What to know about H5N1 bird flu in humans as a girl dies in Cambodia and her father tests positive

• A girl has died in Cambodia from bird flu, health officials said.
• The girl's dad is infected, but we don't know if he caught it from her.
• Experts have said the risk of the virus spreading among people is low.

An 11-year-old girl has died in Cambodia from bird flu, health authorities in the country said.

The girl initially fell ill with a high fever and cough on February 16 and later died in the National Children's Hospital in Phnom Penh, Cambodia's capital city, on Wednesday, the authorities said, per Reuters.

The case comes amid an outbreak of bird flu that has lead to the deaths of more than 200 million birds worldwide since early 2022, either from disease or mass culls, the World Organisation for Animal Health told Reuters.

The bird flu strain "H5 Highly Pathogenic Avian Influenza A" or "H5N1" has infected 868 people since it was first detected in humans in 1997, and 457 of those confirmed cases died, according to the World Health Organization. Officials in Cambodia said that the girl was the first human case in a Southeast Asian country since 2014, per Reuters.

Officials believe that the young girl caught the virus from dead wild birds or animals near her home in the Prey Veng province in south Cambodia, close to the border with Vietnam — 22 chickens and three ducks were found dead nearby, per The Telegraph.

Officials have taken samples from those birds as well as at least 12 people who came into contact with the girl, according to Reuters. As of Friday, the girl's father had tested positive for the virus, but we don't know how he caught it. 

Jonathan Ball, a professor of molecular virology at the University of Nottingham, UK, told the Science Media Centre on Friday that human infections are rare, and the likelihood of onward human to human transmission was  "very low."

"There is always a risk of human infection, particularly in people in close contact with poultry or wild birds, and this risk increases during times where circulation of avian influenza is particularly high, as it is now," he said.

Humans don't usually catch bird flu, but it can be deadly

H5N1 causes fever, cough, and then can rapidly progress to respiratory failure, acute respiratory distress syndrome — a life-threatening condition when fluid builds up in the tiny air sacs in the lungs — and multi-organ failure, according to the European Centre for Disease Control and Prevention. It states that 50% of people who catch it die, but that figure can vary between countries.

James Wood, head of the department of veterinary medicine at the University of Cambridge, UK, told the SMC that many people will have been exposed to H5N1 in recent years, but only a few had caught it.

"This one case in itself does not signal the global situation has suddenly changed," he said. 

Ball said that the risk to humans is still "very low."

Experts, including Ball and Wood, told the SMC that H5N1 needs to be closely monitored, in part due to recent reports of it infecting mammals like sea lions in Peru.

"There are two ways H5N1 can change – the mutations it accumulates itself over a period of time, or the mutations it develops as it links with other species," David Heymann, an infectious disease epidemiologist at the London School of Hygiene and Tropical Medicine,UK, told The Telegraph.

But he cautioned that "no one can say the risk is low, high or intermediate," because a mutation or "spillover" from another species was an unpredictable, "chance event."

"By far the most likely scenario for H5N1 is that nothing happens right now," Francois Balloux, the director of the UCL Genetics Institute, UK, tweeted on Friday.