Dive Brief:
- The United States confirmed its first case of the rare avian influenza strain H5N9, raising concern among experts who worry the finding shows that the bird flu virus is mutating.
- The strain was found on a duck meat farm in California in November 2024, the World Organization for Animal Health said in an update Monday. Officials quarantined the farm, which subsequently killed all 119,000 birds.
- The farm detected H5N9 alongside cases of H5N1. The latter strain is associated with the ongoing bird flu outbreak that has killed more than 145 million birds since 2022.
Dive Insight:
The H5N9 strain was first identified in China a decade ago, and it’s considered a genetic mix of other strains including H5N1, H7N9, and H9N2, according to a study from the Journal of Virology. Public health experts say the detection in the U.S. may pave the way for “unpredictable new viruses” that could affect animals and humans alike.
“This is bad news,” Angela Rasmussen, a virologist with the Vaccine and Infectious Disease Organization at the University of Saskatchewan in Canada, said on X, formerly Twitter. “Reassortment makes pandemics.”
The rare strain’s N9 gene stems from the subtype H7N9, according to the Journal of Virology, which was the cause of a number of human and poultry outbreaks that led to the deaths of 616 people in China.
While there’s limited research on H5N9’s impact on humans or animals, clinical signs on the California farm included “increased mortality,” according to the update from WOAH. The virus caused low mortality rates in mice, but it’s unclear whether “this novel H5N9 virus will cause human infections from its avian host and become a pandemic subtype,” the Journal of Virology said.
“It is therefore imperative to assess the risk of emergence of this novel reassortant virus with potential transmissibility to public health,” according to the report, published in 2015.
Rasmussen said ducks are considered “great hosts” for reassortment, which occurs when two or more viruses infect the same host and combine to create a new strain. While the H5N9 case indicates reassortment of avian viruses, it could still pose a threat to people if it were to combine with human viruses.
“We need to do more surveillance to limit opportunities for different viruses to reassort,” Rasmussen said.
Bird flu in the U.S. has become a pressing issue for the agriculture industry, with the virus jumping from chickens to cows in 2024. More than 17 million birds have been impacted by the virus in the last 30 days, with 66 commercial flocks reporting outbreaks.
Farmers have depopulated flocks to prevent further spread, which created supply shocks at the grocery store. Egg prices have jumped considerably with a resurgence in the virus over the past two months, becoming a political flashpoint in a larger debate around inflation.