Vox Scientists have never seen anything like it.
In the past two years, a viral disease has swept across much of the planet — not Covid but a type of avian flu. It’s devastated the poultry industry in the US, Europe, and elsewhere, sickening millions of farmed birds, which either die from infection or are killed by farmers seeking to stem the spread.
The poultry outbreak has become an animal welfare crisis. It’s also one reason eggs have become so expensive; there are simply fewer hens to lay them.
But the virus is causing another major crisis that’s drawn far less attention: the death of wild birds.
The ongoing outbreak of avian flu has killed hundreds of thousands — if not millions — of wild birds, including endangered species like the California condor. It’s one of the worst wildlife disease outbreaks in history. Having now spread across five continents and hundreds of wildlife species, scientists call the current outbreak a panzootic, meaning a pandemic among animals.
“What we’re seeing right now is uncharted territory,” said Andrew Ramey, a wildlife geneticist at the US Geological Survey, one of the federal agencies involved in testing wild birds for the virus.
The number of dead birds in itself is historic, but so is the virus’s biology. Typically, avian influenza viruses only cause severe disease and death in domestic birds like chickens and farmed ducks; they sweep through populations, killing upward of 90 percent of the flock.
This virus, however, is different. It’s hammering wild birds and other wildlife, including mammals.
“It’s causing a high amount of mortality in a huge breadth of wild birds, which is not something that has been seen before,” said Wendy Puryear, a molecular virologist at Tufts University who studies viral evolution.
This is especially concerning because birds are already at risk across the world. North America alone has lost an astonishing 3 billion breeding birds in the last half-century, due to threats like climate change, predation by feral and pet cats, and the loss of grasslands and other habitats. This panzootic is only making an ongoing extinction crisis worse.
The virus could also pose a threat to us. While it doesn’t readily infect and spread among people today, the avian virus could evolve traits that make it more dangerous to humans as it circulates among wild animals. That’s another reason scientists are taking the outbreak among wild birds so seriously.
An unusual avian flu
Viruses that cause avian flu are actually pretty common. They’ve been circulating for eons among wild birds — and especially waterfowl, such as ducks and geese — without causing them much harm. These mild forms of infection are called low-pathogenic avian influenza, or LPAI, which means they’re typically not deadly.
On occasion, a low-pathogenic virus can jump from wild birds to poultry farms. As the virus replicates in densely packed warehouses of farmed birds, it can quickly evolve and pick up adaptations that make it highly deadly to poultry. At that point, it gets dubbed a highly pathogenic avian influenza virus, or HPAI virus. Historically, however, most of these HPAI viruses haven’t killed large numbers of wild birds, even if they did spill out of the farm and back into wild populations.
Then came an avian flu outbreak on a goose farm in China.