A lethal strain of bird flu has infected an eighth turkey flock in Minnesota, the nation's top turkey producer, in just over a month, officials said on Tuesday, a day after a team of epidemiologists arrived to investigate how the disease is spreading.

Minnesota has detected five cases of the H5N2 flu, which can kill nearly an entire flock of poultry within 48 hours, in commercial turkey flocks since Thursday alone.

Commercial poultry operations and backyard flocks in states ranging from Arkansas to Washington also have been infected with the deadly strain since the beginning of the year, triggering overseas buyers to limit imports of U.S. poultry from companies like Tyson Foods Inc and Pilgrim's Pride Corp.

On Tuesday, the Canadian Food Inspection Agency said Japan and Taiwan imposed trade restrictions on poultry from Ontario after bird flu was confirmed in the province.

The latest U.S. infection of the H5N2 flu was the second case in two days to be found in Kandiyohi County, Minnesota, the U.S. Department of Agriculture said. The county, located west of Minneapolis, is the state's top turkey-producing county.

On Monday, a team of USDA epidemiologists arrived in Minnesota to investigate how the virus is making its way into turkey flocks, said Erica Gunderson, spokeswoman for the Minnesota Board of Animal Health. State officials asked the U.S. government to send the team because they needed help responding to the increasing number of infections, she added.


"Basically, we just needed more people," she said.

The USDA has said it believes migratory ducks are spreading the flu, but does not know exactly how the virus is moving into poultry flocks from wild birds.

The latest infected flock of 30,000 turkeys in Minnesota will be culled to prevent the virus from spreading, and the birds will not enter the food supply, according to the USDA. In the last week, the number of birds to be culled in the state because of the flu has topped 180,000.

Farmers in Minnesota raise about 46 million turkeys a year, accounting for more than $600 million in income, according to the Minnesota Turkey Growers Association. Nationwide, farmers raised about 240 million turkeys in 2013, according to the USDA.

So far, no human infections of the bird flu have been detected.