During the last week of September, Inuit residents in the community of Arviat on the northwest coast of Hudson Bay were surprised to see a mysterious whale following a small boat heading back to the village. The whale was at least twice the size of the 15- to 20-foot-long beluga whales that are traditionally seen in this part of the world.

Based on the photos taken, scientists concluded that the whale was a humpback, the first ever seen in that part of Hudson Bay, and one of a handful that have recently been spotted in the North American Arctic.

Humpbacks are not the only marine mammals that have been expanding their range northward. Most notably, as sea ice melts, ice-avoiding killer whales have been moving deeper into the Arctic Ocean, hunting and killing both narwhal and beluga whales. Other whale species — including minke, bottlenose, fin, and sperm whales — are also making their way north as the Arctic heats up. At the same time, on land, grizzly bears, white-tailed deer, coyotes, and other animals and birds have been expanding their range into the warming boreal forest and Arctic tundra.

For the indigenous people who subsist on Arctic animals such as muskoxen, caribou, seals, polar bears, and eider ducks — species that are in decline in some places — the newcomers are potentially a welcome addition to their diet. But emerging evidence suggests that some of these newly arriving species may be bringing rare or novel pathogens to the Arctic. In recent years, a plethora of deadly and debilitating diseases have struck reindeer in Scandinavia and Russia, muskoxen on Banks and Victoria islands in Arctic Canada, polar bears and seals off the coast of Alaska, and eider ducks in northern Hudson Bay and the Bering Sea.

Susan Kutz — a University of Calgary veterinary parasitologist who identified a novel form of the parasitic nematode worm, the lungworm, in muskoxen in the High Arctic — is one of a small number of veterinarians and biologists trying to decipher the causes and impacts of changing disease outbreaks in the Arctic. One possibility, she and other scientists say, is that climate warming and ecosystem changes are causing some bacteria, such as those that cause avian cholera, to mutate, or may be making Arctic animals more susceptible to pathogens that previously did them no serious harm.

Another possibility being investigated by scientists is that bacteria such as anthrax — an outbreak of which resulted in the culling of 250,000 reindeer in western Siberia in 2016 and 2017 — are being liberated by rapidly thawing permafrost. The anthrax outbreak in the far northern Yamal-Nenets Autonomous Okrug of Siberia compelled Russia’s Department of Defense to launch an emergency task force to help vaccinate 730,000 reindeer. One person died from anthrax, and several dozen reindeer herders got sick when the animals succumbed to the disease. A record heat wave that swept across the tundra that summer is thought to have thawed out reindeer carcasses that were infected with the spores.

“Our ability to detect and monitor the movement of pathogens in the Arctic is abominable,” says Kutz, who specializes in studying how changes in the climate and landscape can alter the relationship of hosts and parasites. “In most cases, we don’t know whether these pathogens are new and being brought in from the south, or whether they have always been there.”

Kutz was brought in to determine what was killing thousands of muskoxen on Banks and Victoria islands in the western Arctic from 2010 to 2014. Of the 38,000 animals on Banks Island in 2010, only about 14,000 remain today; the population worldwide is less than 140,000. She concluded that the muskoxen died from erysipelothrix rhusiopathiae, a bacterium normally found in pigs and poultry, and carried by wild birds and rodents, such as lemmings. Pigs are now routinely vaccinated against the bacterium because it can cause arthritis, skin disease, and sudden death when it creates lesions on the heart valves of animals.

While it is possible that nesting snow geese that migrate to Banks and Victoria islands brought the disease in from the south, Kutz suspects that the bacteria may have already been there, and that ecosystem stresses brought on by climate change — especially rising temperatures — may have made the animals more vulnerable to infection. “We know that these muskoxen died quickly and that they may have been highly stressed by hot temperatures or ecosystem changes on the landscape,” said Kutz.

Kutz has little doubt that the northward movement of novel parasites will accelerate as more wildlife species expand their range, as humans move northward with their pets and livestock, and as more cruise and cargo ships travel through an increasingly ice-free Arctic with pathogens attached to their hulls or in their bilge water, which is routinely flushed out without monitoring or penalty.

Kutz and five other scientists recently made the case for the need for an Arctic Wildlife Health Observing Network, which would establish partnerships with the Inuit and First Nations people, coordinate existing wildlife health monitoring programs and develop new ones, and provide mechanisms for storing and accessing specimens.

“Understanding the possible impacts of disease to Arctic wildlife is not only of interest for conservation and management of wildlife,” said John Pearce, supervisory wildlife biologist at the Alaska Science Center of the U.S. Geological Survey (USGS). “It’s of interest to people who rely on birds and animals for food. At this point, we are trying to understand what is normal, what is new, and which diseases might be of concern for wildlife health.”

Because most Arctic animals have been isolated for so long, scientists say, many of them have no immunity to diseases such as phocine distemper, which was first identified in the Arctic in 1988 and resulted in a massive die-off of harbor and gray seals in northwestern Europe. There is now mounting evidence of phocine distemper-like viruses in the North Pacific and Western Arctic, where beluga whales have no immunity to the disease.

