Bird flu strikes flock of 4.2 million chickens in Iowa’s Sioux County

This week's avian influenza confirmation is the first in Iowa poultry this year. (Getty Images)

Avian influenza that is very transmissible and lethal for domestic birds has been detected in a flock of 4.2 million egg-laying chickens in Sioux County, according to the Iowa Department of Agriculture and Land Stewardship.

It is the first confirmation of highly pathogenic avian influenza in a commercial or backyard poultry flock this year in Iowa. The agency reported it Tuesday.

Entire flocks are culled — and their carcasses isolated — to prevent the spread of the virus to other flocks.

The virus outbreak has been ongoing since early 2022 and is primarily driven by migrating birds, which can be contagious without showing symptoms.

In the past month, Minnesota is the only neighboring state of Iowa that has had infected flocks, according to the U.S. Department of Agriculture. Five of those confirmations happened about two weeks ago. They included four commercial turkey operations and one commercial egg-layer flock that totaled about 1.5 million birds.

Minnesota has had more than three times the number of infected flocks compared with Iowa since the start of the outbreak, but Iowa has had about three times the total number of affected birds because of its large egg-laying operations. It is the top egg-producing state.

A total of more than 23 million birds in 52 flocks have been culled in Iowa since early 2022 because of the infections. The flock in Sioux County — which is in northwest Iowa, north of Sioux City — is the state’s third-largest affected in that time. Two others in Buena Vista and Osceola Counties had more than 5 million birds apiece.

The state agency recommends that poultry and dairy operations take additional precautions to limit the potential for new infections.

The virus has been found in sick dairy cattle in at least 67 herds in nine states, according to the U.S. Center for Disease Control and Prevention. That includes four herds in South Dakota but none in Iowa.

The first cattle infections happened in Texas and were confirmed in March. Cows typically recover from infection in 10 to 14 days, but the virus is often fatal for poultry.

Federal officials have said eggs and milk in the commercial food supply are safe to consume. They have warned against drinking unpasteurized cow milk.

This article first appeared in the Iowa Capital Dispatch, a sister site of the Nebraska Examiner in the States Newsroom network.

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