MEMPHIS, Tenn. — Led by researchers from St. Jude Children’s Research Hospital, an international team has studied and mapped a dominant strain of highly pathogenic avian influenza’s entry and spread through birds across the North American continent.
The St. Jude team detected a dominant and novel strain of the H5N1 avian influenza, called D1.1, in late 2024. It’s tracking was coordinated with several institutions and mapped across Canada and the United States to see where it was geographically having impact. This virus strain was noted to have started in Alaska and British Columbia and moved south and eastward along the recognized wild bird migratory flyways.
The current outbreak of bird flu has been ongoing for more than four years and is known to spread among wild waterfowl like ducks and geese and researchers have continually been looking for any changes in the virus. This group of scientists also looked at the virus and how it compares to what has been causing human infections, and it is reported to still be at a minimal risk, in its current form, for human-to-human spread.
“Combining information collected from multiple partners, we’ve documented the entire continental spread of a newly dominant strain of highly pathogenic avian influenza virus through wild bird populations,” Dr. Richard Webby, St. Jude faculty member and corresponding author of this study.
“We’ve shown the value of connecting what are usually regional findings into a single comprehensive map to understand the strain’s spread,” said Webby, who is also director of the World Health Organization Collaborating Centre for Studies on the Ecology of Influenza in Animals and Birds.
The researchers noted that every severe human case of avian influenza infection was from this new D1.1 dominant strain. However, with cases in diverse geographical locations, it made the understanding of the source unsure. The mapping research gave more distinct interpretation.
“We could connect all the severe cases with the wild bird map,” Dr. Walter Harrington, St. Jude Department of Host-Microbe Interactions postdoctoral research associate, and study co-first author, said. “We had reason to suspect wild birds played a role, but the extent of spread in wild bird populations wasn’t clear. Without that context, the human infections appeared geographically scattered; with it, the strain’s emergence correlated with where we saw it becoming the dominant strain in wild birds.”
The mapping gave the researchers a reasonable source for the human D1.1 infections, but it did not provide how great the risk was of the virus becoming more transmissible among humans. The current human versions of a bird flu vaccine did show to be successful against the virus, the study announcement noted.
“Fortunately, we saw that these viruses remained mostly avian, with none of the major mutations known to enable efficient human infections,” Dr. Lisa Kercher, St. Jude Department of Host-Microbe Interactions director of lab operations, and study co-first author, said.
“They did have a mutation that gives resistance to a common antiviral drug, but when we tested existing candidate vaccines, they showed significant cross-reactivity, suggesting they will likely be effective to help control the virus,” Kercher added.
This study did agree with organizations such as the Centers for Disease Control and Prevention that the virus presently remains at a negligible risk to humans and for human spread. CDC reports there have been 2 deaths and 71 cases of bird flu in the United States. The researchers add that surveillance needs to continue to gain increased understanding of potential human risks.
“We were lucky enough to join groups from Canada and throughout the U.S. to understand this virus,” Webby noted. “That lets us put human cases in the context of the strain’s greater spread and gives us a model to continue to monitor and assess the threat of these highly pathogenic influenza viruses in the future.”
Findings from this study were published in the April 15 edition of Nature Medicine.
