Unless comprehensive steps are taken to tackle Chronic Wasting Disease (CWD), it will continue to spread within the Norwegian cervid population. The disease will not disappear by itself. This is the main conclusion of a new risk assessment report published by the Norwegian Scientific Committee for food safety (VKM).
VKM completed the risk assessment at the request of the Norwegian Environment Agency and the Norwegian Food Safety Authority. The objective was to highlight the various risk factors that contribute to disease transfer and appropriate management measures based on those factors.
Chronic Wasting Disease
CWD is a prion disease that affects cervids. Cervid species in Norway include roe deer, reindeer, moose and red deer. Prion diseases affect the nervous system and are always fatal.
In April 2016, a reindeer in the Nordfjella wild-reindeer area between Hemsedal and Lærdal was diagnosed with CWD. This was the first time CWD had been diagnosed outside North America and South Korea and the first case of natural CWD in reindeer. Since then, two moose in Selbu and two more reindeer in Nordfjella have been diagnosed with CWD.
The clinical profile of the disease agent found in the reindeer is very similar to that of the contagious CWD agent found in North America. It is therefore probable that the disease outbreak in Nordfjella will have similar characteristics to outbreaks observed there.
As discovered in the USA and Canada, CWD is highly contagious. It is directly transferable between animals or indirectly from the environment, for example via infected soil and plants. Prions may survive in the environment and remain contagious for many years.
There is currently no scientific evidence that CWD can be transferred to domestic animals or humans, be that via direct contact with cervids, cervid meat, other cervid products, or via the environment.
- The risk of disease transfer to humans caused by eating meat infected with CWD seems to be very low, says Bjørnar Ytrehus, a member of the project group. VKM therefore continues to support the conclusion made in phase I of the CWD risk assessment.
Preliminary analysis indicates that the CWD agent found in the two moose is very different to that found in the Norwegian reindeer and the North American cervids.
The disease agent bears resemblance to what known as a less contagious “atypical prion-disease” found in domestic animals. Knowledge about this disease agent is poor thus VKM is not able to conclude on how this disease agent may transfer between cervids.
- Furthermore, we are not able to conclude on whether it is more or less safe to eat meat from cervids infected with this type of CWD, compared to the CWD variant found in animals in North America, says Ytrehus.
Risk reducing measures
Prions may cause disease and stay contagious in the environment for many years, making eradication of the disease extremely difficult once it has been allowed to develop and contaminate the environment.
- Effective measures must be implemented as soon as possible if the goal is to eradicate CWD from Norway, says Ytrehus.
The efficacy of a particular measure will vary dependent on a range of factors. For confineable populations, such as the wild reindeer population in Nordfjella, VKM argues that effective measures could be culling the host population and fallowing the area for a minimum of 5 years.
- If one is quick, thorough and lucky and if the disease has not spread to other cervid populations, you may be able to eradicate the disease, says Ytrehus.
In non-confinable populations - which is the situation for most populations of deer, moose and roe-deer - spatially targeted culling of cervids within the infected areas could limit the scope and spread of the disease.
Other effective measures are to reduce the number of animal contact places, such as supplemental feeding stations for cervids in CWD-infected areas. The risk of disease transfer is particularly high in such places.
- We suspect that supplemental salt licks are a risk factor in regard to spread of the disease. An effective measure could be to remove these salt licks as well as the soil underneath them. The animals eat the soil because of the salt content, and the soil can be contaminated with prions, says Ytrehus.
Other potential measures could be to set up fences, herd the animals or reduce population density in the areas surrounding CWD infected areas, to ensure as little contact as possible between infected and healthy animals.
Furthermore, it is important that people avoid spreading the disease from one area to another, for example by transporting animals, carcasses, feed and soil, or via clothing, vehicles and other equipment that could be infected.
An interdiciplinary project
The risk assessment report was completed by a multidisciplinary project group. The group included the VKM Panel on Biological Hazards, the VKM Panel on Microbiology, five external experts and the VKM Secretariat. The Panel on Biological Hazards approved the final report.