Bird flu infections in humans 'still rare' despite Cambodian girl's death
The world is on high alert for human cases of bird flu.
The death of an 11-year-old girl in Cambodia - and confirmation that her father is also infected - has caused a ripple of concern around the world.
It could become a cluster. Several other people are being tested and a small number are reported by local media to be showing symptoms.
But that doesn't necessarily mean the H5N1 virus has mutated to start transmitting between people.
The family kept chickens and ducks, all of which had recently died.
While health authorities are still investigating the source of the infections, suspicion will be high that the virus spread from the birds.
According to the World Health Organisation (WHO), H5N1 has caused at least 870 human cases and 457 deaths since 1997.
Most have had direct contact with infected poultry and the WHO's latest assessment is that the risk of sustained human transmission is low.
Professor of molecular virology at the University of Nottingham, Jonathan Ball, said: "This is a very sad outcome for the young girl infected with a particularly aggressive form of avian influenza or 'bird flu'.
"Thankfully, human infections are still rare, and the likelihood of onward human-to-human transmission is very low."
But the virus is mutating.
Cambodia girl dies from bird flu, health officials say
Bird flu has jumped to mammals in the UK
The UK Health Security Agency's latest technical briefing on H5N1 says it has undergone genetic changes that "provide an advantage for mammalian infection", putting the current risk in the UK at level 3 on a five-point scale.
H5N1 spread through a mink farm in northern Spain last year, almost certainly being passed from animal to animal.
And the virus has also infected other mammals, including foxes and otters in the UK.
It may just be a matter of time before the virus mutates further to infect and spread between humans more easily.
The WHO's director general Dr Tedros Adhanom Ghebreyesus has warned that "we must prepare for any change in the status quo."
The COVID pandemic has shown that it would be foolish to be complacent about animal viruses.
Professor Ball added: "The risk to humans is still very low, but it's important that we continue to monitor the circulation of flu in both bird and mammal populations and do everything we can to reduce the number of infections seen.
"It also highlights why efforts to develop next-generation cross-reactive vaccines are so important."