The US has reported its first outbreak of highly pathogenic H5N9 bird flu in poultry in California

First U.S. Outbreak of H5N9 Bird Flu Detected on California Duck Farm

The United States has reported its first outbreak of H5N9 avian influenza in poultry, detected on a duck farm in California, according to the World Organization for Animal Health (WOAH) on Monday.

In addition to H5N9, authorities also found the more common H5N1 strain on the same farm in Merced County, California. Nearly 119,000 birds at the facility had been culled as of December 2, according to a report submitted to WOAH, which is based in Paris.

Bird Flu’s Global Spread and Growing Risks

Highly pathogenic avian influenza (HPAI)—commonly known as bird flu—has rapidly spread across the world in recent years, leading to the mass culling of hundreds of millions of poultry. The virus has also jumped to dozens of mammal species, including dairy cows in the U.S., and has even resulted in a human fatality in Louisiana.

While H5N1 has been the dominant strain responsible for widespread outbreaks, H5N9 is much rarer.

“This is the first confirmed case of HPAI H5N9 in poultry in the United States,” the U.S. Department of Agriculture (USDA) stated in its report to WOAH.

Response and Investigation

The USDA Animal and Plant Health Inspection Service (APHIS), in collaboration with state animal health and wildlife officials, has launched a comprehensive epidemiological investigation and enhanced surveillance efforts in response to the outbreak.

Authorities are now working to assess the extent of the spread and mitigate further risks to livestock and public health.