A deadly strain of avian flu may have passed between people for the first time, experts believe.
The avian influenza A (H7N9) virus is thought to have been transmitted between father and daughter in eastern China, according to research published online by the British Medical Journal (BMJ).
The findings provide the strongest evidence yet of H7N9 transmission between humans, but its ability to transmit itself is "limited and non-sustainable," the experts believe.
Researchers, including from the Jiangsu Provincial Centre for Disease Control and Prevention and the Wuxi Municipal Centre for Disease Control and Prevention, presented evidence on the strain, which emerged in eastern China in February.
As of the end of June, 133 cases have been reported, leading to 43 deaths. Most cases have been among people visiting markets selling live birds or among those who had contact with live poultry in the seven to 10 days before becoming ill.
The latest study examined the case of a 60-year-old father who regularly visited a live poultry market and became ill five to six days after his last visit in March.
He was admitted to hospital with fever, cough and shortness of breath but, despite intensive care treatment, died of multiple organ failure on May 4.
His 32-year-old daughter, who was previously healthy, looked after him at his bedside before he was admitted to intensive care. She had no known exposure to live poultry before falling ill with a very high temperature, cough and fever.
The daughter developed symptoms six days after her last contact with her father and was admitted to hospital. Despite intensive care treatment, she died of multiple organ failure on April 24. Follow-up investigations revealed almost genetically identical virus strains from each patient, suggesting transmission from father to daughter.
Another 43 people were also tested who had had close contact with the father, daughter or both. One had suffered a mild illness but did not test positively for the avian flu strain. The others showed no signs of exposure.