindeer within that herd has already occurred. Further, this information will help regulatory and wildlife officials developing plans to reduce or eliminate CWD and cervid farmers that want to ensure that their herd remains CWD-free, but were previously unsure of the potential for reindeer to transmit CWD.
Technical Abstract: Chronic wasting disease (CWD) is a naturally-occurring, fatal prion disease of cervids. Reindeer (Rangifer tarandus tarandus) are susceptible to CWD following oral challenge, and CWD was recently reported in a free-ranging reindeer of Norway. Potential contact between CWD-affected cervids and Rangifer species that are free-ranging or co-housed on farms presents a potential risk of CWD transmission. The aims of this study were to 1) investigate the transmission of CWD from white-tailed deer (Odocoileus virginianus; CWDwtd), mule deer (Odocoileus hemionus; CWDmd), or elk (Cervus elaphus nelsoni; CWDelk) to reindeer via the intracranial route, and 2) to assess for direct and indirect horizontal transmission to non-inoculated sentinels. Three groups of 5 reindeer fawns were challenged intracranially with CWDwtd, CWDmd, or CWDelk. Two years after challenge of inoculated reindeer, non-inoculated negative control reindeer were introduced into the same pen as the CWDwtd inoculated reindeer (direct contact; n=4) or into a pen adjacent to the CWDmd inoculated reindeer (indirect contact; n=2). Experimentally inoculated reindeer were allowed to develop clinical disease. At death/euthanasia a complete necropsy examination was performed, including immunohistochemical testing of tissues for disease-associated CWD prion protein (PrPcwd). Intracranially challenged reindeer developed clinical disease from 21 months post-inoculation (months PI). PrPcwd was detected in 5 out of 6 sentinel reindeer although only 2 out of 6 developed clinical disease during the study period (< 57 months PI). We have shown that reindeer are susceptible to CWD from various cervid sources and can transmit CWD to naïve reindeer both directly and indirectly.
3.2.1.2 Non‐cervid domestic species
The remarkably high rate of natural CWD transmission in the ongoing NA epidemics raises the question of the risk to livestock grazing on CWD‐contaminated shared rangeland and subsequently developing a novel CWD‐related prion disease. This issue has been investigated by transmitting CWD via experimental challenge to cattle, sheep and pigs and to tg mouse lines expressing the relevant species PrP.
For cattle challenged with CWD, PrPSc was detected in approximately 40% of intracerebrally inoculated animals (Hamir et al., 2005, 2006a, 2007). Tg mice expressing bovine PrP have also been challenged with CWD and while published studies have negative outcomes (Tamguney et al., 2009b), unpublished data provided for the purposes of this Opinion indicate that some transmission of individual isolates to bovinised mice is possible (Table 1).
In small ruminant recipients, a low rate of transmission was reported between 35 and 72 months post‐infection (mpi) in ARQ/ARQ and ARQ/VRQ sheep intracerebrally challenged with mule deer CWD (Hamir et al., 2006b), while two out of two ARQ/ARQ sheep intracerebrally inoculated with elk CWD developed clinical disease after 28 mpi (Madsen‐Bouterse et al., 2016). However, tg mice expressing ARQ sheep PrP were resistant (Tamguney et al., 2006) and tg mice expressing the VRQ PrP allele were poorly susceptible to clinical disease (Beringue et al., 2012; Madsen‐Bouterse et al., 2016). In contrast, tg mice expressing VRQ sheep PrP challenged with CWD have resulted in highly efficient, life‐long asymptomatic replication of these prions in the spleen tissue (Beringue et al., 2012).
A recent study investigated the potential for swine to serve as hosts of the CWD agent(s) by intracerebral or oral challenge of crossbred piglets (Moore et al., 2016b, 2017). Pigs sacrificed at 6 mpi, approximately the age at which pigs reach market weight, were clinically healthy and negative by diagnostic tests, although low‐level CWD agent replication could be detected in the CNS by bioassay in tg cervinised mice. Among pigs that were incubated for up to 73 mpi, some gave diagnostic evidence of CWD replication in the brain between 42 and 72 mpi. Importantly, this was observed also in one orally challenged pig at 64 mpi and the presence of low‐level CWD replication was confirmed by mouse bioassay. The authors of this study argued that pigs can support low‐level amplification of CWD prions, although the species barrier to CWD infection is relatively high and that the detection of infectivity in orally inoculated pigs with a mouse bioassay raises the possibility that naturally exposed pigs could act as a reservoir of CWD infectivity.
CWD AND SCRAPIE TRANSMIT TO PIGS BY ORAL ROUTES
Research Project: TRANSMISSION, DIFFERENTIATION, AND PATHOBIOLOGY OF TRANSMISSIBLE SPONGIFORM ENCEPHALOPATHIES Location: Virus and Prion Research
Title: Disease-associated prion protein detected in lymphoid tissues from pigs challenged with the agent of chronic wasting disease
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.
Research Project: Pathobiology, Genetics, and Detection of Transmissible Spongiform Encephalopathies Location: Virus and Prion Research
Title: The agent of chronic wasting disease from pigs is infectious in transgenic mice expressing human PRNP
Author item MOORE, S - Orise Fellow item Kokemuller, Robyn item WEST-GREENLEE, M - Iowa State University item BALKEMA-BUSCHMANN, ANNE - Friedrich-Loeffler-institut item GROSCHUP, MARTIN - Friedrich-Loeffler-institut item Greenlee, Justin Submitted to: Prion Publication Type: Abstract Only Publication Acceptance Date: 5/10/2018 Publication Date: 5/22/2018 Citation: Moore, S.J., Kokemuller, R.D., West-Greenlee, M.H., Balkema-Buschmann, A., Groschup, M.H., Greenlee, J.J. 2018. The agent of chronic wasting disease from pigs is infectious in transgenic mice expressing human PRNP. Prion 2018, Santiago de Compostela, Spain, May 22-25, 2018. Paper No. WA15, page 44.
Interpretive Summary:
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.
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.
Title: Chronic wasting disease in a Wisconsin white-tailed deer farm
Author item KEANE, DELWYN item BARR, DANIEL item BOCHSLER, PHILIP item HALL, S item GIDLEWSKI, THOMAS item O'Rourke, Katherine item SPRAKER, TERRY item SAMUEL, MICHAEL
Submitted to: Journal of Veterinary Diagnostic Investigation Publication Type: Peer Reviewed Journal Publication Acceptance Date: 5/5/2008 Publication Date: 9/2/2008
Citation: Keane, D.P., Barr, D.J., Bochsler, P.N., Hall, S.M., Gidlewski, T.E., O'Rourke, K.I., Spraker, T.R., Samuel, M.D. 2008. Chronic wasting disease in a Wisconsin white-tailed deer farm. Journal of Veterinary Diagnostic Investigation. 20(5):698-703. Interpretive Summary: Chronic wasting disease is a fatal disease of deer and elk. Clinical signs, including weight loss, frequent urination, excessive thirst, and changes in behavior and gait, have been reported in mule deer and elk with this disorder. Clinical signs in captive white tailed deer are less well understood. In a previous study, a captive facility housed 200 deer, of which half were positive for the disease with no clinical signs reported. In this study, we examined 78 white tailed deer from a captive facility with a history of chronic wasting disease and no animals with clinical signs. Examination of the brain and lymph nodes demonstrated that the abnormal prion protein, a marker for disease, was observed in 60 of the deer. Biopsy of the rectal mucosa, a test that can be performed on live deer, detected 83% of the infected animals. The prion genetics of the deer was strongly linked to the rate of infection and to disease progression. The results demonstrate that clinical signs are a poor indicator of the disease in captive white tailed deer and that routine testing of live deer and comprehensive necropsy surveillance may be needed to identify infected herds.
