Reindeer CWD prion ecology: Risk of dissemination by sheep

In this project, we are going to investigate if reindeer chronic wasting disease (CWD) is transmissible to sheep and elucidate which role sheep that graze in Nordfjella may play in further spread of the disease.

prosjekt

About/Aims

Background

Chronic wasting disease (CWD) is a highly infectious prion disease in cervids caused by a misfolded form of the prion protein. In April 2016, CWD was diagnosed in a Norwegian wild reindeer belonging to the Nordfjella mountain area. This was the first case in Europe, and furthermore in a new species. To prevent further spread of the disease, the reindeer population in this area was culled in 2017 and 2018. Of about 2000 reindeer, 19 were diagnosed with CWD. Prions are very persistent and can reside in the environment for a long time. Every summer this region hosts about 70 000 grazing sheep, which are potentially exposed to CWD prions. Today there is no evidence of natural spread of CWD to distant species as sheep. However, a thorough study of the transmission potential to sheep is warranted to gain in depth knowledge about the disease.

Objectives

Our primary objective is to investigate if reindeer CWD is transmissible to sheep, and to elucidate which role sheep that graze in Nordfjella may play in further spread of the disease. In order to address this we want to: 1, investigate to what extent exposed sheep can passively transport CWD prions through the gut, or if they can become infected themselves and have the potential to actively transmit the disease as silent carriers; 2, investigate the CWD prion ecology; the environmental contamination and the exposure for sheep; and 3, study transmission properties and agent characteristics of the Norwegian CWD isolate.

Knowledge about the potential exposure for CWD and risk of transmission to sheep is essential for the management of pasture resources where reindeer (both wild and semi-domesticated) and sheep share pastures, and further important for critical animal health management, mitigation decisions and information to the public.

More about the project

Detection of prions

An important part of this project is to be able to detect prions with a high sensitivity and specificity. In animals with contagious prion disease such as CWD or scrapie, prions accumulate in both the brain and peripheral tissues. In addition, prions are found in circulating blood and can be shed into feces, urine, saliva or amniotic fluid. We will use a combination of traditional methods for prions detection, such as immunohistochemistry, western blot and enzyme immunoassay in addition to the more recently developed real-time quaking-induced conversion (RT-QuIC) and protein misfolding cyclic amplification (PMCA). Picture below shows immunolabeling of prions (red color) in a lymph node from a sheep with scrapie.