Avian (Bird) Influenza Causes Death of Alaska Polar Bear- a Sign of the Virus’ Persistence
Avian influenza death of Alaska polar bear is a global first and a sign of the virus’ persistence
A polar bear walks along the shore in Alaska on Sept. 6, 2019. A different animal discovered dead in October is now confirmed to be the world’s first documented case of highly pathogenic avian influenza in a polar bear. (Courtesy of U.S. Fish and Wildlife Service)
A polar bear found dead on Alaska’s North Slope is the first of the species known to have been killed by the highly pathogenic avian influenza that is circulating among animal populations around the world.
The polar bear was found dead in October near Utqiagvik, the nation’s northernmost community, the Alaska Department of Environmental Conservation reported.
The discovery of the virus in the animal’s body tissue, a process that required sampling and study by the North Slope Borough Department of Wildlife Management and other agencies, confirmed earlier this month that highly pathogenic avian influenza was the cause of death, said Dr. Bob Gerlach, Alaska’s state veterinarian.
“This is the first polar bear case reported, for anywhere,” Gerlach said. As such, it was reported to the World Organisation for Animal Health and has gotten attention in other Arctic nations that have polar bears, he said.
This was also the first Endangered Species Act-listed animal in Alaska known to fall victim to the disease. Polar bears, dependent on sea ice that is diminishing because of climate change, were listed as threatened in 2008.
While polar bears normally eat seals they hunt from the sea ice, it appears likely that this bear was scavenging on dead birds and ingested the influenza virus that way, Gerlach said. Numerous birds on the North Slope of various species have died from this avian influenza, according to the Department of Environmental Conservation.
However, the bear need not have directly eaten an infected bird to have become sick, Gerlach said.
“If a bird dies of this, especially if it’s kept in a cold environment, the virus can be maintained for a while in the environment,” he said.
The polar bear death is a sign of the unusually persistent and lethal hold that this strain of highly pathogenic avian influenza has on wild animal populations two years after it arrived in North America, officials said.
“What we’re dealing with now is a scenario that we haven’t dealt with in the past. And so there’s no manual,” said Andy Ramey, a U.S. Geological Survey wildlife geneticist and avian influenza expert.
No longer just a poultry problem
Highly pathogenic avian influenza is called that because it spreads rapidly in flocks of domestic poultry, often requiring massive culls to control the contagions. Such outbreaks have been of concern in the past because of their economic consequences for global agriculture. Until recently, wild birds were afterthoughts. Though they were known to carry the viruses, ferrying them between domestic poultry populations, they were largely unaffected.
That has changed dramatically. The prior U.S. outbreak of highly pathogenic avian influenza, in 2014-15, resulted in some wild bird infections, and some influenza-caused bird die-offs occurred in Europe shortly thereafter. But the current version is considered unprecedented in its effect on wild birds and other wildlife.
“Across North America, and really around the world, lots of wild birds these days – I mean, thousands of wild birds these days, tens of thousands in some cases — are dying because of these highly pathogenic avian influenza viruses,” Ramey said.
The deaths are of particular concern when they occur in populations that are already vulnerable, he said. An extreme example he cited is the highly endangered California condors, with a population of just a few hundred. After 21 influenza deaths were documented, federal wildlife officials launched what promises to be a challenging vaccination program in that population.
The disease has also killed a variety of mammals around the world.
In Alaska, three foxes, a black bear and a brown bear have died from this avian influenza. Elsewhere, more bears have been found dead after being infected by the virus, along with skunks, raccoons, mountain lions and large numbers of seals in eastern Canada and off the coasts of Maine and Washington state, as well as outside of North America. The nation’s first detection of the disease in a squirrel was confirmed earlier this month in an animal found in Arizona.
To Gerlach, the polar bear case was not surprising, considering that black and brown bears have died. It is possible that more polar bears succumbed to the disease, but in remote places out of the view of people to record the events, he said.
“You’re really dependent on the public that’s out there, or the wildlife biologists that are doing surveillance,” he said. Documenting cases in any wild mammal population can be difficult, he added: “How long is a carcass going to be in the wild before it gets scavenged or eaten by something else?”
Aside from the large and wide-ranging death toll in the wild, the current outbreak has some other differences, particularly its durability, as seen in its persistence away from domestic flocks.
The virus that caused the 2014-15 outbreak spread in the wild bird populations for a while, but it “sort of fizzled out,” Ramey said, probably because it was eventually stamped out in poultry operations.
But this one continues to be maintained in the wild, as evidenced by monitoring in Western Alaska, a place far from any big farms raising chickens or turkeys, he said.
Gerlach gave the same assessment. “After the second year, that all of sudden disappeared,” he said of the 2014-15 version. “It didn’t stick around, where this virus seems like it’s sticking around.”
Rather than winding down, it is continuing to spread across the world, he noted, even into bird populations in Antarctica, as has been recently documented. There are signs that it is now endemic in the wild, a fixed feature into the foreseeable future, he said. If so, “it’s not going to go away. It’s going to be here, and we have to have some way to deal with it,” he said.
Alaska a disease crossroads
For Alaska, “a mixing area” for global bird migrations, spread of avian diseases is always an issue, Gerlach said. “Alaska is a catchall area for birds from North America or the Americas, as well as from Asia,” he said.
The highly pathogenic avian influenza of 2014 and 2015 was introduced from Asia to North America by wild birds migrating through Alaska. The current influenza is also crossing continents through Alaska, though from multiple directions, Ramey’s research has found.
In a newly published study, Ramey and his research partners found what is likely to have been three separate and independent introductions of highly pathogenic avian influenza into Alaska last year. His research, with colleagues from the USGS and other agencies, used genetic analysis to trace one form of influenza to North America and two to Asia.
“To have three introductions in Western Alaska, two from East Asia and one from the Lower 48, I mean, we haven’t seen anything like that before,” he said. “It really, I think, exemplifies how these viruses now are clearly able to be maintained.”
That study examined birds harvested in the fall of 2022 by hunters in the Izembek National Wildlife Refuge area at the southern tip of the Alaska Peninsula. Ramey and his colleagues found only a tiny number of hunted birds that were infected with the currently active highly pathogenic influenza virus: out of 811 swab samples taken directly from birds and another 199 samples from feces, the only harvested birds identified as infected were eight pintails, one cackling goose and one widgeon.
It can take months to get test results from samples, so what happened to those harvested birds is unknown, he said. But their meat was safe to eat as long as it was properly cooked to the recommended 165 degrees, he said. “Heat is remarkably good at deactivating viruses,” he said. Along with the cooking advice, there are other longstanding recommendations about safely handling hunted birds, such as regular handwashing and avoidance of obviously sick animals.
There is little evidence that the current avian influenza wave poses an infection risk to humans. Only a few cases have been documented in the world, and those were general among people working with poultry.
For Alaskans dependent on wild game, this highly pathogenic influenza poses a different type of risk: possible food-security problems. If large numbers of birds wind up dying, that might mean less food on the table in rural Alaska, Ramey and Gerlach said.
“Obviously, less birds could equate to less availability, and also less resiliency in the population from things like disease, or climate change, or toxins, et cetera, that could in fact, impact these populations of birds,” Ramey said.
Plenty of stressors already exist in wild populations, he said, “so adding another threat to these populations isn’t doing them any favors.”
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