Tuesday, March 26, 2019

USDA ARS 2018 USAHA RESOLUTIONS Investigation of the Role of the Prion Protein Gene in CWD Resistance and Transmission of Disease


Investigation of the Role of the Prion Protein Gene in Chronic Wasting Disease Resistance and Transmission of Disease 






The farmed cervidae industry supports research investigating Prion Protein genotypes that may be resistant to Chronic Wasting Disease (CWD) and their impact on transmission of disease. This work could result in tools for breeders to use in selection for CWD resistant genotypes, and potentially provide options for conserving animal genetics in infected herds.


The United States Animal Health Association encourages the United States Department of Agriculture, Agricultural Research Service to allocate funding for research efforts to identify Chronic Wasting Disease susceptibility in different cervid genotypes and the role they have on transmission of disease. 




The farmed cervidae industry and free ranging cervidae continue to be plagued with Chronic Wasting Disease (CWD) outbreaks and more needs to be known about the characteristics of the CWD prion.

The European Union uses the Western Blot test as a standard on every positive transmissible spongiform encephalopathy (TSE). The Canadian Food Inspection Agency uses the Western Blot and immunohistochemistry (IHC) on every confirmed CWD positive sample. The United States uses IHC as the gold standard CWD test.

Scrapie is a TSE, as is CWD. Many different Scrapie strains have been found by using the Western Blot test. More work needs to be performed to evaluate whether there are different CWD strains.

There are epidemiological reasons why determining the different strains of CWD is necessary.


The United States Animal Health Association urges the United States Department of Agriculture, Agricultural Research Service to evaluate the potential diversity of Chronic Wasting Disease strains. 

Subject: Estimating chronic wasting disease susceptibility in cervids

***> at present, no PrPC allele conferring absolute resistance in cervids has been identified. 

J Gen Virol. 2017 Nov; 98(11): 2882–2892.

Published online 2017 Oct 23. doi: 10.1099/jgv.0.000952

PMCID: PMC5845664

PMID: 29058651

Estimating chronic wasting disease susceptibility in cervids using real-time quaking-induced conversion

Chronic wasting disease (CWD) resistance in cervids is often characterized as decreased prevalence and/or protracted disease progression in individuals with specific alleles; at present, no PrP
C allele conferring absolute resistance in cervids has been identified. 


In summary, evaluating the amplification rates and efficiencies of recombinant PrPC substrates by RT-QuIC could be a useful tool for estimating the susceptibility of rare or newly discovered PRNP alleles, allowing researchers to target specific alleles for downstream evaluation in challenge studies. In the face of an ever-expanding CWD-endemic area, it is increasingly important to characterize the natural susceptibility of these alleles, as well as their geographical distribution and the evolutionary basis for their rarity. Do the QGAK, 225F and 225Y alleles represent recent, random anomalies, or are they more primitive mutations that adversely affect reproductive fitness? Perhaps they are an indication that cervids with these rare alleles were themselves once the target of a primordial prion strain. While some evidence has been presented for distinct strains of CWD, little is known about their geographical distribution or virulence in cervid hosts of diverse PRNP backgrounds. It is possible that, with the appropriate framework, RT-QuIC could allow for the discrimination of known and novel prion strains. Without further research into disease management and prevention, including resistance, the only certainty seems to be that CWD will continue its insidious spread, with further discoveries in new hosts and geographical locations.

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 CWO 

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.


***at present, no cervid PrP allele conferring absolute resistance to prion infection has been identified.

''There are no known familial or genetic TSEs of animals, although polymorphisms in the PRNP gene of some species (sheep for example) may influence the length of the incubation period and occurrence of disease.'' 

c) The commonest form of CJD occurs as a sporadic disease, the cause of which is unknown, although genetic factors (particularly the codon 129 polymorphism in the prion protein gene (PRNP)) influence disease susceptibility. The familial forms of human TSEs (see Box 1) appear to have a solely genetic origin and are closely associated with mutations or insertions in the PRNP gene. Most, but not all, of the familial forms of human TSEs have been transmitted experimentally to animals. There are no known familial or genetic TSEs of animals, although polymorphisms in the PRNP gene of some species (sheep for example) may influence the length of the incubation period and occurrence of disease. 

''There are no known familial or genetic TSEs of animals, although polymorphisms in the PRNP gene of some species (sheep for example) may influence the length of the incubation period and occurrence of disease.'' 

