Control strategies for bird flu are failing, according to findings from a recent study by researchers with The Pirbright Institute in Surrey, England.
The team’s conclusion is based on a comprehensive literature review examining European and United States outbreaks.
Avian flu, commonly known as “bird flu,” refers to strains of the Influenza A virus that have been circulating globally since their identification in Europe between 1878 and 1880. Studies on confirmed cases estimate that the virus has a mortality rate exceeding 50% in avian livestock. However, due to the underreporting of mild cases, some estimates suggest that the actual fatality rate may be lower—potentially as low as 14% to 33%.
The most concerning strain today is H5N1, first detected in Scotland in 1959. The first recorded human deaths occurred in Hong Kong in 1997. In 2020, a new subtype, 2.3.4.4b, emerged, drawing significant attention due to its rapid spread.
Two years ago, the virus jumped to mammals when a mink farm in Spain suffered an outbreak following a mass bird die-off. Four percent of the farm’s mink population succumbed to the virus. Earlier this year, an even more alarming incident occurred when 95% of the seal pups on the Valdés Peninsula in Argentina died from the infection, totaling close to 17,000 animals.
The virus continues to edge closer to becoming a direct threat to human health. It has even been detected in raw cow milk intended for human consumption, and on infected farms, half of the cats fed contaminated milk died.
Although large-scale culling of poultry stocks eradicated a previous outbreak in North America a decade ago, current outbreaks are being sustained by infections in wild birds, which bypass earlier quarantine measures. In some areas, where outbreaks were believed to be controlled, the virus has reemerged due to wild birds. Meanwhile, in industries like U.S. dairy farming, the virus has become a persistent issue.
Tracing the Bird Flu
Dr. Thomas Peacock, a zoonotic influenza specialist, led the research team behind the study, which focused on the molecular evolution of the virus and its ecological jump from birds to mammals. A significant challenge in their research was the lack of data compared to other diseases, such as hoof-and-mouth disease.
Dr. Peacock explained that, while H5N1 is a reportable disease in poultry, the same does not apply to mammals in the U.S. In fact, the U.S. Department of Agriculture only requires H5N1 testing in lactating cattle before interstate movement.
The study also identified significant gaps in monitoring wildlife for the virus. Currently, only dead animals are tested, which means that sick but surviving animals go undocumented. This lack of data makes it difficult to track the virus’s spread between animal populations. As demonstrated in the 2023 mink farm incident, wildlife infections have become directly linked to agricultural outbreaks.
An Evolving Threat
The spread of panzootic viruses like bird flu is driven by a process called “genomic reassortment.” This occurs when a host is infected by more than one virus simultaneously, allowing them to exchange genetic material and produce hybrid strains. These hybrids can sometimes be stronger and harder to control. Of particular concern is the virus’s growing ability to transmit directly from mammal to mammal.
Limited transmission data hampers efforts to understand why Europe has replaced Asia as the main source of new variants. According to Dr. Peacock, swine have historically served as intermediary hosts for avian influenza, helping the virus adapt to mammals before jumping to humans. However, changes in the ecology of H5N1 have opened new evolutionary pathways.
The study warns that unseen chains of transmission—particularly among farm workers or in regions with limited resources—could allow the virus to evolve undetected.
Are Humans Facing an H5N1 Pandemic?
Although human cases of H5N1 remain rare in the U.S., two significant changes would need to occur for the virus to become a pandemic threat. First, the glycoprotein haemagglutinin (HA), which the virus uses to attach to cells, would need to evade human immune recognition. Second, the virus must develop a more efficient mechanism for mammal-to-mammal transmission.
While there are currently 17 types of H5N1 found in wild aquatic birds that meet the first criterion, the second remains more complex. Although replication proteins are adapting, the necessary changes to HA are more constrained. It is statistically unlikely that a single strain will evolve to meet all the required criteria, but genomic reassortment could potentially combine the necessary traits from different strains into one highly dangerous virus.
Controlling for a Pandemic
Dr. Peacock emphasized that the situation does not have a simple solution. “New control strategies, including vaccination, are necessary,” he said. While influenza vaccines exist for poultry, they do not prevent infection and have varying success rates. Additionally, no oral vaccine exists for wildlife, which has been an effective tool in rabies control.
However, the team pointed out that mRNA vaccine platforms could be used to quickly produce effective vaccines for humans in the event of an H5N1 outbreak. Preventing such a scenario through enhanced monitoring remains the preferred goal.
Going forward, more detailed reporting on livestock infections, human workers in agricultural facilities, and wildlife could hold the most promise in terms of halting the virus’s spread.
Ryan Whalen covers science and technology for The Debrief. He holds a BA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.