New Genotype of H5N1 Detected in Dairy Cattle in Nevada
In a significant development for animal health, the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) has confirmed the discovery of a new genotype of the H5N1 avian influenza virus in dairy cattle located in Nevada. This finding marks a noteworthy addition to the ongoing monitoring efforts for highly pathogenic avian influenza (HPAI) in the United States.
The detection of H5N1 was initially identified through silo testing as part of the USDA’s National Milk Testing Strategy (NMTS). Following this initial discovery, USDA officials initiated a comprehensive investigation to trace the virus. Whole genome sequencing conducted by the National Veterinary Services Laboratories ultimately confirmed the presence of H5N1 clade 2.3.4.4b, specifically genotype D1.1, in the dairy cattle population.
The D1.1 genotype of H5N1 is primarily associated with wild birds; however, it has been reported in mammals and domestic poultry during the past fall and winter seasons. Prior to this incident, all known instances of H5N1 in dairy cattle had been linked to the B3.13 genotype of clade 2.3.4.4b. This development underscores the evolving nature of the virus and its transmission pathways.
Despite this new finding, the USDA has clarified that the emergence of the D1.1 genotype in dairy cattle will not alter its current eradication strategies for HPAI. The agency emphasized that this detection serves as a testament to the robustness of the National Milk Testing Strategy, which currently encompasses 40 states across the nation.
The USDA is actively collaborating with the Nevada Department of Agriculture to conduct further on-farm investigations and testing. This cooperative effort aims to gather vital epidemiological data to better understand the circumstances surrounding the introduction of this new genotype and to implement measures to mitigate any potential spread of the disease.
Recent Human Cases and Public Health Implications
In a related context, the Centers for Disease Control and Prevention (CDC) reported the first instance of the D1.1 genotype affecting a human in December 2024. A patient in Louisiana was hospitalized due to severe H5N1 illness, representing a significant case as prior to this, the B3.13 genotype had been identified in the majority of human cases. In total, the CDC has confirmed 68 human cases of H5N1, indicating that while rare, the virus does pose a risk to humans.
The seriousness of H5N1 infections was underscored when, on January 6, the CDC announced the first death attributed to the disease in the U.S., occurring in the same Louisiana patient. In the wake of this tragic event, the CDC remarked, “While tragic, a death from H5N1 bird flu in the United States is not unexpected because of the known potential for infection with these viruses to cause severe illness and death.”
Globally, the situation remains concerning. The World Health Organization (WHO) reports that more than 950 human cases of H5N1 have been documented outside the United States, with approximately half of these resulting in fatalities. This statistic highlights the virulence of the virus and the importance of ongoing surveillance and research.
Despite these alarming developments, the CDC maintains that the overall risk of HPAI to the general public remains low. The agency continues to monitor the situation closely, ensuring that public health measures are in place to protect both animal and human populations.
To date, the implications of H5N1 have been extensive, affecting nearly 12,000 wild birds, 157.8 million poultry, and 968 dairy herds across the nation. The breadth of this impact underscores the necessity for rigorous testing and monitoring protocols, as well as the importance of inter-agency cooperation in responding to emerging infectious diseases.
Conclusion
The recent discovery of the H5N1 D1.1 genotype in dairy cattle in Nevada serves as a critical reminder of the ongoing challenges posed by avian influenza. The USDA’s proactive measures, coupled with the CDC’s continued vigilance regarding human cases, reflect a comprehensive approach to managing the risks associated with this virus. As the situation evolves, stakeholders in animal health and public health must remain alert and engaged to ensure the safety and well-being of both livestock and the human population.