ADOPTED: 6 December 2017doi: 10.2903/j.efsa.2018.5132

Scientific opinion on chronic wasting disease (II)

3.2.1. Selection of animals

The importance of selecting the most relevant animals for a robust surveillance programme–able to detect CWD–should be emphasised and is discussed in detail in the 2017 EFSA Opinion (EFSA BIOHAZ Panel, 2017a). 

In summary, testing high-risk animals (e.g. found dead, hunted or slaughtered animals considered not fit for human consumption, vehicle/predator kills and animals killed because they are sick or in poor body condition and not fit for human consumption) of any susceptible cervid species will maximise detection probabilities. Because there is no prior knowledge of differences in species susceptibility (with the exception of fallow deer which appear likely to have reduced natural susceptibility to CWD in North America), and multiple species coexist within most habitats, all species could contribute. However, a subset of these species may be selected or emphasised based on local or national risk assessments (EFSA BIOHAZ Panel, 2017a), or expand as new data on susceptibility emerges.


Current data indicate that at least two strains of CWD have been detected in North American wild cervid populations as identified after passage intomice (Tamguney et al., 2006), but it cannot be assumed that these are the only ones. Strain classification and host susceptibility data ultimately inform case attribution, epidemiological patterns,outbreak control and the assessment of zoonotic potential.

ADOPTED: 2 December 2016 doi: 10.2903/j.efsa.2017.4667 

Chronic wasting disease (CWD) in cervids

Article DOI: https://doi.org/10.3201/eid2309.161474

Chronic Wasting Disease Prion Strain Emergence and Host Range Expansion

Technical Appendix

Additional Data

Brain homogenates from all mice (experimentally infected animals and uninfected controls) were analyzed for the presence of PrP-res. Proteinase K-resistant PrP was detected in all mice infected with H95+ prions (Figure 1) demonstrating that H95+ is 100% penetrant. PrPres was not, however, detected in mice infected with the Wisc-1 strain from wt/wt or S96/wt deer or CWD2 from elk.

A similar analysis of brain homogenates from hamsters was also performed. Wisc-1 CWD was preferentially transmitted to hamsters upon primary passage (Figure 2). Wt/wt CWD caused clinical disease or subclinical accumulation of PrP-res in exposed hamsters. Transmission of S96/wt and H95/wt CWD prions resulted, primarily, in subclinical disease. Inoculation of elk CWD prions resulted in clinical disease in two out of five hamsters and subclinical disease in one animal. The H95/S96 isolate transmitted inefficiently with only one of eight hamsters having subclinical disease. This subclinical infection may be due to Wisc-1 in the H95/S96 deer isolate. Hamsters inoculated with uninfected deer brain homogenate did not show signs of prion disease nor accumulate PrP-res.


Genetic susceptibility to chronic wasting disease in free-ranging white-tailed deer: Complement component C1q and Prnp polymorphisms§ 

Julie A. Blanchong a, *, Dennis M. Heisey b , Kim T. Scribner c , Scot V. Libants d , Chad Johnson e , Judd M. Aiken e , Julia A. Langenberg f , Michael D. Samuel g


Identifying the genetic basis for heterogeneity in disease susceptibility or progression can improve our understanding of individual variation in disease susceptibility in both free-ranging and captive populations. What this individual variation in disease susceptibility means for the trajectory of disease in a population, however, is not straightforward. For example, the greater, but not complete, resistance to CWD in deer with at least one Serine (S) at amino acid 96 of the Prnp gene appears to be associated with slower progression of disease (e.g., Johnson et al., 2006; Keane et al., 2008a). If slower disease progression results in longer-lived, infected deer with longer periods of infectiousness, resistance may lead to increased disease transmission rates, higher prion concentrations in the environment, and increased prevalence, as has been observed in some captive deer herds (Miller et al., 2006; Keane et al., 2008a). Alternatively, if the slower progression of disease in resistant deer is not associated with longer periods of infectiousness, but might instead indicate a higher dose of PrPCWD is required for infection, transmission rates in the population could decline especially if, as in Wisconsin, deer suffer high rates of mortality from other sources (e.g., hunting). Clearly, determining the relationship between genetic susceptibility to infection, dose requirements, disease progression, and the period of PrPCWD infectiousness are key components for understanding the consequences of CWD to free-ranging populations. 


