Zoonotic transmission: Bird flu is our fault

We don’t yet know if H5N1 bird flu will spill over from animals to infect a large number of humans. Based on the few cases of transmission so far, the World Health Organization has expressed concerns that infection in humans “can cause severe disease with a high mortality rate.”

But already it has wrought devastation upon so many lives. The deaths of millions of birds and mammals around the globe in the last few years directly and indirectly from this outbreak should be enough to spur urgent action to stop the spread of the virus, as well as remind us of the role humans play in the proliferation of infectious diseases.

It’s my belief that humans have an obligation to the nonhuman life we share this planet with to mitigate the harm we’ve enabled this virus to cause. Our unsustainable activities — factory farming, climate-warming emissions and habitat destruction, to name a few — have helped turn bird flu from a natural phenomenon into an anthropogenic disaster. But even if you don’t share that conviction, it is still in our best interest to keep this virus from spreading.

Disease has always been part of avian natural history. Wild birds are routinely exposed to mild viruses, but are seldom killed by them. Humans, however, have introduced factors that favor disease: A warming climate can weaken avian immune systems, and infections spread more easily when birds come into more frequent contact while sharing what little habitat remains.

And factory farming makes things even worse. When farm animals are kept in large numbers and close quarters in poultry and dairy farms, viruses can spread and mutate more easily. It’s a human-facilitated training ground for diseases. The progenitor of today’s H5N1 strain, for example, emerged in 1996 when a virus infecting farmed geese in Guangdong Province in southern China spilled back into wild populations.

Maintaining the health of their animal holdings and their businesses — not to mention the potential risk to farm workers and the ever-present threat of human spillover — requires farmers to act quickly. And when bird flu hits farms, often the only real way to contain it is the precautionary culling of entire flocks, which has resulted in tens of millions of dead hens since 2022. The United States Department of Agriculture recommends that farms use killing methods that avoid suffering. But as many as 66 million chickens and turkeys have been culled with a technique that animal welfare groups call unnecessarily cruel: ventilation shutdown, which kills over several hours through overheating.

Given the animal suffering at stake, minimizing interactions between wild and captive birds is all the more important in preventing the spread of bird flu in both populations. But it’s a daunting task for the agriculture industry, given how difficult it can be to isolate dense animal populations kept in close quarters. When biosecurity measures at farms fail — or aren’t even properly attempted — wild populations take an extremely hard hit.

Though wild bird deaths are harder to tally than poultry culls, the numbers that we do have are disturbing. The strain of bird flu coursing through North America ignited a season of plague for Atlantic seabirds when it first appeared in late 2021 at a Newfoundland farm. From April to September 2022, bird flu killed about 41,000 wild birds in Canada. At least 17 percent of northwestern Europe’s breeding population of Sandwich terns — over 20,000 birds — died. And from November 2022 to January 2023, the virus killed thousands of wild Ross’s and snow geese in North Dakota, Kansas, Indiana and California.

The overall death toll may lie in the millions, with millions more threatened by potential infection thanks to the long-range migrations of waterfowl.

Under normal circumstances, most bird populations can bounce back from die-offs. But climate-warming human activity could impair future recoveries in North America.

When bird flu caused “unprecedented reproductive failure” at a Newfoundland breeding colony of northern gannets in 2022, it was probably worsened by a marine heat wave that coincided with the outbreak. Heat stress weakens birds’ immune responses, and is likely to become more common as the planet warms. Warmer temperatures can also make recovery from H5N1 more difficult by deepening the effects of decreased food supplies, pollution and habitat loss.

None of this is encouraging for North American birds, which have already lost billions in the last half-century because of habitat loss and other forces. We contributed to the conditions that helped bird flu mutate into a highly pathogenic form. “Now it’s taken off, and it’s totally out of our control,” said Samantha Gibbs, the lead wildlife veterinarian at the U.S. Fish and Wildlife Service.

Worse may lie in store. If the virus spreads unencumbered, it could spell further disaster for species like the beloved Atlantic puffin or the regionally endangered roseate tern. Colony-nesting seabirds like these nest in close quarters and in high numbers, reducing predation but magnifying the effects of disease. Recent asymptomatic cases in Adélie penguins on the Antarctic Peninsula have spurred fears of outbreaks in tight-knit penguin colonies. The blurring of the lines between the wild and the domestic, as infections spill over and back again, also heightens the threats to livestock — and humans.

But to fret only about the prospect of human infection betrays an ecological narcissism. We must not ignore the nonhuman suffering for which, through factory farming, anthropogenic climate change and habitat destruction, we are responsible.

While you most likely need not worry about catching bird flu from meat, eggs or dairy, this is as good a time as any to cut down on products that contribute to climate change (like greenhouse gas-intensive beef) or perpetrate cruelty (like eggs from caged chickens). The same factory farms that cause excessive animal suffering can also function as a reservoir for disease.

An enduring commitment to nonhuman life on Earth would bring down the risk of zoonotic disease spreading to humans. But saving the planet for our own benefit is only by degrees less shortsighted than destroying it to our own detriment. As its most influential and destructive denizens, we owe a duty of care to all of nature — not just its human inhabitants.