The H5N1 virus, behind a record outbreak of bird flu across the world, is changing rapidly, experts warn as calls mount for countries to vaccinate their poultry. If the risk for humans remains low, the increasing number of cases among mammals is considered worrying, according to specialists interviewed by Agence France-Presse.
Since its appearance in 1996, the H5N1 avian influenza virus has caused essentially seasonal epizootics. But "something happened" in mid-2021 that made it much more infectious, according to Richard Webby, virologist and director of the World Health Organization's (WHO) Center for Avian Pathology Research. Since then, epizootics have become annual, extended to new areas and synonymous with massive deaths of wild birds and the slaughter of tens of millions of poultry.
For Richard Webby, it is the most important epizootic of bird flu ever known. The researchers also infected a ferret with one of the new strains of bird flu. They found an "enormous" and unexpected amount of virus in his brain, indicating a more severe disease than with previous strains, he told AFP. While pointing to a still low risk in humans, he observed that "this virus is not static, it evolves", which "increases the risk that, even by chance", the virus could "acquire genetic traits allowing it to be more of a human virus."
Cases of humans contracting the sometimes fatal virus, usually after close contact with infected birds, are rare. But the detection of the disease in an increasing number of mammals, including new species, is "a really worrying sign", according to Richard Webby. Last week, Chile announced that nearly 9,000 sea lions, penguins, otters, porpoises and dolphins have died of bird flu on its northern coast since early 2023. Most are believed to have contracted the virus by eating infected birds.
"Recent transmissions to mammals should be closely monitored," WHO boss Tedros Adhanom Ghebreyesus warned in February. Admittedly, there is "no clear evidence that this virus is easily maintained in mammals", according to Ian Brown, head of virology at the UK Animal and Plant Health Agency.
And while the virus evolves to become "more efficient in birds", it remains "unsuitable for humans", he told AFP. Avian viruses do indeed bind to different receptors on the host cell compared to human viruses, said Richard Webby, explaining that it would take "two or three minor mutations in a virus protein" for them to become more adapted. to humans.
One of the ways to decrease the number of bird flu cases and reduce the risk to humans would be to vaccinate poultry, said Richard Webby. Some countries, including China, Egypt or Vietnam, have already organized such vaccination campaigns. But many others are reluctant due to possible import restrictions and fears of infected birds slipping through the cracks. 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.
Vaccination of poultry is not "a magic bullet because the virus is constantly changing", according to Christine Middlemiss, UK Chief Veterinarian. But traditionally reluctant countries should consider using it more often, she told AFP at an event at the UK embassy in Paris last week. For the Director General of the World Organization for Animal Health, Monique Éloit, the issue of vaccination of poultry should be "on the table". After all, she recalls, "everyone now knows that a pandemic isn't just a fantasy, it could be a reality."
