“It has no biological features for human-to-human transmission,” Chinese Health Ministry spokesman Mao Qun'an was cited by China’s Xinhua news agency as saying. An epidemiological investigation showed the father was infected through close contact with his son, Mr Mao said.

The cases took place in the provincial capital of Nanjing. The father was hospitalised and confirmed positive for the lethal virus just a day after his son, 24, died on December 2, 2007.

Local authorities had kept 83 people who had close contact with these men under close observation but none had shown unusual symptoms so far, the ministry said.

Xinhua quoted experts as saying they had found that the virus that infected the son had originated from poultry and had not mutated. But it remained unclear how the son was infected in the first place, as neither man had any known contact with dead poultry.