Bird flu has wiped out 7.4 million chickens in Pennsylvania in the past month, a swift and devastating loss that veterinarians and industry members suspect may be linked to an unusually cold winter.
Infections of flocks raised to produce eggs and meat extend a U.S. outbreak that began four years ago and has eliminated 196 million birds nationwide. The virus, often spread by wild birds, has also infected U.S. farm workers and poultry and mammals across the planet.
“We are obviously in crisis mode,” Pennsylvania Governor Josh Shapiro said at a public forum this week, noting that cases were occurring “dramatically earlier in the season than what we expected.”
Wild birds, including snow geese, that spent the winter in Pennsylvania were suspected to be the source of outbreaks in poultry, Shannon Powers, spokesperson for the Pennsylvania Department of Agriculture, said in an email.
Pennsylvania is the fourth-largest egg-producing state.
FRIGID TEMPERATURES
Unusually frigid weather was thought to have sent wild birds away from rivers and ponds that froze and toward farms, said Dr. Megan Lighty, a veterinarian at Penn State University. Though the flu is fatal for poultry, some wild birds carry the virus without dying.
“The theory is that they were looking for sources of food and may have ventured closer to farms than they normally would,” Lighty said on Friday, noting she could not confirm that happened.
Most losses have occurred about an hour west of Philadelphia in Lancaster County, where farms are densely packed.
“We had birds in this area maybe a little bit earlier than we normally would have had,” said Chris Herr, executive vice president of Pennsylvania agribusiness association PennAg, referring to wild birds.
“In some cases, they got stuck here. They were looking for open water.”
FARMS REPORT OUTBREAKS
The highest risk periods for the virus to infect poultry flocks have historically been in spring and fall, when wild waterfowl migrate.
In 2025, Pennsylvania’s first commercial case of the year came in February, and it was the state’s first outbreak in more than a year, according to U.S. government data. This year, a farm with 1.5 million egg-laying hens reported an infection in late January after a commercial duck farm tested positive in December 2025.
All birds are culled at infected farms, and Pennsylvania farms with more than 7 million birds have reported outbreaks since January 28, according to U.S. data.
“If things are this bad now, once spring migration starts and we’ve got more birds moving through the area … my gut feeling is it’s probably going to get worse,” Lighty said.
(Reporting by Tom PolansekEditing by Rod Nickel)
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Pennsylvania
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