Commonground
Senior Moderator
September 23, 2026
A new study led by an Arizona State University researcher found that a fast-moving strain of bird flu went undetected in North American wild birds for roughly three months before health officials identified it.
The authors say the gap exposes a critical weakness in the nation's disease surveillance network.
The study was led by Matthew Scotch — an ASU professor and senior associate dean in the College of Health Solutions who also holds an appointment as assistant center director at the Biodesign Center for Environmental Health Engineering — in collaboration with the Arizona Game & Fish Department.
The research focuses on D1.1, a genetic variant of the H5N1 clade 2.3.4.4b virus that has been driving the global bird flu outbreak of the past several years.
The team’s “evolutionary analysis,” as Scotch described, compared genetic sequences gathered in Arizona with thousands of publicly available viral sequences from across the country. He described the result as "a period of cryptic, or unsampled, circulation."
The analysis suggests the lineage that became D1.1 broke off from its relatives well before it was ever detected, and that "the major expansion of D1.1 probably began around the summer of 2024, before the first recognized detection in September (2024)."
D1.1 has already infected humans, including a fatal case in Louisiana in early 2025, the first U.S. death tied to H5N1 bird flu.
The Arizona viruses his team examined did not carry the Q226L mutation, which laboratory studies have linked to a shift toward binding human-type receptors. However, Scotch cautioned that influenza is continually evolving, and said officials should track not just case counts but which genetic variants are circulating and how they are changing.
"What we saw was a predominantly west-to-east pattern, with the strongest evidence for movement between neighboring flyways, from the Pacific into the Central Flyway, then from the Central into the Mississippi Flyway, and from the Mississippi into the Atlantic Flyway," Scotch said.
Movement occurred in both directions between neighboring regions, he noted, so the flyways are "not strict barriers." There was, however, much less evidence of the virus moving directly between the two most distant corridors, the Pacific and the Atlantic.
The researchers also tracked how each flyway's role changed over the course of the fall migration. Early on, the Pacific Flyway acted as a "source," sending the virus out to other regions more than it took it in, which aligns with the region playing an early role in the outbreak. The Central Flyway started out as a "sink," taking in the virus from elsewhere, before shifting into a more balanced role that helped carry it onward.
The Mississippi Flyway followed a similar pattern, shifting from receiving cases early in the season to spreading them later as its own case counts grew. The Atlantic Flyway, on the other hand, remained primarily a sink throughout the period studied, taking in far more cases of the virus than it sent back west.
"Rather than thinking of a particular flyway as permanently being a source or a sink, our results show a dynamic process," Scotch said.
Much of the underlying data came from the Arizona Game & Fish Department, which supplied samples from sick and dead wild birds collected through routine wildlife surveillance. The ASU team screened and sequenced the viruses found in those samples.
"Local surveillance does not stay local once genomic data are generated and shared," Scotch said. "A relatively small number of sequences from one state can help resolve a much larger epidemiologic picture."
He said other states could contribute to a similar distributed network, and his team is already extending the model through a collaboration with the University of Kentucky and the Kentucky Department of Fish and Wildlife Resources as part of an NSF-funded Pandemic Center.
For the public, he said, the message is "awareness rather than alarm." These viruses are still mainly an animal-health issue, he said, but because they can infect several kinds of mammals, detecting changes in them early on can be beneficial for animal and human health alike.
That gap is why Scotch sees the study as more than simply a record of one outbreak. Closing it, he said, does not mean sequencing every bird, but rather building a smarter, more coordinated surveillance network, with "enough sampling in the right places and at the right times,” so that future variants will not go undetected.
news.asu.edu
A new study led by an Arizona State University researcher found that a fast-moving strain of bird flu went undetected in North American wild birds for roughly three months before health officials identified it.
The authors say the gap exposes a critical weakness in the nation's disease surveillance network.
