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New bird flu strain threatens North American wildlife

Thousands of seabirds, geese, eagles and vultures are dead, as wildlife health experts recommend a revolution in disease management.

The July 5 trip was routine: From the deck of an airboat, two wildlife biologists scanned the cattail marsh — one of many seasonal wetlands in the Sacramento National Wildlife Refuge — on their weekly lookout for sick or dead birds. In the summer months, avian botulism is a major concern in California’s Central Valley, and removing carcasses can stem its spread. But this year, there was added worry: A new and devastating strain of highly pathogenic avian influenza (HPAI) had been creeping West across the continent since December 2021, affecting millions of poultry and countless wild birds.

That day, the biologists carefully collected several carcasses, including two Canada geese and two American white pelicans, and sent the remains on to the U.S. Geological Survey’s National Wildlife Health Center lab for routine testing. Days later, the lab and then the U.S. Department of Agriculture confirmed: The avian flu’s H5N1 strain had finally reached California. 

This year’s avian flu epidemic — the first in North America since 2015 — is caused by a version of this virus unlike any that virologists and wildlife managers have ever seen. “It’s behaving by a different set of rules,” said Bryan Richards, emerging disease coordinator at the National Wildlife Health Center. For the first time, it’s spreading widely among wild birds, which has far-reaching implications for wildlife and human health.

Ben Walker, a wildlife technician at International Bird Rescue, examines a bird in the HPAI screening tent at San Francisco Bay-Delta Fish and Wildlife Office, California.Mackenzie Preble

Wildlife already face unprecedented stressors, from drought to wildfire to habitat loss. Now, emerging and widely infectious forms of avian influenza are yet another new and serious threat — one that wildlife biologists say requires a new approach to disease management on farms, refuges and landscapes nationwide. “We are in the midst of a completely unprecedented wildlife disease outbreak in North America,” said Rebecca Poulson, a University of Georgia research scientist who’s been studying bird flus for 15 years. “We’ve never seen anything like this.” 

BEFORE 1996, it was widely assumed that highly pathogenic avian influenzas only infected commercial poultry farms: These were virulent but contained outbreaks caused by on-farm mutations of a wild-bird-origin flu virus. While devastating to those farms, the mutated strains seemed unable to spread back into wild birds. This made outbreaks simple to manage with biosecurity prevention, isolation of exposed flocks, and swift culls.

In 1996, virologists first detected the H5N1 strain in domestic geese in Guangdong, China. That virus received global attention in 1997 when it sickened 18 people in Hong Kong, killing six. The outbreak prompted international fears of a human pandemic, but the virus never mutated in a way that enabled human-to-human transmission. International media paid less attention to the fact that, by 2002, H5N1 had acquired the ability to move from domestic flocks back into wild birds. The virus has been evolving ever since.

Though no infections have been documented in California condor yet, the endangered species is considered at risk of contracting avian influenza. Other scavenger species, including vultures, are among those most commonly infected.Parker Seibold

Today, several variants of HPAI are associated with “sporadic mortality events” in wildlife. In Newfoundland and Labrador in 2021, the current strain emptied seaside cliffs of thousands of gannets, puffins and murres. This August, it killed 700 black vultures at a Georgia sanctuary. Waterfowl, shorebirds, raptors and scavengers are at the highest risk. In Western states most recently hit by the virus, such species include threatened and endangered birds like the California condor and snowy plover, though agencies have not yet documented infections in either species. Common urban and suburban-dwelling Canada geese and corvids and nationally symbolic bald eagles are also at risk, as are the hundreds of millions of waterfowl whose migrations are beginning to peak now in Northern states and will continue south through late October.

“I think we’re just at the tip of the iceberg. We’re just sort of holding our breath to see what’s going to happen.”

