A case of highly pathogenic avian influenza has been detected among a massive flock of egg-laying chickens in Sioux County, Iowa, officials confirmed.

The last case of the virus was detected in a backyard mixed species in December, and the last time commercial egg-laying chickens were hit in the state was last November, also in Sioux County.

It also marks the largest number of chickens in a flock impacted by the virus so far this year nationwide, according to data from the USDA.

An official with the state's agriculture department also confirmed the number of birds impacted this week, telling CBS News that "depopulation is ongoing."

Last week, an egg farm in Iowa's northern neighbor Minnesota was also hit by the avian flu, affecting just under 1.4 million of the birds.

According to the Iowa Department of Agriculture and Land Stewardship, chickens and turkeys that are hit with a highly pathogenic strain "may have difficulty breathing or die suddenly."

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