Chronic Wasting Disease: The American experience

Authors: Silva, Christopher - Chris

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 10/3/2018
Publication Date: 10/22/2018
Citation: Silva, C.J. 2018. Chronic Wasting Disease: The American experience. Meeting Abstract. [abstract]. University of Santiago de Compostela, Spain.

Interpretive Summary:

Technical Abstract: Unlike most other prion diseases, CWD is readily transmitted from infected animals to uninfected animals (horizontal) and from prion-contaminated environments to uninfected animals. It is found in both farmed and wild cervids, including white-tailed deer, black-tailed deer, mule deer, elk (American), moose (American and European), red deer (European), and reindeer (European). Asymptomatic animals shed prions in urine, feces, and saliva, thereby contaminating an environment with prions, which may be ingested to infect other animals. Since prions are very stable, they may remain infectious in a prion-contaminated environment for many years. CWD is the only known prion disease naturally spread among wild animals in their natural environment. Since its first description in 1967, 25 US states and two Canadian provinces have diagnosed captive or wild CWD-infected cervid populations. It was unintentionally introduced to South Korea through the importation of infected, but asymptomatic, elk from Canada. In 2016, CWD was identified in reindeer, moose and red deer from three geographically distinct areas of Norway. A deceased CWD-infected moose was found near Kuhmo, Finland in 2018. Finland built a large population (~100,000) of North American white-tailed deer from animals imported from the US state of Minnesota in 1934 (5) and 1949 (4). Between 2006 and 2009, the EU tested more than 13,000 cervid samples from member states for CWD, including 611 hunter harvested Finnish white-tailed deer, and found no positives. It remains an open question as to the origin of the geographically distinct Scandinavian cases. Despite the singular name, chronic wasting disease is caused by at least three different prion strains of CWD; at least two in North America and at least one in Norway. Cervid prion strain propagation is governed by a strong preference for a single PrPC polymorphism. Mass spectrometry can be used to determine the proportion of each PrP polymorphism present in prions isolated from CWD-infected heterozygous animals. It has been used to detect covalent modifications of PrPSc, which allows researchers to discriminate among prion strains that are structurally indistinguishable by protease digestion. Mass spectrometry can provide an important insight into the incidence of which prion strains propagate in wild cervid populations. In North America, the measures implemented to control the spread of CWD have not been successful in arresting the spread of CWD. The Norwegian Environment Agency depopulated the entire reindeer population (1407; 17 CWD positive) of Nordfjella zone 1 where the first Norwegian CWD case was discovered. It remains to be seen if the Norwegian approach to CWD eradication will be more successful than the North American attempts to control the disease. The information gleaned from mass spectrometry may provide a guide to develop a breeding program to reduce the incidence of CWD in wild cervid populations.