Emily Jenkins doesn't typically get stage fright. But as she stepped up to the podium in February 2016 to speak to Inuit hunters, elders and fellow researchers at the first ever Beluga Summit in the remote Canadian town of Inuvik, she was a bundle of nerves. “I was terrified,” recalls Jenkins, a veterinary parasitologist at the University of Saskatchewan in Saskatoon, Canada. “I had these very confusing results,” she says — and she was worried about how the community would react.

Warmer temperatures are causing ice in the Arctic to melt and zoonotic diseases potentially to spread. Credit: Paul Nicklen/Getty

Two years earlier, a pair of scientists from the University of British Columbia (UBC) in Vancouver, Canada, had announced at the annual meeting of the American Association for the Advancement of Science that they had found the parasite Toxoplasma gondii in hunter-harvested beluga whales (Delphinapterus leucas) from the region. This tiny protozoan doesn't usually make people sick, but it can cause toxoplasmosis, which poses serious dangers to unborn babies and to individuals with weakened immune systems (see page S52). And although the parasite's infectious stage is usually killed off at freezing temperatures, climate change was helping T. gondii to survive in places that were previously too cold. Instead of just being transmitted by domestic cats through their faeces, T. gondii seemed to be infecting new hosts, including marine mammals — and the UBC scientists warned that people living in the western Canadian Arctic should stop consuming uncooked whale meat.

The message didn't go over well in Inuvik, where beluga is a staple of the Inuit diet. It was especially jarring because the locals only learned of the finding through the media, which posted stories with headlines such as “Belugas with 'kitty-litter disease' threaten Inuit,” and “Deadly cat parasite attacks beluga whales, humans may be next.” The researchers, one of whom had been systematically screening and studying belugas from the region with the help of the Inuit for more than a decade, weren't invited back.

The courtesy, however, was extended to Jenkins, who, with her baby son in tow, travelled more than 2,000 kilometres in winter to share her latest findings. Unlike the UBC team, which had looked for antibodies in the whales that would indicate a previous immune response to T. gondii, Jenkins and her colleagues had used a genetic test that could detect evidence of T. gondii itself in the brain and heart tissue of 16 hunter-harvested whales. As Jenkins told attendees of the Beluga Summit, she couldn't find the parasite's DNA in a single whale.

The results from the UBC scientists and Jenkins' unpublished study were confusing and contradictory. “People wanted to know: Is my food safe to eat? And I'm there saying: 'I don't know, maybe our test could be wrong',” Jenkins says. Thankfully, the locals didn't seem to mind the ambiguity. “They had no problems understanding the challenges of certainty when you're working in the Arctic.”

These difficulties plague research in the shifting north, where data on the prevalence, diversity and distribution of animal to human (or zoonotic) diseases are limited at best — but it's exactly this kind of information that's needed now more than ever. With the Arctic warming about twice as fast as anywhere else on the planet, and the prospect of an ice-free Arctic summer now all but inevitable, scientists fear that zoonoses will spread, threatening the indigenous people and wildlife that inhabit the region. Unless action is taken soon, researchers warn, infection rates will soar, people will die, species will go extinct and traditional food practices will be a thing of the past.

Part of  Nature Outlook: Animal health

“It's kind of scary when you look at the predictions,” says Jenkins.

Surveillance tactics

One way to predict what could happen in the region is to look to the past. At the US Centers for Disease Control and Prevention's Arctic Investigations Program (AIP) in Anchorage, Alaska, director Thomas Hennessy and his colleagues are testing biological samples from the Alaska Area Specimen Bank to see whether people from the region have been exposed to a range of pathogens. Specimens include blood taken from more than 100,000 people, mostly Alaska Natives, over the past 56 years.

“We can look at different time periods to see if there were changes in the levels of exposure over time,” Hennessy explains. And there are similar biorepositories of animal blood, he adds. Over the years, the AIP team has used the Alaska bank to determine the historical prevalence of the bacterium Helicobacter pylori among Alaska Native people1 and the link between previous infection and stomach cancer2. Now, the team is examining the specimens in the bank for signs of zoonotic disease.

Of course, scientists can only detect the emerging pathogens that they're looking for, and it's impossible to test for everything. So in 2011, the Arctic Council, an intergovernmental forum for promoting cooperation between countries with territory in the northern polar region, created a working group of infectious-disease researchers from Russia, Europe, Canada and the United States to make a shortlist of priority zoonoses. Alan Parkinson, who worked with Hennessy at the time as the AIP's deputy director, chaired the group. “The idea, at the very beginning, was to sit down with everybody who was involved in infectious-disease research in the Arctic and try to put together a list of potential things we should be watching,” says Parkinson, now retired. “That would give us an idea of what sorts of surveillance systems need to be set up.”

