Scientists fear Canadian polar bears could be threatened by the spread of bird flu after authorities confirmed the disease killed a bear in Alaska.
“There’s a very high probability that this is the case (in Canadian bears),” said Andrew Derocher, a leading polar bear biologist at the University of Alberta.
“It’s there. We’re just not looking for it.”
Last month, USDA officials confirmed that the H5N1 strain of bird flu killed a polar bear, found in October near the Alaska town of Utqiagvik, about 500 kilometers from the Yukon border. Polar bears travel hundreds of kilometers and the dead bear was part of a population shared by both countries.
The virus first appeared in Yukon more than a year ago in a red fox, said territorial veterinarian Jane Harms.
“This strain of bird flu appears to have the ability to infect and cause disease in mammals of various types,” he said. “The fact that this virus can cause illness and death in polar bears, as well as other species, is concerning.”
It is still unclear to what extent the virus has spread among Arctic mammals. Alaska has found it in red foxes, a black bear and a Kodiak bear.
Harms said so far it appears to be spreading when mammals eat infected birds.
“In most cases, wild mammals become infected through scavenging tissues from infected birds. It does not appear to be transmitted from mammal to mammal.”
But Derocher said climate change is likely increasing the bears’ exposure, as declining sea ice keeps them on shore longer and forces them to subsist on prey such as dead birds. These prolonged periods of relative scarcity on the coast also weaken the bears.
“Immune system function declines. With weakened immune systems, they are more likely to succumb.”
Additionally, polar bears are more vulnerable to viruses than other bears, said John Whiteman, chief researcher at Polar Bears International and a professor at Old Dominion University in Virginia. As they evolved toward the Arctic, they lost much of their genetic “library” of potential pathogens and how to resist them.
“If you can recognize many pathogens, you’ll be better able to fight them,” Whiteman said. “Polar bears don’t recognize many pathogens.”
Climate change has stirred the pot of viruses around the world, he said.
“We know that pathogens are changing their distribution and some of them that may not have been able to survive on Alaska’s North Slope are gaining ground.”
Bird flu is now found on every continent except Australia.
Both Whiteman and Derocher called for better monitoring of wild animal diseases.
Harms said Yukon regularly performs necropsies on dead wildlife, but more needs to be done. Confirming bird flu requires additional testing, he said.
“The reality is that we would probably have more avian flu virus infections in mammals if we had the ability to look for them.”
The southern Beaufort population, of which the dead bear was a member, is estimated to be about 900 individuals, although it is difficult to be sure with polar bears. That population is considered to have declined by about 50 percent since the 1980s, Derocher said.
The virus has hit other mammals hard. Scientists have linked it to the deaths of nearly 500 seals in Maine over the past two years.
But both Derocher and Whiteman say the death of a bear is not enough to hit the virus’s panic button.
“I would put it in the category of a little alarming,” Whiteman said. “There are still many unknowns about this threat. But there is a potential for mortality.
“By far the biggest threat to this species is the loss of sea ice.”
This report by The Canadian Press was first published Jan. 4, 2024.