http://forest.wisc.edu/files/pdfs/s...al genetic susceptibility chronic wasting.pdf






Prion protein gene sequence and chronic wasting disease susceptibility in white-tailed deer (Odocoileus virginianus)

Adam L Brandt,1 Amy C Kelly,1 Michelle L Green,1,2 Paul Shelton,3 Jan Novakofski,2,* and Nohra E Mateus-Pinilla1,2 Author information ► Article notes ► Copyright and License information ► 

The sequence of the prion protein gene (PRNP) affects susceptibility to spongiform encephalopathies, or prion diseases in many species. In white-tailed deer, both coding and non-coding single nucleotide polymorphisms have been identified in this gene that correlate to chronic wasting disease (CWD) susceptibility. Previous studies examined individual nucleotide or amino acid mutations; here we examine all nucleotide polymorphisms and their combined effects on CWD. A 626 bp region of PRNP was examined from 703 free-ranging white-tailed deer. Deer were sampled between 2002 and 2010 by hunter harvest or government culling in Illinois and Wisconsin. Fourteen variable nucleotide positions were identified (4 new and 10 previously reported). We identified 68 diplotypes comprised of 24 predicted haplotypes, with the most common diplotype occurring in 123 individuals. Diplotypes that were found exclusively among positive or negative animals were rare, each occurring in less than 1% of the deer studied. Only one haplotype (C, odds ratio 0.240) and 2 diplotypes (AC and BC, odds ratios of 0.161 and 0.108 respectively) has significant associations with CWD resistance. Each contains mutations (one synonymous nucleotide 555C/T and one nonsynonymous nucleotide 286G/A) at positions reported to be significantly associated with reduced CWD susceptibility. Results suggest that deer populations with higher frequencies of haplotype C or diplotypes AC and BC might have a reduced risk for CWD infection – while populations with lower frequencies may have higher risk for infection. Understanding the genetic basis of CWD has improved our ability to assess herd susceptibility and direct management efforts within CWD infected areas.

KEYWORDS: CWD, diplotype, G96S, PRNP, prion, synonymous polymorphism, haplotype 


A solid understanding of the genetics of CWD in white-tailed deer is vital to improve management of CWD on the landscape. Most TSEs are found in domestic or captive animals where management of infected individuals is feasible. For example, scrapie infected flocks can be handled through a process generally involving genetic testing, removal and destruction of infected or suspect animals, followed by decontamination of facilities and equipment.55Containment of free ranging deer in wild populations potentially infected with CWD and decontamination of the environment is not reasonably possible. The long term effects of CWD are not yet known but it is conceivable that an unmanaged infected population would be gradually extirpated as the disease progresses56,57 or at least reduced to low densities with high disease prevalence.58,59 Either outcome would have severe ecological effects (e.g., deer play a major role in affecting plant communities60 and as a prey source61,62) as well as negative economic impacts to hunting. Overall disease prevalence has remained at relatively low levels in Illinois compared to Wisconsin.11 It is important to note that at the time of sampling, CWD had been found in 6 Illinois counties and has since been detected in 14.9Complete eradication of CWD among free ranging white-tailed deer may not be possible; however, an active containment effort in Illinois appears to have prevented significant increases in prevalence.9,11,12 Further examination of PRNP haplotype and diplotype frequencies across northern Illinois and southern Wisconsin in conjunction with population structure and movement45,63,64 will be useful in identifying localities with greater or reduced susceptibility risk. Effectiveness of CWD containment efforts can be aided through genetic testing and redirecting management resources.


The role of genetics in chronic wasting disease of North American cervids 

Stacie J. Robinson, Michael D. Samuel, Katherine I. O'Rourke & Chad J. Johnson Pages 153-162 | Received 19 Oct 2011, Accepted 06 Feb 2012, Published online: 01 Apr 2012



