How deadly bird flu sparked explosive outbreaks in 2022 and why it matters for global health

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Throughout the last decade, the global spread of bird flu has been a growing concern in Canada, but most farms managed to avoid outbreaks.

The situation changed in 2022.

This year, a highly contagious strain of avian influenza tore across the country, hitting close to 270 farms and production facilities, sparking concerns over poultry shortagesand exposing workers from coast to coast to a potentially deadly pathogen.

So far, roughly 4.7 million domestic birds have caught the virus. That's not counting untold numbers of wild birds falling ill, whose numbers are far tougher to track.

"I would describe the scope as explosive and sort of all-encompassing," said Angela Rasmussen, a virologist with the Vaccine and Infectious Diseases Organization at the University of Saskatchewan. "I mean, it really is a huge problem globally, and here in Canada."

And it's a brewing crisis on two fronts, both to global bird populationsand potentially to human health, if this highly infectious form of the influenza virus eventually evolves to better transmit between people in the decades ahead.

"Eventually it could mutate itself such that it could gain the capacity and capability to transmit from poultry to humans," said Dr. Shayan Sharif, a professor with the Ontario Veterinary College at the University of Guelph in southern Ontario.

"And unfortunately this is the sort of worst-case scenario that we don't want to happen."

'Detections haven't stopped'

Since 2003, a particularly deadly H5N1 avian influenza strain has led to a high number of deaths in poultry and wild birds around much of the world, including Asia, the Middle East, Europeand Africa.

In 2014, Canada had its first detection of what's known as a"highly pathogenic" form of avian influenza virus, linked to poultry at a farm in British Columbia. A dozen farms and production facilities wound up dealing with cases that year, according to data provided to CBC News by the Canadian Food Inspection Agency (CFIA).

In the years since, there were few if any facilities affected anywhere in the country, the same data shows.

The explosion of cases across Canadathis year follows a similar pattern globally.The highly contagious straincan transmit quickly in areas with highconcentrations of poultry farms, such as Canada's Western regions, and its ongoing global spread may be linked to bird migration patterns.

"We can't really control migratory birds," said Sharif.

Given the scope of 2022 outbreaks across much of North America, there's concern the virus is now establishing itself on this continent.

"Historically, North America hasn't had tons of problems with avian influenza," said Louise Moncla, an assistant professor of pathobiology at the University of Pennsylvania school of veterinary medicine.

"This outbreak has been a little bit differentbecause it's been going on for a long time. And unlike the past outbreaks, detections haven't stopped."

The scale of global spread of this H5N1 strain has been enormous, with tens of millions of deaths, either through the spread of the virus itself or the preventative culling of farmed birds.

More than 70 countries have reported cases, said Gregorio Torres, head of the science department at the World Organization for Animal Health (WOAH). This severe form of the disease also spread further south this year into regions where infections weren't previously reported, including Colombia and Peru.

The U.S. also hit a grim new record for birds lost to avian influenza, at more than 50 million in 2022, surpassing the largest previous outbreak in 2015 while the number of states impacted this year is also more than double those affected seven years prior.

The other element making this outbreak different from prior ones isn't just the sheer numbers of birds being killed, but the number of species affected, Moncla said.

On farms, turkeys and chickens are being impacted. But cases have also been reported among cranes in Israel and hawks and bald eagles in parts of Canada and the U.S.. In Stratford, Ont., the virus likely claimed the lives of several of the theatre city's iconic swans.

"And then we've also had more infections in mammals," said Moncla.

"So we have what appears to be widespread transmission in seals, which is unusual for this type of influenza. We've had detections in bears and foxes, and [some] human infections. So it's been bigger in scope, more species infected, and then it hasn't stopped."

Put together, all those factors make it likely that bird flu will become endemic more commonplace in North American bird species going forward.

WATCH | 'Explosive' global outbreaks of avian influenza:

'Explosive' avian flu surge hits global bird populations

2 years ago

Duration 2:02

Global bird populations are being ravaged by a deadly strain of avian flu, wiping out flocks of domestic poultry and killing wild birds. Some researchers warn the virus could eventually evolve to better infect humans and potentially start a future pandemic.

Looming threat for human health

That's bad news for birds, both wild and farmed. But it's also a looming threat for humans, many scientists agree.

"We definitely need to be doing more human surveillance to understand the extent to which these viruses are actually spilling over into the human population," said Rasmussen.

"We only really notice human caseswhen it makes somebody really sick. But how often are people actually getting infected with this and may not know about it?"

The 1918 flu pandemic emerged from an avian influenza outbreak, she said, and was likely linked to a virus that quietly evolved to better infect humans decades earlier.

Alongside human surveillance, it's worth keeping an eye on other animal species that can provide "mixing vessels" for the influenza virus, Rasmussen said.

Pigs, for instance, are often living alongside farmed birds, allowing viruses to spread easily between those species. That's particularly worrisome when it comes to influenza, given its capacity for reassortment the process by which influenza viruses swap gene segments.

"So if a pig gets infected with a strain of human flu, and a strain of bird flu, they can essentially shuffle their viral genes and make new viruses," said Rasmussen. "And that, in fact, is how several pandemics throughout history have occurred a sort of a middleman or a 'middle pig' between these two speciesto further transmission of new viruses that might arise."

After a recent spike in bird flu outbreaks on commercial farms, the B.C. Centre for Disease Control sent out a communicable disease advisory in early Decemberasking doctors to be on the lookout for any instances of bird flu spreading to humans.

"Exposure to novel influenza viruses is concerning because of the potential for human adaptation and associated pandemic risk. Such risk may be considered a 'low probability, high impact' event," the advisory said.

Long-term, this influenza strain would also need to gain the ability to transmit swiftly person-to-person before it posed a true threat to human health.

For now, it only appears capable of infecting people in sporadic instances, and hasn't adapted to transmit efficiently among human populations.

Only four human cases of the virus have been reported globally this year, including one in the U.S., one in the U.K. and two in Spain.

"If it does transmit from humans to humans, then we will be seeing yet another pandemic," said Sharif. "Because this is an airborne virus, and it can be transmitted through aerosols or large droplets very similar to what we saw for COVID-19."

Concerns over poultry shortages, higher prices

Sharif's lab, at the University of Guelph, is one of the global research teams hoping to eventually create a vaccine against avian influenza to ensure future outbreaks aren't quite so devastating since at this pointthere's no shot against this strain available for use in Canada.

But he worries there's not much political will to develop a shot to fight a virus that, for now, mainly infects birds. Other scientists stress there's an economic argument to be made for keeping this influenza strain at bay.

"Bird flu would be a whole lot less of an issue for farmers and producers if there were a vaccine that could protect their flock from these various subtypes that are causing so much devastation," said Rasmussen.

This month in B.C., the province's poultry association even warned of a 20 per cent drop in available turkeys compared to previous yearsright before the winter holidays.

Food policy researcher Sylvain Charlebois, director of the Agri-Food Analytics Lab at Dalhousie University in Halifax, said bird flu outbreaks could lead to ongoing poultry shortages, pushing up food prices.

"Avian flu really represents a menace to our food security and to our own public health as well," he said.

"So it's a bit of a double whammy that I think requires a little bit more attention."