The recent bird flu outbreak in North America has taken a devastating toll on wild birds, agriculture, and mammals. Unlike previous outbreaks, the aggressive culling of domestic birds has failed to contain the spread, indicating a shift in transmission patterns since 2022.
In a groundbreaking study published in Nature, Louise H. Moncla and her team from the School of Veterinary Medicine have uncovered a critical factor driving this ongoing crisis: wild birds.
Highly pathogenic avian influenza (HPAI) viruses, responsible for bird flu outbreaks, continue to pose significant challenges to both human and animal health.
"The landscape of HPAI influenza has dramatically shifted for North America and the U.S. in recent years," Moncla explains. "What was once primarily an Asian and Northern African virus, circulating in domestic birds, has now spread across Europe and North America, with wild birds playing a key role in transmission."
By analyzing publicly available data from various agencies, including the Canadian Food Inspection Agency and the U.S. Department of Agriculture, the researchers traced the introduction and spread of H5N1 viruses during the first 18 months of the outbreak in North America. Their findings highlight the critical role of wild migrating birds, particularly Anseriformes (ducks, geese, and swans), in spreading the virus.
"The outbreak was unique compared to past ones in North America," Moncla emphasizes. "These viruses were primarily spread by wild migrating birds, which is a significant departure from previous patterns."
Moncla notes that an evolutionary shift in H5N1 occurred around 2020, allowing the virus to better adapt to wild birds. "This adaptation has made it much more efficient at spreading during migration," she explains, adding that Europe experienced a similar shift two years earlier.
However, despite these findings, H5N1 viruses in North America are still classified as foreign animal diseases. "Our current policies assume that these viruses don't continuously circulate in our birds," Moncla says. "Our study challenges this assumption and highlights the need for policy updates to reflect this new reality."
The study also reveals that agricultural outbreaks are the result of repeated virus introductions from wild birds. Additionally, backyard birds, defined as populations of fewer than 1,000 domestic birds, were infected approximately nine days earlier than commercial poultry, suggesting they could serve as an early warning system.
"Backyard birds have different epidemiological features," Moncla explains. "They are often raised outdoors with potential access to wild birds, and their farms tend to have lower biosecurity measures."
Previous viruses transmitted well between domestic chickens and turkeys, but the transmission by wild migrating birds presents a unique challenge.
"The solution is a series of seemingly mundane steps," Moncla suggests. "We need to invest in biosecurity measures, as they have proven effective. Ensuring that people have robust biosecurity plans and adhere to them is crucial to prevent transmission between farms and interactions between wild and domestic birds."
Moncla also highlights the need for a layered approach to encourage adherence to physical and behavioral protocols that prevent virus introduction. Additionally, she suggests exploring vaccination for domestic birds and investing in innovative ways to separate domestic and wild birds to reduce spillovers.
"Continuous surveillance of wild birds, especially Anseriformes, is essential for viral tracking and outbreak reconstruction," she adds.
Looking ahead, Moncla's lab is focused on risk modeling. "If we can better understand how these viruses circulate in wild birds and the extent to which different migratory birds drive transmission, could we develop a forecasting system for risk over time?"
For example, if risk is highest in a particular region in September, backyard bird owners in that area could be advised to strictly follow biosecurity measures during that month.
While Moncla acknowledges that completely eradicating the disease is unlikely, she emphasizes the importance of managing its spread into agricultural animals.
"We can't solve this problem entirely, but we can work towards containing it and minimizing its impact on our agricultural systems."
[Related Stories: AI model predicts flu vaccine strains more accurately than WHO, Generative AI model identifies high-risk avian influenza exposures, Bird flu virus survives in raw-milk cheese for months]
[Source: Nature]
