WHO regional director for the Western Pacific, Shigeru Omi, said on Monday more information was needed on the potentially grave development in the spread of a virus which had killed 27 people across Asia this year.
Speaking to AFP after the Chinese government admitted on Monday that the H5N1 virus was found in pigs last year, Omi said: "We would like to know how widespread it is and how this infection took place.
"We have asked for information, but so far there have been no additional details. Overall the Chinese government has been cooperative and I hope they will remain so."
Omi, who was in Penang for a regional health conference, said he did not want to pass judgment on China's delay in announcing the infection in pigs until he had a clearer idea of the situation.
'A little bit closer'
Asked at a news conference earlier about the threat of a global epidemic if pigs had been infected, Omi said: "Of course it's a little bit closer but how close we don't know. This is one factor we have to monitor very closely.
"At this point, there is no need for the global community to
panic but it doesn't mean we can relax. We need to remain
China's Ministry of Agriculture confirmed on Monday the deadly strain of bird flu was found in pigs in 2003, but said none had been found this year, the Xinhua news agency reported.
The report came just days after a leading Chinese scientist, Chen Hualan, told reporters in Beijing the potentially lethal virus had been found in pigs in both 2003 and 2004.
"The Chinese government attaches great importance to the
prevention and control of bird flu," an official from the ministry's Veterinary Administration said.
The ramifications of infection among pigs could be extremely
grave, as researchers fear it might be the first step of a mutation of the virus into a form that could spread more easily to humans.
Until now H5N1 had been found only in poultry. While it was suspected to be carried by swine no cases in pigs had been officially reported, according to the United Nations Food and Agriculture Organisation.
"At this point, there is no need for the global community to panic but it doesn't mean we can relax. We need to remain vigilant"
WHO regional director for the Western Pacific
Omi said research indicated the virus "was circulating more widely than we had thought", and warned of a "long battle" before bird flu is wiped out in Asia due to poor management and surveillance of animal husbandry.
"The WHO view is that this is a long battle that we have to fight for several years at least," Omi said. "We cannot finish it this year because the virus is circulating among poultry, wild birds and migratory birds.
"There is always a chance that this virus will gain the ability to transmit on a human-to-human basis."