Arctic animals are battling more diseases in recent decades. Here’s why.

Living off one of the richest oceans in the Arctic, the polar bears by the Chukchi Sea appear to be thriving. Females are in good health and give birth to healthy cubs. Overall, this Alaskan population seems strong.

But blood and fecal samples are starting to tell a different story inside the bears: There’s an emerging battle against pathogens many bears have never encountered before.

“The polar bears are a good indicator for what’s happening in the ecosystem,” said Karyn Rode, a research wildlife biologist at U.S. Geological Survey’s Alaska Science Center. “We know that pathogens’ transmission pathways are changing, including in the Arctic.”

In recent decades, the Arctic ecosystem has been transforming rapidly in front of our eyes. The Arctic is warming up four times faster than the global average. As a result, sea ice is melting faster and more dramatically in a season. Trees and plants are growing where they haven’t in recent decades.

Wildlife is also encountering diseases not previously seen in their lifetimes.

Stories have surfaced of animals fighting off new diseases and sometimes losing that fight. The bird flu infected and killed a polar bear and walruses in the Arctic for the first time. Phocine distemper virus appeared in sea otters in Alaska, after killing thousands of European harbor seals in a different ocean. Anthrax reemerged from melting Siberian permafrost and killed reindeer, and even a human child.

As the world continues to warm, scientists are taking stock of current threats and how to prevent major losses - especially in the delicate Arctic environment.

Arctic animals are exposed to more diseases

It’s been harder for Rode, a polar bear researcher for nearly two decades, to do her job in recent years. Every spring, she and her team would sample Alaskan polar bears to check their health. But in 2017, they had to prematurely call off their field studies because the melting ice was too unstable - breaking up while they were on the ice. The thin sea ice forced them to cancel excursions for the following seasons.

When they returned last year, Rode recalls “lots of open water, really thin ice, looked very different than what we’ve seen in the past.”

These are the obvious changes from warm temperatures pushing Arctic sea ice to new lows over the past four decades, shrinking its area by the size of South Carolina each year.

Like Rode and her colleagues, the polar bears off the coast of Alaska also avoided the thinning sea ice and spent more time on land. But the extra time on the land, the team found, increased their exposure to uncommon pathogens.

The polar bears by the Chukchi Sea, a new study found, face a greater risk of contracting many pathogens than they did three decades ago. In studying blood samples, the researchers found antibodies for five pathogens, which were more than twice as common in today’s bears than from samples in the 1980s and 1990s.

The results are only somewhat curious, because Chukchi Sea polar bear populations appear relatively healthy compared with other populations, given the wide area and abundance of seals to eat. But previous studies have shown that other populations in the Beaufort Sea and western Hudson Bay have seen pathogen changes, so scientists already knew pathogens were spreading.

These diseases on their own probably aren’t lethal enough to kill polar bears, but Rode said it can weaken them or become an additional stressor they must battle. Her team is highlighting a change that has the potential to become a major issue in the future. For right now, surveillance of these species is key.

Some of the antibody pathogens aren’t so unfamiliar outside of the Arctic. The team found evidence of the parasites that cause toxoplasmosis, a disease usually discussed in the context of cat feces and especially concerning for pregnant women.

They also detected the antibody for the bacteria that cause rabbit fever and the canine distemper virus.

The most shocking antibody detection was Neospora caninum, which causes neurological issues and fetal death in cattle. In the 1980s and 1990s, only about 13.7% of the bear samples tested positive. The recent samples showed an increase to 65.1% - some of the most rapid increases in exposure ever reported among polar bears, the authors said.

“Some of these pathogens primarily occur on land,” said Rode, who was the lead author of the study. “We think that some of those may be obtained from being on land.”

But most pathogens, she said, are probably getting picked up from their prey, which “suggests that the prey have higher pathogen levels than they probably had in the past as well.”

Once an animal is infected, there are numerous ways the disease can spread.

For example, a warming Arctic melts away barriers that previously kept species away from one another. In 2002, a pathogen known as phocine distemper virus killed off thousands of European harbor seals in the North Atlantic. Two years later, the virus showed up in sea otters in Alaska - jumping to a different ocean and to a different species. Researchers found that the outbreak occurred around low sea concentrations, opening up a new road for the Arctic and sub-Arctic species to come into contact.

A warmer Arctic is also creating new ecosystems for animals to move into. The melting permafrost is allowing room for more forests, where ticks can survive. Ticks have become more common in Alaska in recent decades, research shows. At least one pathogen for Lyme disease has been detected in the Arctic too.

Not only is the location of these parasites expanding, but the “warmer temperatures accelerate the growth rates of pathogens and vectors, such as ticks and mosquitoes,” said Khaled Abass, a toxicologist at Finland’s University of Oulu.

When a graveyard thaws, pathogens can jump to humans

Pathogen biologist Becky Hess is most concerned with graveyards, specifically what happens when they melt. Bacteria and viruses trapped in soils, corpses or carcasses could bring disease to a society and wreak havoc. In fact, it’s already happened.

In 2016, a heat wave accelerated the thawing of frozen soil in Siberia - and a reindeer carcass thought to be infected with anthrax spores. The spores reactivated, and an anthrax outbreak occurred in the area for the first time in decades. The outbreak affected many people, killing at least one child and thousands of reindeer.

The permafrost thawing is tied to years of ongoing warming and precipitation changes, only to be finally tipped over by an extreme summer heat wave.

Ekaterina Ezhova, a researcher at the University of Helsinki, said she expected an outbreak to occur within the next 50 to 100 years at the rate the permafrost was thawing. But the preceding summer, winter precipitation and a heat wave in the same area “created favorable conditions for an outbreak in just six years.”

But it’s important to note, Ezhova said, that the anthrax jumped back into the population because the bacteria in the soil hit live reindeer in the area. If there were no host (or reindeer, in this case), then there would be no outbreak.

“Bacteria are really wonderful at surviving extreme conditions,” said Hess, who leads the pathogen biology team at the National Security Directorate at Pacific Northwest National Laboratory. “A spore can remain dormant for thousands of years” but can reactivate and create toxins when the conditions are right.

Hess, working with researchers at the Army’s Cold Regions Research and Engineering Laboratory, is studying thawed permafrost from Alaska to determine if any pathogens are present. Then they can come up with a plan to highlight the exposure risk of that area and potentially create treatments for humans to fight off uncommon viruses and bacteria.

“We don’t know what new or emerging pathogen could be present,” Hess said. She said that if a pathogen existed in the Alaskan permafrost, there is a potential risk as humans travel to and from the area - although that risk hasn’t been quantified yet.

Her biggest concern at the moment is cholera. She said several graveyards - outside the Arctic as well - contain people who died from cholera and are currently thawing.

“We don’t have any evidence of an outbreak or spread or anything like that,” Hess said. “It’s something that we’re trying to get ahead of.”