Technical Abstract: Chronic wasting disease CWD is a transmissible spongiform encephalopathy or prion disease of deer and elk in North America. All diseases in this family are characterized by long preclinical incubation periods following by a relatively short clinical course. Endpoint disease is characterized by extensive deposits of aggregates of the abnormal prion protein in the central nervous system,. In deer, the abnormal prion proteins accumulate in some peripheral lymphoid tissues early in disease and are therefore suitable for antemortem and preclinical postmortem diagnostics and for determining disease progression in infected deer. In this study, a herd of deer with previous CWD diagnoses was depopulated. No clinical suspects were identified at that time. Examination of the brain and nodes demonstrated that 79% of the deer were infected. Of the deer with abnormal prion in the peripheral lymphoid system, the retropharyngeal lymph node was the most reliable diagnostic tissue. Biopsy of the rectal mucosal tissue, a site readily sampled in the restrained or chemically immobilized deer, provided an accurate diagnosis in 83% of the infected deer. The retina in the eye of the deer was positive only in late stage cases. This study demonstrated that clinical signs are a poor indicator of disease, supports the use of the retropharyngeal lymph node as the most appropriate postmortem sample, and supports a further evaluation of the rectal mucosal tissue biopsy as an antemortem test on a herd basis.
Chronic wasting disease: a cervid prion infection looming to spillover
Alicia Otero 1 2 3, Camilo Duque Velásquez 1 2, Judd Aiken 2 4, Debbie McKenzie 5 6
Affiliations expand
PMID: 34488900 DOI: 10.1186/s13567-021-00986-y
Abstract
The spread of chronic wasting disease (CWD) during the last six decades has resulted in cervid populations of North America where CWD has become enzootic. This insidious disease has also been reported in wild and captive cervids from other continents, threatening ecosystems, livestock and public health. These CWD “hot zones” are particularly complex given the interplay between cervid PRNP genetics, the infection biology, the strain diversity of infectious prions and the long-term environmental persistence of infectivity, which hinder eradication efforts. Here, we review different aspects of CWD including transmission mechanisms, pathogenesis, epidemiology and assessment of interspecies infection. Further understanding of these aspects could help identify “control points” that could help reduce exposure for humans and livestock and decrease CWD spread between cervids.
Keywords: Chronic wasting disease, prion, prion disease, prion pathogenesis, interspecies transmission
Introduction
Chronic wasting disease (CWD) is a highly prevalent prion disease affecting various species of the Cervidae family and has been described in North America, South Korea and Scandinavia [1, 2]. Prion diseases are fatal neurodegenerative disorders affecting numerous mammalian species. In addition to CWD, prion diseases include scrapie in sheep and goats, bovine spongiform encephalopathy (BSE), transmissible mink encephalopathy (TME), and Creutzfeldt-Jakob disease (CJD) in humans. CWD is the only prion disease affecting both wild and farmed animals and stands out for being highly contagious, widespread and persistent in the environment, which facilitates the transmission of the disease and hinders its control in deer populations [3,4,5,6].
Pathogenesis of CWD, as described for other prion diseases, occurs over extended asymptomatic periods and depends on the misfolding of the cellular prion protein (PrPC), encoded by the PRNP gene, into an infectious template-directing conformation (PrPSc) [7]. Following exposure to prions, the host’s susceptibility to develop disease, the clinical presentation, and the neuropathology are regulated by the interaction between the host PrPC primary structure and the invading prion agent or strain [8,9,10].
The neuropathology of affected cervids includes spongiform degeneration, neuronal loss, gliosis, and accumulation of PrPCWD (cervid PrPSc) in the form of aggregates [3, 4, 11]. Variation in the disease presentation between cervids, including survival period, distribution of brain lesions and PrPCWD properties occur in concert with different prion strains [12,13,14,15]. Prion strains are reproducible biological information encoded in specific PrPCWD conformers that are replicated by the templated-misfolding of the host PrPC [16,17,18]. While the transmission of a prion strain between hosts sharing similar PrPC is more efficient given the compatibility of selected strain-specific PrPSc conformers, transmission between hosts species expressing different PrPC primary structures is relatively inefficient and can introduce permanent conformational modifications resulting in the emergence of strains with novel properties [14, 19,20,21]. Alternatively, a strain can be transmitted back and forth between two species expressing various PrPC amino acid differences and remain unaltered informationally [22,23,24]. Strain selection from a host co-infected with multiple strains can also occur following transmission between species expressing different PrPC molecules [12, 25]. In addition, some tissues may show differential susceptibility for some strains compared to the brain (e.g. spleen) [26].
The transmission cycle of CWD in wild and captive cervids also involves the propagation of prion strains within and between various host species expressing distinct PrPC primary structures [12, 27, 28]. As CWD outbreaks become enzootic in cervid populations, circulating CWD strains must adapt to the shifting PrPC landscape that each new host provides which might result in novel strain emergence [13, 14, 21, 29]. These shifts in the prion replication substrate (PrPC) also occur at the population level, with allele frequencies of protective PrPC polymorphisms increasing in response to CWD in deer and elk [27, 30]. Here, we review the current understanding of the CWD transmission cycle, pathogenesis, infection biology and infer from numerous bioassay studies the potential for transmission to other species, including humans.
Transmission of CWD
The progression of CWD is less understood in wild free-ranging cervids given its direct relationship with the infectious dose, the route of exposure, the prion strain and the host PRNP genotype. Under controlled conditions, the incubation period (i.e., time to onset of clinical signs) of experimentally infected, orally dosed white-tailed deer, mule deer and reindeer expressing different PrPC ranged between 1.5 and 6 years post-exposure [13, 31,32,33]. Similarly in elk, differences in incubation period were observed to range between 1.8 to 5.2 years depending on the elk PRNP genotype [34,35,36]. During the asymptomatic period, both captive and wild infected cervids contribute to the spread of CWD as they accumulate considerable amounts of prion infectivity throughout the body, which is shed through secretions and excretions into the environment [6, 37, 38].
The age range documented for cervids infected with CWD in captivity is fairly similar to that described for free-ranging animals [39, 40]. However, depending on the historical CWD prevalence and given the social nature of cervids it is possible to find pre-clinical CWD positive fawns (< 1 year-old animals) and yearlings (1–2 year old) [41]. The youngest identified clinically-positive free-ranging deer and elk were 16 and 21 months of age, respectively [4, 42]. An age range of 2.5–7.5 years has been reported for free ranging clinical deer and 1.8 to 10.5 years for elk [4]. More recently, evaluation of the prevalence of CWD infection by age as determined by detection of abnormal prion protein in 28 954 deer collected over seven years of surveillance in Wisconsin and Illinois enzootic zones reached similar conclusions as in the previous studies; the risk of CWD infection increases with age in both male and female deer (prevalence in adults 1.93%, yearlings 0.89 and 0.45% in fawns) [43]. Previous analyses of prevalence in a sample of 4510 deer culled within Wisconsin eradication zones, where CWD incidence has historically been and remains the highest, confirmed CWD infection in 3 to 3.4% of yearling deer irrespective of sex [44]. These findings suggest the higher prevalence in younger animals (yearlings and fawns) could be related to the extent to which CWD has been historically prevalent within a particular cervid population. The detection of prions in fawns could as well represent mother to offspring transmission [45].
Differences in age at which clinical CWD is observed can vary between species and are likely to depend on the source or origin of the infection. The first cases of CWD Scandinavian cervids, were described in various 9–16 year old moose, a 16 year-old red deer and 3–4 year old reindeer [2, 46, 47].
The prevalence of CWD in wild cervids also varies by sex. In CWD enzootic areas the incidence of infection is much higher in males than females [44, 48, 49]. Considering that no differences in susceptibility have been detected between captive male and female deer [3, 39, 40, 50, 51], the higher prevalence in free ranging males may be attributable to differences in behavior, particularly during the breeding season when males roam widely and interact with other males more avidly, increase the risk of contact with contaminated environments and infected animals [52, 53].
The clinical progression and signs of CWD in both captive and experimentally infected cervids vary within and between species [3, 13, 31]. A brief summary is included in Table 1. Initial clinical features are often subtle and transitory [13]. The most prominent clinical features include behavioral alterations and progressive deterioration of body condition (i.e., weight loss) that worsen over the course of weeks to months [54]. Altered postures with lowered head and ears, arching of the back and ataxia can also be displayed [13, 31, 42]. Advanced clinical disease may involve odontoprisis, polydipsia, polyuria, difficulty swallowing, regurgitation of rumen contents and excessive salivation with drooling. Following recumbency, aspiration pneumonia, dehydration, or hypothermia during the winter season (in wild affected animals) are the most likely causes of death [42]. Compared to deer, CWD-affected elk can present with nervousness and hyperesthesia and are more likely to display motor disturbances but less likely to develop polydipsia [54].
