The World Health Organization has expressed concern about the spread of H5N1 bird flu, which has an “extremely high” mortality rate in humans.
An outbreak that began in 2020 has resulted in the death or culling of tens of millions of poultry. Recently, the spread of the virus among several mammal species, including domestic livestock in the US, has increased the risk of spillover to humans, the WHO said.
“I think this remains a huge concern,” Jeremy Farrar, chief scientist at the U.N. health agency, told reporters in Geneva.
Cows and goats were added to the list of affected species last month – a surprising development for experts as they were not thought to be susceptible to this type of flu. U.S. authorities reported this month that a person in Texas was recovering from bird flu after being exposed to dairy cattle 16 herds spread across six states apparently infected after exposure to wild birds.
The A(H5N1) variant has become “a global zoonotic animal pandemic,” Farrar said.
“The big concern, of course, is that in infecting ducks and chickens and then increasingly mammals, that virus is now evolving and developing the ability to infect humans and then, crucially, the ability to pass from human to human, ” he added.
So far, there is no evidence that H5N1 spreads between people. But in the hundreds of cases in which people have been infected through contact with animals over the past two decades, “the mortality rate is extremely high,” Farrar said, because people have no natural immunity to the virus.
According to the WHO, between 2003 and 2024, 889 cases and 463 deaths due to H5N1 have been reported worldwide from 23 countries, bringing the mortality rate to 52%.
The recent US case of human infection following contact with an infected mammal highlights the increased risk. When you “get into the mammal population, you get closer to humans,” Farrar said, warning that “this virus is just looking for new, new hosts.”
Farrar called for more monitoring, saying it was “very important to understand how many human infections are happening… because that is where adaptation (of the virus) will happen.”
“It’s tragic to say, but if I get infected with H5N1 and die, that’s the end,” he said. “If I go around the community and spread it to someone else, you start the cycle.”
He said efforts are underway to develop vaccines and therapies for H5N1, and stressed the need to ensure that regional and national health authorities around the world have the capacity to diagnose the virus.
This was done so that “if H5N1 were to spread to humans, with human-to-human transmission,” the world “would be able to respond immediately,” Farrar said, calling for equitable access to vaccines, therapeutics and diagnostics. .