Outbreak of bird flu should make agriculture sit up and take notice

It should be bigger news that a bird flu has mutated to spread through mammals and is 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 moved 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.

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 U.S. birds were destroyed in H5N1 outbreaks.

The outbreak that has spurred the latest fears happened at a mink farm in Spain. In this case, surveillance 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.

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. 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.

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 hot spots, 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 many 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 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? From the point of view of a virus, humans are the equivalent of captive animals.