26.03.2008

Research

High concentrations of ducks, rice fields, and human populations—rather than chickens—pose the highest risk of sparking deadly H5N1 avian influenza outbreaks in Southeast Asia, according to a recent study.
"Mapping H5N1 highly pathogenic avian influenza risk in Southeast Asia" was recently published in the latest issue of the Proceedings of the National Academy of Sciences of the United States. In the report researchers affiliated with the United Nations Food and Agriculture Organization (FAO) collected data from three waves of hundreds of avian flu outbreaks in Vietnam and Thailand in 2004 and 2005, and then used statistical modeling to determine what factors most contributed to infection and spread of the disease. They found that human population concentration and high rice production were both strong risk factors for H5N1 outbreaks, as were numbers of both free-ranging and farm ducks. Ducks feed mainly on leftover rice grains in harvested paddy fields, so free-ranging ducks in both countries move to many different sites in line with rice harvest patterns. In Thailand, for example, the proportion of young ducks in flocks was found to peak in September-October; these rapidly growing young ducks can therefore benefit from the peak of the rice harvest in November-December. Meat ducks are slaughtered around the Chinese New Year, a time when the volume of sales-related duck movement rises considerably.
These peaks in congregation of ducks indicate periods in which there is an increase in the chances for virus release and exposure, and rice paddies often become a temporary habitat for wild bird species.
Ninety percent of the world's 1 billion domestic ducks live in Asia.