The working group came up with 16 “climate-sensitive zoonotic pathogens of circumpolar concern”, consisting of 7 types of bacterium, 4 families of virus, 3 protozoans and 2 kinds of worm3. The first job, says Birgitta Evengård, an infectious-disease researcher at Umeå University in Sweden, is simply to collect incidence data on all these pathogens in both human and animal populations. “It's not perfect,” she says, “but it's the best we can do.”

Muzzle of a musk ox infected with parapoxvirus. Credit: Courtesy of Matilde Tomaselli/ref. 9

One of these zoonotic pests is the bacterium responsible for Lyme disease in the United States: Borrelia burgdorferi. In North America, researchers expect Lyme disease to keep spreading to higher latitudes as rising temperatures make the environment more hospitable for both the black-legged tick (Ixodes scapularis) that harbours the bacterium and the tick's main sources of food, the white-tailed deer (Odocoileus virginianus) and the white-footed mouse (Peromyscus leucopus). However, according to Nicholas Ogden, a wildlife disease ecologist at the Public Health Agency of Canada's Centre for Food-borne, Environmental & Zoonotic Infectious Diseases in Saint-Hyacinthe, Quebec, who models risk maps under projected climate conditions, Lyme disease still has “a long way to go” before it reaches the North American Arctic.

Not so in the Russian Arctic, where a more cold-hardy tick species is the main vector for Lyme disease. Last year, for example, a team from Russia and France reported the first known cases of Lyme disease in Arctic dwellers from a remote part of northeastern Siberia4. “The zoonosis could be spreading, perhaps due to climate change,” says one of the study's authors Jean-François Magnaval, a medical parasitologist at the University of Toulouse in France. But, he says, “our surveys are too patchy to allow general conclusions”.

One tick-mediated disease for which there is solid evidence of a northward shift in Russia is tick-borne encephalitis. This potentially fatal, nervous-system disorder is caused by one of the viruses singled out by the AIP working group. According to Boris Revich, an ecological epidemiologist from the Russian Academy of Sciences in Moscow, even though incidence of the disease has been dropping in the country as a whole, large swathes of northwestern Russia — including the Arkhangelsk region and the republics of Komi and Karelia — have recently seen an explosion in cases, as warmer temperatures have boosted tick survival in winter and extended seasonal periods of the parasite's activity in the spring and summer5.

On thin ice

As with so much when it comes to forecasting disease dynamics in the warming Arctic, researchers are often just making their best guess. But one scientist, Susan Kutz, a wildlife-health researcher at the University of Calgary, Canada, has been particularly prescient. As a graduate student in the late 1990s, Kutz studied an emerging lungworm infection among musk oxen (Ovibos moschatus) living on the mainland of the Canadian Arctic. “Impacts on wildlife and human health are inevitable,” she concluded in the paper that followed6.

We went, 'holy crap, our predictions have come true.'

Her prediction came to fruition when, in 2008, as part of routine surveillance conducted in partnership with the territorial government of Nunavut, Kutz and her colleagues found lungworm on the southwest corner of Victoria Island, Canada7. The parasite had expanded northward and jumped the 35 kilometres or so from the mainland across the sea ice of the frozen Dolphin and Union Strait. “We went, 'holy crap, our predictions have come true',” recalls Kutz. That wasn't all. Within a few years, musk oxen started mysteriously dropping dead on Victoria Island and neighbouring Banks Island. Post-mortem analyses revealed the presence of Erysipelothrix rhusiopathiae, a bacterium more commonly associated with pig farms8.

Kutz set up a community-based monitoring programme to figure out what was going on. It showed that the numbers of musk oxen on the islands were dwindling and those animals that remained were in bad shape. Along with E. rhusiopathiae, Kutz and her team also found musk oxen infected with Brucella spp. bacteria and parapoxvirus9. These pathogens are potentially zoonotic and can make people unwell. Lungworms, which pose no threat to humans, were only the first indicator that changing conditions were allowing parasites to spread.

Kutz is quick to point out that there have been no known human cases of either E. rhusiopathiae or Brucella associated with exposure to musk oxen — but it's possible, especially for hunters who kill the animals for their meat, leather and fur. Kutz has not made prescriptions to the locals, however. After the 2014 backlash against the researchers who warned against consuming beluga meat, “I am more careful,” she says. The best way to put findings into action, she adds, is to let the local public health officials know “so they can communicate that to the community in a way that doesn't cause massive panic”.

Cédric Yansouni, an infectious-disease physician and medical microbiologist at McGill University in Montreal, Canada, echoes these concerns. “Any recommendations we make have to be strongly supported by evidence and developed in close conjunction with the local communities,” he says.

Hysteria does no good, but a greater sense of urgency may be needed. As Karsten Hueffer, a veterinary microbiologist at the University of Alaska Fairbanks, points out, the infrastructure for tracking human and animal disease is “set up for something that worked reasonably well 50 years ago”. But the pace of warming in the north makes those systems obsolete.

“Things are drastically changing up here and we have no clue what's going on,” Hueffer says. The only thing he's certain of: “We are in for some trouble.”