The WHO, along with the UN s Food and Agriculture Organization (FAO) and the World Organisation for Animal Health (WOAH), urged countries to work together to save animals and protect people. AFP
Since late 2021, Europe has been gripped by its worst-ever outbreak of bird flu, while North and South America have also experienced severe outbreaks.
This has led to the culling of tens of millions of poultry worldwide, many with the H5N1 strain of the virus, which first emerged in 1996.
But there has recently been a worrying spike in infections in mammals.
"Avian influenza viruses normally spread among birds, but the increasing number of H5N1 avian influenza detections among mammals, which are biologically closer to humans than birds are, raises concern that the virus might adapt to infect humans more easily," the WHO said in a statement.
"In addition, some mammals may act as mixing vessels for influenza viruses, leading to the emergence of new viruses that could be more harmful to animals and humans."
Outbreaks have been reported in 26 species, including farmed mink in Spain and sealions in Chile. H5N1 was recently detected in cats in Poland.
The WHO, along with the UN's Food and Agriculture Organization (FAO) and the World Organisation for Animal Health (WOAH), urged countries to work together to save animals and protect people.
"There is a recent paradigm change in the ecology and epidemiology of avian influenza which has heightened global concern as the disease spread to new geographical regions and caused unusual wild bird die-offs, and alarming rise in mammalian cases," said WOAH science chief Gregorio Torres.
Infections in humans can cause severe disease with a high mortality rate.
Human bird flu cases are usually the result of direct or indirect exposure to infected live or dead poultry or contaminated environments.
"The virus does not appear to be able to transmit from one person to another easily, but vigilance is needed to identify any evolution in the virus that can change that," said the WHO's pandemic preparedness chief Sylvie Briand.
Experts were looking for changes that could be more dangerous to humans, and urged countries to boost their monitoring capabilities, she added.
"This is especially important as the virus is now affecting countries with limited prior experience in avian-flu surveillance," Briand said.
Devastating Spread In Birds
The WHO said that since 2020, a variant had led to an "unprecedented" number of deaths in wild birds and poultry in many countries in Africa, Asia and Europe.
The virus spread to North America in 2021 and then to Central and South America in 2022.
Last year, 67 countries in five continents reported highly pathogenic H5N1 bird flu outbreaks, with more than 131 million domestic poultry lost due to death or culling in affected farms and villages.
In 2023, another 14 countries reported outbreaks, mainly in the Americas, as the disease continues to spread.
These outbreaks have caused "devastation" in poultry and had harmed farmers' livelihoods and the food trade, the WHO said.
"Several mass death events have been reported in wild birds," the UN health agency added.
"Although largely affecting animals, these outbreaks pose ongoing risks to humans," it said.
"The epidemiology of H5N1 continues to rapidly evolve," said the FAO's chief veterinary officer Keith Sumption.
He pleaded for timely sharing of genetic sequences to monitor for changes, resulting in better risk assessment and disease control.