The identification and characterization of prion strains is increasingly important for the diagnosis and biological definition of these infectious pathogens. Although well-established in scrapie and, more recently, in BSE, comparatively little is known about the possibility of prion strains in chronic wasting disease (CWD), a disease affecting free ranging and captive cervids, primarily in North America. We have identified prion protein variants in the white-tailed deer population and demonstrated that Prnp genotype affects the susceptibility/disease progression of white-tailed deer to CWD agent. The existence of cervid prion protein variants raises the likelihood of distinct CWD strains. Small rodent models are a useful means of identifying prion strains. We intracerebrally inoculated hamsters with brain homogenates and phosphotungstate concentrated preparations from CWD positive hunter-harvested (Wisconsin CWD endemic area) and experimentally infected deer of known Prnp genotypes. These transmission studies resulted in clinical presentation in primary passage of concentrated CWD prions. Subclinical infection was established with the other primary passages based on the detection of PrPCWD in the brains of hamsters and the successful disease transmission upon second passage. Second and third passage data, when compared to transmission studies using different CWD inocula (Raymond et al., 2007) indicate that the CWD agent present in the Wisconsin white-tailed deer population is different than the strain(s) present in elk, mule-deer and white-tailed deer from the western United States endemic region.



Wednesday, September 08, 2010 


NOVEMBER 16, 2017 

Chronic Wasting Disease Strikes Montana And Continues Its March On Yellowstone 



Not long ago, Game and Fish researchers broke their own rule when they bestowed a moniker on a wild wapiti mother kept in captivity. She wore ear tag No. 12 and they dubbed her “Lucky”.

Lucky was born a wild cow elk who initially survived a close brush with doom. For those studying Chronic Wasting Disease, she represents either a cryptic symbol of hope for the persistence of elk in the Greater Yellowstone Ecosystem, or, in the eyes of scientists thinking about zoonotic diseases, a frightening potential harbinger.

In 2002, 39 healthy elk calves were captured at the National Elk Refuge in Jackson Hole, Wyoming and transported across the state to a research facility at Sybille Canyon near the town of Wheatland. There, the young ungulates were placed in pens.

Over the course of a decade, every single one contracted CWD and perished—all except for Lucky. 

"Lucky" the cow elk, pictured here at the state-run Thomas Thorne/Elizabeth Williams Wildlife Research Center at Sybille, Wyoming. Lucky then, in 2015, was a CWD survivor, 13 years old and weighing 600 pounds. Photo: Wyoming Game and Fish Department

So what is the most disturbing aspect of the Wyoming study involving Lucky the elk that CWD experts find so unsettling?

What ever happened to 'LUCKY' the Wapiti cow elk thought to be immune from CWD with LL genotype?

Lucky’s wapiti cohort group contracted CWD naturally—simply by being placed in an environment where diseased animals previously had been. Researchers didn’t have to do anything to overtly expose the elk to CWD through feed or injection; they merely kept them in pens where CWD had been present and yet its disease-causing prions persisted after sickened animals were removed. 

If 38 elk out of 39 at Sybille became stricken and died, how might that rate of infection be extrapolated to wild settings? The elk calves removed from the Elk Refuge and raised at Sybille have a genetic make-up—an MM genotype— that is widespread and the most common in western Wyoming elk herds. Lucky had different genotype—LL—that exists in two percent of a normal population. Some elk also carry a third genotype (ML) that, for some reason, has a resistance characteristic that delays infection but still is 100 percent lethal.

Which leads us back to Lucky. In that study involving her at Sybille, the wild elk calves taken from the Elk Refuge were shown to have three different genetic makeups. Most had MM genotypes and are representative of about 70 percent of wild wapiti in the Elk Refuge herd. All of those died relatively quickly from CWD when exposed to environmental contamination.

Then there were elk with ML genotypes, representing about 28 percent of the herd. They survived longer before getting infected and succombing but they all died, too.

And then there was Lucky, a rarity with an LL genotype. Just two percent of elk have a genetic code like her.

Kreeger tried to put a positive spin on the results when he still worked for the agency. His is a belief in “evolutionary adaptation”, i.e. the premise that CWD infected mothers will produce offspring before they die and CWD-resistant elk will be giving birth to seed-stock to rebuild populations if they crash.

Lucky and some of the other elk cows produced offspring and Kreeger speculated it was possible that reproduction could outpace death caused by CWD. However, the model showed that over a century, hunting would need to be curtailed if not eliminated and that elk with genomes MM and ML would likely vanish. 

Can and should the persistence of some of America’s greatest elk herds, in America’s most iconic ecosystem, be pinned on the survival of Lucky? How did Lucky’s story end?

