Ducks, rice and human beings, and not chickens are the "most significant factors' behind persistent outbreaks of bird flu, a new study has claimed. The study released by United Nations Food and Agriculture Organisation (FAO) found ducks, rice and people not chickens to be the "most significant factors' in the spread of the bird flue in Thailand and Vietnam. "Mapping H5N1 highly pathogenic avian influenza risk in Southeast Asia: ducks, rice and people' also concludes that these factors are probably behind persistent outbreaks in other countries such as Cambodia and Laos. The study, which examined a series of waves of H5N1 highly pathogenic avian influenza in Thailand and Vietnam between early 2004 and late 2005, was initiated and coordinated by FAO senior veterinary officer Jan Slingenbergh and is published in the latest issue of the Proceedings of the National Academy of Sciences of the United States. Through the use of satellite mapping, researchers looked at a number of different factors, including the numbers of ducks, geese and chickens, human population size, rice cultivation and geography, and found a strong link between duck grazing patterns and rice cropping intensity.