By Erik Stokstad Apr. 3, 2017 - sciencemag.org
A year after a deadly and highly contagious wildlife disease surfaced in Norway, the country is taking action.

Chronic wasting disease (CWD), caused by misfolded proteins called prions, has already ravaged deer and elk in North America, costing rural economies millions in lost revenue from hunting. Its presence in Norway’s reindeer and moose—the first cases in Europe—is “a very serious situation for the environment and for our culture and traditions,” says Bjornar Ytrehus, a veterinary researcher at the Norwegian Institute for Nature Research in Trondheim.
Last week, Norway’s minister of agriculture and food gave the green light for hunters to kill off the entire herd in which three infected individuals were found, about 2000 reindeer, or nearly 6% of the country’s wild population. “We have to take action now,” says Karen Johanne Baalsrud, director of plant and animal health at the Norwegian Food Safety Authority in Oslo. The deer’s habitat will be quarantined for at least 5 years to prevent reinfection. The odds of a successful eradication, experts say, will depend largely on how long CWD has been present in Norway.
CWD, discovered in 1967, has been found in 24 U.S. states and two Canadian provinces, and it has been spread in part by shipments of infected animals. Many species of cervids are susceptible, including elk, moose, and several kinds of deer. Infected animals typically begin showing symptoms such as weight loss, lethargy, and drooling 2 to 3 years after infection and then die within months. In Wyoming, where CWD has been endemic for decades, up to 40% of some herds are infected, and white-tailed deer populations are declining by 10% a year.
CWD is very contagious: Prions spread easily through saliva, urine, and feces, and can linger in the environment for years, which suggests that feeding stations and salt licks are hot spots of infection. Once the disease has become firmly established, environmental contamination makes eradication very hard, says Christina Sigurdson, a prion researcher at the University of California, San Diego. “It hasn’t been shown so far to be possible,” she says. There’s no evidence that humans can get sick from eating infected deer, but it is not recommended. (Mad cow disease, also caused by prions, can infect people who eat contaminated meat and has caused more than 200 deaths so far.)
Norway’s first CWD case was detected by chance after wildlife biologists working in the rugged mountains of Nordfjella found a sick young reindeer on 15 March 2016. After its death, tests at the Norwegian Veterinary Institute (NVI) in Oslo pointed to CWD. “I couldn’t believe it,” says NVI prion researcher Sylvie Benestad. But international reference labs confirmed her diagnosis.
The prions resemble those found in North American deer, Benestad and her colleagues have found. How the disease got to Norway is a mystery. Prions may have arrived in deer urine, which is bottled in the United States and sold as a lure, or perhaps they hitched a ride on hiking boots or hunting gear. But prion diseases can also start spontaneously, after proteins begin to misfold in a single individual, and Benestad’s hunch is that this is a more likely scenario.
After the initial discovery, Norwegian officials began looking for other cases. A local hunter found two moose with CWD near the town of Selbu, 40 kilometers southeast of Trondheim (see map), in May 2016. During last fall’s hunting season, thousands of hunters and other volunteers collected about 8000 brain samples from all over the country, turning up two more cases of infected reindeer near Nordfjella. The cases in Nordfjella and Selbu are likely not linked, says Benestad, as the reindeer and moose have different types of prions.
An advisory panel convened by the Norwegian Scientific Committee for Food Safety last week suggested different approaches for the two locations. Around Selbu, it recommended increased surveillance, but no culling of moose yet. The two infected moose were older animals, suggesting that these were cases of spontaneous disease, which are less likely to be infectious. (The reason why: In spontaneous cases of prion disease, such as in sheep, prions are only found in the brain.) And even even if the unusual prions in moose are contagious, the solitary nature of these animals lowers the chances of transmission.
Reindeer, however, are the most gregarious of cervids, and the three sick individuals in Nordfjella could easily have spread prions. Culling the entire herd would be “drastic,” the panel acknowledged, but should be attempted as soon as possible. The slaughter, to start in August, will be carried out by amateur hunters, who can eat the meat if prion tests come back negative. Professional sharpshooters will be used to find any elusive survivors. “We will do whatever it takes,” says Erik Lund, a senior wildlife adviser at the Norwegian Environment Agency in Trondheim.
Until the operation begins, wildlife rangers are patrolling to prevent animals from leaving or entering the herd’s 2000-square-kilometer habitat. The area is ringed by paved roads, which reindeer don’t like to cross, but if any do, the rangers have orders to track down and kill them. Repopulation won’t begin until at least 2022. Benestad says testing old feces may be a way to check whether prions lingering in the environment have degraded.
Based on the prevalence in Nordfjella—estimated at 1%—Lund guesses that CWD may have been present for only 5 to 7 years, which could mean contamination is minimal. “There’s a good chance they can solve the problem,” says wildlife ecologist Michael Samuel of the University of Wisconsin in Madison. Quick response has been shown to work before: In 2005, routine testing revealed CWD on two deer farms in central New York. Strict regulations prevented the disease from spreading. The state has seen no cases since.
But it’s also possible that CWD is lurking elsewhere in Norway, the panel noted. The agencies will collect another 20,000 samples in the coming hunting season, and they plan to continue monitoring for years to come. The specter of CWD has also alarmed the European Food Safety Authority, which released a report in January recommending that seven nearby countries all begin 3-year sampling programs.