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.)

The H5N9 strain of avian influenza is much more rare than the H5N1 which has been responsible for most of the reported human cases and the first human death.

Nearly 119,000 birds have been culled at a farm in California after a bird flu called H5N9 was detected among the poultry

State officials say the highly pathogenic avian influenza – more commonly known as bird flu – is widespread in much of the state.

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.