Various factors contribute to the efficiency of the CWD transmission cycle. The primary mode of transmission between cervids, early in an outbreak, is likely by direct animal to animal interactions following exposure to an infected animal or environment [53, 55]. Although experimental infection in pregnant muntjac deer (Muntiacus reevesi) and detection of PrPCWD in tissues from wild pregnant elk dams provide evidence for in utero transmission [45, 56], other studies indicate it plays a minor role in epidemiology compared to deer-to-deer transmission [57]. Given the rapid pre-clinical accumulation of PrPCWD aggregates in lymphoid tissues associated with the alimentary and the intestinal mucosa, the oral route of infection is most likely [31, 58, 59]. However, inhalation of CWD-fomites has also been proposed as a mechanism of exposure [60]. The presence of CWD infectivity in antler velvet [61] leads to the question of whether prions can persist in the calcified antler and favor male to male intradermal inoculation during the rut, or represent a risk factor in terms of oral CWD transmission, as antler gnawing is common among cervids. Antler gnawing has been suggested as a factor involved in the transmission of CWD in the reindeer population from Nordfjella, Norway [62].
The spread of CWD into “naïve” cervids also occurs through exposure to contaminated environments previously inhabited by infected animals [38, 57, 63]. This mode of transmission becomes more relevant as the prevalence of CWD in affected cervid populations increases and the disease becomes enzootic. Secretions (saliva) and excretions (urine and feces) of CWD-infected cervids contain considerable CWD infectivity. The minimum infectious dose in saliva required for a deer to become infected, assuming a single oral exposure to CWD prions, is equivalent to the infectivity contained in 100–300 ng of brain (approximate equivalent of 30 mL of CWD-positive saliva) [6]. Secretions and excretions from CWD positive animals and the decomposition of diseased carcasses contaminate the environment, in which prions can persist in a bioavailable state for years [38, 64,65,66]. The physical association of prions with certain soil microparticles enhances transmissibility [67, 68]. Environmental persistence of CWD infectivity depends on the composition of minerals and organic constituents of soil, which vary between geographical areas [69]. Minerals such as montmorillonite, can enhance the experimental transmission of prions by the oral route [67]. Deer consume a significant amount of soil, especially in adjacent areas to mineral licks, which have tested positive for infectivity in CWD endemic regions [70]. Soils, depending on their composition, represent an important reservoir of CWD infectivity in the environment. Although determination of the degree of contamination of a particular soil surface becomes more difficult with time, the soil-bound prion infectivity is not significantly altered [66].
Plants can also represent an important reservoir for CWD contamination and transmission. CWD contaminated pastures can remain infectious for at least 2 years after prion exposure [65]. Regarding the uptake of prions by plants, results are more controversial. One study, using protein misfolding cyclic amplification (PMCA), an ultrasensitive technique for the detection of prions, demonstrated that grass plants exposed to brain or excretions from CWD-infected cervids can uptake prions from the soil and transport them to the aerial parts of the plant [71]. Another study, however, showed that wheat plants do not transport CWD prions from the roots to the stems [72].
Prion neuroinvasion and body distribution of infectivity
The pathological hallmarks of CWD in deer resemble those observed in sheep with scrapie and other prion diseases acquired by ingestion of contaminated material. In orally infected deer, PrPCWD crosses the intestinal epithelial barrier and can be detected, within the first 30–42 days post-exposure, in lymphoid tissues associated with the alimentary tract such as the gut-associated lymphoid tissue (GALT), the tonsils and the retropharyngeal lymph nodes [31, 59, 73, 74]. Modified enterocytes, called M cells, participate in the uptake of the prion, incorporating it into the subepithelial lymphoid tissue. The pathological prion protein then accumulates and replicates in follicular dendritic cells and tingible body macrophages [58, 75, 76]. PrPCWD cellular targeting during early pathogenesis suggests that prions are transported by dendritic cells and/or macrophages to Peyer’s Patches and regional mesenteric lymph nodes [58, 59].
Once infection has been established in the GALT, prion colonization of the nerve endings of the Enteric Nervous System (ENS) and leakage into the lymph and blood facilitates the spread to other organs [77, 78]. Prion infection of the ENS results in the spread of infectivity through sympathetic and parasympathetic nerves [75]. The initial site of PrPCWD detection within the deer brain is the dorsal motor nucleus of the vagus nerve (DMNV), suggesting this nerve as the major route for PrPCWD traffic from the alimentary tract to the brain [73].
CWD infectivity trafficked via the lymph and the blood can reach multiple organs, including the brain. Prion neuroinvasion by this route likely occurs via the circumventricular organs [79]. Consistent with this observation, considerable prion infectivity has been demonstrated in numerous blood cell types from CWD-infected deer, suggesting that the haematogenous dissemination of infection may be important during the pathogenesis of the disease [80].
Another major route of prion neuroinvasion involving the entry via ENS is by retrograde transport of prions through the splanchnic nerve circuitry. This is consistent with the presence of prion aggregates in the intermediolateral columns of the thoracic spinal cord during early stages of prion infection [81, 82]. This route is particularly important during neuroinvasion by BSE prions in cattle, however, analysis of CWD prion accumulation following oral infection did not detect prion deposits in the coeliac ganglion of deer. This suggests that the accumulation of PrPCWD in the intermediolateral column of orally infected cervids results from the centrifugal dissemination of prions replicated within the central nervous system (CNS) [73].
The early lymphoid replication phase is particularly important for the neuroinvasion of CWD prions in deer [73, 74]. Interestingly, North American elk as well as Scandinavian moose and red deer accumulate PrPCWD in the brainstem with little to no accumulation in lymphoid tissues [46, 47, 83, 84]. This could be explained by a predominantly neural route of neuroinvasion (as in BSE pathogenesis), sporadic misfolding of PrPC or differences in the route of exposure. Differences in pathogenesis and neuropathology of sheep inoculated via different routes were not seen [85]. Similarly, no significant differences have been detected in the peripheral burden of CWD prions from deer infected through different routes [64]. Once neuroinvasion has occurred, PrPCWD accumulates producing the characteristic lesions of prion diseases, including intraneuronal vacuolation, neuropil spongiosis, gliosis and formation of amyloid plaques [86].
In addition to lymphoid and brain tissues, CWD prions have been detected in nasal mucosa, salivary glands, urinary bladder, pancreas, kidney, intestine and reproductive tract of female and male deer [15, 31, 64, 73, 87, 88]. The accumulation of PrPCWD in some of these tissues is tightly associated with shedding of infectivity through secretions and excretions [64]. Similar to scrapie in sheep [89], PRNP genotype can influence CWD pathogenesis in deer affecting PrPCWD deposition in peripheral tissues [13, 15, 31, 74, 90].
CWD in cervids
The origin of CWD remains unknown. In North America, epidemiological data suggests emergence occurred in Colorado and Wyoming [55], in the late 1960s, in captive mule deer (Odocoileus hemionus) and black-tailed deer (Odocoileus hemionus columbianus) at research facilities. These herds were captured cervids from different wild populations, including pregnant females that were released after parturition. Transfer of animals between facilities was a common practice [3]. CWD was subsequently detected in Rocky Mountain elk (Cervus elaphus nelsoni) at these facilities and, thereafter, in free-ranging populations of mule deer and elk in Wyoming and Colorado [3, 50, 91].
Cervid migration and commercial movement of preclinical animals contributed to the geographic expansion of CWD into free-ranging and captive populations of North America [42, 55]. To date, CWD occurs in at least 26 U.S. states and three Canadian provinces (Saskatchewan, Alberta and Québec). In Canada, CWD was first identified in farmed elk from Saskatchewan in 1996 [42]. In the following years, CWD was reported in farmed white-tailed deer in Alberta and in wild cervid populations from Saskatchewan and Alberta [92]. Epidemiological studies suggested that the infection was introduced into Saskatchewan farms via import of captive elk from a farm in South Dakota [42]. The origin of the CWD epidemic in wild cervids of Canada remains unknown. Transmission by contact exposure between wild deer and infected farmed elk is a possibility [92]. CWD was first detected in 2013 in wild moose from Alberta [93]. CWD has not, to date, been detected in the wild North American subspecies of caribou (Rangifer tarandus spp).
