Bird flu cases have slowed their vicious spread across Minnesota turkey farms in recent weeks after a new wave of the virus landed in the state earlier this fall.

Since a Meeker County turkey producer became the state's first commercial poultry operation to report avian influenza in 2023 in October, 33 more sites have suffered an outbreak. But just four farms have confirmed cases so far in December.

That brings this year's toll above 2 million birds killed by the virus or culled to prevent its spread. Since the bird flu outbreak started in March 2022, Minnesota poultry farms have lost 6 million turkeys and chickens to highly pathogenic avian influenza, or HPAI.

"While we're always hopeful our last HPAI case of the year is behind us, it only takes one viral particle to jumpstart the process on another infected farm," said Dr. Shauna Voss, veterinarian for poultry programs at the state Board of Animal Health.

Minnesota, which leads the nation in turkey production, raises more than 37 million turkeys a year.

Bird flu is not a threat to food safety, public health officials say. But it can have an economic toll on farmers and, as evidenced by last year's record egg prices, consumers.

Since October, 16 million birds have been killed in bird flu outbreaks nationwide — many of them in large egg operations — for a total death toll above 75 million since the outbreak started in early 2022.

Hopkins-based Michael Foods, which provides eggs and egg products to restaurants, retailers and other institutions, reported 10% of its suppliers' flocks were wiped out by bird flu outbreaks in Iowa and Ohio earlier this month.

"The facilities house approximately 4.2 million egg-laying hens," parent company Post Holdings said in a news release.

Yet the price of eggs has fallen so far in December, according to the U.S. Department of Agriculture, and is averaging around $2 per dozen.

At this time last year, prices were on their way up to nearly $5 a dozen after the first wave of bird flu wiped out egg-laying operations, limiting supplies of the typically low-cost grocery staple.

Cold weather doesn't deter the hardy virus, which is spread mainly by migratory waterfowl like geese and ducks that can carry the virus without getting sick.

"The virus is tough and can survive cold and freezing temperatures, as well as survive in aquatic environments," according to the Raptor Center at the University of Minnesota, which has reported 92 great horned owl deaths and 50 bald eagle deaths from bird flu since March 2022.

"Colder weather doesn't necessarily do much to stop the virus itself," Voss said. "Instead, cold weather limits migration, which means fewer hosts on the landscape to give the virus a ride to a new location where it could spill over into more poultry farms."

As this year's southward migration winds down, officials are still urging commercial operations and backyard flocks alike to take strict biosecurity measures to prevent the spread of the virus.