Geneva: The World Health Organisation warned Thursday that its ability to manage the risk to humans posed by the H5N1 bird flu virus was being compromised by patchy surveillance.
The WHO said the United States last week reported a fourth human case of H5N1 avian influenza following exposure to infected dairy cows, while Cambodia had reported two cases in children who had contact with sick or dead chickens.
"For the moment, no human to human transmission has been reported, which is why WHO continues to assess the risk to the general public as low," the UN health agency's chief Tedros Adhanom Ghebreyesus said.
"However, our ability to assess and manage that risk is compromised by limited surveillance for influenza viruses in animals globally," he told a press conference.
"Understanding how these viruses are spreading and changing in animals is essential for identifying any changes that might increase the risk of outbreaks in humans, or the potential for a pandemic."
The WHO called on all countries to step up influenza surveillance and reporting in animals and humans, and for countries to share samples and genetic sequences.
It also urged greater protection for farm workers who may be exposed to infected animals, and for greater research on bird flu.
Spread in US cattle
Avian influenza A(H5N1) first emerged in 1996.
The 2.3.4.4b clade of the virus, first detected in 2020, is behind an exponential growth in the number of outbreaks in birds, alongside an increase in the number of infected mammals.
The strain has led to the deaths of tens of millions of poultry, with wild birds and land and marine mammals also infected.
The human cases recorded in Europe and the United States since the virus surged have largely been mild.
H5N1 has been spreading among dairy cow herds in the United States, with now four recorded cases of the disease jumping from cattle to people.
Maria Van Kerkhove, the WHO's head of epidemic and pandemic preparedness and prevention, said H5N1 had now been detected in 145 herds in 12 US states.
"I think that's only going to continue, given that we've seen some expanse of spread, given that we have some, limited sampling that's happening in dairy cattle - not just in the United States, but globally," she said.
"We really need to understand the extent of the circulation in dairy cattle."
WHO emergencies director Michael Ryan said it was typically easier to eradicate disease from domesticated animals, because it is known where the animals are, and bio-security measures can be applied.
"The difficulty is when that disease exists in pockets of wild animals," he said, due to the risk of mixing.