Outside of North America, CWD outbreaks in captive cervids in South Korean farms occurred following cohabitation with asymptomatic infected elk and deer imported between 1994 and 2003 from a farm in Saskatchewan (later determined to house CWD-infected animals [94]. A direct consequence was the transmission into South Korean captive red deer (Cervus elaphus), sika deer (Cervus nippon) and crosses of these two species [28]. Epidemiological studies of CWD in wild cervids from the Korean peninsula are lacking.
In 2016, CWD was identified in a free-ranging Norwegian reindeer (Rangifer tarandus tarandus), representing the first CWD case detected in Europe [2]. Since this event, thousands of cervids have been surveyed, leading to the detection of the CWD in 19 reindeer, 4 moose and one red deer in Norway, 3 moose in Sweden and one moose in Finland, suggesting that CWD has been quietly emerging in European cervids [46, 47, 95]. The origin of these cases is still unknown. Transmission of Norwegian CWD isolates into bank voles demonstrated the presence of strains different than those seen in North America, suggesting these epizootics are not epidemiologically linked [96]. In addition, importation of cervids to Norway is not allowed and, therefore, it is unlikely that these CWD infections emerged from imported positive animals as was the case for CWD in Korea [1].
The prevalence of CWD in North America has been increasing exponentially during the last 6 decades. In farmed herds the prevalence of CWD positive animals can be higher than 80% and higher than 45% in wild populations [41]. In areas where CWD has become enzootic, the CWD prevalence can be greater than 50% in adult males [97]. The latest Alberta CWD surveillance update (2019 fall hunting season) indicates that the prevalence of CWD continues to increase in all cervid species. Compared to the 2018 fall hunting season, the prevalence in the 2019 season saw an increase of 3.8% (from 7.4% in 2018 to 11.2% 2019 prevalence). Consistent with previous years, white-tailed and mule deer in Alberta and Saskatchewan show differences in prevalence between species and sexes. The prevalence rank among Alberta deer is mule deer males > mule deer females > white-tailed males > white-tailed females. The burden of CWD in Alberta wild elk has not been as extensive as in deer. In 2019, 1.3% of the tested elk resulted positive for CWD (0.8% in 2018). In addition, for the first time, CWD was detected in two hunter-harvested moose [98].
Population declines are observed in cervid herds with high CWD prevalence. CWD positive deer not only succumb to the disease but are also more prone to be killed by predators or hunters, and are more vulnerable to vehicle collisions [99]. Average declines in elk survival in Rocky Mountain National Park were attributed almost entirely to CWD [100] Mean annual survival rates of CWD-negative and CWD-positive deer were estimated as 76% and 32%, respectively, and CWD was considered a significant contributor to mule deer population decline [101]. Miller et al. also observed that the 2-year survival of infected and uninfected tagged wild mule deer was 47 and 82%, respectively [99].
Experimental CWD in cervid species
No natural cases of CWD have been described in some species of cervids, although they have proven to be susceptible to CWD following experimental exposure. These include the Asian muntjac (Muntiacus reevesi) [45] and fallow deer (Dama dama) [102]. Muntjac deer were successfully infected through oral and subcutaneous routes with CWD from white-tailed deer. Interestingly, PrPCWD was detected in fetuses from CWD-infected does, demonstrating vertical CWD transmission in this species [45]. Although fallow deer were suggested to show certain resistance to infection with CWD [103], Hamir et al. reported that this species is susceptible to the disease after intracerebral inoculation with elk and white-tailed deer prions [102]. The differences in these studies may have arisen because intracranial inoculation is more efficient to produce disease compared to environmental exposure, however, PrPC sequence and prion strain compatibility could also explain these differences [102, 103]. No natural cases of CWD have been reported in North American caribou, although these species are susceptible to experimental infection with CWD from mule deer, white-tailed deer and elk. Naive caribou can acquire the disease after oral infection [33] and environmental exposure [63]. A summary of this transmission experiments and the ones described below is included in Table 2.
Evaluating the potential transmission of CWD to non-cervid species
Most of the transmission studies of CWD into various animal species have been conducted with North American CWD isolates and have revealed different transmission patterns. The host range of European CWD isolates is still to be determined [95].
Livestock species The interactions between different animal species in captivity is a known factor favoring the emergence of new pathogens with novel zoonotic properties, as has been recently proposed as the origin of BSE in cattle by contact with sheep infected with atypical/Nor98 scrapie [104]. The distribution of CWD in North America could favor the interspecies transmission of cervid prions into cattle (i.e., overlapping of these species is common in CWD enzootic areas of North America). The transmission of a prion disease to the cattle is cause for alarm due to the potential emergence of BSE-like zoonotic capacity. CWD from different species (white-tailed deer, mule deer and elk) has been successfully transmitted to domestic cattle after intracerebral challenge with different attack rates [105,106,107,108]. The neuropathological and biochemical characteristics of bovine CWD are, however, clearly distinct from BSE [105]. In addition, oral infections in cattle with mule deer prions have been unsuccessful, and no positive transmission has been detected in this species after 10 years of environmental exposure to mule deer and elk CWD [109]. This demonstrates that an important species barrier limits the oral transmission of CWD to cattle.
In 2006, Hamir et al. reported the transmission of mule deer CWD into sheep via the intracranial route [110]. Only 2 of 8 inoculated lambs developed lesions compatible with a prion disease, and they expressed different PRNP genotypes at codons 136, 154 and 171, which are known to determine sheep susceptibility to scrapie [111,112,113]. One animal expressed ARQ/ARQ (subclinical) and one ARQ/VRQ (clinical) sheep. ARQ/ARR sheep were completely resistant to CWD inoculation, suggesting that the transmission of CWD to small ruminants is strongly determined by the host genotype, as seen with scrapie [110]. Clinical disease was described, however, in ARQ/ARQ sheep inoculated with elk CWD prions, which suggests a different strain in the elk isolate. Transgenic mice overexpressing the ovine VRQ PrP allele (tg338 mice) do not accumulate prions in the brain after experimental infection with a number of different CWD isolates [26, 114, 115]. These tg mice, however, efficiently replicate CWD prions in the spleen, suggesting that the lymphoid tissue is more permissive than the brain for interspecies transmission [26].
The susceptibility of pigs to CWD has also been investigated. Moore et al. found that white-tailed deer CWD prions can be detected by real-time quaking-induced conversion (RT-QuIC) in some orally and intracranially inoculated pigs when euthanized at market weight (8 months age, 6 months after inoculation). One aged pig showed clinical signs and, in these aged animals, PrPCWD was detectable by immunohistochemistry and Western blotting in 4/10 intracranially inoculated and in 1/10 orally inoculated pigs. Passages in transgenic mice expressing the porcine PrP showed reduced attack rates. Therefore, they concluded that pigs could support a low-level propagation of CWD prions, albeit with a high species barrier. These results are not necessarily encouraging since it is possible that feral pigs, whose ranges are shared with CWD affected cervids, could act as a reservoir of CWD [116].
Other wildlife species
Comparison of the PRNP sequences of different species of ungulates that inhabit CWD endemic areas showed high sequence identity between bighorn sheep (Ovis canadensis), mountain goats (Oreamnos americanus) and domestic sheep suggesting that these species are potentially susceptible to CWD [117]. No experimental challenges of these wildlife species, sympatric to deer in CWD-endemic areas have been performed yet.
Rodents
Several different rodent species sympatric with deer in CWD endemic areas including meadow voles (Microtus pennsylvanicus), red-backed voles (Myodes gapperi), white-footed mice (Peromyscus leucopus) and deer mice (P. maniculatus) have proven to be susceptible to CWD after experimental inoculation [118]. Among these species, meadow voles showed to be the most susceptible, but incubation periods were shortened in all the rodent species upon second passage, indicating CWD adaptation to these hosts. House mice (Mus musculus) live in close proximity to humans, and their susceptibility to particular CWD strains has been demonstrated [29]. It is possible that wild rodents represent a reservoir for CWD in ecosystems considering that these animals are scavengers, and one of the main sources of food for predators. In addition, they can be accidentally consumed by deer or livestock since rodent carcasses contaminate pastures and forage [118].
