In late January, the World Organization for Animal Health (WOAH) scientists identified the first U.S. cases of H5N9 avian influenza on a California duck farm.
Public health experts aren’t surprised by this latest strain, as influenza constantly mutates and manifests differently across species. However, H5N9’s emergence is concerning, particularly given ongoing H5N1 outbreaks in chickens and cows.
Here’s what you need to know.
The current widespread bird flu
“We’ve never witnessed such a global spread of avian influenza,” states Michael Osterholm, director of the University of Minnesota’s Center for Infectious Disease Research and Policy. “Poultry and duck operations have experienced a surge in outbreaks in recent weeks. This reflects the high prevalence of H5N1 in migrating waterfowl.”
According to Osterholm, North America has approximately 40 million migratory aquatic waterfowl—a significant reservoir for the virus, with their droppings spreading the disease.
“We’re seeing more outbreaks in poultry because this virus is prevalent in the environment and airborne,” he explains. “This is unprecedented.”
H5N9 vs. H5N1
H5N9 is “not typically found in poultry,” says Eman Anis, assistant professor at the University of Pennsylvania School of Veterinary Medicine. (Anis’s lab conducts national avian influenza testing on poultry samples.)
Research in China, analyzing samples from 2015 bird markets, indicates the virus is a combination of H5N1, H7N9, and H9N2. At the time, scientists noted uncertainty about its human infection capability—a question that persists—but stressed the need to assess its potential public health risk.
Reasons for concern about H5N9
The recent duck-farm detection of H5N9 coincided with H5N1 detection.
This is worrisome because viruses can recombine and rearrange their genetic material. The widespread circulation of H5N1 increases the risk of it interacting with other avian viruses—like H5N9—potentially creating new, mutant strains. The fear is that one of these could easily infect and spread among humans.
By largely ignoring the spread of bird flu among animals, “We’re increasing the risk of a truly catastrophic event,” warns Dr. Ashish Jha, dean of Brown University’s School of Public Health. “Taking risks can be lucky sometimes. You could close your eyes and cross a busy street and not get hit. But that doesn’t make it a good idea.”
Future concerns
“We urgently need a globally coordinated strategy,” Jha emphasizes. “Migratory waterfowl don’t respect national borders; avian influenza surveillance must be multinational.”
Jha argues that President Trump’s actions regarding the WHO and federal employees hinder such coordination, increasing the likelihood of larger outbreaks from viruses, including bird flu.
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