China's health authorities said on Monday that no human-to-human transmission had been confirmed in the two human cases of bird flu and the means of transmission in these cases, involving two family members in the Nanjing area, remained unknown.

"The virus in the first case originated with poultry and has not mutated. It has no biological features for human-to-human transmission," Mao Qun'an, spokesman of the Ministry of Health, said, citing laboratory results.

But Mao said there were several possibilities for transmission in the second human case, which involved the father of the man in first case.

He said epidemiological investigation showed that the father could have become infected through contact with the son, but it was also possible that both men were either infected by same source or separately from different sources.

"Neither of the three possibilities has been confirmed and in-depth investigation is still being conducted," Mao said.

China confirmed on Dec. 7 that the father of a 24-year-old Chinese man who died of bird flu on Dec. 2 had also been infected with the H5N1 virus that causes the disease.

The 52-year-old man, surnamed Lu, was a native of Nanjing, capital of Jiangsu. He developed fever and was hospitalized for lower lobe pneumonia on Dec. 3, according to the Ministry of Health.

Lu's son was said to have no known contact with dead poultry and the Jiangsu Animal Husbandry and Veterinary Bureau said earlier last week that no bird flu epidemic had been discovered in the province.

(Xinhua News Agency December 10, 2007)