CWD is also transmissible to other rodent species that do not cohabitate with deer in CWD-affected regions. These include Syrian golden hamsters (Mesocricetus auratus) [119] and European bank voles (Myodes glareolus) [120]. Curiously, the adaptation of CWD to the European bank vole resulted in the identification of a prion strain (CWD-vole strain) with the shortest incubation period observed to date [120].
Carnivores
Ferrets (Mustela putorius) are a valuable model for the study of prions, including CWD [121,122,123]. Mink (Mustela vison) can also be infected with CWD, but only by intracerebral inoculation. The disease characteristics differed from those of TME-affected mink, demonstrating different strains cause CWD and TME, and suggest that mink are unlikely involved in natural CWD transmission [124].
Oral and intracerebral inoculation of mule deer prions into domestic cats (Felis catus) resulted in no clinical disease or low attack rates, respectively, on first passage. A second passage of the prions from the intracerebrally inoculated cats resulted in 100% of the recipient cats presenting with clinical disease while the second oral passage resulted in a 50% attack rate demonstrating the adaptability of CWD prions to felines [125]. The PrPC sequence similarity between cats and mountain lions (Puma concolor) suggests that these wild carnivores would be susceptible to CWD infection [126]. As mountain lions selectively prey CWD-infected cervids, it would be of interest to test dead animals for CWD to evaluate for prion spillover [127].
CWD prions from white-tailed deer and elk transmitted with low attack rates (25%) following intracerebral challenge in raccoons (Procyon lotor) [128]. Accumulation of protease resistant prions in the cerebrum and obex differed depending on the inoculum. Interestingly, prions from mule deer did not transmit to raccoons after 6 years following intracerebral challenge [129, 130]. This further suggests strain differences in CWD prions from the various cervid species affected.
Among all mammals, canids are probably the most resistant to prion diseases, with the amino acid residue 163 of canine PrPC conferring protection [131,132,133]. Oral exposure of captive coyotes (Canis latrans) to elk prions demonstrated the presence of prions in the coyote fecal material during the first days after consumption [134]. However, even after a large volume of infectious brain homogenate was inoculated, only 50% of exposed coyotes had detectable infectivity in feces between 1- and 4-days post-exposure (dpe) as evaluated by bioassay in tg12 mice (expressing elk PrPC), while the other half lacked detectable prions or were only recovered in feces after 1 day. No evidence of CWD accumulation in the coyote lymph tissue was detected [134]. These results suggest that coyotes were capable of degrading the CWD infectivity. Consistent with this interpretation, the attack rates were incomplete in tg12 mice inoculated with feces collected at various times following exposure. When inoculated with brain homogenates from CWD-infected elk, this transgenic mouse line develops prion disease with full attack rates after incubation periods of < 150 days post-infection [135]. In addition, in the wild, coyotes will likely consume a smaller infective dose as CWD infectivity in muscle and fat is lower than in the brain [51, 136]. The role of canine predators in the control of CWD has been discussed previously, suggesting that the selective predation exerted by wolves (Canis lupus), which hunt weak and vulnerable cervids, could represent an important natural tool to limit CWD contamination of the environment [137]. The reintroduction and protection of wolves in CWD-affected areas, although controversial, could be very efficient for the natural control of the disease.
Humans
To date, there is no clear evidence that CWD can cross the transmission barrier and infect humans, as other animal prions such as BSE [138]. Several epidemiological studies have been developed to assess whether, statistically, there are more cases of prion diseases in population groups living in endemic areas for CWD. These studies mainly consider people exposed to CWD-infected cervids, such as consumers of deer meat and hunters. None of these studies have found a clear correlation between CWD exposure and an increase in human prion disease frequency [90, 139,140,141]. Evaluating the risk of humans to CWD through this type of studies is difficult due to the variety of strains present in the environment, the transport of hunted animals between long distances and the long incubation period of prion diseases in humans (even decades).The identification of the zoonotic ability of an agent requires an abnormally high number of human cases within a particular geographical location or period of time, which necessitates a large number of human exposures to the disease. Prevalence of CWD in several areas has increased exponentially in the last decade, therefore, there may not historically have been a sufficient level of exposure to the disease to detect a zoonotic transmission of CWD.
There are tools, however, to evaluate the susceptibility of humans to CWD. These include bioassays in non-human primates and transgenic mice expressing human PrPC and in vitro studies of the human transmission barrier to CWD.
Squirrel monkeys (Saimiri sciureus) are susceptible to CWD prions from mule deer, elk and white-tailed deer after oral and intracerebral challenge [142, 143]. Race et al. did not observe evidence for CWD transmission to macaques (Macaca fascicularis) at 13 years post-inoculation and using ultra-sensitive techniques for the detection of prions [144]. In an ongoing study, macaques were exposed to different sources of CWD through various routes. Analysis of the tissues identified PrP deposition in the dorsal horns of the spinal cord in a subset of the macaques [145]. Similar PrP immunopositive staining affecting the spinal cord was also reported by Race et al.; these deposits were found in both CWD-challenged and uninoculated, aged macaques, suggesting that this staining was likely due to cellular PrP [144]. Evaluating the zoonotic potential to humans through bioassays in non-human primates has, however, several drawbacks. The degree of sequence similarity between human PrP and the PrP from non-human primates varies between 92.2 and 99.7% [146]. Even species with high sequence homology, such as chimpanzees, express amino acid substitutions in key structural motifs of PrP that could alter the transmission barrier of prions [146, 147]. Although chimpanzees are more closely related to humans, the presence of 2 amino acid polymorphisms adjacent and within the α2-β2 loop, an important structural motif modulating interspecies transmission of some prion strains [148], undermines their utility in testing the species barrier. In particular, the residue E168 in humans (Q168 in chimpanzees) appears to be fundamental for human reduced susceptibility to CWD and other prion strains from ruminants [149].
Transgenic mice expressing different variants of human PrPC (MM129, MV129 and VV129) at 1–16-fold the levels expressed in the human brain were challenged with US and Canadian CWD isolates in seven different studies. Elegantly reviewed by Waddell et al., none of these studies found evidence of transmission to any of the transgenic mice (reviewed by [141]). Studies in chimeric mice suggested that the α2–β2 loop of the prion protein is the key to the transmission barrier of humans to CWD [148]. However, a recent study found low levels of RT-QuIC seeding activity in four mice overexpressing human prion protein (MM129) inoculated with elk and white-tailed deer isolates (2 mice per inoculation group). These results need to be interpreted with caution, as these reactions were inconsistently positive perhaps representing poorly adapted CWD prions into human PrP or alternatively, persistence of the inoculum in the brain of these mice since human prions can physically persist even in knock-out mice for extended periods post-inoculation [149]. In addition, these RT-QuIC positive mice (tg66) express the highest levels of human PrP tested in CWD transmission studies (8–16 × compared to human brain), which could facilitate the replication of CWD in human PrP [150]. In contrast, the same CWD isolates when inoculated into the tgRM (2–4×) resulted in less clinical suspects and no positive detection by RT-QuIC [150].
Finally, the transmission barrier of humans for CWD has been studied using ultra-sensitive in vitro techniques. The first in vitro study suggested a substantial molecular barrier limiting susceptibility of humans to CWD [151]. Davenport et al. demonstrated positive seeding activity when human recombinant PrP was seeded with CWD, but not when using BSE, contradicting results observed in vivo [152]. Successful conversion of human PrP using different CWD seeds in PMCA has been reported by Barria et al. Their studies suggest that CWD from MM132 elk and CWD from reindeer have the highest potential to convert human PrP, followed by white-tailed deer prions and, finally, mule deer CWD isolates, which require an intermediate step of in vitro conditioning to deer substrate [153,154,155]. This positive conversion was achieved, however, in PMCA reactions using a large CWD prions-to- human substrate ratio [154].
Conclusions
The prevalence and geographic spread of CWD continues to rise, expanding the likelihood of transmission to other species. Particularly of concern in North America is the risk to caribou, an endangered species. Although canids appear to have resistance to infection by CWD prions, other carnivores, i.e., the big felids, are predicted to be susceptible to infection. The zoonotic potential is still unclear but the increased prevalence of CWD in cervids will result in greater likelihood of human exposure.
Abbreviations...snip...end
Classical BSE prions emerge from asymptomatic pigs challenged with atypical/Nor98 scrapie
Open Access
Published: 31 August 2021
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
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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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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.
