The newly reported H5N9 strain was found Monday at a duck farm in Merced County, California, according to the World Organization for Animal Health. The Paris-based organization that studies animal diseases said it's the first verified U.S. case of H5N9 in poultry. The organization said the more common strain H5N1 was also found.

Most of the bird flu cases reported so far in the U.S. have belonged to an influenza subtype known as HPAI H5N1. The newly reported subtype in Merced County is called “HPAI H5N9.” Although H5N9 has been reported before in the U.S., this was the first time it was reported as “highly pathogenic.”