The last major outbreak — caused by a related strain, H5N8 — reached North America in 2014, causing $3 billion in losses to U.S. farmers, who had to cull 50 million chickens, turkeys and waterfowl. This year’s outbreak has so far affected a similar number of commercial birds, but it is orders of magnitude larger in wild landscapes. Via wild-bird transmission, it has reached nearly 10 times the number of backyard poultry, and while the 2014-15 outbreak was documented in just 18 wild bird species across 16 states, this year it’s been confirmed in at least 108 wild bird species, with cases in nearly every state. In another unusual development, many mammal-crossover cases and deaths have been confirmed, too, in foxes, skunks, opossums, raccoons, bobcats, minks, harbor seals, a juvenile black bear and one bottlenose dolphin. Labs are so overwhelmed that wildlife officials say they’ve stopped submitting carcasses of species that have already been documented in their county. They’re also only submitting a few birds per mortality event, making the official wild bird death figures a gross underestimate.

The next few months could be even worse. Flocks across the continent are migrating now toward Central and South America, home to the largest diversity of bird species on Earth. “I think we’re just at the tip of the iceberg,” Poulson said. “We’re just sort of holding our breath to see what’s going to happen.”

Jennifer Martines, a wildlife technician at International Bird Rescue, examines a female mallard while screening for avian influenza.Ariana Gastelum

AMONG WESTERN STATES THIS FALL, California is most likely to feel the brunt of the impacts: It’s one of the nation’s largest egg producers, and commercial poultry meat is the state’s sixth-largest commodity, worth $1 billion annually. California’s Central Valley provides essential migration and wintering grounds for wild birds: The Sacramento National Wildlife Refuge Complex alone is visited by tens of millions of migrants each fall. It supports nearly 40% of the continent’s northern pintails (one of the most numerous duck species in the world), and hosts a total overwintering population of some 1.5 million birds.

This year’s drought means wintering flocks may be both unusually crowded and especially mobile, heightening the risk of viral spread, said Michael Derrico, the refuge’s lead wildlife biologist. Since the refuge’s wetlands are half their normal size, birds will be forced into closer proximity and may move frequently to find resources, which Derrico thinks may also push birds farther south.

“Once a disease becomes established in a free-ranging population, then you really lose the upper hand.” 

Derrico’s concern for birds in the Pacific Flyway is somewhat tempered by the fact that, so far, the country’s westernmost migratory channel doesn’t seem to have as much of the virus as other regions do. But he and other wildlife managers are also very limited in what they can do to mitigate potential impacts.

“Once a disease becomes established in a free-ranging population, then you really lose the upper hand,” said Richards, from his USGS home office near Madison, Wisconsin. “We’re really, really good at documenting disease on the landscape, but we’re less good at altering disease outcomes.” Instead, he said, “some of us are beginning to pivot towards a conversation of wildlife health as opposed to wildlife disease.”

Left, Adriaan Dokter/BirdCast, Cornell Lab of Ornithology; Right, National Wildlife Health Center/USGS

For Derrico, at the Sacramento refuge complex, promoting health instead of preventing disease might involve investing more in wetland management to ensure that birds have access to the largest habitat possible, and minimizing human disturbance to prevent scattering birds to new areas. In many parts of the country, bald eagles and other raptors are already experiencing widespread mortality from lead poisoning by bullets and fishing tackle, and Richards said that addressing that issue might be a better use of resources.

“That’s something we can control, right?” he said. Combined with improving biosecurity measures on farms, by tackling environmental factors that are within human reach, Richards believes wildlife managers may be able to increase bird resilience even in the face of deadly new diseases.

The pressure to change wildlife disease management is only increasing. “When you look globally at emerging infectious diseases, we’ve seen some pretty interesting trends,” Richards said. “We have seen more new diseases, larger disease outbreaks, more frequently, and with larger impacts.” That includes some with the potential to cause species extinction, and, as seen recently with COVID-19, ones that could mutate to become widely infectious and transmissible in humans. Virologists believe the risk of that happening in this H5N1 strain is low, but recommend that hunters, farmworkers and other bird handlers take extra precautions this year anyway. Of all the emerging diseases that threaten people, Richards said, a majority have originated in wildlife.

Sarah Trent is an editorial intern for High Country News based in southwest Washington. Email her at sarah.trent@hcn.org or submit a letter to the editor. See our letters to the editor policy.

Source: HCN