Perhaps we can blame Covid fatigue for numbing us to the risks of other viruses. But it should be bigger news that a bird flu has mutated to spread through mammals and is ominously appearing among wild and domesticated animals around the globe. In the past, the inability to spread from one mammal to another was the barrier that prevented bird flu, H5N1 — which has a 50% fatality rate in humans — from becoming a human pandemic. It’s not clear this version, which spread through minks, would be easily transmitted in people, but it has made a step in a dangerous direction.
It’s unthinkable to consider lockdowns or mask mandates over some new disease, which is why it’s better to take simpler, less costly action early. What matters now is surveillance among farmed animals and giving up particularly dangerous practices. Maybe we just can’t have mink coats and cheap eggs.
One reason there so many dangerous animal viruses around now is that the crowded conditions of mass-farmed animals tend to spread viruses — and there has never been more worldwide demand for meat, dairy products and eggs. As one investigation revealed, egg-laying chickens in big operations are genetically identical, have no immunity to influenza and make easy kindling for viral bonfires.
While it might cost money to move to safer chicken farming practices, doing nothing is expensive, too. Last year, egg prices rose as 58 million US birds were destroyed in H5N1 outbreaks.
The outbreak that has spurred the latest fears happened at a mink farm in Spain. “The fact that it spread through the facility is quite concerning,” said Jeff Bender, a professor of veterinary medicine at the University of Minnesota.
In this case, the surveillance system worked — the outbreak was identified, people were tested and found to be negative, and more than 50,000 minks were euthanized. But it’s not clear all farms around the world are under good surveillance, and since getting a positive test means being forced to kill valuable animals, farmers may have an incentive to avoid it.
“We’re getting better but there’s a value for integrating surveillance systems,” Bender said. We’ve been talking about improving it, but there’s a long way to go.”
Mink farms may pose a pandemic risk that’s not worth having. They aren’t a source of food — and there are safer sources of fur. They are typically raised in close quarters, and unlike most farm animals, they are carnivores and can pick up viruses from the animals they are fed. Farmed minks sometimes get fed discarded chicken carcasses, Bender said, which can harbor H5N1. And there are plenty of opportunities for people working on mink farms to get infected. In a worst-case scenario, a worker would pick up a variation of this virus capable of moving from human to human. “That’s exactly the pandemic scenario we worry about,” said Bender.
It isn’t yet clear whether multiple animals picked up the virus separately from a contaminated batch of food, but researchers have found that the virus emanated from a couple of hotspots, indicating that one or two infected animals likely spread the disease to their neighbors. Genetic tests showed that this virus carried a mutation that allows it to spread in mammals as well as one that has been identified in gulls. That suggests gulls are still carrying this concerning variant.
H5N1 has a natural host in wild waterfowl, and some of them carry the virus around the globe with their migrations. It was first discovered to be capable of jumping to humans in southern China and Hong Kong in the 1990s, and has been bubbling up around the world ever since. What’s worrisome now is that it’s getting into so may new hosts — eagles, owls, as well as foxes, grizzly bears and seals.
In birds, H5N1 is a gastrointestinal virus, spread by droppings, but it can become a respiratory virus in mammals, said Purdue University virologist David Sanders. The gastrointestinal tracts and respiratory tracts are similar enough that the virus can adapt easily from one to the other.
Most bird influenza isn’t equipped to get into the cells of mammals, said Sanders, but this bird flu virus is what scientists call promiscuous. “If it’s transmitted to mink, it hasn’t had time to be a mink-specific thing — so there’s a good chance it can go to humans,” he said. So far, we haven’t seen a version that can spread from human to human — but only by pure luck.
Sanders said the deadly 1918 flu pandemic started with a bird flu that jumped to humans, and the 2009 swine flu was a descendant of this virus, having jumped from humans to pigs in the 1920s before jumping back to humans. Likewise, there is still a school of thought that the omicron variant of SARS-CoV-2 had acquired its large number of mutations by jumping from a human to another animal and then back to humans.
As a point of counterintuitive reassurance, Sanders said that if H5N1 did start spreading in humans and it remained 50% lethal, it might be more easily contained, like SARS1 was in 2005. The Covid-19 pandemic is being fueled by a combination of transmission before symptoms start and people who get such minimal symptoms that they have no idea they’re sick while they circulate and spread disease. And by staying in the upper respiratory tract, omicron is even more wildly contagious than its predecessors.
So there is no guarantee that an H5N1 pandemic would be “even deadlier” than SARS-CoV-2. Plus, we already have a vaccine for H5N1, although it would take months to scale up production.
Even so, why wait to find out how deadly a human H5N1 pandemic would be? Cost-saving measures and mass farming already gave us foot and mouth disease and mad cow disease. And from the point of view of a virus, we humans, with our urban lifestyles, are just the equivalent of captive animals in one vast, interconnected worldwide farm.
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This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.
Faye Flam is a Bloomberg Opinion columnist covering science. She is host of the “Follow the Science” podcast.
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