SUNDAY, AUGUST 15, 2021
Cervid Prion Protein Polymorphisms: Role in Chronic Wasting Disease Pathogenesis
***> However, to date, there are no reports of polymorphic cervid PrP alleles providing absolute resistance to CWD.
Cervid Prion Protein Polymorphisms: Role in Chronic Wasting Disease Pathogenesis
***> However, to date, there are no reports of polymorphic cervid PrP alleles providing absolute resistance to CWD.
SUNDAY, AUGUST 15, 2021
Cervid Prion Protein Polymorphisms: Role in Chronic Wasting Disease Pathogenesis
***> However, to date, there are no reports of polymorphic cervid PrP alleles providing absolute resistance to CWD.
Cervid Prion Protein Polymorphisms: Role in Chronic Wasting Disease Pathogenesis
***> However, to date, there are no reports of polymorphic cervid PrP alleles providing absolute resistance to CWD.
***> at present, no PrPC allele conferring absolute resistance in cervids has been identified.
P-145 Estimating chronic wasting disease resistance in cervids using real time quaking- induced conversion
Nicholas J Haley1, Rachel Rielinqer2, Kristen A Davenport3, W. David Walter4, Katherine I O'Rourke5, Gordon Mitchell6, Juergen A Richt2
1 Department of Microbiology and Immunology, Midwestern University, United States; 2Department of Diagnostic Medicine and Pathobiology, Kansas State University; 3Prion Research Center; Colorado State University; 4U.S. Geological Survey, Pennsylvania Cooperative Fish and Wildlife Research Unit; 5Agricultural Research Service, United States Department of Agriculture; 6Canadian Food Inspection Agency, National and OlE Reference Laboratory for Scrapie and CWD
In mammalian species, the susceptibility to prion diseases is affected, in part, by the sequence of the host's prion protein (PrP). In sheep, a gradation from scrapie susceptible to resistant has been established both in vivo and in vitro based on the amino acids present at PrP positions 136, 154, and 171, which has led to global breeding programs to reduce the prevalence of scrapie in domestic sheep. In cervids, resistance is commonly characterized as a delayed progression of chronic wasting disease (CWD); at present, no cervid PrP allele conferring absolute resistance to prion infection has been identified. To model the susceptibility of various naturally-occurring and hypothetical cervid PrP alleles in vitro, we compared the amplification rates and efficiency of various CWD isolates in recombinant PrPC using real time quaking-induced conversion. We hypothesized that amplification metrics of these isolates in cervid PrP substrates would correlate to in vivo susceptibility - allowing susceptibility prediction for alleles found at 10 frequency in nature, and that there would be an additive effect of multiple resistant codons in hypothetical alleles. Our studies demonstrate that in vitro amplification metrics predict in vivo susceptibility, and that alleles with multiple codons, each influencing resistance independently, do not necessarily contribute additively to resistance. Importantly, we found that the white-tailed deer 226K substrate exhibited the slowest amplification rate among those evaluated, suggesting that further investigation of this allele and its resistance in vivo are warranted to determine if absolute resistance to CWD is possible. ***at present, no cervid PrP allele conferring absolute resistance to prion infection has been identified.
PRION 2016 CONFERENCE TOKYO
Second passage of chronic wasting disease of mule deer in sheep compared to classical scrapie after intracranial inoculation
Research Project: Pathobiology, Genetics, and Detection of Transmissible Spongiform Encephalopathies Location: Virus and Prion Research
Title: Second passage of chronic wasting disease of mule deer in sheep compared to classical scrapie after intracranial inoculation
Author item Cassmann, Eric item FRESE, RYLIE - Orise Fellow item Greenlee, Justin Submitted to: Journal of Veterinary Diagnostic Investigation Publication Type: Peer Reviewed Journal Publication Acceptance Date: 11/25/2020 Publication Date: N/A Citation: N/A
Interpretive Summary: Chronic wasting disease (CWD) is a fatal and uncurable brain disease of deer and elk that is related to a similar disease in sheep called scrapie. Both diseases are cause by a misfolded protein called a prion. The exact origin of CWD is unknown, but a possible origin could have been spread of sheep scrapie to deer. Previous research found indistinguishable traits in common between CWD in deer and scrapie in sheep. Additionally, it is unknown if deer CWD can naturally transmit to sheep. In this research, we show that abnormal prions spread throughout the body of sheep intracranially infected with CWD similar to how scrapie spreads in sheep. We compared two US classical scrapie strains to CWD in sheep and found that one of these strains is indistinguishable from sheep CWD. These results demonstrate that current diagnostic techniques would be unlikely to distinguish CWD in sheep from scrapie in sheep if cross-species transmission occurred in a natural setting. This research reinforces the need to continue ongoing cross-species transmission studies focusing on oral susceptibility of sheep to CWD and develop techniques to discriminate sheep CWD from sheep scrapie.
Technical Abstract: The origin of chronic wasting disease (CWD) in cervids is unclear. One hypothesis suggests that CWD originated from scrapie in sheep. In this experiment, we had two main objectives. The first objective was to determine if CWD adaptation in sheep alters the disease phenotype. The second objective was to determine if the disease phenotype of sheep adapted CWD is distinct from classical scrapie. We intracranially inoculated sheep with brain homogenate from first passage mule deer CWD in sheep (sCWDmd). The attack rate in second passage sheep was 100% (12/12). Sheep had prominent lymphoid accumulations of PrPSc reminiscent of classical scrapie. The pattern and distribution of PrPSc in the brains of sheep with CWDmd was similar to scrapie strain 13-7 but different from scrapie strain x124. The western blot glycoprofiles of sCWDmd were indistinguishable from scrapie strain 13-7; however, independent of sheep genotype, glycoprofiles of sCWDmd were different than x124. When sheep genotypes were evaluated individually, there was considerable overlap in the glycoprofiles that precluded significant discrimination between sheep CWD and scrapie strains. Taken together, these data suggest that the phenotype of CWD in sheep is indistinguishable from some strains of scrapie in sheep. Given the results of this study, current diagnostic techniques would be unlikely to distinguish CWD in sheep from scrapie in sheep if cross-species transmission occurred naturally. It is unknown if sheep are naturally vulnerable to CWD; however, the susceptibility of sheep after intracranial inoculation and lymphoid accumulation indicates that the species barrier is not absolute.
''We inoculated WTD by a natural route of exposure (concurrent oral and intranasal (IN); n=5) with a US scrapie isolate. All scrapie-inoculated deer had evidence of PrPSc accumulation.''
Research Project: TRANSMISSION, DIFFERENTIATION, AND PATHOBIOLOGY OF TRANSMISSIBLE SPONGIFORM ENCEPHALOPATHIES
Title: Scrapie transmits to white-tailed deer by the oral route and has a molecular profile similar to chronic wasting disease Authors
item Greenlee, Justin item Moore, S – item Smith, Jodi – item Kunkle, Robert item West Greenlee, M –
Submitted to: American College of Veterinary Pathologists Meeting Publication Type: Abstract Only Publication Acceptance Date: August 12, 2015 Publication Date: N/A
Technical Abstract: The purpose of this work was to determine susceptibility of white-tailed deer (WTD) to the agent of sheep scrapie and to compare the resultant PrPSc to that of the original inoculum and chronic wasting disease (CWD). We inoculated WTD by a natural route of exposure (concurrent oral and intranasal (IN); n=5) with a US scrapie isolate. All scrapie-inoculated deer had evidence of PrPSc accumulation. PrPSc was detected in lymphoid tissues at preclinical time points, and deer necropsied after 28 months post-inoculation had clinical signs, spongiform encephalopathy, and widespread distribution of PrPSc in neural and lymphoid tissues. Western blotting (WB) revealed PrPSc with 2 distinct molecular profiles. WB on cerebral cortex had a profile similar to the original scrapie inoculum, whereas WB of brainstem, cerebellum, or lymph nodes revealed PrPSc with a higher profile resembling CWD. Homogenates with the 2 distinct profiles from WTD with clinical scrapie were further passaged to mice expressing cervid prion protein and intranasally to sheep and WTD. In cervidized mice, the two inocula have distinct incubation times. Sheep inoculated intranasally with WTD derived scrapie developed disease, but only after inoculation with the inoculum that had a scrapie-like profile. The WTD study is ongoing, but deer in both inoculation groups are positive for PrPSc by rectal mucosal biopsy.
