Norway takes its reindeer seriously. Europe’s last remaining wild mountain reindeer (Rangifer tarandus tarandus) live in central and southern Norway. So the country’s veterinarians are naturally worried after finding a reindeer that died of a deadly and contagious brain disease—the reindeer version of mad-cow disease.
The reindeer’s natural habitat has reduced by half in the last 50 years. Though the International Union for Conservation of Nature lists has the species on its “least concern” list, it is worried about its future population.
Chronic wasting disease (CWD), which afflicted the reindeer found by researchers last month in southern Norway, is related to bovine spongiform encephalopathy (mad-cow disease) and Creutzfeldt-Jakob disease in humans. It occurs when cellular proteins fold into abnormal shapes that allow them to make other healthy proteins misfold too. Eventually, these mutant proteins, called prions, aggregate in the brain to cause cognitive and behavioral disabilities, and eventually death. There is no known cure.
CWD is highly contagious; it’s spread through animal excretions. There are almost certainly more cases out there, which is why veterinarians told Nature that they are “very afraid.”
What’s more baffling is that nobody knows how the disease got there. CWD was thought to be restricted to deer, elk, and moose in the US and South Korea. Though it’s theoretically possible that it jumped from another species in Norway (such as cows) to the reindeer, there are no previous known cases of that happening. The other possibility is that it just arose spontaneously—a protein misfolding into a prion by pure chance.
Mad-cow disease was brought under control after governments stopped the use of animal meat as food for cows. That limited the spread of prions from sick animals to healthy animals. In the case of wild reindeer, however, there is no simple way to stop them from being exposed.