First H5N9 Case Reported In US After Deadly Bird Flu Hits California Duck Farm

The United States has confirmed its first case of highly pathogenic H5N9 avian influenza in poultry, following an outbreak at a duck meat farm in Merced County, California, the World Organization for Animal Health (WOAH) stated Monday.

Both H5N9 and H5N1 strains of avian flu were identified through tests by the US Department of Agriculture's National Veterinary Services Laboratory (USDA NVSL), after the outbreak was first detected last November. The outbreak was initially detected last November, after clinical signs emerged at the farm, including an increase in duck deaths.

"This is the first confirmed case of HPAI H5N9 in poultry in the United States," the U.S. Department of Agriculture said in the report to the WOAH.

As the outbreak was reported, California state officials had placed the affected farm under quarantine, and completed a culling operation of nearly 119,000 ducks, by early December.

The USDA's Animal and Plant Health Inspection Service (APHIS), along with state and wildlife authorities, has initiated an extensive epidemiological investigation to assess the situation and understand the potential spread of the virus.

Outbreaks Widens Impacting Poultry And Dairy

In the last few days, APHIS reported a series of new H5N1 avian flu outbreaks across 11 states, affecting both commercial and backyard poultry flocks, particularly in the Northeast.

Farms in Indiana, Missouri, Ohio, and Washington state have been heavily impacted, with at least 1.5 million birds culled—worsening the ongoing egg shortage crisis.

The virus has also affected turkey farms in Minnesota and Ohio, along with broiler farms in Arkansas and Missouri. Additionally, infections have been reported at backyard flocks in Connecticut, Massachusetts, Rhode Island, Vermont, and California.

APHIS also confirmed six additional cases of H5N1 in California's dairy herds, raising further alarms over the virus's spread to mammal species.

One person in Louisiana has been reported dead after contracting the virus, reported CNBC.

The most widespread and destructive strain in recent years has been H5N1, while H5N9 remains a much less common variant.

Potential Risks

Virologist Angela Rasmussen from the Vaccine and Infectious Disease Organization at the University of Saskatchewan warned that the detection of H5N9 suggests a reassortment between circulating H5N1 viruses and avian flu strains containing the N9 neuraminidase (NA).

Rasmussen emphasized that ducks, which often show mild symptoms of avian flu, can serve as hosts for reassortant viruses. These ducks, still able to fly and interact with other birds, may spread the virus further, aiding the virus to adapt.

While the exact risk to humans is still unclear, Rasmussen cautioned that reassortant viruses could combine with human flu strains. She also stressed the importance of preventing H5N1 from infecting pigs, which are susceptible to both human and animal flu viruses, including reassortants.