In summary, this work demonstrates that WTD are susceptible to the agent of scrapie, two distinct molecular profiles of PrPSc are present in the tissues of affected deer, and inoculum of either profile readily passes to deer.
Fri, Sep 3, 2021 5:02 pm
comments comments@tahc.texas.govHide
To Terry Singeltary flounder9@verizon.net
Cc comments comments@tahc.texas.gov
Mr. Singeltary,
This email is to acknowledge receipt of your proposed rule comments. Thank you for your interest and participation in the Texas Animal Health Commission’s rulemaking process.
Sincerely,
Amanda
Amanda Bernhard
Assistant to the Executive Director
Texas Animal Health Commission
512-719-0704
***> 1st and foremost your biggest problem is 'VOLUNTARY'! AS with the BSE 589.2001 FEED REGULATIONS, especially since it is still voluntary with cervid, knowing full well that cwd and scrapie will transmit to pigs by oral route. VOLUNTARY DOES NOT WORK! all animal products should be banned and be made mandatory, and the herd certification program should be mandatory, or you don't move cervid. IF THE CWD HERD CERTIFICATION IS NOT MANDATORY, it will be another colossal tse prion failure from the start.
***> 2nd USA should declare a Declaration of Extraordinary Emergency due to CWD, and all exports of cervid and cervid products must be stopped internationally, and there should be a ban of interstate movement of cervid, until a live cwd test is available.
***> 3rd Captive Farmed cervid ESCAPEES should be made mandatory to report immediately, and strict regulations for those suspect cwd deer that just happen to disappear. IF a cervid escapes and is not found, that farm should be indefinitely shut down, all movement, until aid MIA cervid is found, and if not ever found, that farm shut down permanently.
***> 4th Captive Farmed Cervid, INDEMNITY, NO MORE Federal indemnity program, or what i call, ENTITLEMENT PROGRAM for game farm industry. NO MORE BAIL OUTS FROM TAX PAYERS. if the captive industry can't buy insurance to protect not only themselves, but also their customers, and especially the STATE, from Chronic Wasting Disease CWD TSE Prion or what some call mad deer disease and harm therefrom, IF they can't afford to buy that insurance that will cover all of it, then they DO NOT GET A PERMIT to have a game farm for anything. This CWD TSE Prion can/could/has caused property values to fall from some reports in some places. roll the dice, how much is a state willing to lose?
***> 5th QUARANTINE OF ALL FARMED CAPTIVE, BREEDERS, URINE, ANTLER, VELVET, SPERM, OR ANY FACILITY, AND THEIR PRODUCTS, that has been confirmed to have Chronic Wasting Disease CWD TSE Prion, the QUARANTINE should be for 21 years due to science showing what scrapie can do. 5 years is NOT near long enough. see; Infectious agent of sheep scrapie may persist in the environment for at least 16 to 21 years.
***> 6th America BSE 589.2001 FEED REGULATIONS CWD TSE Prion
***> 7TH TRUCKING TRANSPORTING CERVID CHRONIC WASTING DISEASE TSE PRION VIOLATING THE LACEY ACT
***> 8TH ALL CAPTIVE FARMING CERVID OPERATIONS MUST BE INSURED TO PAY FOR ANY CLEAN UP OF CWD AND QUARANTINE THERE FROM FOR THE STATE, NO MORE ENTITLEMENT PROGRAM FOR CERVID GAME FARMING PAY TO PLAY FOR CWD TSE PRION OFF THE TAX PAYERS BACK.
***> 9TH ANY STATE WITH DOCUMENTED CWD, INTERSTATE, NATIONAL, AND INTERNATIONAL MOVEMENT OF ALL CERVID, AND ALL CERVID PRODUCTS MUST BE HALTED!
***> 10TH BAN THE SALE OF STRAW BRED BUCKS AND ALL CERVID SEMEN AND URINE PRODUCTS
***> 11th ALL CAPTIVE FARMED CERVID AND THEIR PRODUCTS MUST BE CWD TSE PRION TESTED ANNUALLY AND BEFORE SALE FOR CWD TSE PRION
SEE FULL SCIENCE REFERENCES AND REASONINGS ;
***> 2nd USA should declare a Declaration of Extraordinary Emergency due to CWD, and all exports of cervid and cervid products must be stopped internationally, and there should be a ban of interstate movement of cervid, until a live cwd test is available.
***> 3rd Captive Farmed cervid ESCAPEES should be made mandatory to report immediately, and strict regulations for those suspect cwd deer that just happen to disappear. IF a cervid escapes and is not found, that farm should be indefinitely shut down, all movement, until aid MIA cervid is found, and if not ever found, that farm shut down permanently.
***> 4th Captive Farmed Cervid, INDEMNITY, NO MORE Federal indemnity program, or what i call, ENTITLEMENT PROGRAM for game farm industry. NO MORE BAIL OUTS FROM TAX PAYERS. if the captive industry can't buy insurance to protect not only themselves, but also their customers, and especially the STATE, from Chronic Wasting Disease CWD TSE Prion or what some call mad deer disease and harm therefrom, IF they can't afford to buy that insurance that will cover all of it, then they DO NOT GET A PERMIT to have a game farm for anything. This CWD TSE Prion can/could/has caused property values to fall from some reports in some places. roll the dice, how much is a state willing to lose?
***> 5th QUARANTINE OF ALL FARMED CAPTIVE, BREEDERS, URINE, ANTLER, VELVET, SPERM, OR ANY FACILITY, AND THEIR PRODUCTS, that has been confirmed to have Chronic Wasting Disease CWD TSE Prion, the QUARANTINE should be for 21 years due to science showing what scrapie can do. 5 years is NOT near long enough. see; Infectious agent of sheep scrapie may persist in the environment for at least 16 to 21 years.
***> 6th America BSE 589.2001 FEED REGULATIONS CWD TSE Prion
***> 7TH TRUCKING TRANSPORTING CERVID CHRONIC WASTING DISEASE TSE PRION VIOLATING THE LACEY ACT
***> 8TH ALL CAPTIVE FARMING CERVID OPERATIONS MUST BE INSURED TO PAY FOR ANY CLEAN UP OF CWD AND QUARANTINE THERE FROM FOR THE STATE, NO MORE ENTITLEMENT PROGRAM FOR CERVID GAME FARMING PAY TO PLAY FOR CWD TSE PRION OFF THE TAX PAYERS BACK.
***> 9TH ANY STATE WITH DOCUMENTED CWD, INTERSTATE, NATIONAL, AND INTERNATIONAL MOVEMENT OF ALL CERVID, AND ALL CERVID PRODUCTS MUST BE HALTED!
***> 10TH BAN THE SALE OF STRAW BRED BUCKS AND ALL CERVID SEMEN AND URINE PRODUCTS
***> 11th ALL CAPTIVE FARMED CERVID AND THEIR PRODUCTS MUST BE CWD TSE PRION TESTED ANNUALLY AND BEFORE SALE FOR CWD TSE PRION
SEE FULL SCIENCE REFERENCES AND REASONINGS ;
Control of Chronic Wasting Disease OMB Control Number: 0579-0189 APHIS-2021-0004 Singeltary Submission
Docket No. APHIS-2018-0011 Chronic Wasting Disease Herd Certification
Sunday, January 10, 2021
APHIS Concurrence With OIE Risk Designation for Bovine Spongiform Encephalopathy [Docket No. APHIS-2018-0087] Singeltary Submission June 17, 2019
APHIS Concurrence With OIE Risk Designation for Bovine Spongiform Encephalopathy [Docket No. APHIS-2018-0087] Singeltary Submission
Greetings APHIS et al,
I would kindly like to comment on APHIS Concurrence With OIE Risk Designation for Bovine Spongiform Encephalopathy [Docket No. APHIS-2018-0087], and my comments are as follows, with the latest peer review and transmission studies as references of evidence.
