A strain of avian flu is being blamed for the deaths of nearly 15,000 turkeys in Pope County, Minnesota. The Minnesota Department of Agriculture said Thursday that only workers handling the birds, all from the same commercial flock, are at risk of infection. Minnesota Public Radio (MPR) reports that four workers who had direct contact with the infected birds are being monitored by MDH for respiratory illnesses. The workers say that the birds started dying around Feb. 26, reports KARE News.

The virus was detected inside one turkey barn in the county. State officials said they will quarantine some birds and euthanize others to keep the flu from spreading. The Minnesota Department of Agriculture said it was going to euthanize an additional 29,000 birds over the weekend as a preventative measure.

Since the announcement of the virus was made, more than 40 countries have banned poultry imports from Minnesota. The state is the largest turkey producer in the United States.

Minnesota Turkey Growers Association Executive Director Steve Olson says the H5N2 strain will have "a huge impact" on exports. The group says about 6 million Minnesota turkeys are sent to international markets every year. One of the countries banning Minnesota poultry is Mexico.

"It is our largest market by far. Half to 2/3 of the production, the export market goes down to Mexico," said Olson.

In addition, the virus has also been discovered in commercial flocks in Missouri. Agriculture officials there have quarantined two commercial poultry facilities after the same strain of virus found elsewhere in the United States — H5N2 — was detected in flocks in Asbury and Fortuna. It was not clear how many birds were affected, but officials said that the remaining turkeys in the involved flocks will be euthanized.

Sources: KARE News, AP/CBS News