A case of highly pathogenic avian influenza has been detected among a massive flock of egg-laying chickens in Sioux County, Iowa, officials confirmed. Officials confirmed to CBS News that 4.2 million birds were impacted and will be killed.

The Iowa Department of Agriculture and Land Stewardship and the USDA confirmed the bird flu detection on Tuesday, marking the first case of bird flu in the state this year. 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. 

According to the Iowa Capital Dispatch, the most recently impacted flock contains 4.2 million chickens – the largest number of impacted flock in the state since more than 5 million were hit by bird flu in Osceola County in 2022. 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. Iowa is the top producer of eggs in the U.S., USDA data shows. 

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

The Dispatch reported that the entire flock will be culled, with the remains isolated, to help prevent further spread. The steep loss triggered a disaster proclamation for the county from Iowa Gov. Kim Reynolds, which will be in effect through June 27. 

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. At the same time, more than 81,000 commercial turkey meat birds and breeder hens were also hit in Minnesota.  

The avian flu can be fatal for poultry. 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." 

The ongoing bird flu outbreak has been disastrous, spreading beyond birds. Last month, it was detected in U.S. dairy cattle for the first time and two people have also been infected, both of whom had mild symptoms after coming across infected cattle. The virus has also been detected in beef and milk.

In:
• Iowa
• Bird Flu
• Agriculture
• Avian Flu
• Avian Influenza

Li Cohen

Li Cohen is a senior social media producer at CBS News. She previously wrote for amNewYork and The Seminole Tribune. She mainly covers climate, environmental and weather news.

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