How mud samples help scientists track ‘unprecedented’ levels of avian flu in B.C.

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It’s the ultimate needle in a haystack.

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A minuscule strand of avian flu DNA in a scoop of mud and bird droppings is helping B.C. virus detectives track how avian flu is spreading through wild bird populations, with implications for animal and human health.

“This year we’ve seen unprecedented levels of environmental contamination,” said Chelsea Himsworth, the provincial deputy chief veterinary officer and an associate professor at the University of B.C.

Every two weeks, the vet and her team take samples from seven wetlands across the Fraser Valley, or “Mother Nature’s outhouses,” as she sometimes calls them, including Mill Lake in Abbotsford, Sardis Pond in Chilliwack and the Roberts Bank foreshore in Tsawwassen.

Within the last month, 21 sediment samples have tested positive for avian flu DNA. The team also tests dead birds, recording 50 positive cases.

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B.C. is the only area in North America that Himsworth is aware of that includes environmental testing as part of a regular program to track avian flu outbreaks. The sediment samples give officials “situational awareness” and have proved the best predictor of “spillover” into domestic poultry flocks.

“The wild birds aren’t actually getting into the barns,” she said. “They’re contaminating the environment, which increases the probability that a farm will be exposed.”

Passing on testing information to poultry farmers allows them to adjust their practices. As migratory birds began their descent from northern regions to arrive in the Fraser Valley this fall, farmers ramped up biosecurity measures to “red” alert.

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The testing also provided health officials with important data as B.C. detected its first case of bird flu in a human.

When a teen was hospitalized with H5N1 three weeks ago, B.C. health officials began extensive contact tracing to try to determine the source of the exposure — a mystery that, if solved, could tell scientists more about how avian flu is mutating and moving.

More than 25 dogs, cats, reptiles, birds and rodents were tested, along with 16 of the teen’s close family and friends. All came back negative for H5N1.

In a press conference earlier this week, Dr. Bonnie Henry, B.C.’s provincial health officer, said the strain that infected the teen has been detected in wild birds and poultry outbreaks, but is not related to the strain found in U.S. dairy cattle. Its genome is most closely related to a sample found in October in two cackling geese, a species that looks like a smaller version of a Canada goose.

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“That tells us a lot. It helps us understand where the potential exposures might be,” said Henry.

Because the genome is not a direct match, there was likely an intermediary, either another bird or animal, between the geese and the teen, she said.

The severity of the B.C. teen’s case and growing number of bird flu cases in the U.S. raises the spectre of another pandemic, with experts concerned about a mutation that could allow for human-to-human transmission.

“We are very aware of the pandemic potential of avian H5N1,” said Henry, advising people to get a flu shot, avoid sick animals and birds and keep away from ponds and marshes where wild birds live.

B.C. is a haven for many species of wild birds, particularly waterfowl, with its mix of estuary habitat and productive agricultural land, said Jasper Lament, CEO of the Nature Trust of B.C. and biologist who finds migratory birds “endlessly fascinating.”

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Every fall, a “river of birds” move north to south on the Pacific flyway, he said. Some stop to refuel on their migration, while others spend the winter. Snow geese, in particular, impress crowds of bird watchers as they arrive in the Fraser Valley after flying 5,000 kilometres from their summer nesting grounds on Wrangel Island in northeast Russia.

On a recent November day, several vehicles were stopped on the edge of a corn field in Abbotsford, where hundreds of snow geese were feeding among the stubble. A passing car was enough to send the birds whirling into the air in seemingly perfect unison, obscuring the sky in a rush of gleaming white feathers before settling down again.

Less appreciative of the sight are farmers, particularly chicken farmers who understand the risks of sick birds, but also those who grow forage crops for cows and see their grass crops consumed.

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“It puts you on edge,” said Derek Janzen, an Aldergrove chicken farmer.

Since October, 54 flocks across B.C. have tested positive for avian flu. More than 7.2 million birds, including chickens, turkeys and other domestic poultry, have been infected since 2022.

Janzen said farmers have noticed outbreaks seem to follow windstorms, where more wild birds are blown in from the coast. In a mild winter, birds seem to linger longer in the Fraser Valley, while a “nice hard freeze” will send them south.

While avian flu has reappeared annually with migrating wild birds, farmers haven’t grown accustomed to the uncertainty and fear, said Janzen. “When you open the barn door in the morning and you look in, you’re hoping everyone is OK.”

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An outbreak at a farm, and the ensuing bird cull, is “scary and traumatic.”

Jesse Zeman, executive director of the B.C. Wildlife Federation, said “hunting is a tool” that can be used to reduce bird populations and disturb flocks grazing in fields near chicken barns.

He said hunting is limited because many of the birds graze on private land and farmers may not let hunters on their fields due to avian flu concerns. The province could help by building a program that “incentivizes” hunting of certain species.

Snow geese numbers are exploding across North America.

The population on Wrangel Island has gone from around 50,000 in the 1970s to over 300,000 last year, according to a news story by Northwest Public Broadcasting in Washington State, which quoted several American biologists.

For Himsworth, whose mud samples help to determine how the virus is moving across the landscape, the fall migration is a source of tension, but also an opportunity to see how wild bird populations are adapting to the virus — and how humans may have to adapt as well.

With files by Cheryl Chan

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