The World Organization for Animal Health said in a Jan. 27 notification that the H5N9 strain of avian bird flu has been detected for the first time at a duck farm in Merced County, California. The more common H5N1 strain was also found in the flock. All 119,000 ducks on the farm were culled by Dec. 2. Disease experts classify the H5N1 virus in two types, low-pathogenic (LPAI) and high-pathogenic (HPAI). The low-pathogenic variety infects birds without making them visibly sick, enabling them to spread it. The high-pathogenic type quickly produces signs of illness. H5N9 is a much rarer strain than the H5N1 that was first discovered in China 10 years ago and is believed to be less transmissible to humans than H5N1. The “H” and “N” letters refer to which proteins combine to produce each type: hemagglutinin or “H” proteins, of which there are 16 (H1 to H16), and neuraminidase or “N” proteins, of which there are nine (N1 to N9). Many different combinations of “H” and “N” proteins are possible. Each combination is considered a different subtype and can be further broken down into different strains. H5N1 has spread around the globe in recent years and infected many mammalian species. Millions of wild mammals, including seals, are thought to have died from it. About 600 dairy herds in the U.S. have been reported infected to date. There have been at least 67 human infection cases, according to the Centers for Disease Control and Prevention. Millions of birds have been destroyed to try to contain avian bird flu, contributing to the rise in egg prices. In April, the CDC confirmed the first reported case of human H5N1 infection in a person with exposure to dairy cows in Texas that were presumed to be infected with the virus. The first human death attributed to H5N1 was reported in Louisiana on Jan. 6. The Louisiana Department of Health said the individual contracted the virus after exposure to a combination of a backyard flock and wild birds. The victim was elderly who had many chronic health challenges and officials believe it was an isolated case. The Centers for Disease Control and Prevention said that no person-to-person transmission has been identified. As of Jan. 7, the CDC said, there have been 67 confirmed human cases of H5N1 bird flu in the U.S. since 2022 and the risk of bird flu to the general public remains low.