Prion disease: first case detected in Europe in a wild reindeer

A case of chronic wasting disease in deer, detected in a wild reindeer (Rangifer tarandus tarandus) living in southern Norway, was confirmed by the Norwegian Veterinary Institute in early April. Biochemical and immunohistochemical tests conducted on the affected animal as part of the national surveillance program for prion diseases in wild ungulates confirmed the positive result.   This is the first case of chronic wasting disease (CWD) detected on European soil, as well as the first documented instance of natural infection in a wild reindeer worldwide. This contagious and fatal neurological disease had previously affected only wild and farmed cervids (mule deer, white-tailed deer, elk, and moose) in North America and South Korea. As with bovine spongiform encephalopathy (BSE) and variant Creutzfeldt-Jakob disease in humans, the infectious agents responsible for chronic wasting disease are prions. These abnormally shaped proteins cause healthy proteins to misfold as well, forming aggregates in the brain and sometimes in other tissues. Affected deer exhibit symptoms such as a decline in general health, weight loss, impaired coordination, and altered behavior. Although the clinical course of the disease is slow, the outcome is always fatal, as there is neither a treatment nor a vaccine. Although the disease is not believed to be transmissible to humans, it is highly contagious among deer, elk, and related animals, which can transmit infectious prion proteins through saliva, urine, and feces. Chronic wasting disease is endemic in about 20 states in the United States and in two provinces in Canada. The disease has also been detected in captive animals in South Korea, which imported the disease into its territory via infected elk in the late 1990s. The infection of a reindeer in a mountainous area of Norway, however, remains a mystery. Scientists consider it unlikely that the disease was introduced. Instead, they suspect a spontaneous outbreak or cross-species transmission via sheep infected with scrapie, although this hypothesis has yet to be proven. The question that arises, therefore, is whether this Norwegian case is rare—or even unique—or whether chronic wasting disease in deer has imperceptibly spread among wild reindeer herds without having been detected until now. The European surveillance program for transmissible spongiform encephalopathies (TSEs) in wildlife, established about ten years ago, failed to detect this case, likely due to the small number of animals tested. The Norwegian Veterinary Institute will conduct a large-scale epidemiological investigation among Norway’s wild reindeer populations. This is because, once the disease appears in a new area, it is very difficult to eradicate.