More than three years into a worldwide outbreak of bird flu, the virus continues to expand in the U.S., with growing impacts to food production and animals. Over 80 million chickens, thousands of wild birds and dozens of mammal species, including a polar bear, have been infected.
Now it's running rampant among dairy cows, turning up in 94 herds across 12 states since March. The latest animal to test positive was an alpaca on an Idaho farm.
“It's gigantic, the scope and scale of the presence of the disease,” said Julianna Lenoch, national coordinator for the Department of Agriculture’s wildlife disease program.
This scale ‒ and related concerns ‒ are reflected in the price of eggs, renewed warnings to cook ground beef and eggs thoroughly, and in extraordinary measures dairy and poultry farmers are being asked to take to prevent its spread.
As the outbreak lingers and expands, it’s prompting growing concerns about the risks to humans and the influence of warmer temperatures and more extreme weather events in making this and future pandemics worse.
How widespread is this bird flu outbreak?
The highly contagious H5N1 virus has spread to six continents since the first detections in Europe and Asia in 2020. It has been reported across North and Central America and most of South America and has been found on every continent. It turned up in Antarctica last fall raising alarm about potential consequences for some of the world's most beloved birds: penguins.
Timeline: From chickens to foxes, here's how bird flu is spreading across the US
The U.S. has experienced avian influenza outbreaks in the past, but this one is lasting longer and is more widespread. Domestic poultry flocks, either in commercial operations or backyard flocks and farms, have been infected in every state except Louisiana and Hawaii, including more than 5.9 million birds just since May 1.
Since 2022, infections have been reported in 14 million turkeys and 80 million chickens, including 71 million egg layers. Farmers must kill chickens and turkeys when a poultry flock tests positive, and experts say the slaughter to prevent human infection has helped drive up the cost of eggs.
Infected mammals have been found in 31 states, with the greatest number of infections found in foxes, mice, striped skunks, mountain lions, cats and harbor seals.
Research studies find the prolonged presence and spread of the virus increase the risk of genetic mutations that could allow it to pass more easily from animals to people and among people.
“The longer we have virus out there, the more possibility there is for changes,” said Lenoch, who oversees the federal program responsible for tracking the virus in wild birds.
Can humans get bird flu?
Yes, but the risk in the U.S. is still very low, federal officials reiterated in a Thursday briefing. They say the public should be “alert but not alarmed.”
Since it arrived during the winter of 2021-2022, four people have tested positive in the U.S. All were exposed to the virus on farms. In the first case, in 2022, the worker was helping to cull infected poultry on a farm. All three patients this year had exposure to dairy cows. Two only reported conjunctivitis, or pink eye, while the third also experienced upper respiratory symptoms. No one in the U.S. has died from the virus, according to federal officials, but deaths