Within the last few weeks, I was in touch with Brant Schumaker, who was involved with the decade-long study of Lucky and with Dr. Mary Wood, Wyoming’s state wildlife veterinarian and the successor to Kreeger and Thorne. I asked them about Lucky: was she still alive or dead? Did she outrace the plague as an animal with hyper-rare, hopeful immunity and what is the status of her offspring? They were coy and wouldn’t tell me. They only said that she is part of a new study. I asked for an updated photograph of Lucky to use in this story. Lucky is, after all, a named animal and arguably a celebrity. My request went unanswered.

I am still waiting to hang a picture of Lucky on the wall. 

NOVEMBER 16, 2017 

Chronic Wasting Disease Strikes Montana And Continues Its March On Yellowstone 


by Todd Wilkinson

Beth Williams


What ever happened to 'LUCKY' the Wapiti cow elk thought to be immune from CWD with LL genotype MIA?

P68 Transmission of Chronic Wasting Disease (CWD) into Syrian Golden Hamsters selects novel CWD strains

Elizabeth Triscott (1), Camilo Duque Velásquez (1), Jacques van der Merwe (1), Judd M. Aiken (1) and Debbie McKenzie (1)

(1)Centre for Prions and Protein Folding Diseases, University of Alberta, Edmonton, Alberta, Canada. Chronic wasting disease (CWD) is currently increasing in prevalence and expanding its geographic range in wild and farmed cervids in North America and Europe. Given that this disease affects multiple cervid species with distinct polymorphisms, the diversification and emergence of prion strains seems likely. To this end, we are characterizing hunter-harvested CWD isolates and have identified novel CWD strains based on their biochemical properties and host range. Eleven CWDpositive hunter-harvested isolates (five from mule deer and six from white-tailed deer) were used to inoculate Syrian Golden hamsters and cervidized (Tg33; G96) mice. While all eleven isolates resulted in clinical infection of cervidized mice, transmission into Syrian Golden hamsters varied; four of the eleven isolates were negative for PrP-res at 2 years post-inoculation. Furthermore, two distinct PrPres profiles were present, by western blot analysis, in brains of hamsters inoculated with one whitetailed deer isolate (WTD-02). One glycotype resembled other hamster-passaged white-tailed deer isolates, while the other resembled elk CWD passaged in hamsters. Interestingly, analysis of the deer brain homogenates by cervid cell assay (Elk21- cells), showed that WTD-02 had spot counts between those observed for white-tailed deer and elk, suggesting that WTD-02 may be a mix of white-tailed deer and elk prions. These data suggest host range variation in CWD isolates from wild type cervids, and demonstrate the utility of Syrian Golden hamsters in differentiating strains from cervids.

P83 Diversity of Chronic Wasting Disease (CWD) strains in Canadian enzootic regions

Duque Velásquez C (1), Triscott E (1), Kim C (1), Hannaoui S (2), Bollinger T (3), Gilch S (2), Aiken J (4) McKenzie D (1)

1) Department of Biological Sciences, Centre for Prions and Protein Folding Diseases, University of Alberta, Edmonton, Alberta, Canada. 2) Department of Ecosystem and Public Health, Calgary Prion Research Unit, University of Calgary, Calgary, Alberta, Canada. 3) Department of Veterinary Pathology, Canadian Wildlife Health Cooperative, University of Saskatchewan, Saskatoon, Saskatchewan, Canada. 4) Department of Agricultural, Food and Nutritional Sciences, Centre for Prions and Protein Folding Diseases, 114 Brain and Aging Research Building, University of Alberta, Edmonton, Alberta T6G 2M8.

Chronic wasting disease (CWD) is a contagious prion disease that occurs in various species of freeranging and/or captive cervids in the United States (US), Canada, South Korea, Norway and Finland. CWD prions exist as multiple strains that produce different pathology and differ in their proclivity to infect hosts. PRNP allelic variants resulting in amino acid changes in the cellular prion protein (PrPC ) can greatly influence the susceptibility of cervids to particular prion strains. We have shown that new prion strains can emerge following transmission between cervids expressing different PRNP alleles. Emergent strains can have novel transmission properties that enable them to infect hosts considered resistant to CWD, indicating that a diverse pool of circulating cervid prion strains is a concern for wildlife, agricultural and public health. We are determining the diversity of CWD strains responsible for CWD epizootics in Canada‘s wild and captive cervids. The strain properties of field CWD isolates (including a wt/G116 white-tailed deer isolate) and a pool of three experimentally-infected M132 homozygous elk are being characterized in various animal models. Elk CWD prions produced significantly different lesion profiles upon transmission in transgenic mice compared to other CWD isolates. In addition, S96-PrPC expressing mice infected with this agent accumulated PrP-res in brain in the absence of disease signs at the time of experiment termination. The A116G isolate caused clinical disease in mice expressing S96-PrPC . The PrP-res glycotypes produced by G116+ and elk (CWD2) prions in these mice was novel. Our data indicate the existence of multiple CWD strains in wild deer and captive elk.

