Sensitive detection of chronic wasting disease prions recovered from environmentally relevant surfaces

Prion forensics: a multidisciplinary approach to investigate CWD at an illegal deer carcass disposal site

Infectious prions are resistant to degradation and remain infectious in the environment for several years. Chronic wasting disease (CWD) has been detected in cervids inhabiting North America, the Nordic countries, and South Korea. CWD-prion spread is partially attributed to carcass transport and disposal. We employed a forensic approach to investigate an illegal carcass dump site connected with a CWD-positive herd. We integrated anatomic, genetic, and prion amplification methods to discover CWD-positive remains from six white-tailed deer (Odocoileus virginianus) and, using microsatellite markers, confirmed a portion originated from the CWD-infected herd. This approach provides a foundation for future studies of carcass prion transmission risk.

Detection of Chronic Wasting Disease Prions in Prairie Soils from Endemic Regions

Chronic wasting disease (CWD) is a contagious prion disease that affects cervids in North America, Northern Europe, and South Korea. CWD is spread through direct and indirect horizontal transmission, with both clinical and preclinical animals shedding CWD prions in saliva, urine, and feces. CWD particles can persist in the environment for years, and soils may pose a risk for transmission to susceptible animals. Our study presents a sensitive method for detecting prions in the environmental samples of prairie soils. Soils were collected from CWD-endemic regions with high (Saskatchewan, Canada) and low (North Dakota, USA) CWD prevalence. Heat extraction with SDS-buffer, a serial protein misfolding cyclic amplification assay coupled with a real-time quaking-induced conversion assay was used to detect the presence of CWD prions in soils. In the prairie area of South Saskatchewan where the CWD prevalence rate in male mule deer is greater than 70%, 75% of the soil samples tested were positive, while in the low-prevalence prairie region of North Dakota (11% prevalence in male mule deer), none of the soils contained prion seeding activity. Soil-bound CWD prion detection has the potential to improve our understanding of the environmental spread of CWD, benefiting both surveillance and mitigation approaches.

Where we stand on chronic wasting disease: A systematic literature review of its prevalence patterns, impacts, and management interventions

With high fatality and no cure, chronic wasting disease (CWD) has infected cervids in multiple regions, including the United States, Canada, Europe, and South Korea. Despite the rapid growth of literature on CWD, the full scope of its ecological, social, and economic impacts and the most effective and socially acceptable management strategies to mitigate the disease is unclear. Of 3008 initially identified published peer-reviewed papers, 134 were included in a final systematic literature review to synthesize the current knowledge on CWD transmission patterns, impacts, and the effectiveness of management interventions. The number of publications on CWD has increased steadily since 2000 with an average of six papers per year. Most papers were related to CWD prevalence (39 %), human behavior (33 %), CWD impacts (31 %), and management interventions (16 %). Environmental factors such as soil, water, and plants were identified as the most common transmission medium, with a higher prevalence rate among adult male cervids than females. Hunters showed a higher risk perception and were more likely to change hunting behavior due to CWD detection than non-hunters. Ecological impacts included the decreased survival rate accompanied by lower population growth, eventually leading to the decline of cervid populations. Culling was found to be an effective and widely implemented management strategy across countries, although it often was associated with public resistance. Despite potentially high negative economic impacts anticipated due to CWD, studies on this subject were limited. Sustained surveillance, ongoing research, and engagement of affected stakeholders will be essential for future disease control and management.

