Rapid recontamination of a farm building occurs after attempted prion removal

Prion Seeding Activity in Plant Tissues Detected by RT-QuIC

Prion diseases such as scrapie, bovine spongiform encephalopathy (BSE), and chronic wasting disease (CWD) affect domesticated and wild herbivorous mammals. Animals afflicted with CWD, the transmissible spongiform encephalopathy of cervids (deer, elk, and moose), shed prions into the environment, where they may persist and remain infectious for years. These environmental prions may remain in soil, be transported in surface waters, or assimilated into plants. Environmental sampling is an emerging area of TSE research and can provide more information about prion fate and transport once shed by infected animals. In this study, we have developed the first published method for the extraction and detection of prions in plant tissue using the real-time quaking-induced conversion (RT-QuIC) assay. Incubation with a zwitterionic surfactant followed by precipitation with sodium phosphotungstate concentrates the prions within samples and allows for sensitive detection of prion seeding activity. Using this protocol, we demonstrate that prions can be detected within plant tissues and on plant surfaces using the RT-QuIC assay.

Assessing Different Chronic Wasting Disease Training Aids for Use with Detection Dogs

Chronic wasting disease (CWD) is a highly infectious, fatal prion disease that affects cervid species. One promising method for CWD surveillance is the use of detection dog-handler teams wherein dogs are trained on the volatile organic compound signature of CWD fecal matter. However, using fecal matter from CWD-positive deer poses a biohazard risk; CWD prions can bind to soil particles and remain infectious in contaminated areas for extended periods of time, and it is very difficult to decontaminate the affected areas. One solution is to use noninfectious training aids that can replicate the odor of fecal matter from CWD-positive and CWD-negative deer and are safe to use in the environment. Trained CWD detection dogs' sensitivity and specificity for different training aid materials (cotton, GetXent tubes, and polydimethylsiloxane, or PDMS) incubated with fecal matter from CWD-positive and CWD-negative deer at two different temperatures (21 °C and 37 °C) for three different lengths of time (6 h, 24 h, and 48 h) were evaluated. Cotton incubated at 21 °C for 24 h was identified as the best aid for CWD based on the dogs' performance and practical needs for training aid creation. Implications for CWD detection training and for training aid selection in general are discussed.

Combinatorial treatment of brain samples from sheep with scrapie using sodium percarbonate, sodium dodecyl sulfate, and proteinase K increases survival time in inoculated susceptible sheep

The agent of scrapie is resistant to most chemical and physical methods of inactivation. Prions bind to soils, metals, and various materials and persist in the environment confounding the control of prion diseases. Most methods of prion inactivation require severe conditions such as prolong exposure to sodium hypochlorite or autoclaving, which may not be suitable for field conditions. We evaluated the efficacy of a combinatorial approach to inactivation of US scrapie strain x124 under the mild conditions of treating scrapie-affected brain homogenate with sodium percarbonate (SPC), sodium dodecyl sulfate (SDS), or in combination followed by proteinase K (PK) digestion at room temperature. Western blot analysis of treated brain homogenate demonstrates partial reduction in PrP^Sc immunoreactivity. Genetically susceptible VRQ/ARQ Suffolk sheep were oronasally inoculated with 1 g of SPC (n = 1), SDS (n = 2), SDS + PK (n = 2), and SPC + SDS + PK (n = 4) treated brain homogenate. Sheep were assessed daily for clinical signs, euthanized at the development of clinical disease, and tissues were assessed for accumulation of PrP^Sc. Scrapie status in all sheep was determined by western blot, enzyme immunoassay, and immunohistochemistry. Mean incubation periods (IPs) for SPC (11.9 months, 0% survival), SDS (12.6 months, 0% survival), SDS + PK (14.0 months, 0% survival), and SPC + SDS + PK (12.5 months, 25% survival) were increased compared to positive control sheep (n = 2, 10.7 months, 0% survival) by 1.2, 1.9, 3.3, and 1.8 months, respectively. Treatment did not influence PrP^Sc accumulation and distribution at the clinical stage of disease. Differences in mean IPs and survival indicates partial but not complete reduction in scrapie infectivity.

