Bird flu has returned to South Dakota, with federal officials confirming detections in two flocks this month after nearly a month without U.S. cases.

The highly pathogenic avian influenza virus — H5N1, a strain that spreads quickly and kills birds rapidly — struck a flock of 74,900 commercial meat turkeys in Beadle County on August 12 and a backyard flock of 2,800 birds in Brule County on Thursday. Euthanizing the entire affected flock is the standard practice when a detection is confirmed.

The Animal and Plant Health Inspection Service of the U.S. Department of Agriculture tracks detections nationwide. Federal officials also confirmed the virus in two Idaho backyard flocks of 10 and 50 birds on Thursday.

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The South Dakota Department of Health issued an alert Friday for potential human infections among patients who may have been exposed to infected animals. Providers should ask patients with flu-like symptoms — fever, chills, cough or sore throat — about recent contact with sick or dead animals, the alert said.

Since the national bird flu outbreak began in 2022, the virus has affected 8.1 million birds in South Dakota from 144 commercial flocks and 31 backyard flocks.

Federal policy requires officials to kill all birds at affected sites to prevent the virus from spreading to nearby farms. Former South Dakota State Veterinarian Beth Thompson told South Dakota Searchlight previously that “foaming” is the most common method in turkey barns, where foam is sprayed atop turkeys inside the barn to suffocate them.

Federal and state officials oversee the process, and the federal government reimburses farmers for their losses through indemnity payments.

Avian influenza detections rise as wild birds spread the virus during seasonal migrations, which are underway.