Prion Conference 2018 Abstract




USDA APHIS CDC Cervids: Chronic Wasting Disease Specifics Updated 2019


Chronic Wasting Disease CWD TSE Prion United States of America Update March 16, 2019

FRIDAY, MARCH 15, 2019 

Saskatchewan Chronic Wasting Disease TSE Prion 349 Cases Positive for 2018



FRIDAY, MARCH 15, 2019 

USDA APHIS SCRAPIE TSE PRION Sheep and Goat Health Update 2019

***> This is very likely to have parallels with control efforts for CWD in cervids.

Rapid recontamination of a farm building occurs after attempted prion removal

Kevin Christopher Gough, BSc (Hons), PhD1, Claire Alison Baker, BSc (Hons)2, Steve Hawkins, MIBiol3, Hugh Simmons, BVSc, MRCVS, MBA, MA3, Timm Konold, DrMedVet, PhD, MRCVS3 and Ben Charles Maddison, BSc (Hons), PhD2


The transmissible spongiform encephalopathy scrapie of sheep/goats and chronic wasting disease of cervids are associated with environmental reservoirs of infectivity. 

Preventing environmental prions acting as a source of infectivity to healthy animals is of major concern to farms that have had outbreaks of scrapie and also to the health management of wild and farmed cervids. 

Here, an efficient scrapie decontamination protocol was applied to a farm with high levels of environmental contamination with the scrapie agent. 

Post-decontamination, no prion material was detected within samples taken from the farm buildings as determined using a sensitive in vitro replication assay (sPMCA). 

A bioassay consisting of 25 newborn lambs of highly susceptible prion protein genotype VRQ/VRQ introduced into this decontaminated barn was carried out in addition to sampling and analysis of dust samples that were collected during the bioassay. 

Twenty-four of the animals examined by immunohistochemical analysis of lymphatic tissues were scrapie-positive during the bioassay, samples of dust collected within the barn were positive by month 3. 

The data illustrates the difficulty in decontaminating farm buildings from scrapie, and demonstrates the likely contribution of farm dust to the recontamination of these environments to levels that are capable of causing disease.


As in the authors' previous study,12 the decontamination of this sheep barn was not effective at removing scrapie infectivity, and despite the extra measures brought into this study (more effective chemical treatment and removal of sources of dust) the overall rates of disease transmission mirror previous results on this farm. With such apparently effective decontamination (assuming that at least some sPMCA seeding ability is coincident with infectivity), how was infectivity able to persist within the environment and where does infectivity reside? Dust samples were collected in both the bioassay barn and also a barn subject to the same decontamination regime within the same farm (but remaining unoccupied). Within both of these barns dust had accumulated for three months that was able to seed sPMCA, indicating the accumulation of scrapie-containing material that was independent of the presence of sheep that may have been incubating and possibly shedding low amounts of infectivity.

This study clearly demonstrates the difficulty in removing scrapie infectivity from the farm environment. Practical and effective prion decontamination methods are still urgently required for decontamination of scrapie infectivity from farms that have had cases of scrapie and this is particularly relevant for scrapiepositive goatherds, which currently have limited genetic resistance to scrapie within commercial breeds.24 This is very likely to have parallels with control efforts for CWD in cervids.

Acknowledgements The authors thank the APHA farm staff, Tony Duarte, Olly Roberts and Margaret Newlands for preparation of the sheep pens and animal husbandry during the study. The authors also thank the APHA pathology team for RAMALT and postmortem examination.

Funding This study was funded by DEFRA within project SE1865. 

Competing interests None declared. 

Saturday, January 5, 2019 

Rapid recontamination of a farm building occurs after attempted prion removal 




Terry S. Singeltary Sr.


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