Avian flu has infected a record number of birds and some mammals across the United States, and scientists are keeping close watch.
World Health Organization Director General Tedros Adhanom Ghebreyesus said Thursday that the risk to humans remains low but added, “we cannot assume that will remain the case.”
As with the coronavirus that causes Covid-19 that is believed to have started in animals before spreading to humans, some animal viruses can mutate, jump species to make humans sick and spread quickly around the world.
But highly pathogenic avian influenza is no Covid-19. Scientists are reassuring the public that, with a few rare exceptions, the virus hasn’t made the jump to humans at a large enough scale to trigger an outbreak.
It has gone far beyond birds, though, and its recent spread among members of a separate species has some experts concerned about the way the virus is changing.
What is bird flu?
Avian flu is a type A influenza virus that originated in birds. The version that’s predominantly causing problems in the Americas and Europe is called H5N1. There are several subtypes, and H5N1 bird flu viruses commonly in circulation now are genetically different from earlier versions of the virus, according to the US Centers for Disease Control and Prevention.
Since late 2022, scientists have detected this virus in more than 100 species of wild birds like ducks, seagulls, geese, hawks and owls in the US.
Globally, this strain of the virus has actually been around a lot longer, said Richard Webby, an infectious disease researcher at St. Jude Children’s Research Hospital in Memphis, Tennessee, and director of WHO’s Collaborating Centre for Studies on the Ecology of Influenza in Animals and Birds.
“We saw the sort of great-great-granddad of the virus in the late 1990s in Southeast Asia, and we’ve been following its evolution and change ever since,” Webby said.
By the 2000s, it had spread into parts of Europe and Africa and then got carried into the rest of the world through infected migratory birds. It came to the Americas more recently, Webby said.
The first infection with this version of the virus was reported in wild birds in the US in January 2022, according to the CDC. The next month, the US Department of Agriculture announced an outbreak among turkeys in a commercial facility.
Studies have shown that bird flu may spread to songbirds, but the ones that typically gather at feeders – such as cardinals, sparrows or blue jays – and those you may see on the street like pigeons or crows do not typically carry bird flu viruses that would be a threat to humans, according to the CDC.
Ducks and geese can carry the virus without appearing sick. Poultry isn’t always so lucky.
Highly pathogenic avian influenza carries “very high mortality rates” among chickens and turkeys. The disease can affect multiple internal organs, causing death in 90% to 100% of chickens within 48 hours of infection, according to the CDC.
Because it can spread rapidly, farmers usually have to cull uninfected birds along with infected ones to prevent a wider outbreak. It is considered one of the largest known threats to domestic birds.
As of Wednesday, 6,111 cases had been detected in wild birds in all 50 states, the USDA says. The virus has affected more than 58.3 million poultry birds in 47 states, according to the CDC.
The sheer volume of cases means that the virus has a better chance of spilling over into other species, experts say.
More animals getting sick
Bird flu spreads through things like feces and saliva. It can also spread through contact with a contaminated surface.
The virus has infected many mammals in the US, mostly in the West and Midwest, as part of the latest outbreak.
In Alaska, cases have been reported among bears and foxes, according to the USDA. The virus has also been found in a bobcat in California, a skunk in Colorado, a raccoon in Washington, possums in Illinois and Iowa, a mountain lion and grizzly bear in Nebraska, seals in Maine and even a bottlenose dolphin in Florida.
In total, 17 non-bird species have been infected in 20 states.
Scientists say that all of those sick mammals probably caught the virus when they ate or otherwise interacted with infected birds.
But in a concerning development last fall, the virus seemed to spread between mammals – perhaps for the first time – at a mink farm in Spain, according to a study published in the journal Eurosurveillance.
The mink got bloody noses, developed tremors, lost their appetite and seemed depressed, the scientists said, and had to be killed to keep the threat in check.
The virus did not spread to humans who worked at the mink farm, but what worried scientists were the multiple mutations found in the virus that made it distinct from sequences found in birds. One mutation made it better at replicating in mammals, although it’s not clear whether the mutation was in the virus before it got to the farm.
“But it’s when it starts to spread from one mammal to the next mammal to the next mammal, it’s in those environments where we think it’s most likely that it will pick up these changes that allow us to switch hosts, and that’s why we get concerned,” Webby said.
A handful of human cases
There have been less than 10 known avian flu cases in humans since December 2021, and none has come from human-to-human transmission, the CDC says.
The most recent US case was in a person in Colorado who got sick after culling infected birds in April. The person reported being tired for a few days. They were isolated and treated with an antiviral, according to the CDC.
The agency said at the time that the threat to public health remained low, but it urged people who had any kind of exposure to birds to take precautions.
“People who’ve typically become ill are one of those individuals who have very intense interactions with wildlife either alive or dead,” said Dr. W. Ian Lipkin, director of the Center for Infection and Immunity and the John Snow professor of epidemiology at the Columbia University Mailman School of Public Health. “I wouldn’t say there’s another pandemic upon us, because it’s not. We’re not there.
“What we need to do right now is to watch very closely the way this spreads. We need to contain it in farms and wildlife as best we can,” he added.
How to stay safe
Although the threat to people is low, the CDC suggests avoiding direct contact with wild birds.
Webby says that if you need to handle a dead bird, such as removing it from a feeder, use gloves and a mask. Always wash your hands after touching birds or feeders.
It’s safe to eat poultry and eggs that are properly handled and cooked, the CDC said. Bird flu is not a foodborne illness, and the poultry industry is closely monitored and has strict health standards that include monitoring and controlling bird flu.
Always cook poultry and eggs to 165 degrees, a temperature that kills bacteria and viruses, including bird flu.
In the highly unlikely case that someone became sick, the CDC recommends getting treated right away. Most bird flu infections can be treated with currently available flu antiviral drugs, the agency says.
The US government also has a stockpile of vaccines, including against bird flu viruses, that could be used if this flu were ever to spread easily from person to person, the CDC says.
“The chances are not zero that you could get this, and anything you can do to further reduce that risk is a good thing,” Webby said. “But you probably really have to work hard to be infected with this virus.”