Many pathways exist for disease and pathogens to enter the Arctic. Toxoplasma gondii, a parasitic pathogen normally associated with house cats, has been found in polar bears and Arctic fox in the Norwegian Arctic archipelago of Svalbard, even though cats are banned there. One study suggests that warm ocean currents may have transported the pathogen into that part of the Arctic. Another suggests it was brought in by migrating geese.

Toxoplasma gondii — which can infect virtually all warm-blooded animals — has also entered the beluga whale population of western Canada. The concern is not so much for the whales, which so far appear to be unaffected, but for the Inuit who eat the blubber of the animal, since the parasite can be transmitted to humans if the blubber or meat is uncooked.

Veterinarians and biologists are also increasingly concerned about the spread of parasites and diseases into the Arctic on land. A major concern is white-tailed deer, which are carriers of the meningeal brain worm. While deer are unaffected by this pathogen, moose and caribou often die once infected. White-tailed deer have moved north and are now well established in the Yukon and southern parts of the Northwest Territories, and biologists say it is only a matter of time before they migrate into Alaska.

Connecting diseases to rapid changes to ecosystems in the Arctic is often difficult because so many factors are at play and so few scientific and veterinary resources exist in such a large territory. The USGS, which has five scientists working full-time on disease at its Alaska Science Center, can barely keep up. But the links in many cases are difficult to ignore.

In 2012, the year in which sea ice reached a record low, more than one in four polar bears captured in the Beaufort Sea were suffering from alopecia, which is characterized by severe hair loss and flesh sores. An unusually large number of seals in the region also died that year of unknown causes.

An unprecedented outbreak of avian cholera in northern Hudson Bay from 2004 to 2013 is yet another example of how multiple stresses in a warming Arctic may be laying the groundwork for the spread of diseases and parasites. The disease was thought to be absent in the eastern Arctic of North America, but in 2007 scientists discovered an outbreak on Southampton Island at the northern end of Hudson Bay that killed 3,500 common eiders. When biologists from Canada’s National Wildlife Research Center arrived in June of that year, the eiders appeared normal. But in August, the birds were suddenly seized by convulsions and died en masse. By the time it was over, five weeks later, a third of the nesting females had died.

The spread of the disease did not end there, according to Samuel Iverson, a biologist who was on the island in 2009 and is now with the Canadian Wildlife Service. “There were significant outbreaks year after year from 2006 to about 2010, and smoldering die-offs for about three years thereafter,” said Iverson. “In total, the colony declined by 56 percent from its peak abundance.”

Iverson spent the next three years investigating islands in Hudson Bay looking for evidence of past and ongoing outbreaks of avian cholera. He discovered that since 2004, at least 13 outbreaks occurred in 1,300 bird colonies spread across more than 750 miles of the Arctic. A warmer climate, said Iverson, “could be making the Arctic environment more suitable for avian cholera to persist in wetlands and sediments. That could allow for more transmission.”

In addition, he said that climate change is also beginning to affect bird movements and migrations, which means that populations that didn’t previously interact now do so. And avian cholera — usually found in waterfowl and shorebirds — “may have already been circulating in the population harmlessly until the eider’s body conditions were lowered by stresses brought on by ecosystem changes,” Iverson said. “These are ideas worth exploring, but we don’t have answers.”

The eider die-off occurred at a time when other birds in the region, such as thick-billed murres, were being stressed by early hatches of mosquitoes, an increasingly common occurrence as the Arctic rapidly warms. In addition, polar bears were beginning to exploit eider eggs because of the absence of the springtime sea ice on which the bears hunt seals. In 2018, polar bears ate every egg that was hatched at the East Bay Migratory Bird Sanctuary, the main site of the avian cholera outbreak.

In addition to the arrival of previously rare or unknown diseases, some scientists are increasingly worried about a growing load of chemicals and toxic substances in apex predators like polar bears and killer whales.

“A pathogen, whether new or established, may not be of great concern in itself,” said University of Alberta polar bear biologist Andrew Derocher. “But when you have polar bears fasting weeks longer now than they did before, while being increasingly loaded with chemicals such as mercury, DDT, PCBs, and hundreds of pollutants, it raises questions about how effectively these bears can handle parasites or disease.”

Derocher noted that most of these chemicals are stored in the fat, where they do little harm. But as bears are increasingly forced to fast as their traditional hunting platform, sea ice, declines, they are using up more of these fat stores, meaning that more of the pollution in their fat cells is moving into their bloodstreams. “That’s where it’s biologically active,” said Derocher. “And that’s when you may see some serious effects on the health of an animal.” These include causing brain damage, weakening animals’ immune systems, and adversely affecting reproduction.

Steve Ferguson, a biologist with Canada’s Department of Fisheries and Oceans, says he was skeptical in 2005 when he began investigating Inuit reports of killer whales in the Arctic. Now he’s regularly tagging killer whales and telling the Inuit not to hunt and eat them because they are so loaded with contaminants.

“I think we’re going to see a lot more twists and turns as more southern species migrate into the Arctic regions,” he says. “In some cases, disease will come with them. The question now is whether Arctic species can adapt to the very rapid changes that are taking place.”