As bird flu devastated poultry flocks around the world in recent years, it has also infected an increasing number of mammals – seals, sea lions, bears, minks, domestic cats and, most recently cows in Texas.
So far, only a few human beings have caught the disease, mostly people working with infected birds, but the United Nations and the World Health Organisation (WHO) have expressed concern about where bird flu might go next.
The UN described the spread of the H5N1 virus to mammals and, potentially to humans, as a “significant public health concern”.
In Geneva, the WHO’s top scientist, Dr Jeremy Farrar, said the risk of an increasing spillover to humans is “an enormous concern”.
He told a news conference that the H5N1 variant has become “a global zoonotic (animal) pandemic”, the Guardian newspaper reported.
“The great concern of course is that in … infecting ducks and chickens and then increasingly mammals, that virus now evolves and develops the ability to infect humans and then critically the ability to go from human to human,” Farrar said.
So far, there is no evidence that H5N1 is spreading between humans. But in the hundreds of cases where humans have been infected through contact with animals over the past 20 years, “the mortality rate is extraordinarily high”, Farrar said, because humans have no natural immunity to the virus.
From 2003 to 2024, 889 cases and 463 deaths caused by H5N1 have been reported worldwide from 23 countries, according to the WHO, putting the case fatality rate at 52%.
The New York Times has just published a lengthy feature on the spread of bird flu and what it might mean for the world’s human population. The biggest concern is that the rapidly mutating bird flu virus is adapting to mammals, edging closer to spreading among people.
“In my flu career, we have not seen a virus that expands its host range quite like this,” said Dr Troy Sutton, a virologist who studies avian and human influenza viruses at Penn State University.
A human pandemic is by no means inevitable, Dr Sutton told the newspaper as the changes in the virus did not signal that H5N1 could cause a pandemic.
Still, he said, “We really don’t know how to interpret this or what it means.”
