In a significant and concerning development, US officials have detected a second strain of bird flu in dairy cattle in Nevada, different from the version that has been circulating in US herds since last year. The discovery, made public on February 6, 2025, is raising alarms about the broader spread of the H5N1 virus and the difficulty of controlling infections in both animals and humans, especially those who work closely with them.
The Detection of a New Strain: H5N1 in Dairy Cattle
The bird flu, specifically the H5N1 strain, has been a major concern for both agriculture and public health authorities globally. Historically, wild birds have been the primary source of transmission, particularly when they interact with domesticated poultry. However, the recent detection of this virus in dairy cattle represents a worrying new dimension in the way animal viruses may be spreading. While outbreaks in poultry have been well-documented, the possibility of cross-species transmission to cattle is a relatively new and uncharted phenomenon.
In late 2023, a version of the H5N1 virus, known as B3.13, was first detected in dairy cattle in the US. This strain has spread to over 950 herds across 16 states, prompting significant concern about its implications for the broader agricultural industry. The new strain, D11, was confirmed in Nevada cattle in early February 2025. Unlike the earlier strain, which had been introduced through wild birds, this second version was detected in milk collected as part of a surveillance program that the USDA initiated in December 2024. These findings are significant because they mark a clear shift in the virus’s ability to infect dairy cattle, a species previously not thought to be a primary target for avian influenza.
Implications for the Agriculture Industry
The detection of this second strain is raising questions about how widely the virus may have spread and what its long-term impact on the agricultural sector might be. Richard Webby, an influenza expert at St. Jude Children’s Research Hospital, remarked on the unexpected nature of this discovery. He noted that transmission from birds to cows was once considered a rare event, but this incident suggests that such transmissions might be more common than previously believed. This development prompts further investigation into the role of wildlife in the spread of the virus and its potential to jump from birds to other species, including livestock like cattle.
The discovery of the D11 strain has implications not only for the health of cattle but also for the safety of dairy products, including milk and cheese. Given that the virus was detected in milk, there is heightened concern about the safety of consuming dairy products from affected herds. However, there is currently no evidence to suggest that the virus is transmitted through milk or that it poses a direct risk to human consumers. Nevertheless, the agricultural and public health sectors are working together to understand the full extent of the infection and how it may affect food production and safety.
Human Health Concerns and Risk of Zoonotic Transmission
While the primary concern with bird flu outbreaks has traditionally been the health of poultry and other livestock, there is an increasing focus on the potential risk to humans. At least 67 people in the US have been infected with the H5N1 virus, many of whom were individuals who worked closely with infected dairy cattle or poultry. The Centers for Disease Control and Prevention (CDC) has been closely monitoring these cases, with particular attention paid to the fact that several human infections have occurred in those directly handling infected animals.
The first confirmed human death related to this outbreak occurred in January 2025, when a person in Louisiana died after developing severe respiratory symptoms. The individual had been in close contact with infected wild and backyard birds, underscoring the risk of zoonotic transmission — the transfer of viruses from animals to humans. In British Columbia, Canada, a teenage girl was hospitalized for months after contracting a virus traced to infected poultry. These cases highlight the potentially severe health impacts of the H5N1 virus in humans, particularly among those working in agriculture or environments where they are exposed to infected animals.
Angela Rasmussen, a virus expert at the University of Saskatchewan in Canada, emphasized the importance of continuous testing to track the virus’s spread. The discovery of the D11 strain reinforces the need for ongoing surveillance of animal populations and the potential risk posed to human health. As the virus has now been detected in both wild birds and cattle, its capacity to spread across species boundaries remains a critical concern for both public health and veterinary officials.
What’s Next for Surveillance and Control Efforts
The USDA and CDC are committed to taking immediate steps to control the spread of the virus and to understand its potential for wider transmission. USDA officials have promised to share genetic sequences and other relevant information about the D11 strain with the public later this week. These data will be essential in determining whether the D11 strain is a recent introduction or whether it has been circulating undetected in cattle populations for months.
Michael Worobey, an evolutionary biologist at the University of Arizona, stressed the importance of quickly sharing such data to prevent further spread and better prepare for the potential of a pandemic. His comments underscore the urgency of studying viruses like H5N1, which has the potential to cause widespread harm to both animal populations and human health. Worobey cautioned that, should the virus continue to spread unchecked, it could have far-reaching consequences, possibly even surpassing the devastation caused by the COVID-19 pandemic in terms of global disruption.
The Broader Implications for Public Health and Biosecurity
The discovery of this new strain of bird flu in dairy cattle raises larger questions about the global biosecurity landscape and the preparedness of countries to deal with emerging infectious diseases. As viruses like H5N1 continue to mutate and spread, governments, agricultural bodies, and health organizations must work together to develop more effective strategies for monitoring, controlling, and preventing outbreaks in both animals and humans.
A critical part of this effort is ensuring that both animal and human health officials have access to real-time data and research on the virus. As experts have pointed out, timely information about the virus’s genetic makeup and spread is vital to ensuring that appropriate measures are taken to prevent a global health crisis. The situation also highlights the need for ongoing vigilance and adaptation in biosecurity protocols, as pathogens like H5N1 can evolve in unexpected ways.
Moving Forward with Caution
In conclusion, the detection of the second strain of H5N1 bird flu in dairy cattle in Nevada serves as a stark reminder of the complex and evolving nature of infectious diseases. The virus’s ability to cross species boundaries, from wild birds to poultry and now to cattle, presents new challenges for both animal health and public health. As scientists and officials continue to monitor the situation, it is crucial that all sectors involved in biosecurity, from agriculture to healthcare, work together to better understand the virus and implement measures to mitigate its impact. The public must also be made aware of the potential risks and the importance of following guidelines to ensure safety and prevent further spread of the disease.
