With 55 human cases in the US and avian influenza impacting bird populations across the globe, here’s a look at why scientists are closely paying attention to any evolution of this virus.
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Cases of bird flu across the globe are being closely watched by scientists who are looking for any signs that this type of influenza virus could turn into a more serious threat to humans.
While avian influenza, or H5N1, is widespread in birds, it’s rare in humans and typically only transmits to people in close contact with an infected animal.
There’s been a great deal of attention on the outbreak of avian influenza in dairy cattle and dozens of human cases in the United States, but a recent first human case in Canada this month has also raised concerns among scientists looking for any signs that the virus could change to spread among people.
Why did a teenager’s bird flu case in Canada raise alarm about H5N1?
Canadian health authorities reported the country’s first H5N1 case earlier this month in a teenager who was hospitalised with severe illness in British Columbia.
There have been no additional cases or human-to-human transmission linked to the case, local authorities said in their most recent update this week, but the teenager remains in critical condition.
There are several reasons that the teenager’s case was particularly worrying, including that it was a severe case, had no known source of contamination, and that there were certain mutations in the viral sequence, Dr Marie-Anne Rameix-Welti, head of the national reference centre for respiratory infections at France’s Pasteur Institute, told Euronews Health.
“The virus sequence shows some adaptation markers, which is expected when a virus infects a mammal,” she said.
Rameix-Welti added that in this case, however, there was a mutation on the hemagglutinin - a glycoprotein that influences how the virus binds to host cells - “that we rarely see on H5 viruses”.
Professor Ian Brown, who leads the avian virology group at the Pirbright Institute in the UK, told Euronews Health that this case concerned a relatively new genotype of the virus “associated with quite a large outbreak in British Columbia right now,” but that the data was at an “early juncture”.
He added that the international community was concerned about some of the changes in the virus since it was unusual for bird flu viruses which generally aren’t very good at infecting humans.
“These changes could mean that the virus is finding a way to better infect the individual,” he said, adding, that the virus would still have to overcome a lot of barriers to do so.
The teenager was infected with a strain of bird flu that is circulating in wild bird and poultry populations in Canada, which is distinct from the virus circulating in cattle in the US.
Tests on humans, animals, and environmental samples related to the case were negative for the virus, local British Columbia authorities said.
What is the current global situation for bird flu?
According to the World Organisation for Animal Health (WOAH), there were 88 reported outbreaks of highly pathogenic avian influenza in October 2024, with the number currently increasing.
Some 1.7 million birds or poultry died or were culled that same month.
Rameix-Welti says that what has been seen in the last three to four years with bird flu is “a very significant genetic diversification of the virus, an extremely wide geographical dispersal of it” and a longer season.
“In Europe, we can find it all year round whereas before it was only during (bird migration),” she said, adding that it’s also now affecting a significant number of mammal species as well.
In the US, there’s an ongoing outbreak among dairy cattle, with around 675 herds being infected in 15 states since March.
There have been 55 human cases mostly among farm workers, but last week the first case in a child was reported in California.
The US Centers for Disease Control and Prevention (CDC) said the child had mild symptoms and that there was no evidence of person-to-person spread but the source of infection has yet to be identified.
In Europe, there have been no human cases of H5N1 and no infections in cattle. The genotype circulating in the US has also not been detected in the region, the European Centres for Disease Prevention and Control (ECDC) indicated.
“The current situation in Europe is we're coming back into the autumn/winter period now that's the higher risk period because migratory birds come into Europe in much greater numbers,” said Brown, meaning they can spread it to domestic birds.
Moritz Kraemer, a professor of epidemiology and data science at the University of Oxford’s Pandemic Sciences Institute, added in an e-mail that “there is some work ongoing to understand what the pathways of introduction might be if infected birds (were) to travel to Europe and rest in close proximity to cattle”.
“With limited transmission in humans, the risk is mainly to cattle and bird populations. Preventing rapid spread in cattle should be a central priority for Europe,” he added.
How could bird flu evolve to become a larger threat to humans?
Both the CDC and ECDC have said the risk to the general population is low. Scientists are closely monitoring the virus to see if it could evolve to impact humans.
“The longer these infections stay in avian populations, particularly when they're in domestic populations of birds, then that increases the opportunity for exposure to humans that may occupationally look after these birds or be involved in that industry,” said Brown.
The cases in humans have so far been mostly mild, with people often reporting conjunctivitis as a symptom, but scientists are looking for a signal that the virus can cause flu symptoms or be transmitted between humans.
This would be very concerning, Rameix-Welti added, because there’s no preexisting immunity in the human population so it would run the risk of the virus becoming a pandemic.
But at the moment, we are not at a stage of “major risk,” she said, although “it is a situation that must be monitored because it is evolving quite quickly”.