Avian Flu’s Toll on Wild Birds Alarms Experts

A great black-backed gull migrating from Europe to Eastern Canada last winter may have been the first carrier to strain the avian influenza of North America that killed tens of millions of domestic poultry and devastated wild bird populations.

The wide-scale outbreaks have provided researchers with a new opportunity to fine-tune their understanding of the disease by which wild bird species, behaviors and ecologies play key roles in transmission.

“Previous studies looking at bird flu made these large categorizations of wild and domestic birds,” said Dr. Nichola Hill, an assistant professor of biology at the University of Massachusetts Boston and lead author on a new paper on the topic.

But “wild birds are incredibly species-rich,” she said, adding that “each of them has a unique natural history and behavior.”

Knowing which migratory species carry the pathogen, for example, can help predict when and where it may be based on migration routes.

After the migrating gull came ashore, the highly pathogenic avian influenza, also known as the H5N1 virus, exploded across North America. More than 77 million poultry, most raised in crowded conditions that fueled the spread and evolution of the virus, have been culled in dozens of countries.

For some experts, the toll wrought by this H5N1 strain on wild birds – it has struck more than 100 species so far – has been alarming and unprecedented in its depth and breadth. Among wild birds, the spread can be very difficult to contain, posing a greater threat to spillover to other wildlife. And some wild bird species, like cranes and some seabirds, are particularly vulnerable, especially those with low reproductive rates and those already endangered.

The World Organization for Animal Health estimates that more than 383,000 wild bird deaths can be attributed to the virus since October 2021, though the count may be a huge underestimate because of how difficult it is to track sick and dead birds.

The pathogen has spread rapidly through various regions and species, at much higher rates than during the last outbreak in 2014-2015.

“It’s impacting a larger host range and doesn’t dead-end in the wild like it used to,” Dr. Hill said. “It is sustained in wild birds, and that is a frightening prospect. For many of us in this field, my God, what do we do when we get a spillover in a wild animal for which there is no control? “

It has long been assumed that the avian flu for the primary hosts are dabbling ducks, such as mallards, teals and shovelers, that feed on the surface and just below their rumps in the air. They are critical to the spread because they have mild or no symptoms and they carry it far and wide. The new study, however, found that other birds, like geese, played an underestimated role because of their natural history.

“Geese are a little more tolerant of human-disturbed areas,” Dr. Hill said. “Imagine a commercial poultry operation or backyard operation where they spread grain around.” That attracts “geese and other scavenging birds, like gulls and crows and magpies, so there’s an interface between them,” she said.

The unique natural history of the black-backed gull, for example, plays a role in transmission. “Gulls were really rare hosts for highly pathogenic forms of the virus,” Dr. Hill said. “When they did carry it, those rare occasions, they spread it really quickly. There is nothing like a gull for a really rapid dispersal of the virus and really long distances. They will catch a tail wind and cross the Atlantic in 24 hours. “

The study may help other researchers track not only the continued spread of this year’s pathogen, but the paths taken by other viruses that are harmful to wildlife.

“Knowing that gulls, geese and ducks may be moving into this virus is a different contribution to understanding or eventually modeling how to expect more accuracy with a virus like this spread,” said Jonathan Runstadler, professor and chair of the department. Infectious Disease and Global Health at Tufts University’s Cummings School of Veterinary Medicine and a co-author of the paper.

The data “allows us to predict if there is a virus emerging, when a bird may enter North America and what bird populations we may target to detect surveillance,” Dr. Runstadler said.

The highly pathogenic lineage of this year’s avian flu originated around 1996, found first in a domestic goose in China. It has been circulating around the world in wild and domestic birds ever since, evolving as it travels from host to host.

In 2005, after a decade of evolution, the strain caused a large outbreak in wild birds in wetlands in China.

The strain showed up in the United States for the first time in 2014, migrating birds from Eurasia across the Pacific to Alaska and Farther East, causing outbreaks at US poultry farms that resulted in the killing of 40 million turkeys and chickens.

After it reached the Midwest, however, mass cullings stopped, eliminating the viral spread for both wild and domestic populations.

“We don’t have a vaccine,” said Dr. Hill said. “All we have in our tool kit is the swapping out of our poultry, which is awful, but to some degree it was successful.”

But killing off infected poultry has not worked this time around, in part because the virus has been able to find a home in so many wild birds, spawning the largest outbreak of avian influenza ever.

In some places, officials have been warning chicken producers and even people who keep their birds indoors, while in other places, the threat seems to have passed.

“This virus is so good because it ping-pongs back and forth between wild and domestic,” Dr. Hill said. “There is no better way to amplify a virus than to take a wild reservoir and domesticate it to a close relative. That ‘s exactly what we’ve done with chickens and ducks. Highly pathogenic forms of the virus only occur when the virus goes into agricultural animals. “

On Quebec’s Magdalen Islands, wildlife officials have recently discovered thousands of white gannets of carcasses that were wiped out by the flu.

There is no way to predict if the flu outbreaks will dwindle or grow worse.

Some species, such as raptors, seabirds and shorebirds, are also at great risk of catching the virus because of their behavior. Dozens of bald eagles are known to have died of the flu, mainly because they ducks on prey and other birds that carry the pathogen.

Birds that gather in large numbers are also at risk. “There are a lot of flocking birds – shorebirds, terns and seabirds – that form huge, massive groups and that could just be a virus for a field day,” said Dr. Hill.

The extent of the devastation to various species is difficult to assess, because surveillance is lacking. Better tracking along migration routes will help experts figure out ways to mitigate the spread of the virus.

Large numbers of shearwaters and other seabird species have been reported along the Atlantic coast in Massachusetts, Maine, New Hampshire and Connecticut. The avian flu is a suspect, though tests have not confirmed that.

“The detection of the geographic range, the number of species that we’re getting with the detections, the amount of disease we’re seeing in the wild, it’s all unprecedented,” said Andy Ramey, a US Geological Survey research wildlife geneticist in Alaska. who studies avian influenza. “It’s an unknown language and hard to know what to expect.”

There is also concern that during this year’s breeding season for many species, parents could pass on the disease to offspring in the nest, which has underdeveloped immune systems. Young wild birds are often exposed to low-pathogenic viruses, which are common and can serve almost as inoculations, helping strengthen their immune systems.

An endangered species is being monitored on the roseate tern of Buzzards Bay off the coast of Massachusetts. Testing is just getting underway, and no sick birds have been found yet.

“It does appear to be a rough food year for the terns,” said Carolyn Mostello, a coastal bird biologist for the Massachusetts Division of Fisheries and Wildlife. “Nesting has been slow. Hopefully we don’t have a combination of poor food resources and avian flu; That could act together to really injure the populations. “

Experts say the avian flu poses a very low risk to people and so far has been detected in only two humans. However, as it persists and evolves, it could gain the potential to pose a serious threat to spillover into humans.

Dr. Hill said that a major handicap to better understand the outbreak has been the lack of funding to track the spread. “Surveillance is really, really, really bad,” she said. “We are spending very little money and time getting ahead of this.”

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