H5N9 is “not commonly seen in poultry in general,” says Eman Anis, assistant professor at the University of Pennsylvania School of Veterinary Medicine. (Anis is part of a lab that conducts national testing of poultry samples for avian influenza.)

Bird flu (H5N1) primarily affects birds but has spread to mammals, including humans. While human transmission remains rare, scientists fear mutation could make it airborne, potentially triggering a global health crisis.