The possibilities of regional bird flu outbreaks were "very high" in the winter and coming spring, said Vice Minister of Agriculture Yin Chengjie on Monday.

Yin said although the country had made major achievements in preventing the disease, his ministry still considered the situation was "not optimistic" as there had been cases of poultry infection with a "relatively large contaminated area".

Yin said the critical point was to improve the disease control in the country's southern areas.

He said the methods of poultry breeding, slaughter, delivery and processing needed radical changes, adding the prevention measures were not fully carried out in some regions.

He ordered local departments to step up immunization measures ahead of the Chinese Spring Festival in early February next year.

He urged authorities to intensify supervision over bird activities along the border and in water areas by increasing sample test numbers and examination frequencies.

He also required managers of live poultry markets in the southern regions continue to implement sterilization measures on a regular basis and "take compulsory measures" once the bird flu virus was spotted.

Bird flu, or avian influenza, is a contagious disease of animal origin caused by viruses that normally infect only birds and, less commonly, pigs.

China's health authorities said on Monday that no human-to-human transmission had been confirmed in the two human cases of bird flu involving a father and son in the Nanjing area.

The means of transmission in these cases was unknown.

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.

The father was in stable condition and showing signs of improvement on Monday.

The latest cases bring the number of confirmed human infections of bird flu in China to 27 since 2003, with 17 deaths.

The World Health Organization has warned that the virus could mutate into a form that is highly infectious among humans and easily transmissible from person to person. Such a change could mark the start of a global outbreak.

(Xinhua News Agency December 11, 2007)