Bird flu appears to be on the move. A particularly nasty strain of the H5N1 virus is currently causing the worst outbreak of the disease among birds since it was first identified in China in 1996. Europe is deep into its second commercial season of widespread contagion, and the U.S. is seeing its deadliest 12-month period for poultry in recorded history, with 58 million animals affected so far. Records are also being broken in Japan, where a plan to cull 10 million poultry was announced in mid-January amid the appearance of a different but similar subtype, H5N2.
The past few years have taught us all how quickly a virus can spread, and avian influenza is no exception. Already, the current strain has affected a wider geographic area and more species than any other bird flu in the last two decades. Though it’s still too early for experts to say exactly why this is, the unique features of this outbreak (and what we do know about avian flu as a category of viruses), can get us a bit closer to understanding what might come next.
Is avian flu going to be the next human pandemic?
According to experts, the current form of avian flu spreading among poultry is unlikely to significantly impact human populations. For as long as the virus has been around, there have been cases of infection in humans, of which over 50% have been fatal. But overall cases have been fairly rare.
This is primarily due to the way that flu viruses bind to cells during the process of infection. The receptors that they exploit on the outside of cells look a bit different in every vertebrate class, and viruses tend to play favorites, evolving to stick to certain creatures’ cells more effectively than others. For H5N1, the target is birds. Still, “just because it has an avian-receptor binding preference does not mean that it cannot bind at all to human cells,” says Samantha Lycett, a University of Edinburgh researcher who studies how disease evolves and spreads. “It just doesn’t do it very well.” In fact, it does it so poorly that there are only a handful of recorded instances of H5N1 being spread from one human to another—and a virus can’t pose a real pandemic risk unless it’s great at that.
As we’ve seen with SARS-CoV-2, however, viruses can evolve to sidestep biological obstacles. If H5N1 mutates into a strain better suited to attack human cells, we could be in trouble. H5N1 has already been found in other mammalian species, including foxes, bears, and most concerningly, in an outbreak at a Spanish mink farm in October. “The thing that was different about the mink farm was that it was clearly spreading from mink to mink,” says Paul Digard, chair of virology at the University of Edinburgh. “That that variant of it was a mammalian-transmissible virus makes it intrinsically more worrying.” It’s unclear how exactly the minks contracted the virus in the first place, but after numerous infected wild birds were found in the surrounding area, experts have suggested that excrement or remains from the wild birds could have somehow been tracked into the farm.
Why the current bird flu has spread so far, so fast
Even among birds, the current H5N1 strain also seems to be more infectious than past iterations. Most wild birds are generally less susceptible to infection than domestic poultry, primarily because more dramatic cellular differences across the many species of birds out in nature make it harder for the virus to be equally effective everywhere. But the recent outbreaks have spread to more unusual bird species, explains Lycett, including those who may be responsible for carrying the virus to new areas. In Scotland, where she and Digard live, there’s been a record number of deaths among seabirds. “We’ve lost a substantial fraction of the world population of things like gannets and skewers,” says Digard. “It’s a bit too soon to say whether they’ll bounce back or not.” Seabirds generally don’t catch avian flus, and the distances they travel have been a main cause of the recent spread.
“Seabirds have a slightly different mix of flu subtypes than do other migrating wildlife. So it’s kind of unusual, because they normally seem to have their own separate circulation,” Lycett says. As far as animals go, wild birds make for a nearly impossible-to-track disease vector, as they move around before researchers can formally count the infected. Even rats needed help from ships to spread the plague.
Without better understanding the current strain of the virus, it’s hard for experts to say exactly why this one is so much more virulent or how likely it is that mutations that make it more of a threat to mammals will occur in the future. In the meantime, the burden of the outbreak in the U.S. is being shouldered by farmers who keep commercial poultry, more of whom have had to kill off their flocks this year than ever before—and consumers who have had to pay high prices for eggs over the past few months.
“It is devastating to see these animals dying,” says Gino Lorenzoni, assistant professor of poultry science and avian health at Penn State. “Especially to the people that work with poultry. I mean, they get attached to their flocks. It’s devastating, emotionally and also economically.”
Should you worry about bird flu right now?
Across the U.S., some 58 million birds have died or had to be killed because of infection. These nationwide depopulations are one of the main reasons that eggs are so expensive right now—a shortage of laying hens means a shortage of eggs.
The good news: Aside from the damage they’ll cause to your wallet, there are no other dangers to eating eggs and poultry right now, especially if they’re well-cooked. In the past, when humans have occasionally caught avian flu, none have been infected by consuming eggs or poultry products. There are also good failsafe measures in place to prevent sick birds from entering the production line in the first place. When a chicken has avian flu, it’s not that hard to tell. The incubation period is relatively short, and when they get sick, they get really sick, and can even drop dead, seemingly out of nowhere. The U.S. Department of Agriculture also keeps a complete and public record of all reported detections of disease in commercial flocks, and people who work regularly with poultry have long lists of protocols and protective measures that they’re already used to—for them, the threat is currently larger, but not new.
For the rest of us, the main priority for the time being should be to “treat the virus with respect,” as Lorenzoni puts it. If you keep one or two chickens in your backyard, that means keeping them where wild animals can’t touch them and making extra sure to wear full protective gear like goggles, Tyvek suits, and most importantly, shoe coverings that eliminate the risk of tracking potentially virus-ridden bird poop inside any enclosure. If you have pets, this means keeping a close eye on them when they’re outside the home, and preventing them from picking up any bird carcasses or excrement that may be laying around. And if a seagull tries to steal your sandwich, maybe let him have it this time.
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