THE OIE/USDA BSE Minimal Risk Region MRR is nothing more than free pass to import and export the Transmissible Spongiform Encephalopathy TSE Prion disease. December 2003, when the USDA et al lost it's supposedly 'GOLD CARD' ie BSE FREE STATUS (that was based on nothing more than not looking and not finding BSE), once the USA lost it's gold card BSE Free status, the USDA OIE et al worked hard and fast to change the BSE Geographical Risk Statuses i.e. the BSE GBR's, and replaced it with the BSE MRR policy, the legal tool to trade mad cow type disease TSE Prion Globally. The USA is doing just what the UK did, when they shipped mad cow disease around the world, except with the BSE MRR policy, it's now legal.
Also, the whole concept of the BSE MRR policy is based on a false pretense, that atypical BSE is not transmissible, and that only typical c-BSE is transmissible via feed. This notion that atypical BSE TSE Prion is an old age cow disease that is not infectious is absolutely false, there is NO science to show this, and on the contrary, we now know that atypical BSE will transmit by ORAL ROUTES, but even much more concerning now, recent science has shown that Chronic Wasting Disease CWD TSE Prion in deer and elk which is rampant with no stopping is sight in the USA, and Scrapie TSE Prion in sheep and goat, will transmit to PIGS by oral routes, this is our worst nightmare, showing even more risk factors for the USA FDA PART 589 TSE PRION FEED ban.
The FDA PART 589 TSE PRION FEED ban has failed terribly bad, and is still failing, since August 1997. there is tonnage and tonnage of banned potential mad cow feed that went into commerce, and still is, with one decade, 10 YEARS, post August 1997 FDA PART 589 TSE PRION FEED ban, 2007, with 10,000,000 POUNDS, with REASON, Products manufactured from bulk feed containing blood meal that was cross contaminated with prohibited meat and bone meal and the labeling did not bear cautionary BSE statement. you can see all these feed ban warning letters and tonnage of mad cow feed in commerce, year after year, that is not accessible on the internet anymore like it use to be, you can see history of the FDA failure August 1997 FDA PART 589 TSE PRION FEED ban here, but remember this, we have a new outbreak of TSE Prion disease in a new livestock species, the camel, and this too is very worrisome.
WITH the OIE and the USDA et al weakening the global TSE prion surveillance, by not classifying the atypical Scrapie as TSE Prion disease, and the notion that they want to do the same thing with typical scrapie and atypical BSE, it's just not scientific.
WE MUST abolish the BSE MRR policy, go back to the BSE GBR risk assessments by country, and enhance them to include all strains of TSE Prion disease in all species. With Chronic Wasting CWD TSE Prion disease spreading in Europe, now including, Norway, Finland, Sweden, also in Korea, Canada and the USA, and the TSE Prion in Camels, the fact the the USA is feeding potentially CWD, Scrapie, BSE, typical and atypical, to other animals, and shipping both this feed and or live animals or even grains around the globe, potentially exposed or infected with the TSE Prion. this APHIS Concurrence With OIE Risk Designation for Bovine Spongiform Encephalopathy [Docket No. APHIS-2018-0087], under it's present definition, does NOT show the true risk of the TSE Prion in any country. as i said, it's nothing more than a legal tool to trade the TSE Prion around the globe, nothing but ink on paper.
AS long as the BSE MRR policy stays in effect, TSE Prion disease will continued to be bought and sold as food for both humans and animals around the globe, and the future ramifications from friendly fire there from, i.e. iatrogenic exposure and transmission there from from all of the above, should not be underestimated. ...
5 or 6 years quarantine is NOT LONG ENOUGH FOR CWD TSE PRION !!!
QUARANTINE NEEDS TO BE 21 YEARS FOR CWD TSE PRION !
FRIDAY, APRIL 30, 2021
Should Property Evaluations Contain Scrapie, CWD, TSE PRION Environmental Contamination of the land?
***> Confidential!!!!
***> As early as 1992-3 there had been long studies conducted on small pastures containing scrapie infected sheep at the sheep research station associated with the Neuropathogenesis Unit in Edinburgh, Scotland. Whether these are documented...I don't know. But personal recounts both heard and recorded in a daily journal indicate that leaving the pastures free and replacing the topsoil completely at least 2 feet of thickness each year for SEVEN years....and then when very clean (proven scrapie free) sheep were placed on these small pastures.... the new sheep also broke out with scrapie and passed it to offspring. I am not sure that TSE contaminated ground could ever be free of the agent!! A very frightening revelation!!!
---end personal email---end...tss
WEDNESDAY, AUGUST 11, 2021
TAHC Chapter 40, Chronic Wasting Disease Terry Singeltary Comment Submission
TUESDAY, AUGUST 31, 2021
TEXAS CHRONIC WASTING DISEASE CWD TSE PRION HAS CONFIRMED 260 CASES TO DATE
Hunters are reminded to review information about Chronic Wasting Disease (CWD) for information about testing requirements and carcass movement restrictions in the CWD zones for the 2021-22 season. Discovery of new cases of CWD in Hunt, Lubbock, and Uvalde counties has prompted TPWD to establish new containment and surveillance zones in those areas to mitigate the potential spread of CWD.
Texas Scrapie Confirmed in a Hartley County Sheep where CWD was detected in a Mule Deer
April 22, 2016
Scrapie Confirmed in a Hartley County Sheep
AUSTIN - Texas Animal Health Commission (TAHC) officials have confirmed scrapie in a Hartley County ewe. The ewe was tested by TAHC after the owner reported signs of weight loss and lack of coordination to their local veterinarian. The premises was quarantined and a flock plan for monitoring is being developed by the TAHC and USDA.
"The TAHC is working closely with the flock owner, sharing all of the options for disease eradication," said Dr. David Finch, TAHC Region 1 Director. "We are thankful the producer was proactive in identifying a problem and seeking veterinary help immediately."
Texas leads the nation in sheep and goat production. Since 2008, there have been no confirmed cases of scrapie in Texas. The last big spike in Texas scrapie cases was in 2006 when nine infected herds were identified and the last herd was released from restrictions in 2013.
According to USDA regulations, Texas must conduct adequate scrapie surveillance by collecting a minimum of 598 sheep samples annually. Since USDA slaughter surveillance started in FY 2003, the percent of cull sheep found positive for scrapieat slaughter (once adjusted for face color) has decreased 90 percent.
Scrapie is the oldest known transmissible spongiform encephalopathies, and under natural conditions only sheep and goats are known to be affected by scrapie. It is a fatal disease that affects the central nervous system of sheep and goats. It is not completely understood how scrapie is passed from one animal to the next and apparently healthy sheep infected with scrapie can spread the disease. Sheep and goats are typically infected as young lambs or kids, though adult sheep and goats can become infected.
The most effective method of scrapie prevention is to maintain a closed flock. Raising replacement ewes, purchasing genetically resistant rams and ewes,or buying from a certified-free scrapie flock are other options to reduce the risk of scrapie. At this time the resistant genetic markers in goats have not been identified, therefore it is important to maintain your sheep and goat herds separately.
The incubation period for Scrapie is typically two to five years. Producers should record individual identification numbers and the seller's premise identification number on purchase and sales records. These records must be maintained for a minimum of five years.
Producers should notify the Texas Animal Health Commission (800-550-8242) or the USDA-Austin Office (512-383-2400) if they have an adult sheep or goat with neurologic signs such as incoordination, behavioral changes, or intense itching with wool loss. Producers may order scrapie identification tags by calling 866-873-2824. For more information, please visit our website at:
TEXAS Sheep and Goats
• Most recent scrapie positive animal in Texas was found in April, 2008.
• USDA-APHIS-VS set the national goal for surveillance at 46,000 traceable, mature sheep or goats. Target for Texas is 1,472.
• The Scrapie Program Review is being scheduled for this summer. No problems expected.
WEDNESDAY, FEBRUARY 03, 2021
Scrapie TSE Prion United States of America a Review February 2021 Singeltary et al
THURSDAY, JANUARY 7, 2021
Atypical Nor-98 Scrapie TSE Prion USA State by State Update January 2021
TUESDAY, SEPTEMBER 07, 2021
Atypical Bovine Spongiform Encephalopathy BSE OIE, FDA 589.2001 FEED REGULATIONS, and Ingestion Therefrom
Terry S. Singeltary Sr., Bacliff, Texas USA flounder9@verizon.net
posted by Terry S. Singeltary Sr. at
2:14 PM
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