Experts have warned that the recent detection of bird flu in mammals including foxes, ottersmink, sealsand even grizzly bears is worrying, but stresses that the virus would have to mutate significantly to spread between people.
Since the end of 2021, Europe was captured by the worst outbreak of avian influenza to date, with North and South America also experiencing severe outbreaks.
This has led to the culling of tens of millions of domestic fowl worldwide, many with the H5N1 strain. The global outbreak is also responsible for the deaths of tens of thousands wild birds.
Tom Peacock, a virologist at Imperial College London, told AFP it was a “panzootic” – a Pandemic among animals, in this case birds.
“We’re not exactly sure why it’s happening now, but we think it could be caused by a slightly different strain of H5N1 that’s very effective at spreading in wild migratory birds,” Peacock said.
It is rare for bird flu to spread to mammals, and even rarer for humans to contract the potentially deadly virus.
On Thursday, the UK Health Authority said a fox had recently tested positive for H5N1.
It joins eight foxes and otters that tested positive in the UK last year, all with a PB2 mutation.
Peacock said this mutation “allows the virus to better replicate in mammalian cells.”
However, more mutations are “required for the virus to cause a flu pandemic in humans,” he added.
France announced last week that a cat was euthanized after testing positive for H5N1.
And last month, the Montana State Parks Service said three grizzly bears with bird flu had been euthanized.
All of these mammals were suspected of eating infected birds.
Paul Wigley, professor of animal microbial ecosystems at the University of Bristol in the UK, said that while “there is no transmission within mammalian populationsthe risk for humans remains low”.
Pandemic potential?
However, two recent major infections have raised concerns that avian flu has the potential to spread between mammals.
One was an outbreak of H5N1 with the PB2 mutation on a Spanish farm in October, resulting in the culling of more than 50,000 mink.
research published in the diary euro surveillance Last month it said its results “suggest that further transmission of the virus to other mink in the affected farm may have occurred”.
Transmission between mink has not been confirmed, further research is ongoing.
The mass death of around 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 early samples from the seals “tested positive for avian flu,” adding that they were still investigating whether the virus caused the die-off.
Peacock warned there are mixed reports from Russia of seals catching the virus from eating infected seabirds.
But if the seals were to transmit bird flu to each other, “that would be another very worrying development,” he added.
“The mink outbreaks, the increased number of infections from scavengers and the possible outbreak of seals suggest that this virus has the potential to cause a human pandemic,” he said.
mixing point
David Heymann, an infectious disease specialist at the London School of Hygiene and Tropical Medicine, urged caution.
More cases of bird flu could be detected in mammals as countries have stepped up testing, he said.
“It may have been like this for years and nothing really happened,” he told the AFP news agency.
But there has always been concern when a flu virus enters mammals “because they are often the mixing point of influenza virusesor they create an environment in which mutations can occur and then adapt in humans,” he added.
Even if that were to happen, he said excellent surveillance systems exist in Europe and North America and that H5N1 has been extensively researched since it first appeared in China and Hong Kong in 1996.
If H5N1 mutates into a strain that could circulate among humans, the current seasonal flu vaccine could be updated to accommodate it fairly easily, he said.
Britain’s Health Safety 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 World Health Organization. There have been four confirmed cases and one death in the past year.
Last month, Ecuador reported South America’s first case of the A(H5) avian influenza virus in a human — a nine-year-old girl who had contact with backyard fowl.
The experts called for continuous surveillance of avian influenza in wild birds, poultry and mammals so people can limit their exposure.
