The epidemic became annual and spread to new areas, causing the death of large numbers of wild birds, in addition to the slaughter of tens of millions of poultry.
Experts have warned that the H5N1 virus, which is behind the record outbreak of bird flu around the world, is changing rapidly with increasing calls for poultry vaccinations.
While the risk to humans remains low, the increasing number of cases among mammals is worrying, experts told AFP.
Since its appearance in 1996, the avian influenza virus has caused mainly seasonal epidemics. But “something happened” in mid-2021 that made it more infectious, according to Richard Webby, a virologist and director of the World Health Organization’s Avian Disease Research Center.
Since then, the epidemic has become annual and spread to new areas, causing the death of large numbers of wild birds, in addition to the slaughter of tens of millions of poultry.
Webby said these bird flu epidemics 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 evolved rapidly as it spread from Europe to North America.
He explained that the researchers infected a ferret with one of the new strains of bird flu and found an “enormous” and unexpected amount of the virus in its brain, and this indicates that the new strains are more dangerous.
Although he indicated that the risk is still low for humans, he noted that “this virus is not fixed, but rather evolving, and this increases the risk of the virus acquiring, even if by chance, genetic features that bring it closer to being a human virus.”
An alarming crisis
But the discovery of the disease in an increasing 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 believed to have contracted the virus by eating infected birds.
“Recent cases of transmission of the virus in mammals must be closely monitored,” WHO chief Tedros Adhanom Ghebreyesus warned in February.
Ian Brown, head of virology at the British Agency for Animal and Plant Health, 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 adapted to humans”.
Avian viruses bind to different receptors on the host cell than human viruses do, Richard Webby said, explaining that it would take “two or three slight mutations in one of the virus’ proteins” to become more adapted to humans.
He added that one of the ways to reduce the number of cases of avian influenza and reduce the risks to humans is to vaccinate poultry.
Some countries, including China, Egypt and Vietnam, have organized such vaccination campaigns. But many other countries are hesitant because of fears of possible import restrictions and infected birds passing through holes in the chain.
In April, the United States began testing several vaccine candidates for potential use in birds. France recently indicated that it hopes to start vaccinating poultry this fall.
The UK’s chief veterinarian, Christine Middlemiss, said vaccinating poultry is not “a magic bullet because the virus is constantly changing”. But she told AFP at an event at the UK embassy in Paris last week that countries hesitating should consider using it more frequently.
Monique Elliott, Director-General of the World Organization for Animal Health, said that the issue of vaccinating poultry should be one of the options, noting that “everyone knows now that the epidemic is not just a fantasy, but can be a reality.”