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Analysis | Bird flu outbreak is a wake-up call for agriculture


Perhaps we can blame Covid fatigue for numbing us to the risks of other viruses. But it should be bigger news that an avian flu has mutated to spread through mammals and is emerging ominously among wild and domestic animals around the world. 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 that this version, which spreads through minks, can be easily transmitted from humans, but it has taken a step in a dangerous direction.

It’s unthinkable to consider lockdowns or masking mandates for a new disease, so it’s better to take simpler, cheaper measures early on. What matters now is monitoring farm animals and abandoning particularly dangerous practices. Maybe we just can’t have mink coats and cheap eggs.

One of the reasons there are now so many dangerous animal viruses out there is that the overcrowded conditions of large-scale animals tend to spread viruses – and there has never been such a global demand for meat, dairy and eggs . As one study found, egg-laying chickens in major surgeries are genetically identical, have no immunity to the flu, and are easily caught in viral bonfires.

While it may cost money to switch to safer chicken farming practices, doing nothing is also expensive. Last year, egg prices soared as 58 million US birds were wiped out in H5N1 outbreaks.

The outbreak that has fueled the latest fears occurred at a mink farm in Spain. “The fact that it has spread throughout 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 that all farms around the world are under proper surveillance, and since a positive test means they’re forced to kill valuable animals, farmers may have an incentive to avoid doing so.

“We’re getting better, but there’s a value to integrating surveillance systems,” Bender said. We have talked about improving it, but there is still a long way to go.”

Mink farms can pose a pandemic risk not worth having. They are not a source of food – and there are safer sources of fur. They are usually raised in close proximity and unlike most farm animals, they are carnivores and can pick up viruses from the animals they are given. Farmed minks sometimes get discarded chicken carcasses, Bender said, which may contain H5N1. And there are plenty of opportunities for people who work on mink farms to become infected. In the worst case, an employee would pick up a variant of this virus that can pass from person to person. “That’s exactly the pandemic scenario we’re concerned about,” Bender said.

It’s not yet clear whether multiple animals picked up the virus individually from a contaminated batch of food, but researchers have found that the virus originated from a number of hot spots, indicating that one or two infected animals likely spread the disease to their neighbors. Genetic testing showed that this virus carried a mutation that allowed it to spread in both mammals and gulls. This suggests that seagulls still carry this variant in question.

H5N1 has a natural host in wild waterfowl, and some of them carry the virus around the world with their migrations. It was first discovered capable of jumping at humans in southern China and Hong Kong in the 1990s, and has been bubbling up around the world ever since. What’s worrying now is that it’s invading so many new hosts – eagles, owls, as well as foxes, grizzly bears and seals.

In birds, H5N1 is a gastrointestinal virus, spread through feces, but it can become a respiratory virus in mammals, said Purdue University virologist David Sanders. The gastrointestinal tract and respiratory tract are similar enough that the virus can easily adapt from one to the other.

Most bird flu isn’t equipped to get into mammalian cells, Sanders said, but this bird flu virus is what scientists call promiscuous. “If it’s transferred to mink, it hasn’t had time to be a mink-specific thing — so there’s a good chance it could go to humans,” he said. So far we haven’t seen a version that can spread from human to human, but only through sheer luck.

Sanders said the deadly 1918 flu pandemic started with an avian flu that jumped to humans, and that the 2009 swine flu was a descendant of this virus, having jumped from human to pig in the 1920s before passing back to humans. Similarly, there is still a view that the omicron variant of SARS-CoV-2 acquired its large number of mutations by jumping from one human to another animal and then back to humans again.

As counterintuitive reassurance, Sanders said that if H5N1 started spreading in humans and it remained 50% lethal, it could be more easily controlled, like SARS1 in 2005. The Covid-19 pandemic is fueled by a combination of transmission before symptoms begin and people who get such minimal symptoms that they have no idea they are sick as 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 “more deadly” than SARS-CoV-2. In addition, we already have a vaccine for H5N1, although it would take months to scale up production.

Still, why wait to find out just how deadly a human H5N1 pandemic would be? Due to cost-cutting measures and massive agriculture, we already got foot and mouth disease and mad cow disease. And from a virus point of view, we humans, with our urban lifestyles, are exactly the equivalent of captive animals in one big, interconnected global farm.

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This column does not necessarily reflect the views of the editors or Bloomberg LP and its owners.

Faye Flam is a Bloomberg Opinion columnist on science. She hosts the “Follow the Science” podcast.

More stories like this are available at bloomberg.com/opinion

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