Sensitive detection of pathological seeds of α-synuclein, tau and prion protein on solid surfaces

Prions or prion-like aggregates such as those composed of PrP, α-synuclein, and tau are key features of proteinopathies such as prion, Parkinson's and Alzheimer's diseases, respectively. Their presence on solid surfaces may be biohazardous under some circumstances. PrP prions bound to solids are detectable by ultrasensitive real-time quaking-induced conversion (RT-QuIC) assays if the solids can be immersed in assay wells or the prions transferred to pads. Here we show that prion-like seeds can remain detectable on steel wires for at least a year, or even after enzymatic cleaning and sterilization. We also show that contamination of larger objects with pathological seeds of α-synuclein, tau, and PrP can be detected by simply assaying a sampling medium that has been transiently applied to the surface. Human α-synuclein seeds in dementia with Lewy bodies brain tissue were detected by α-synuclein RT-QuIC after drying of tissue dilutions with concentrations as low as 10-6 onto stainless steel. Tau RT-QuIC detected tau seeding activity on steel exposed to Alzheimer's disease brain tissue diluted as much as a billion fold. Prion RT-QuIC assays detected seeding activity on plates exposed to brain dilutions as extreme as 10-5-10-8 from prion-affected humans, sheep, cattle and cervids. Sampling medium collected from surgical instruments used in necropsies of sporadic Creutzfeldt-Jakob disease-infected transgenic mice was positive down to 10-6 dilution. Sensitivity for prion detection was not sacrificed by omitting the recombinant PrP substrate from the sampling medium during its application to a surface and subsequent storage as long as the substrate was added prior to performing the assay reaction. Our findings demonstrate practical prototypic surface RT-QuIC protocols for the highly sensitive detection of pathologic seeds of α-synuclein, tau, and PrP on solid objects.

Optimization of RT-QuIC Assay Duration for Screening Chronic Wasting Disease in White-Tailed Deer

Real-time quaking-induced conversion (RT-QuIC) assays have become a common tool to detect chronic wasting disease (CWD) and are very sensitive provided the assay duration is sufficient. However, a prolonged assay duration may lead to non-specific signal amplification. The wide range of pre-defined assay durations in current RT-QuIC applications presents a need for methods to optimize the RT-QuIC assay. In this study, receiver operating characteristic (ROC) analysis was applied to optimize the assay duration for CWD screening in obex and retropharyngeal lymph node (RLN) tissue specimens. Two different fluorescence thresholds were used: a fixed threshold based on background fluorescence (Tstdev) and a max-point ratio (maximum/background fluorescence) threshold (TMPR) to determine CWD positivity. The optimal assay duration was 33 h for obex and 30 h for RLN based on Tstdev, and 29 h for obex and 32 h for RLN based on TMPR. The optimized assay durations were then evaluated for screening CWD in white-tailed deer from an affected farm. At a replicate level, using the optimized assay durations with TStdev and TMPR, the level of agreement with enzyme-linked immunosorbent assay (ELISA) was significantly higher (p < 0.05) than that when using a 40 h assay duration. These findings demonstrate that the optimization of assay duration via a ROC analysis can improve RT-QuIC assays for screening CWD in white-tailed deer.

The advances in the early and accurate diagnosis of Creutzfeldt-Jakob disease and other prion diseases: where are we today?

INTRODUCTION

Before the introduction of MRI diffusion-weighted images (DWI), the diagnosis of Creutzfeldt-Jakob disease (CJD) relied upon nonspecific findings including clinical symptoms, EEG abnormalities, and elevated levels of cerebrospinal fluid 14-3-3 protein. Subsequently, the use of DWI has improved diagnostic accuracy, but it sometimes remains difficult to differentiate CJD from encephalitis, epilepsy, and other dementing disorders. The revised diagnostic criteria include real-time quaking-induced conversion (RT-QuIC), detecting small amounts of CJD-specific prion protein, and clinically sensitive DWI. Combining these techniques has further improved diagnostic accuracy, enabling earlier diagnosis.

AREAS COVERED

Herein, the authors review the recent advances in diagnostic methods and revised diagnostic criteria for sporadic CJD. They also discuss other prion diseases, such as variant CJD and chronic wasting disease, where the emergence of new types is a concern.

EXPERT OPINION

Despite improvements in diagnostic methods and criteria, some subtypes of prion disease are still difficult to diagnose, and even the diagnosis using the most innovative RT-QuIC test remains a challenge in terms of accuracy and standardization. However, these revised criteria can be adapted to the emergence of new types of prion diseases. It is essential to continue careful surveillance and update information on the latest prion disease phenotypes.

