Evolution of Diagnostic Tests for Chronic Wasting Disease, a Naturally Occurring Prion Disease of Cervids

Abstract

Since chronic wasting disease (CWD) was first identified nearly 50 years ago in a captive mule deer herd in the Rocky Mountains of the United States, it has slowly spread across North America through the natural and anthropogenic movement of cervids and their carcasses. As the endemic areas have expanded, so has the need for rapid, sensitive, and cost effective diagnostic tests—especially those which take advantage of samples collected antemortem. Over the past two decades, strategies have evolved from the recognition of microscopic spongiform pathology and associated immunohistochemical staining of the misfolded prion protein to enzyme-linked immunoassays capable of detecting the abnormal prion conformer in postmortem samples. In a history that parallels the diagnosis of more conventional infectious agents, both qualitative and real-time amplification assays have recently been developed to detect minute quantities of misfolded prions in a range of biological and environmental samples. With these more sensitive and semi-quantitative approaches has come a greater understanding of the pathogenesis and epidemiology of this disease in the native host. Because the molecular pathogenesis of prion protein misfolding is broadly analogous to the misfolding of other pathogenic proteins, including Aβ and α-synuclein, efforts are currently underway to apply these in vitro amplification techniques towards the diagnosis of Alzheimer’s disease, Parkinson’s disease, and other proteinopathies. Chronic wasting disease—once a rare disease of Colorado mule deer—now represents one of the most prevalent prion diseases, and should serve as a model for the continued development and implementation of novel diagnostic strategies for protein misfolding disorders in the natural host.

The ecology of chronic wasting disease in wildlife

“…On the contrary, RT-QuIC does not result in infectious material and does not reproduce strain features ; (C) spinal cord (Baeten et al, 2007); (D) fat (Race et al, 2009); (E) urine, kidneys, bladder ; (F) lymphoid tissue in the intestines including intestinal and rectoanal mucosa (Haley et al, 2011); (G) faeces (Tamgüney et al, 2009); (H) muscle (Angers et al, 2009); (I) spleen (Sigurdson et al, 2002); (J) peripheral nerves (Seelig et al, 2011); (K) blood (Mathiason et al, 2006); (L) medial retropharyngeal lymph nodes (Sigurdson et al, 2002); (M) tonsils (Sigurdson et al, 2002); (N) saliva (Mathiason et al, 2006); (O) nasal tissues (Haley et al, 2016); (P) antler velvet (Angers et al, 2009). Asterisks indicate whether sensitivity is >50% based on Haley & Richt (2017).…”

Amplification Techniques for the Detection of Misfolded Prion Proteins in Experimental and Clinical Samples

“…The PMCA assay (Basic Protocol 1) and the RT‐QuIC assay (Basic Protocol 2) were developed based on our current understanding of the formation of prion amyloid in vivo . Although the two assays overlap conceptually, much like PCR and real‐time PCR, there are important distinctions between PMCA and RT‐QuIC that may favor one or the other in specific applications (Atarashi et al., 2008; Haley & Richt, 2017; Saborio et al., 2001). Both assays ultimately depend on coerced conversion of normal prion protein substrate into an abnormally folded isoform in vitro .…”

“…Those wishing to pursue in vivo experiments in parallel with their amplification studies may also find advantages in having transgenic mouse models available for study. However, the volume of substrate necessary for large‐scale, high‐throughput testing is an important ethical consideration, making PMCA less desirable for diagnostic applications (Haley & Richt, 2017).…”

Differential gene expression in chronic wasting disease‐positive white‐tailed deer (Odocoileus virginianus)

“…Prevalence rates as high as 50% in free‐ranging herds and 90% in captive herds have been documented (Haley & Hoover, ), though prions are difficult to diagnose in live cervids (Cheng et al, ) due to the logistical challenges of collecting diagnostic samples. Tonsil, lymphoid, and third eyelid tissues may be biopsied to confirm CWD infection in live animals; however, these tissue biopsies would require sedation or anesthesia in accordance with Institutional Animal Care and Use Committee (IACUC) protocols, and are impractical in free‐ranging herds (Haley & Richt, ). Clinical signs may help in visual diagnoses of positive animals, but are only apparent in final stages of disease progression (i.e., months to years after initial infection; Gilch et al, ; Williams, ), and may be the result of other chronic disease processes.…”

“…Prevalence rates as high as 50% in free-ranging herds and 90% in captive herds have been documented (Haley & Hoover, 2015), though prions are difficult to diagnose in live cervids (Cheng et al, 2016) due to the logistical challenges of collecting diagnostic samples. Tonsil, lymphoid, and third eyelid tissues may be biopsied to confirm CWD infection in live animals; however, these tissue biopsies would require sedation or anesthesia in accordance with Institutional Animal Care and Use Committee (IACUC) protocols, and are impractical in free-ranging herds (Haley & Richt, 2017).…”