A strain of bird flu infecting poultry in North Korea is different from that which killed scores of people in other parts of Asia, a UN expert has said. Hans Wagner, an official for the Food and Agriculture Organization, said the birds were infected with the H7 strain. The strain that has decimated poultry stocks and caused recent human deaths in Cambodia, Thailand and Vietnam is the more virulent H5N1 strain. North Korea has culled 219,000 birds to tackle the outbreak, Mr Wagner said. "We have a new situation, because H7 has so far not occurred in Asia," he told reporters. We don't know where the virus came from," he said, adding that UN experts would now try to trace the source of the infection, to prevent future outbreaks. H7 can cause illness in humans, but outbreaks of the strain have not been as severe as those caused by H5N1. H5N1 has killed almost 50 people since its resurgence in South East Asia in December 2003. When North Korea first announced that three of its farms had been infected with bird flu last month, analysts warned that the virus could wipe out the poverty-stricken country's chicken industry. Poultry production is one of the few growing sectors in North Korea, which has relied on foreign aid to feed its people since the mid-1990s.