While the risk to humans remains low, the rising number of cases in mammals is concerning, experts told AFP.
Since its appearance in 1996, the bird flu virus has mainly caused seasonal epidemics. But “something happened” in mid-2021 that made it more contagious, according to Richard Webby, virologist and director of the World Health Organization’s Center for Avian Disease Research.
Since then, the epidemic has become annual and has spread to new regions, causing the death of a large number of wild birds, in addition to the slaughter of tens of millions of poultry.
Webby said these bird flu outbreaks are the worst ever. The researcher supervised a study, the results of which were published this week in the journal (Nature Communications), and showed that the virus was evolving rapidly as it spread from Europe to North America.
He explained that researchers infected a ferret with one of the new strains of bird flu and found an unexpected “huge” amount of the virus in its brain, indicating that the new strains are more dangerous.
Although he indicated that the risk was still low for humans, he noted that “this virus is not static, but rather evolutionary… This increases the risk that the virus will, if by chance, acquire genetic characteristics that bring it closer to being a human virus.”
There are still rare cases of human infection with the virus, which has sometimes resulted in death, usually after close contact with infected birds. But the discovery of the disease in a growing number of mammals, including new species, is “a really worrying sign”, says Richard Webby.
Last week, Chile announced that nearly 9,000 sea lions, penguins, otters, porpoises and dolphins had died of bird flu on its northern coast since early 2023.
Most are thought to have contracted the virus by eating infected birds.
World Health Organization chief Tedros Adhanom Ghebreyesus warned in February that “recent cases of virus transmission in mammals should be closely monitored.”
Ian Brown, head of virology at the UK Animal and Plant Health Agency, said there was no “clear evidence of the ability of this virus to survive in mammals”. He told AFP that while the virus has evolved to be “more capable of reproducing in birds”, it is still “not suitable for humans”.
Avian viruses bind to different receptors on the host cell than human viruses, said Richard Webby, explaining that it would take “two or three slight mutations in one of the proteins of the virus” to become more suitable for humans.
He added that one of the ways to reduce the number of bird flu cases and reduce the risk to humans is to vaccinate poultry.
Some countries, including China, Egypt and Vietnam, have organized vaccination campaigns. But many other countries are hesitant for fear of possible import restrictions and infected birds slipping through holes in the chain.
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