Scientists have reported that a deadly strain of avian flu may have passed between people for the first time.
The H7N9 bird flu virus, which has killed over 40 people since March, is thought to have been transmitted between father and daughter in eastern China.
Unlike her father, who had visited a poultry market in the week before falling ill, the daughter had no known exposure to live poultry but fell ill six days after her last contact with him.
Both died in intensive care of multiple organ failure.
Researchers said that strains of the virus isolated from samples taken from both patients were "almost genetically identical" - a strong suggestion that the virus was transmitted directly from father to daughter.
Commenting on the research, experts said while it did not necessarily mean H7N9 is any closer to becoming the next flu pandemic, "it does provide a timely reminder of the need to remain extremely vigilant".
"The threat posed by H7N9 has by no means passed," James Rudge and Richard Coker of the London School of Hygiene and Tropical Medicine said in a commentary in the British Medical Journal.
However, the scientists who led the study stressed that the virus has not yet gained the ability to transmit from person to person efficiently, meaning the risk is very low that it could cause a human pandemic in its current form.
The new bird flu virus was unknown in humans until February.
According to the latest World Health Organisation data, at least 133 people in China and Taiwan have been infected with the virus so far and 43 of them have died.
Most cases have been in people who had visited live poultry markets or had close contact with live poultry in seven to ten days before falling ill.
