In a significant development in the realm of avian health, nearly 119,000 birds were culled at a duck farm in Merced County, California, after the detection of a new strain of bird flu, H5N9, in January 2024. This highly pathogenic virus has raised concerns among health authorities due to its novel presence in the United States. The World Organisation for Animal Health (WOAH) confirmed the discovery, marking a crucial moment in the continuous battle against avian influenza.
H5N9 is a type of avian influenza, commonly known as "bird flu," characterized by its high pathogenicity. The virus is more deadly than other strains, a fact that has necessitated immediate and decisive action. As with all influenza viruses, H5N9 is named based on the structure of two proteins on its surface: hemagglutinin (H) and neuraminidase (N). H5N9 shares the same hemagglutinin protein as the well-known H5N1 but differs in its neuraminidase protein, presenting unique challenges to health officials.
This new strain is the result of genetic reassortment, a process where an organism is infected with at least two different viruses simultaneously. Despite its recent emergence in the U.S., H5N9 has been detected in birds globally since the 1960s. The combination itself is not novel, as Florian Krammer pointed out:
"The combination H5N9 is not new and other versions, like H5N5 also exist" – Florian Krammer
The Centers for Disease Control and Prevention (CDC) is actively monitoring H5 viruses through its flu surveillance systems. While the CDC primarily focuses on H5N1, it maintains vigilance over H5N9 as well. As of January 18, 2024, there has been no evidence indicating human-to-human transmission of this virus in the United States. This ongoing surveillance aims to detect any potential cases in humans and prevent widespread infection.
The emergence of H5N9 in California comes as part of a broader pattern of avian influenza viruses adapting and evolving. The virus's high pathogenicity has warranted drastic measures to prevent further spread. The culling of nearly 119,000 birds at the affected farm was deemed necessary to contain the outbreak and protect both domestic poultry and wild bird populations.
The detection of this virus underscores the importance of continued research and surveillance in understanding and combating avian influenza. Experts emphasize that while H5N9 is highly pathogenic to birds, it has not yet shown signs of posing a direct threat to human health. However, the potential for viruses to mutate and adapt highlights the critical need for preparedness.
