Researchers at the University of California, Irvine have completed the first statistical analysis of H5N1 influenza's genetic diversity. The project helps to explain how the virus migrates, and could enable health officials to determine whether efforts to control the virus are successful. 
The study finds that some countries appear more exposed to bird flu invasion than others
Photo: Jon Ng
The study analyzed nearly 500 hemagglutinin sequences - genetic sequences of proteins found on the surface of the influenza virus collected from 28 locations in Europe, Asia and Africa. The strains of H5N1 circulating in Indonesia, Japan, Thailand and Viet Nam were found to share the most evolutionary history with strains found in several provinces of southern China. These provinces are major players in the international poultry trade, which has been shown to be a key mechanism for the spread of H5N1.
However, a number of strains that were prevalent in southern China were not found in neighboring Thailand and Viet Nam. There was evidence that these newly invasive strains were repeatedly filtered out at these countries' northern borders, even as they suffered recurrent outbreaks of endemic strains. Meanwhile Japan, while successful in controlling outbreaks, suffered multiple introductions of the virus. Avian flu in the UK 
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The study's lead author, Robert G Wallace, said: "Some countries appear more exposed to bird flu invasion than others. Learning that is a good step in discovering which social and ecological factors promote or, on the other hand, hamper the virus' spread."
The results of the study have been published online in the journal PLoS ONE.
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