SIOUX FALLS, South Dakota (AP) — Five commercial turkey farms in South Dakota have now been infected with a bird flu strain that’s led to the deaths of more than 250,000 turkeys in the state and over 2.5 million birds in the Midwest.

The US Department of Agriculture’s Animal and Plant Health Inspection Service confirmed the H5N2 strain of avian influenza in a flock of 66,000 birds in a Roberts County farm in the far north-eastern corner of the state, which is South Dakota’s largest outbreak to date.

The approximately 6-mile quarantine zone that officials set up around the impacted farm also stretches into parts of North Dakota and Minnesota. Dr Dustin Oedekoven, the South Dakota state veterinarian, said Thursday that crews were beginning to euthanize the farm’s surviving birds to prevent the disease from spreading.

The commercial turkey farm is the latest in the state and region to be hit with the disease that’s led to the deaths of millions of birds since early March. Dr John Clifford, the USDA’s chief veterinary officer, told The Associated Press on Thursday the nation’s poultry industry may have to live with the deadly bird flu strain for several years.

Once response teams have “depopulated” the Roberts County farm, approximately 256,000 turkeys in South Dakota will have died as a result of the disease. While that’s a considerable chunk of the approximately 4.5 million turkeys the state’s Hutterite growers produce annually and a severe loss to individual producers, Oedekoven said it shouldn’t threaten the overall health of the state’s industry.

As the weather continues to get warmer and drier, the virus will not survive as well in the environment. Still, growers in the state should be wary of symptoms they notice in birds, like ruffled feathers, discharge from their beaks or isolation.

“But with this particular strain, the most obvious is sign is: they’re dead. They’re suddenly dead,” Oedekoven said.

Even if producers only have a dozen birds, Oedekoven said they should still alert his office if they notice an unusual drop.

“The sooner we know about it, the sooner we can attempt to do something about it,” he said.