Earlier this month, scientists in the University of Minnesota’s College of Veterinary Medicine confirmed the state’s recent bout of avian flu, which has resulted in the death of about 15,000  turkeys.

Now, staff from the college’s Raptor Center is testing waterfowl, like ducks and geese, which carry the avian flu but aren’t affected by it, to see if they brought the virus from the west coast.

State animal health officials finished preliminary testing last week and found no recent deaths related to the disease. Officials have struggled to grasp the disease’s source, and its peculiar spread across the country has further complicated identifying the cause.

Raptor Center executive director Julia Ponder said waterfowl could have carried the strain of influenza if they migrated to the Midwest — which is difficult to determine, as it isn’t migration season yet.

A warm January, coupled with a cold February, may have caused the birds to move into the Midwest earlier than usual, said Carol Cardona, a professor of veterinary sciences.

“This is a virus that is absolutely new,” she said. “How it got to a subzero Minnesota in early March is hard to say.”

The avian flu was detected in farms in Missouri and Arkansas earlier this month, which indicates that it could also be spreading further south.

Wild birds, rather than domestic ones, traditionally carry the flu, Ponder said.

Forty countries have banned turkey imports from Minnesota, the country’s largest turkey producer, to protect their own flocks.

The disease only poses a risk to those working directly with the turkeys, said Jeff Bender, a veterinary public health professor. The state health department is currently monitoring employees of poultry farms.

He said people shouldn’t worry about coming into contact with the disease as long as meat is cooked to a high enough temperature.

The flu kills domestic poultry rapidly, and those at risk in Minnesota were killed by state officials to prevent the virus’ spread. Cardona said the best thing to do in a case like this is to keep other flocks away because they can easily contract the flu.

The Minnesota Board of Animal Health closed 31 backyard turkey farms in western Minnesota this month.

The board, along with University researchers, began a second round of testing over the weekend.

International trade partners will likely allow the state to export turkeys once the state is declared free of infection, which can take a long time, Cardona said.

“Trading partners can be very picky about that kind of thing,” she said. “It can be weeks or months or even years.”