The United States has reported its first outbreak of the rare H5N9 bird flu, confirmed on a commercial duck farm located in Merced County, California. According to the World Organization for Animal Health (WOAH), the outbreak began on November 23, 2024, when increased mortality was observed among the ducks on the farm. Subsequent testing revealed both H5N9 and the more common H5N1 strains at the site.
The U.S. Department of Agriculture (USDA) detailed this incident, stating, "The USDA Animal and Plant Health Inspection Service, in conjunction with State Animal Health and Wildlife Officials, are conducting comprehensive epidemiological investigations and enhanced surveillance in response to the HPAI related events." The authorities quarantined the affected farm, resulting in the culling of nearly 119,000 birds by December 2, 2024. This drastic measure reflects the increasing need for stringent biosecurity protocols due to the highly pathogenic nature of avian influenza.
Background on the H5N9 strain reveals its rarity within the influenza A virus subtypes, as it is considered to be less common than its counterpart, H5N1. The unique characteristics of H5N9 arise from genetic reassortment, which blends genetic material from various influenza subtypes—H5N1, H7N9, and H9N2. Angela Rasmussen, PhD, virologist at the Vaccine and Infectious Disease Organization at the University of Saskatchewan, noted the potential dangers associated with reassortant viruses, especially as ducks do not often display severe symptoms. This characteristic enables them to serve as optimal hosts, facilitating the transmission of these viruses to new host species.
Adding to the urgency of this situation is the recent rise of avian flu outbreaks across the U.S. According to updates from the USDA’s Animal and Plant Health Inspection Service (APHIS), several states are reporting increasing incidences of the more well-known H5N1 strain. The national tally of H5N1-affected poultry stands at over 943 flocks across 16 states, resulting in heightened concern among federal and state health officials. Specifically, California hosts the largest share of cases, with more than 726 infected herds reported so far.
While health officials maintain the public’s risk is currently low, the potential for reassortment introduces alarming possibilities. Regarding human health impact, Dr. Nirav Shah, principal deputy director of the Centers for Disease Control and Prevention, remarked, "100 percent, [the risk] could change. This is a dangerous virus." Meanwhile, the U.S. National Library of Medicine warns, "Whether this novel H5N9 virus will cause human infections from its avian host and become a pandemic subtype is not known yet," underscoring the need for vigilant monitoring.
The ramifications of this outbreak extend beyond individual health concerns to agricultural economics as well. Since 2022, bird flu has led to the culling of hundreds of millions of poultry worldwide, and the economic impacts are starting to become evident, manifesting through higher prices for eggs and poultry products. The daily cost of eggs has surged due to increasing demand and reduced supply, as many farmers struggle to keep their flocks healthy.
The H5N9 case adds to the growing body of evidence pointing toward the necessity for enhanced surveillance and biosecurity measures, as the potential for these viruses to evolve and adapt raises valid concerns. Continuous reassessment of the situation and the implementation of responsive measures will be key to mitigating future risks to both animal and public health.
Authorities have intensified their efforts on the ground, striving to curtail both the spread of the virus and the impact on the poultry industry. APHIS officials are collaborating with local government agencies to conduct thorough epidemiological studies and monitor the situation closely. Given the interconnectedness of animal and public health, it is imperative to adopt proactive strategies to minimize transmission risks.
The emergence of H5N9 serves as yet another reminder of the unpredictable nature of viral reassortment and the necessity for global vigilance. With potential mutations leading to more transmissible or virulent forms of the virus, the scientific and medical communities are urged to stay alert. This commitment to monitoring and research may be the best bulwark against the looming threat of pandemic influenza.
Looking forward, officials are committed to maintaining heightened vigilance until they can ascertain the full extent of H5N9’s impact and behavior. The response encompasses evaluating not only the current outbreaks but also forms of surveillance capable of predicting future developments and minimizing public health risks associated with avian flu.