A severe outbreak of bird influenza in the Netherlands is affecting humans mildly and raising concerns that a mutated version could start a flu epidemic in humans. The Dutch Agricultural Ministry has expressed concern that avian and human flu viruses could mix in pigs and produce a mutation for which humans have no resistance; a number of pigs were recently found to have antibodies to the bird flu. The World Health Organization agreed that it was possible that the disease could eventually develop into a serious human problem, but food and animal health groups, including the International Animal Health Organization, have rejected those fears, saying there is no definitive proof of risk to consumers. In an effort to control the spread of the bird flu, Dutch officials have already slaughtered 15 million birds.