A review of cleaning and disinfection guidelines and recommendations following an outbreak of classical scrapie

Classical scrapie is a prion disease of small ruminants, the infectious agent of which has been shown to be extremely persistent in the environment. Cleaning and disinfection (C&D) after a scrapie outbreak is currently recommended by many governments' veterinary advisors and implemented in most farms affected. Yet, the effectiveness of these procedures remains unclear. The aim of this study was to review existing literature and guidelines regarding farm C&D protocols following classical scrapie outbreaks and assess their effectiveness and the challenges that translation of policy and legislative requirements present at a practical level. A review of the literature was conducted to identify the on-farm C&D protocols used following outbreaks of scrapie, assess those materials with high risk for persistence of the scrapie agent on farms, and review the existing evidence of the effectiveness of recommended C&D protocols. An expert workshop was also organised in Great Britain (GB) to assess: the decision-making process used when implementing C&D protocols on GB farms, the experts' perceptions on the effectiveness of these protocols and changes needed, and their views on potential recommendations for policy and research. Outputs of the literature review revealed that the current recommended protocol for C&D [1 h treatment with sodium hypochlorite containing 20,000 ppm free chlorine or 2 M sodium hydroxide (NaOH)] is based on laboratory experiments. Only four field farm experiments have been conducted, indicating a lack of data on effectiveness of C&D protocols on farms by the re-occurrence of scrapie infection post re-stocking. Recommendations related to the control of outdoor environment, which are difficult and expensive to implement, vary between countries. The expert workshop concluded that there are no practical, cost-effective C&D alternatives to be considered at this time, with control therefore based on C&D only in combination with additional time restrictions on re-stocking and replacement with non-susceptible livestock or more genetically resistant types, where available. Participants agreed that C&D should still be completed on scrapie affected farms, as it is considered to be "good disease practice" and likely to reduce the levels of the prion protein. Participants felt that any additional protocols developed should not be "too prescriptive" (should not be written down in specific policies) because of significant variation in farm types, farm equipment and installations. Under this scenario, control of classical scrapie on farms should be designed with a level of C&D in combination with re-stocking temporal ban and replacement with livestock of limited susceptibility.

Chemical Inactivation of Prions Is Altered by Binding to the Soil Mineral Montmorillonite

Environmental routes of transmission contribute to the spread of the prion diseases chronic wasting disease of deer and elk and scrapie of sheep and goats. Prions can persist in soils and other environmental matrices and remain infectious for years. Prions bind avidly to the common soil mineral montmorillonite, and such binding can dramatically increase oral disease transmission. Decontamination of soil in captive facilities and natural habitats requires inactivation agents that are effective when prions are bound to soil microparticles. Here, we investigate the inactivation of free and montmorillonite-bound prions with sodium hydroxide, acidic pH, Environ LpH, and sodium hypochlorite. Immunoblotting and bioassays confirm that sodium hydroxide and sodium hypochlorite are effective for prion deactivation, although montmorillonite appears to reduce the efficacy of hypochlorite. Acidic conditions slightly reduce prion infectivity, and the acidic phenolic disinfectant Environ LpH produces slight reductions in infectivity and immunoreactivity. The extent to which the association with montmorillonite protects prions from chemical inactivation appears influenced by the effect of chemical agents on the clay structure and surface pH. When clay morphology remains relatively unaltered, as when exposed to hypochlorite, montmorillonite-bound prions appear to be protected from inactivation. In contrast, when the clay structure is substantially transformed, as when exposed to high concentrations of sodium hydroxide, the attachment to montmorillonite does not slow degradation. A reduction in surface pH appears to cause slight disruptions in clay structure, which enhances degradation under these conditions. We expect our findings will aid the development of remediation approaches for successful decontamination of prion-contaminated sites.

Classical Scrapie Did Not Re-occur in Goats After Cleaning and Disinfection of the Farm Premises

After an outbreak of classical scrapie in a dairy goat herd with over 1,800 goats, all goats in the herd were culled in 2008, cleaning and disinfection of the premises was implemented, and restocking with goats took place ~4 months after depopulation. Ten years later the new herd population is over 3,000 goats. This study was carried out to determine whether the measures were effective to prevent re-occurrence of scrapie to the 1% prevalence level seen when scrapie was first detected on this farm. A total of 280 goats with a minimum age of 18 months, which were predominantly at the end of their productive life, were euthanized, and brain and retropharyngeal lymph node examined by immunohistochemistry for disease-associated prion protein. Genotyping was done in all euthanized goats and live male goats used or intended for breeding to determine prion protein gene polymorphisms associated with resistance to classical scrapie. None of the goats presented with disease-associated prion protein in the examined tissues, and 34 (12.2%) carried the K₂₂₂ allele associated with resistance. This allele was also found in four breeding male goats. The study results suggested that classical scrapie was not re-introduced on this goat farm through mass restocking or inadequate cleaning and disinfection procedures. Further scrapie surveillance of goats on this farm is desirable to confirm absence of disease. Breeding with male goats carrying the K₂₂₂ allele should be encouraged to increase the scrapie-resistant population.