Chronic wasting disease (CWD) and the other TSE (transmissible spongiform encephalopathy) diseases in cervids belong to the same group of diseases of the brain as e.g. bovine spongiform encephalopathy (BSE). These TSEs are caused by prion proteins. The CWD form of the disease is mainly found in North America.
CWD was discovered in the USA in the 1960s in mule deer and the affected area has since expanded in the USA and has now also spread into Canada. The disease is found both in cervids living in captivity and in wild cervids. The disease has also been found in South Korea, in cervids brought from North America to live in captivity.
In 2016, the first cases of CWD in Europe were discovered in Norway. The first finding was in wild reindeer (Rangifer tarandus tarandus) in the area of Nordfjella east of Bergen. Due to the finding in Norway, intensified monitoring for TSE in cervids was undertaken in six EU countries including Finland.
In addition to the findings of CWD in wildreindeer in Norway, cervid TSE has been found in a few moose (Alces alces) in Norway, Sweden and Finland and in one red deer (Cervus elaphus) in Norway. Types of the prions causing TSE in cervids vary. While it is clear that the disease identified in wild reindeer in Nordfjella is contagious, this CWD prion strain is distinct from those strains found in North America, implying that the highly contagious North American CWD prions are not the proximate cause of the newly discovered Norwegian CWD cases. Prion research is still ongoing.
The disease is not known to be contagious to humans and it has therefore not been considered to be an actual risk to humans.
The disease progresses slowly and it has not been found in animals younger than one year. The animal loses weight and wastes away even if it eats. At the end stage of the disease symptoms of the brain begin to emerge: the animal withdraws from the others, is lethargic, holds its head down, repeats certain movements and seems agitated. The animal may drink and salivate more than normal.
Diagnosis of the disease and sampling
The disease is usually diagnosed in dead animals. The samples used are taken from a certain location in the brain stem and from lymph nodes in the head. The samples are tested in a laboratory for detection of the pathogen. Typical microscopic changes are also found in the brain, which can be determined by way of a histological analysis.
The mechanisms of the spread of CWD are still not known with absolute certainty, but it seems to spread between animals via bodily secretions such as urine, faeces and saliva. The pathogen tolerates varying environmental conditions very well. The disease spreads most efficiently at feeding places and amongst animals that are fenced in. There is so far no knowledge of the spread of other TSEs amongst cervids.
It is prohibited to import untreated urine-based deer attractant produced outside the EU into the EU. This includes purchasing it online.
The occurrence of TSEs in wild cervids and reindeer has been monitored in Finland since 2003. As a consequence of the findings of CWD in Norway, an intensified monitoring programme for CWD was started in Finland and five other EU countries at the beginning of 2018.
If you find a cervid that has died naturally, you should contact the closest official veterinarian (Municipal Veterinarian or the Regional Veterinary Officers of the Regional State Administrative Agencies). The official veterinarian ensures that the necessary samples are sent to Finnish Food Authority. The police should be contacted if you discover a cervid that is sick, wounded or behaves abnormally. The police and the Finnish executive assistance in large game matters (SRVA) maintained by hunting organisations will organise a search for the animal and handle it in accordance with what the situation requires. Finnish Food Authority will examine whether it is a question of CWD affecting cervids or another TSE affecting cervids.
The place where the dead animal was found and its coordinates have to be noted by for example using a map application for mobile phones. If it is not possible to get the coordinates, the route to the place where it was found has to be marked adequately.
Occurrence in Finland
The first case of TSE in cervids in Finland was found in February 2018. The disease was found in a moose (Alces alces) that had died naturally in Kuhmo. According to the typification carried out by the EU reference laboratory the disease is similar to the TSE found in the moose in Norway and Sweden. The second case of TSE in cervids in Finland was found in October 2020 in a moose put down due to sickness. Prion typification of the second case is still ongoing. Both TSE positive moose in Finland have been old cows.