Since the end of 2021, Europe has been hit by the most devastating avian flu in its history. The disease, which strikes both wild and domestic birds, has led to the slaughter of more than fifty million poultry.
The epidemic, caused by the H5N1 virus, is also spreading in America, both North and South, with tens of millions of birds slaughtered.
It’s a “panzootie”, summarizes with AFP the virologist Tom Peacock. In other words, an epidemic that strikes animals all over the world.
“It may be caused by the appearance of a slightly different strain of H5N1, which would be transmitted very easily in wild and migratory birds”he says.
Can it extend to other animals? And, three years after the appearance of Covid-19, can it cause a new pandemic in humans?
For mammals – including humans – isolated examples of transmission already exist. In animals, several British foxes and otters tested positive last year for H5N1, the virus behind the current outbreak.
In France, a cat died of it at the end of January. In several of these cases, the virus involved carried a specific mutation, called PB2. It allows, a priori, the virus to better replicate in mammals.
Some human cases
However, these examples are not enough to worry about a massive spread in animals other than birds. Each time, it seems that the animal became infected by eating a bird, and not by being contaminated by another mammal.
However, if he “there is no transmission between mammals, the risk remains low for humans”, notes infectious disease specialist Paul Wigley at the British Science Media Center.
Tom Peacock reminds us that it would take many other mutations than PB2 to envisage massive transmission to humans.
Human cases of H5N1 infection exist, of course, but remain marginal: the World Health Organization (WHO) has identified just under 900 over the past 20 years.
Recently, a case of bird flu was identified in a girl in Ecuador, but it remains to be proven that it is indeed the H5N1 virus which is concerned.
These elements therefore lead researchers to a relative serenity regarding the possibility of an avian flu pandemic in mammals and, even more so, in humans.
However, two recent events have fueled the hypothesis that a strain of H5N1 could become transmissible from one mammal to another.
In Spain, a farm of 50,000 mink had to be slaughtered after multiple cases of avian flu, the animals presenting the famous PB2 mutation.
In Russia, seals have tested positive for the disease, after 2,500 of them were found dead near the Caspian Sea.
Optical illusion
In both cases, particularly in Spain, it is suspected that the infection took place between mammals. But this hypothesis remains to be confirmed. For the time being, the experts therefore call rather to avoid alarmism, like the infectiologist David Heyman.
Certainly, he underlines to AFP, it is necessary to carefully monitor the presence of influenza viruses in mammals, because their organism is conducive to the meeting of several strains and to mutations likely to be then transmitted to the ‘human.
He warns against an optical effect: if we see cases accumulating in mammals, it may be because we are testing more and more animals in the current context. “Perhaps it had been going on for years, without anything notable ever happening”he says.
And, even if a strain were to start circulating among humans, it would probably be easy to adapt current flu vaccines to it, he believes, pointing out that H5N1 has been studied very carefully since its appearance in China and Hong Kong in the 1990s.