Detection of Prions in Blood of Cervids at the Asymptomatic Stage of Chronic Wasting Disease

Carlos Kramm,Sandra Pritzkow,Tracy Nichols,Adam Lyon,Rodrigo Morales,Claudio Soto

doi:10.1038/s41598-017-17090-x

Abstract

Chronic wasting disease (CWD) is a rapidly spreading prion disorder affecting captive and free-ranging cervids. The zoonotic potential of CWD is unknown, as well as the mechanism for its highly efficient transmission. A top priority to minimize further spreading of this disease and its potential impact on environmental prion contamination is the development of a non-invasive, sensitive, and specific test for ante-mortem detection of infected animals. Here, we optimized the protein misfolding cyclic amplification (PMCA) assay for highly efficient detection of CWD prions in blood samples. Studies were done using a blind panel of 98 field-collected samples of whole blood from codon 96 glycine/glycine, captive white-tailed deer that were analyzed for prion infection post-mortem by immunohistochemistry (IHC). The results showed a sensitivity of 100% in animals with very poor body condition that were IHC-positive in both brain and lymph nodes, 96% in asymptomatic deer IHC-positive in brain and lymph nodes and 53% in animals at early stages of infection that were IHC-positive only in lymph nodes. The overall mean diagnostic sensitivity was 79.3% with 100% specificity. These findings show that PMCA might be useful as a blood test for routine, live animal diagnosis of CWD.

Highlights

Prion diseases are fatal infectious diseases affecting humans and various species of mammals, including sheep, goats, mink, cervids, cattle and felines
Low sensitivity was observed in animals at the early stage of infection when the obex was negative for PrPSc, and positive staining was only detected in MRPLN25
The exact limit of detection depends on the amount of PrPSc present in the particular animal and on the brain region utilized, which usually ranges between 10−8 and 10−11

Summary

Introduction

Prion diseases are fatal infectious diseases affecting humans and various species of mammals, including sheep, goats, mink, cervids, cattle and felines. Various reports have shown that infectious prions bind tightly to soil and remain infectious after years in this material[17,18,19], suggesting that environmental contamination may play an important role in CWD spreading This conclusion is further supported by recent findings showing that prions bind to a variety of components of the environment, including plants, and remain infectious by oral administration[20]. An important goal to minimize the further spreading of CWD is the development of an assay for highly sensitive, non-invasive, and inexpensive ante-mortem detection of prions in infected, but not clinically sick animals. CWD is definitively diagnosed by post-mortem examinations of brain, brain stem and lymphoid tissues[3] For this purpose, brain, brain stem at the obex, and medial retropharyngeal lymph nodes (MRPLN) samples are collected post-mortem, and analyzed by immunohistochemistry (IHC), ELISA, and/or western blot (WB) to detect PrPSc (ref.[22]). The rectal biopsy is relatively simple, it is an invasive, and expensive procedure

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