The study was led by Matthew Scotch — an ASU professor and senior associate dean in the College of Health Solutions who also holds an appointment as assistant center director at the Biodesign Center for Environmental Health Engineering — in collaboration with the Arizona Game & Fish Department.
The research focuses on D1.1, a genetic variant of the H5N1 clade 2.3.4.4b virus that has been driving the global bird flu outbreak of the past several years.
The team’s “evolutionary analysis,” as Scotch described, compared genetic sequences gathered in Arizona with thousands of publicly available viral sequences from across the country. He described the result as "a period of cryptic, or unsampled, circulation."
The analysis suggests the lineage that became D1.1 broke off from its relatives well before it was ever detected, and that "the major expansion of D1.1 probably began around the summer of 2024, before the first recognized detection in September (2024)."
D1.1 has already infected humans, including a fatal case in Louisiana in early 2025, the first U.S. death tied to H5N1 bird flu.
The Arizona viruses his team examined did not carry the Q226L mutation, which laboratory studies have linked to a shift toward binding human-type receptors. However, Scotch cautioned that influenza is continually evolving, and said officials should track not just case counts but which genetic variants are circulating and how they are changing.
Following the flight path
The study found that the virus's path across the continent was not a single leap but a sequential progression."What we saw was a predominantly west-to-east pattern, with the strongest evidence for movement between neighboring flyways, from the Pacific into the Central Flyway, then from the Central into the Mississippi Flyway, and from the Mississippi into the Atlantic Flyway," Scotch said.
Movement occurred in both directions between neighboring regions, he noted, so the flyways are "not strict barriers." There was, however, much less evidence of the virus moving directly between the two most distant corridors, the Pacific and the Atlantic.
The researchers also tracked how each flyway's role changed over the course of the fall migration. Early on, the Pacific Flyway acted as a "source," sending the virus out to other regions more than it took it in, which aligns with the region playing an early role in the outbreak. The Central Flyway started out as a "sink," taking in the virus from elsewhere, before shifting into a more balanced role that helped carry it onward.
The Mississippi Flyway followed a similar pattern, shifting from receiving cases early in the season to spreading them later as its own case counts grew. The Atlantic Flyway, on the other hand, remained primarily a sink throughout the period studied, taking in far more cases of the virus than it sent back west.
"Rather than thinking of a particular flyway as permanently being a source or a sink, our results show a dynamic process," Scotch said.
Much of the underlying data came from the Arizona Game & Fish Department, which supplied samples from sick and dead wild birds collected through routine wildlife surveillance. The ASU team screened and sequenced the viruses found in those samples.
"Local surveillance does not stay local once genomic data are generated and shared," Scotch said. "A relatively small number of sequences from one state can help resolve a much larger epidemiologic picture."
He said other states could contribute to a similar distributed network, and his team is already extending the model through a collaboration with the University of Kentucky and the Kentucky Department of Fish and Wildlife Resources as part of an NSF-funded Pandemic Center.
Lessons learned
Scotch pointed to several concrete steps to take before the next migration season: sequencing unusual detections faster, strengthening genomic surveillance in the weeks before and during migration, and linking wildlife, poultry and mammalian surveillance through a "One Health" approach, with data shared quickly across regions rather than after case counts climb.For the public, he said, the message is "awareness rather than alarm." These viruses are still mainly an animal-health issue, he said, but because they can infect several kinds of mammals, detecting changes in them early on can be beneficial for animal and human health alike.
That gap is why Scotch sees the study as more than simply a record of one outbreak. Closing it, he said, does not mean sequencing every bird, but rather building a smarter, more coordinated surveillance network, with "enough sampling in the right places and at the right times,” so that future variants will not go undetected.
Bird flu strain circulated undetected for months, ASU study finds | ASU News
A new study led by an Arizona State University researcher found that a fast-moving strain of bird flu went undetected in North American wild birds for roughly three months before health officials identified it. The authors say the gap exposes a critical weakness in the nation's disease...