Bird flu infects another Iowa flock, of 1.6 million chickens

A flock of about 1.6 million, egg-laying chickens in Sioux County has been exposed to the highly transmissible and deadly avian flu, according to the Iowa Department of Agriculture and Land Stewardship.

It is the third infected commercial poultry flock identified by state officials in the past four days. The others include:

Avian influenza often is transmitted by wild, migrating birds, which often do not die from the virus and might show no symptoms. But the virus is more deadly for domestic poultry, and entire flocks with infected birds are culled to prevent its spread.

Humans who have been infected by the virus — most often those who worked closely with infected poultry — typically have mild symptoms and recover.

Outbreaks during the fall bird migration in Iowa have started earlier in past years, and it's possible the relatively late start of outbreaks this year is the result of a warm fall that delayed the migration, said Don McDowell, a spokesperson for the state ag department.

Iowa recently has had among the highest rates of bird migration in the country, according to an analysis by Colorado State University and the Cornell Lab of Ornithology.

All of the recently affected flocks are in northwest Iowa. Eastern Iowa has relatively few commercial chicken and turkey flocks compared with other parts of the state.

The eastern third of the state has about 13 chicken facilities and 24 with turkey, according to data maintained by the Iowa Department of Natural Resources. The western third of the state has about 78 chicken facilities and 74 for turkey.

In the past month, the virus has been found in at least 14 commercial and backyard poultry flocks in Minnesota and North and South Dakota, according to the U.S. Department of Agriculture.

But the number of birds destroyed in those states in that time — about 634,000 — pales in comparison with Iowa's handful of recent cases. Iowa is the nation's leading egg producer, and commercial egg facilities often have millions of birds apiece. Iowa's recent death toll is nearly 6 million birds.

The recent detections were the first this year since July. There were a total of three affected flocks in 2024 before the recent outbreaks.

One of the earlier infected flocks was in Sioux County and had about 4.3 million birds. State ag officials declined to say whether that site, which had a similar number of birds as the detection announced Friday, was the same operation.

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