The USDA has reported finding the first case of avian flu in commercial poultry since 2017.

H7N3 avian influenza, which USDA describes as “highly pathogenic,” was discovered in a commercial turkey flock in Chesterfield, S.C., the agency announced April 9. “It appears this [avian flu] strain mutated from a low pathogenic strain that has been found in poultry in that area recently,” the USDA’s statement said.

The statement said that after the flock demonstrated increased mortality, samples from it were tested at Clemson University’s Veterinary Diagnosis Center and confirmed at the APHIS National Veterinary Services Laboratories (NVSL) in Ames, Iowa.

The USDA’s statement said that turkeys from the affected flock will not enter the food system, and that no human cases of this H7N3 avian influenza virus have been detected.

Avian influenza, which was first detected in 1878, caused the death of millions of chickens and other birds between 1996 and 2008.