A man in China contracted bird flu because he was in close contact with his infected son, although the virus had not mutated into a form that is highly contagious among humans, authorities said Thursday.
A 52-year-old man, identified only by his surname Lu, was hospitalised with the potentially deadly H5N1 strain of the virus soon after his son died from it on December 2. Lu has since recovered.
Chinese health ministry spokesman Mao Qunan said Lu's infection was due to close contact with his son, but that the transmission was not technically "human-to-human".
"It has no biological features for human-to-human transmission," he told journalists.
Like many human cases of bird flu in China, authorities have not been able to identify the source as neither Lu nor his son had close contact with sick or dead poultry prior to infection, he said.
He refused to elaborate on the findings, which was reached by the ministry's expert group on bird flu.
Human-to-human transmission of bird flu remains rare, but experts fear such routes of infection could cause a global pandemic if the virus mutates with each person it infects and becomes more adaptable to humans.
The World Health Organisation (WHO) said Thursday that human-to-human transmission of bird flu in the case of Lu was possible but said it had not mutated into a highly contagious form.
"A human-to-human transmission through close contact between the son and the father cannot be ruled out in this family cluster," Hans Troedsson, the WHO representative in China, told AFP.
"However, the biological findings at this stage show that the virus has not mutated to a form that can be transmitted from human to human efficiently."
Bird flu has so far infected at least 27 people in China, 17 of whom have died.
H5N1 has killed more than 200 people and ravaged poultry flocks worldwide since 2003, according to the WHO.