New strain of bird flu threatens North American wildlife

New strain of bird flu threatens North American wildlife

The July 5 trip was routine: From the deck of an airboat, two wildlife biologists scanned the cattail marsh — one of several seasonal wetlands in the Sacramento National Wildlife Refuge — in search of weekly sick or dead birds. During the summer months, avian botulism is a major concern in California’s Central Valley, and carcass disposal can stem its spread. But this year, concern has grown: a devastating new strain of highly pathogenic avian influenza (HPAI) has been spreading west across the continent since December 2021, affecting millions of poultry and countless birds. wild.

That day, biologists carefully collected several carcasses, including two Canada geese and two American white pelicans, and sent the remains to the US Geological Survey’s National Wildlife Health Center laboratory for routine testing. A few days later, the laboratory and then the US Department of Agriculture confirmed: the H5N1 strain of bird flu had finally reached California.

This year’s bird flu outbreak – the first in North America since 2015 – is caused by a version of the virus unlike any virologists and wildlife managers have ever seen. “It behaves by a different set of rules,” said Bryan Richards, emerging disease coordinator at the National Wildlife Health Center. For the first time, it is spreading widely among wild birds, with profound implications for wildlife and human health.

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

Mackenzie Preble

Wildlife is already facing unprecedented stressors, from drought to wildfires to habitat loss. Today, emerging and widely contagious forms of avian influenza are still 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 epidemic in North America,” said Rebecca Poulson, a University of Georgia research scientist who has studied bird flu for 15 years. “We have never seen anything like it.”

BEFORE 1996, highly pathogenic avian influenza was widely believed to infect only commercial poultry farms: these were virulent but contained outbreaks caused by on-farm mutations of an influenza virus of wild avian origin. Although devastating to these farms, the mutated strains seemed unable to spread to wild birds. This has simplified the management of outbreaks through biosecurity prevention, isolation of exposed herds, and rapid culls.

In 1996, virologists first detected the H5N1 strain in domestic geese in Guangdong, China. This virus captured worldwide attention in 1997 when it sickened 18 people in Hong Kong, killing six. The outbreak sparked international fears of a human pandemic, but the virus never mutated in a way that allowed human-to-human transmission. International media paid less attention to the fact that in 2002, H5N1 acquired the ability to jump from domestic flocks to wild birds. The virus has continued to evolve ever since.

Although no infection has yet been documented in the California condor, the endangered species is considered to be at risk of contracting bird flu. Other scavenger species, including vultures, are among the most frequently infected.

Today, several variants of HPAI are associated with “sporadic mortality events” in wildlife. In Newfoundland and Labrador in 2021, the current strain emptied coastal cliffs of thousands of gannets, puffins and guillemots. This August, he killed 700 black vultures at Georgia sanctuary. Waterfowl, shorebirds, raptors and scavengers are most at risk. In the western states most recently hit by the virus, these species include threatened and endangered birds like the California condor and snowy plover, though agencies have yet to document infections in either or all of them. the other of the species. Canada geese and common urban and suburban corvids and the 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 are will continue south until the end of October.

“I think we’re just the tip of the iceberg. We just hold our breath to see what will happen.

The last major outbreak – caused by a related strain, H5N8 – reached North America in 2014, causing US farmers $3 billion in losses, who had to slaughter 50 million chickens, turkeys and birds aquatic. This year’s outbreak has so far affected a similar number of commercial birds, but is an order of magnitude larger in wild landscapes. Via transmission by wild birds, it reached almost 10 times the number of backyard poultry, and although the 2014-15 outbreak was documented in only 18 species of wild birds in 16 states, this year, it has been confirmed in at least 108 species of wild birds, with cases in nearly every state. In another unusual development, numerous cases and deaths of mammal crosses have also been confirmed in foxes, skunks, opossums, raccoons, bobcats, mink, harbor seals, a juvenile black bear and a big dolphin. The labs are so overwhelmed that wildlife officials say they have stopped submitting carcasses of species that have already been documented in their county. They also only submit a few birds per mortality event, making official wild bird mortality figures a gross underestimate.

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

Jennifer Martines, wildlife technician at International Bird Rescue, examines a female mallard during an avian flu screening.

Ariana Gastelum

AMONG THE WESTERN STATES THIS FALL, California is most likely to feel the brunt of the impacts: it is one of the nation’s largest egg producers, and commercial poultry meat is the state’s sixth-largest commodity, worth $1 billion a year. California’s Central Valley provides critical 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 is home to almost 40% of the continent’s northern pintails (one of the most numerous duck species in the world) and supports a total wintering population of around 1.5 million birds.

This year’s drought means overwintering herds can be both unusually crowded and particularly mobile, increasing the risk of viral spread, said Michael Derrico, the refuge’s senior wildlife biologist. Since the wetlands in the refuge are half their normal size, the birds will be forced closer together and may move frequently to find resources, which Derrico says can also push the birds further south.

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

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

“Once a disease has established itself in a free-ranging population, you really lose the upper hand,” said Richards, from his USGS home office near Madison, Wisconsin. “We’re really, really good at documenting disease in the landscape, but we’re less good at altering disease outcomes.” Instead, he said, “some of us are starting to move towards a conversation about wildlife health versus 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 could mean investing more in wetland management to ensure birds have access to as much habitat as possible and minimizing human disturbance to avoid dispersing birds to new areas. In many parts of the country, bald eagles and other raptors are already experiencing widespread mortality from lead poisoning from bullets and fishing gear, and Richards said solving that problem could be better use of resources.

“It’s something we can control, isn’t it?” ” he said. Combined with improving biosecurity measures on farms, addressing environmental factors that are within human reach, Richards believes wildlife managers may be able to increase the resilience of even birds. 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’ve seen more new diseases, bigger outbreaks, more frequently and with bigger impacts.” This includes some that could cause species extinction and, as seen recently with COVID-19, those that could mutate to become widely infectious and transmissible to humans. Virologists think the risk of that happening in this H5N1 strain is low, but recommend that hunters, farmhands and other bird handlers take extra precautions this year anyway. Of all the emerging diseases that threaten people, Richards said, the majority come from wildlife.

Sarah Trent is a writing intern for High Country News based in southwest Washington. Email him at [email protected] or submit a letter to the editor. See our letters to editor policy.

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