Bird flu cases discovered this past week in Tennessee and Wisconsin have prompted a new wave of anxiety for poultry producers.
The first new outbreak was discovered late last week in a chicken flock in Tennessee, and a second case was confirmed this week on a Wisconsin turkey farm.
• Ongoing coverage: Avian influenza
These cases are a different virus than the one that devastated poultry two years ago in Minnesota and other states. That outbreak infected more than 100 farms in the state, forced the destruction of millions of birds and cost the state economy nearly $650 million.
University of Minnesota avian influenza expert Carol Cardona said these two infections demonstrate that bird flu is still active, and still a potential threat.
"These are really stressful times for people," Cardona said. "2015 was stressful, and what's happening now is really bringing a lot of it back for people. I hope we make it through this season unscathed."
Two different strains of the virus, with different levels of lethality, are involved in the latest outbreaks.
In Tennessee, it was the most dangerous category of bird flu, known as a highly pathogenic virus. Cardona said most likely a low pathogenic virus originally infected the flock and evolved into the deadly, highly pathogenic form. More than 70,000 chickens owned by poultry giant Tyson were destroyed to limit the risk of spreading the disease.
In Wisconsin, it was different genetic strain, and the less dangerous low pathogenic virus, found on a Jennie-O turkey farm. "Low-path" strains, as they're known, produce relatively few symptoms in poultry. In a statement, Jennie-O said the birds will be monitored. The company called the low pathogenic virus a common form of avian influenza.
Avian influenza is not considered a risk to the food system.
In 2015, a virus existed in wild ducks and geese in its deadliest form, the highly pathogenic variety. Wild birds were less vulnerable to the disease, but when it reached a poultry flock, birds started dying immediately. With the low pathogenic version, Cardona said, there's more time to react. Although the 2015 virus hasn't shown up in a poultry flock recently, tests in the last six months did find the bug in wild ducks in the U.S.
"We've seen evidence, in a bird in Alaska and one in Montana, that the 2015 virus is still out there, somewhere," Cardona said, "So I know our poultry producers are on extreme alert right now."
Steve Olson, head of Minnesota's poultry trade groups, said the news from Tennessee and Wisconsin was disappointing, but not surprising. As ducks and geese migrate north for the summer, he said, the danger of a bird flu infection increases. "As we see migration happen in the fall and the springtime, that's when we elevate our level of biosecurity and our testing protocols."
This has been a year of elevated bird flu activity around the globe. Europe and Asia have been hard hit. Over a hundred people in China have died from avian flu infections. Still, even with the Tennessee and Wisconsin cases, the U.S. has avoided the large-scale devastation of 2015 so far.
Poultry producers hope that bit of luck continues.