The US Department of Agriculture on Monday said that leading US turkey producing state Minnesota has uncovered two more commercial turkey flocks to be infected with a lethal avian flu strain, including one in an earlier established quarantine zone.

According to the USDA, H5N2 avian flu has infected seven flocks past month in the state. More than 150,000 birds were culled in Minnesota alone in the last week due to the flu. H5N2 avian strain can kill almost all the birds in a flock in just 48 hours.

All the infected flocks were found in the biggest turkey-producing counties of state. According to the 2012 report of Minnesota Turkey Growers Association, Stearns and Kandiyohi counties were the top two counties in Minnesota that produced turkey.

The figures of Minnesota Turkey Growers Association has shown that the turkey farmers in the state raise approximately 46 million birds on annual basis, accounting for more than USD 600 million in income. The farmers across the nation raised nearly 240 million turkeys in 2013, as per the figures of the USDA.

The recent bird flu infections in states, spread from Arkansas to California, have forced overseas buyers to control their imports of US poultry from firms like Pilgrim’s Pride Corp, Tyson Foods Inc and Sanderson Farms Inc.

The authorities have so far not reported any case of human infections of the virus.