Though the risk to humans is low, scientists warn that outbreaks among farmed birds increase the potential for the virus to mutate and pose a threat to humans.
A highly contagious and deadly form of avian influenza has been barreling across the eastern half of the United States in recent weeks, killing both wild birds and farmed poultry and raising fears that an unchecked outbreak could prove calamitous for an industry that was devastated by a similar virus seven years ago.
Since early January, when it began killing chickens in northeast Canada, the virus has been identified in migratory waterfowl from Florida to Maine, and has infected backyard chickens in Virginia and New York and sickened thousands of turkeys in Kentucky and Indiana, prompting mass cullings and import bans.
On Wednesday, federal officials announced that the virus, a so-called highly pathogenic avian influenza, had been found in a Delaware commercial chicken farm on the Delmarva Peninsula, home to one of the country’s largest concentrations of poultry farms.
Experts suspect wild birds returning from winter feeding grounds are spreading the virus, most likely through contaminated droppings. With the peak springtime migration still weeks away, many fear the worst is yet to come.
“It’s very concerning given how quickly this thing is accelerating,” said Henry Niman, a biochemist in Pittsburgh who studies the genetic evolution of viruses and has been tracking the outbreak’s spread across the country. “I think we could see historic levels of infections.”
Federal officials have been urging poultry growers to report sick or dying birds and to tighten their farms’ biosecurity measures, which includes preventing contact between wild birds and domestic animals.
“It’s important to note that avian influenza is not considered to be a risk to public health and it’s not a food-safety risk,” Mike Stepien, a spokesman for the Department of Agriculture’s Animal and Plant Health Inspection Service, said in an email.
Although the danger to humans is low, scientists are keeping a close eye on the virus, the Eurasian H5N1, which is closely related to an Asian strain that has infected hundreds of people since 2003, mostly those who had worked with infected poultry. That virus does not spread efficiently among humans, but it is extremely deadly, with a fatality rate of 60 percent, according to the Centers for Disease Control and Prevention.
The strain currently spreading across the United States has not jumped to humans, but virologists and epidemiologists say the mounting infections among birds is worrisome because it increases the possibility that the virus could mutate in ways that make it more infectious to people.
Dr. Gail Hansen, a public health veterinarian who is the former state epidemiologist for Kansas, noted that influenza viruses have historically been behind the pandemics that affect humans. Some medical historians have traced the deadly influenza pandemic of 1918 to Army recruits in Kansas who may have caught the pathogen from farm animals and then spread it to military camps in Europe.
“Scientists always assumed the next pandemic would be a respiratory influenza,” she said. “We were wrong with Covid, but it’s these kinds of viruses that keep us awake at night.”
The virus has also been coursing through Asia, the Middle East and Europe. In recent weeks, 300 outbreaks have been reported in 29 European countries. In Israel, an outbreak at a nature reserve killed thousands of cranes.
At the moment turkey farmers, especially those in Indiana and Kentucky, are most worried. Over the past two weeks, several farms in those states have been shuttered after officials discovered the virus among birds that spend their entire lives crammed into massive sheds. Farmers say they have been stunned by how efficiently the virus kills, with animals dying hours after the initial infection.
In Indiana, state officials have moved quickly, euthanizing more than 100,000 birds and throwing a six-mile cordon around affected farms — a containment area within which exports are halted and birds are tested daily.
“Everyone is on super-high alert and trying to be as prepared as possible because we all remember the devastation of 2014 and 2015,” said Dr. Denise Heard, a veterinarian with the U.S. Poultry & Egg Association.
The 2014-15 outbreak is considered the most destructive in the nation’s history. It sent poultry and egg prices soaring and cost the industry more than $3 billion — though the federal government compensated farmers for lost flocks. In the end, nearly 50 million birds were killed by the virus or destroyed to prevent its spread, a vast majority of them in Iowa and Minnesota.
John Burkel, 54, a fourth-generation turkey grower in northern Minnesota, has been watching the spread with trepidation. In 2015, the virus tore through his farm in a matter of days, leaving just 70 survivors in a shed that had held 7,000 birds. The weeks that followed were spent culling, composting the dead and then repeatedly disinfecting the barns.
As a precaution, health officials also advised that he and his son take a course of the antiviral drug Tamiflu. “We’ve never seen a virus that virulent,” said Mr. Burkel, a state legislator who works the farm with his wife and two children. “It was just horrible.”
Since then, agriculture officials across the country have pushed farmers to embrace an array of biosecurity measures aimed at preventing outbreaks. They include sealing up tiny holes that might allow mice or sparrows to enter barns, disinfecting the tires of feed-delivery trucks before they enter a farm and creating “clean” and “dirty” zones where workers can change into fresh footwear and coveralls before stepping inside an animal containment shed.
At the same time, experts say that federal officials have strengthened the nationwide system of surveillance that allows researchers to track, in almost real time, an avian flu’s spread within wild bird populations. “I think the crisis of 2015 made us realize it takes a village to prevent an outbreak and has left us much better prepared,” said Dr. Yuko Sato, a poultry veterinarian at Iowa State University who advises local farmers about improving their biosecurity practices.
But hypervigilance has its limits, especially against a microscopic pathogen that can infiltrate a barn on the leg of a single housefly. For a growing number of scientists, the real threat is the nation’s industrialized system of meat and dairy production, with its reliance on genetically identical creatures packed by the thousands inside huge confinement sheds.
Nearly all the nine billion chickens raised and slaughtered in the United States each year can trace their lineage to a handful of breeds that have been manipulated to favor fast growth and plump breasts. The birds are also exceptionally vulnerable to outbreaks of disease. “They all have the same immune system, or lack of an immune system, so once a virus gets inside a barn, it’s going to spread like wildfire,” said Dr. Hansen, the public health veterinarian.
Andrew deCoriolis, the executive director of Farm Forward, a sustainable agriculture advocacy group, said the lack of genetic diversity isn’t just a threat to the nation’s food supply; it is also a potential threat to public health. More than half the 22 strains of novel influenza virus that the C.D.C. has identified as “of special concern” to human health are avian influenza viruses, he said, noting that a 2018 study examining the emergence of 39 highly pathogenic avian viruses found that all but two of them had emerged on industrial poultry farms.
He said the sector’s emphasis on biosecurity and infection containment obscures a larger, thornier issue that requires a fundamental rethinking of meat and egg production in the United States.
“Instead of asking how factory farms can prevent infections that originate in the environment, which is how they frame it now, we should be asking how they can prevent infections that originate on factory farms,” he said. “If we keep raising more and more animals in these conditions, we should expect the exact outcome we’re getting because that’s how the system is set up.”