Bans on importing turkeys from Minnesota imposed by 40 countries sharply illustrate the gravity of the threat to the state's turkey industry posed by an outbreak of avian flu at a western Minnesota farm.

The highly pathogenic H5N2 strain of avian influenza recently wiped out a flock of about 15,000 birds in Pope County. It marked the first time the particularly deadly flu strain has surfaced at a commercial turkey operation in Minnesota.

Minnesota is the country's largest turkey producer, home to several hundred farmers who raise the birds.

"We think the lid is on, but we are concerned about the possibility it will spread," said Steve Olson, executive director of the Minnesota Turkey Growers Association.

About 12 percent of Minnesota turkey farmers' production — mostly dark meat — is exported. The rest is made into myriad turkey products, including those sold under Hormel Foods Corp.'s Jennie-O brand.

Austin-based Hormel, one of the nation's largest turkey processors, gets most of its birds from Minnesota.

"The recently announced avian influenza outbreak does not involve Jennie-O Turkey Store at this time," the company said in a statement.

Olson said biosecurity measures at the state's turkey farms are being heightened. Entry into bird barns will be more tightly restricted, while trucks coming in and out of farms will be cleaned.

Hormel said it is closely monitoring the health of its flocks. "We take great precautions to minimize the risk of introducing or spreading illnesses on our farms," the company said.

The incubation period for the avian flu is about three weeks. "If we can get through the next 21 days without finding anything, we should be in good shape," said state Agriculture Commissioner Dave Frederickson.

Avian influenza isn't seen as a threat to human health, though farm workers who handled sick birds will be monitored. "We know that the chances are very low that this is a risk to people," said Carol Cardona, a veterinary biosciences professor at the University of Minnesota.

The H5N2 avian flu strain is believed to be carried by wild birds that aren't sickened by it. A variant of the flu surfaced in poultry in recent months in several Western states. It's highly fatal: 99 percent of the infected birds in Pope County died; the rest were destroyed.

The name of the farm isn't being disclosed. It's a turkey breeding farm, not a meat-producing operation. The farm has two turkey barns, and the outbreak was relegated to just one.

That's a good sign, Cardona said, adding, "I don't think it will spread between turkey flocks."

The most imminent commercial threat is trade bans on Minnesota-raised turkey.

The European Union and countries from across the globe have added Minnesota to a poultry import ban that already included Washington, Oregon and California, according to the U.S. Department of Agriculture. China has banned imports from the entire United States.

Mexico, Minnesota's biggest market for turkey exports, had not issued an import ban as of Friday.

Minnesota farmers raise about 45 million birds annually, according to the USDA. Olson said the state has about 250 independent farmers and another 200 or so "contract" farmers who have particularly close ties to one company.

Hormel's Jennie-O relies on those farmers and also has its own turkey barns. It operates three turkey slaughter plants in Minnesota.

"Jennie-O Turkey Store raises its turkeys in barns to protect them from inclement weather, predators and migratory birds, which are a common source for influenza viruses," Hormel said in a statement. "While turkeys raised in barns aren't resistant to influenza infection, they are at a reduced risk of becoming exposed to the virus."

The United States was last hit by a highly pathogenic strain of avian flu in Pennsylvania in 1983 and 1984, Cardona said. That was an indigenous North American strain.

The current outbreak, though, marks the first appearance of a highly pathogenic Asian version of avian influenza.

"It's an unprecedented event," she said.

The Associated Press contributed to this report. Mike Hughlett • 612-673-7003