Bird flu keeps spreading beyond birds. Scientists worry it signals a growing threat to humans, too

As a deadly form of avian influenza continues to ravage bird populations across much of the world, scientists are tracking infections among other animals — including various types of mammals closely related to humans.

throughout the past year, Canadian And US officials Highly pathogenic H5N1 avian influenza has been detected in a range of species, from bears to foxes. In January, the National Reference Laboratory in France announced that a cat had experienced severe neurological symptoms from infection in late 2022, as the virus had shown genetic characteristics to adapt to mammals.

More concerning, several researchers said, was a recent outbreak of the disease at a Spanish mink farm.

This past October, farm workers began noticing a high mortality rate among the animals, with sick mink experiencing a host of serious symptoms such as loss of appetite, excessive salivation, bloody snout, tremors, and an inability to control muscles.

The culprit ended up being H5N1, marking the first known case of this type of avian influenza infection among mink farmed in Europe, a study suggests. Posted in Eurosurveillance this month.

“Our findings also suggest that transmission of the virus to other mink may have occurred on the infected farm,” the researchers wrote.

In the end, the entire mink population—more than 50,000 animals in all—was killed or culled.

This is a significant shift, after only sporadic cases in humans and other mammals over the past decade, according to Michelle Weil, a researcher at the University of Sydney who focuses on the dynamics of wild bird viruses.

“This outbreak indicates a very real possibility of emerging mammalian-to-mammalian transmission,” she said in an email with CBC News.

It’s just one farm, and in particular, none of the workers — who were all wearing face shields, masks, and disposable overalls — became infected.

But the concern now, said Toronto-based infectious disease specialist Dr. Isaac Bogosh, is that if this virus mutates in a way that allows it to become increasingly transmissible among mammals, including humans, “it could have fatal consequences.”

“This is an infection that has epidemiological and epidemiological potential,” he said. “I don’t know if people realize how big of a deal this is.”

watch | Explosive avian influenza affects birds in the world:

H5N1 has a high mortality rate

Among birds, the mortality rate from this highly pathogenic strain of avian influenza can approach 100 percent, wreaking havoc on both wild birds and poultry farms.

It is also often fatal to other mammals, including humans.

The World Health Organization (WHO) has documented 240 cases of H5N1 avian influenza in four Western Pacific countries – including China, Cambodia, Laos and Vietnam – over the past two decades. More than half of those infected died.

Global WHO figures show more than 870 human cases were reported from 2003 to 2022, along with at least 450 deaths – Mortality rate of more than 50 percent.

The reported death toll may have been exaggerated, Bogosh said, as not all infections can be detected, although it is clear that people can “become very, very ill from this infection.”

Most human infections appear to involve people in direct contact with infected birds. Mink-to-mink transmission of the virus in the real world now strongly suggests that H5N1 is now “poised to emerge in mammals” — and while the outbreak in Spain may have been the first reported case of a mammalian spread, Willy says, it may not be the last.

And she warned that “a virus that evolved in a mink farm and then infects farm workers exposed to infected animals is a very plausible route for the emergence of a virus capable of human-to-human transmission.”

Having an “intermediate host” is a common mechanism by which viruses adapt to new host species, explained Louise Moncla, assistant professor of pathobiology at the University of Pennsylvania College of Veterinary Medicine.

“And the concern about this is that this is exactly the kind of scenario you would expect to see that could lead to this kind of adaptation, which might allow these viruses to replicate better in other mammals — like us.”

Surveillance and vaccinations are both required

Even more reassuring is the continued development of influenza vaccines, giving humanity a head start on the known threat posed by avian influenza.

Wiley noted that the early spread of H7N9, another strain of bird flu that caused hundreds of human cases in early 2010, raised similar concerns that the virus would acquire the mutations needed for sustained human-to-human transmission.

“But an aggressive and successful poultry vaccination campaign ultimately stopped all human cases,” she added.

But while many H5N1 avian flu vaccines have been produced, Including one made in CanadaThere is no approved option for general use in this country.

To fend off the potential threat this strain poses to human health, Bogosh said continuous monitoring and vaccine production must remain a top priority for both policymakers and vaccine manufacturers.

Dr. Jan Hajek, an infectious disease physician at Vancouver General Hospital, wondered if it might be time to stop global mink farming, given the spread of various viruses, from avian influenza to SARS-CoV-2, the virus behind COVID-19.

“We’re closely related to minks and ferrets, in terms of the risks of influenza… If it’s circulating in minks, killing minks, that’s a concern to us,” he said.

in 2021, British Columbia officials have announced an end to mink farming across the province, saying that farms can be reservoirs for viruses and represent an ongoing risk to public health. All mink farm operations, with all skins sold, must be closed by April 2025.

However, other provinces – and many countries – intend to keep their mink farms running.

“Is it responsible that these kinds of cultivation conditions are where these kinds of events can occur?” Moncla interrogated. “If we’re going to continue to have these types of farms, what can we do to make this safer?”