Nanoparticle-Enhanced RT-QuIC (Nano-QuIC) Diagnostic Assay for Misfolded Proteins

Misfolded proteins associated with various neurodegenerative diseases often accumulate in tissues or circulate in biological fluids years before the clinical onset, thus representing ideal diagnostic targets. Real-time quaking-induced conversion (RT-QuIC), a protein-based seeded-amplification assay, holds great potential for early disease detection, yet challenges remain for routine diagnostic application. Chronic Wasting Disease (CWD), associated with misfolded prion proteins of cervids, serves as an ideal model for evaluating new RT-QuIC methodologies. In this study, we investigate the previously untested hypothesis that incorporating nanoparticles into RT-QuIC assays can enhance their speed and sensitivity when applied to biological samples. We show that adding 50 nm silica nanoparticles to RT-QuIC experiments (termed Nano-QuIC) for CWD diagnostics greatly improves the performance by reducing detection times 2.5-fold and increasing sensitivity 10-fold by overcoming the effect of inhibitors in complex tissue samples. Crucially, no false positives were observed with these 50 nm silica nanoparticles, demonstrating the enhanced reliability and potential for diagnostic application of Nano-QuIC in detecting misfolded proteins.

Standardization of Data Analysis for RT-QuIC-Based Detection of Chronic Wasting Disease

Chronic wasting disease (CWD) is a disease affecting cervids and is caused by prions accumulating as pathogenic fibrils in lymphoid tissue and the central nervous system. Approaches for detecting CWD prions historically relied on antibody-based assays. However, recent advancements in protein amplification technology provided the foundation for a new class of CWD diagnostic tools. In particular, real-time quaking-induced conversion (RT-QuIC) has rapidly become a feasible option for CWD diagnosis. Despite its increased usage for CWD-focused research, there lacks a consensus regarding the interpretation of RT-QuIC data for diagnostic purposes. It is imperative then to identify a standardized and replicable method for determining CWD status from RT-QuIC data. Here, we assessed variables that could impact RT-QuIC results and explored the use of maxpoint ratios (maximumRFU/backgroundRFU) to improve the consistency of RT-QuIC analysis. We examined a variety of statistical analyses to retrospectively analyze CWD status based on RT-QuIC and ELISA results from 668 white-tailed deer lymph nodes. Our results revealed an MPR threshold of 2.0 for determining the rate of amyloid formation, and MPR analysis showed excellent agreement with independent ELISA results. These findings suggest that the use of MPR is a statistically viable option for normalizing between RT-QuIC experiments and defining CWD status.

Second passage experiments of chronic wasting disease in transgenic mice overexpressing human prion protein

Chronic wasting disease (CWD) is a prion disease of cervids including deer, elk, reindeer, and moose. Human consumption of cervids is common, therefore assessing the risk potential of CWD transmission to humans is critical. In a previous study, we tested CWD transmission via intracerebral inoculation into transgenic mice (tg66 and tgRM) that over-expressed human prion protein. Mice screened by traditional prion detection assays were negative. However, in a group of 88 mice screened by the ultrasensitive RT-QuIC assay, we identified 4 tg66 mice that produced inconsistent positive RT-QuIC reactions. These data could be false positive reactions, residual input inoculum or indicative of subclinical infections suggestive of cross species transmission of CWD to humans. Additional experiments were required to understand the nature of the prion seeding activity in this model. In this manuscript, second passage experiments using brains from mice with weak prion seeding activity showed they were not infectious to additional recipient tg66 mice. Clearance experiments showed that input CWD prion seeding activity was eliminated by 180 days in tg66 mice and PrPKO mice, which are unable to replicate prion protein, indicating that the weak positive levels of seeding activity detected at later time points was not likely residual inoculum. The failure of CWD prions to cause disease in tg66 after two sequential passages suggested that a strong species barrier prevented CWD infection of mice expressing human prion protein.