Chronic wasting disease (CWD) prion detection in blood from pre-symptomatic white-tailed deer harboring PRNP polymorphic variants

Carlos Kramm,Paulina Soto,Tracy A Nichols,Rodrigo Morales

doi:10.1038/s41598-020-75681-7

Abstract

Chronic wasting disease (CWD) is a prionopathy affecting wild and farmed cervids. This disease is endemic in North America and has been recently identified in Europe. Ante-mortem CWD tests of pre-clinical cervids may be an important tool in helping control the spread of this disease. Unfortunately, current CWD diagnostic methods are not suitable for non-tissue type samples. We reported that CWD prions can be detected in blood of pre-clinical CWD-infected white-tailed deer (WTD) with high sensitivity and specificity using the Protein Misfolding Cyclic Amplification (PMCA) assay. However, that report only included animals homozygous for codon 96G, the most common polymorphic version of the prion protein within this animal species. Here, we report CWD prion detection using blood of naturally infected WTD coding one or two copies of the PrP-96S polymorphic variant. Our results, from a blinded screening, show 100% specificity and ~ 58% sensitivity for animals harboring one 96S codon, regardless of their stage within the pre-clinical phase. Detection efficiency for PrP-96S homozygous animals was substantially lower, suggesting that this allele affect peripheral prion replication/tropism. These results provide additional information on the influence of codon 96 polymorphisms and the ability of PMCA to detect CWD in the blood of pre-clinical WTD.

Highlights

Chronic wasting disease (CWD) is the only prion disease found in free-ranging a nimals[1,2,3]
We first evaluated the efficiency of our previously published cervid Protein Misfolding Cyclic Amplification (PMCA) system[12,23] that utilized substrate homozygous for Glycine at codon 96 in the PRNP gene. This experiment was done as this substrate is not homologous to the PRNP polymorphisms of the white-tailed deer (WTD) samples used in this study
The development of in vitro prion conversion assays ( PMCA10 and RT-QuIC11) provides hope towards the development of ante-mortem CWD tests for accessible samples such as blood, feces, urine and saliva[19,27,28]

Summary

Introduction

Chronic wasting disease (CWD) is the only prion disease found in free-ranging a nimals[1,2,3]. The specificity of our assay was 100% These results suggested that PMCA can identify a fraction of CWD positive animals. Animals carrying PrP 96S allele(s) have been associated with lower prion shedding, suggesting lower accumulation of PrPSc in peripheral tissues compared to their wild-type counterpart[19,20]. This variable could have important implications for pre-clinical diagnosis when using peripheral tissue biopsies, bodily fluids and excreta. We evaluated the diagnostic efficiency of the PMCA technology using blood specimens collected from farmed/non-symptomatic WTD carrying one or two PrP 96S allele(s)

Methods

Results

Conclusion