According to a new study by the UN Food and Agriculture Organization (FAO), ducks, rice and people are the most significant factors in the spread of avian influenza in Thailand and Vietnam.
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.
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.
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, the agency said in a news release.
The study also found that these factors are probably behind persistent outbreaks in other countries such as Cambodia and Laos.
In addition, with virus persistence becoming increasingly confined to areas with intensive rice-duck agriculture in eastern and south-eastern Asia, evolution of the H5N1 virus may become easier to predict.
The findings can help better target control efforts and replace indiscriminate mass vaccination, the release said.
FAO estimates that approximately 90 per cent of the worlds more than 1 billion domestic ducks are in Asia, with about 75 per cent in China and Vietnam.