Study finds key factors behind bird flu outbreaks

By Will Dunham

WASHINGTON (Reuters) - Ducks, people and rice paddies are the primary forces driving outbreaks of avian influenza in Thailand and Vietnam, and the number of chickens is less pivotal, scientists said on Wednesday.

U.N. Food and Agriculture Organization experts and others looked at three waves of H5N1 bird flu in Thailand and Vietnam in 2004 and 2005. The virus has killed 236 people in 12 countries since 2003.

They used computer modeling to study how various factors were involved in the spread of the virus, including the numbers of ducks, geese and chickens, human population size, rice cultivation and local geography.

Even though Thailand and Vietnam addressed the outbreaks in different ways, the researchers found that the numbers of ducks and people, and the extent of rice cultivation were the most important contributing factors underpinning the outbreaks.

"This provides better insight on where and when the H5N1 risk is highest, so it's possible to better pinpoint where to look for the virus or where to expect flare-up of disease and also when to expect it," Jan Slingenbergh, senior veterinary officer for the Food and Agriculture Organization, said in a telephone interview.

"It helps to better target the interventions," he added.

Monitoring duck populations for the H5N1 virus and tracking rice farming by satellite are the optimal ways to predict an outbreak's distribution, the researchers said. They added that their model also can be extended to Laos and Cambodia, where there are similar land use patterns.

Avian influenza has been closely linked to chickens in the past, but the study found the number of chickens to be less important as a predictor.