The California duck farm's strain of H5N9 is different from those earlier cases because this time it is closely related to a newer variant of the H5N1 virus. That variant is called H5N1 D1.1, the USDA spokesperson said, which has emerged over the past year to dominate U.S. cases in wild birds and poultry.

The first outbreak of H5N9 bird flu in poultry has been reported in California on a duck farm leading to the culling of nearly 119,000 birds and concerns.