by 
Experts cautioned that the recent detection of bird flu in mammals, including foxes, otters, mink, seals and even brown bears, is concerning, but stressed that the virus would have to mutate significantly to spread between humans.
Since the end of 2021, Europe has been affected by the worst bird flu outbreak in its history, and North and South America have also experienced severe outbreaks.
This has led to the culling of tens of millions of domestic poultry around the world, many with the H5N1 strain. The global outbreak is also responsible for the deaths of tens of thousands of wild birds.
Tom Peacock, a virologist at Imperial College London, told AFP that it is a “panzootia”, a pandemic among animals, in this case birds.
“We’re not entirely sure why it’s happening now, but we think this could be due to a slightly different strain of H5N1 that is spreading very effectively in wild migratory birds,” Peacock said.
It’s rare for bird flu to jump to mammals, and even rarer for humans to contract the potentially deadly virus.
On Thursday, the UK’s Health Security Agency said a fox had recently tested positive for H5N1.
It joins eight foxes and otters that tested positive in the UK last year, all of which had a PB2 mutation.
Peacock said this mutation “allows the virus to replicate better in mammalian cells.”
But “further mutations would be required for the virus to cause an influenza pandemic” in humans, he added.
France announced last week that a cat had been euthanized after testing positive for H5N1.
And last month, the US state park service of Montana said three brown bears with bird flu had been euthanized.
All of these mammals were suspected of having eaten infected birds.
Paul Wigley, professor of animal microbial ecosystems at the UK’s University of Bristol, said that while “there is no transmission within mammalian populations, the risk to humans remains low.”
– ‘Potential to cause a pandemic’? –
However, two recent large-scale infections have raised concerns that bird flu has the potential to spread among mammals.
One was an outbreak of H5N1 with the PB2 mutation on a Spanish farm in October that led to the culling of more than 50,000 mink.
The research published in the journal Eurosurveillance last month said its findings “indicate that further transmission of the virus to other mink may have taken place on the affected farm.”
Transmission between mink has not been confirmed, and further investigation is ongoing.
The mass die-off of some 2,500 endangered seals found along Russia’s Caspian Sea coast last month has also raised concerns.
A researcher at Russia’s Dagestan State University, Alimurad Gadzhiyev, said last week that the first samples from the seals “tested positive for bird flu,” adding that they were still studying whether the virus caused the die-off.
Peacock cautioned that there have been mixed reports from Russia about the seals, which could have contracted the virus by eating infected seabirds.
But if seals were to transmit bird flu to each other, “it would be another very worrying development,” he added.
“The mink outbreaks, the increased number of scavenging mammal infections and the possible seal outbreak would point to this virus having the potential to cause a pandemic” in humans, he said.
– ‘Mix point’ –
David Heymann, an infectious disease specialist at the London School of Hygiene and Tropical Medicine, urged caution.
More cases of bird flu in mammals may be being detected as countries have increased testing, he said.
“This may have been going on for years and nothing really has happened,” he told AFP.
But it was always concerning when a flu virus enters mammals “because they are often the mixing point for influenza viruses, or they create an environment in which mutations can occur and then adapt to humans,” he added.
Even if that happened, he said there were excellent surveillance systems in Europe and North America, and that H5N1 has been heavily investigated since it first appeared in China and Hong Kong in 1996.
If H5N1 were to mutate into a strain that could circulate among humans, the current seasonal flu vaccine could be fairly easily updated to include it, he said.
The UK Health Security Agency said there was “no evidence of sustained human-to-human transmission” of bird flu.
Over the past two decades, there have been 868 confirmed human cases of H5N1 with 457 deaths, according to the World Health Organization. There were four confirmed cases and one death last year.
Last month, Ecuador reported South America’s first case of the A(H5) bird flu virus in a human: a nine-year-old girl who had been in contact with poultry.
The experts called for continued surveillance of avian influenza in wild birds, poultry and mammals so that humans limit their exposure.
dl/gil
