First case of fatal bird flu in polar bears reported in Alaska

Why it matters: The virus is a new threat to many wild mammals.

The infected polar bear provides further evidence of how widespread this virus, a highly pathogenic form of H5N1, has become and how unprecedented its behavior has been. Since the virus emerged in 2020, it has spread to all continents except Australia. It has also infected an unusually wide range of wild birds mammalsincluding foxes, skunks, mountain lions and sea lions.

“The number of mammals affected by infections continues to grow,” said Dr. Bob Gerlach, Alaska’s state veterinarian.

In most cases, the virus has not caused mass deaths in wild mammal populations. (South American sea lions were one notable exception.) But it does pose a new threat to the already vulnerable polar bear, which is endangered by climate change and sea ice loss.

“The concern is that we don’t know the full extent of what the virus can do to the polar bear species,” said Dr. Gerlach.

Background: The bear showed signs of illness.

The polar bear was found dead last fall in far northern Alaska, near Utqiagvik. Swabs taken from the animal initially tested negative for the virus. But when experts conducted a more extensive examination, performed a necropsy and collected tissue samples from the bear, they found clear signs of inflammation and disease, said Dr. Gerlach.

Tissue samples from the bear last month tested positive for the virus, according to the Alaska Department of Environmental Conservation. The virus was eventually identified in multiple organs, Dr. Gerlach said. “I think it’s safe to say the animal died from the virus,” he said.

Alaska has previously reported infections in a brown bear and a black bear, as well as in several red foxes.

What we don’t know: Are other polar bears infected?

It is not clear how the polar bear contracted the virus, but sick birds had been reported in the area. The polar bear may have become infected after eating a dead or sick bird, Dr. Gerlach said.

And scientists don’t know if this case is a one-off or if there are other infected polar bears that have escaped detection. It can be difficult to monitor the virus in wildlife populations, especially those as remote as Northern Alaska. “How do you know how many are affected?” said dr. Gerlach. “We really don’t do that.”

Local scientists, officials and other experts will continue to look for signs of the virus in wildlife, including in polar bears that appear dead or sick, Dr. Gerlach said.