Since the first outbreaks of the strain of avian influenza known as H5N1 appeared in Hong Kong, scientists have debated how to stop the spread of the disease, which has appeared in more than 50 countries in Asia, Europe and Africa. The United States’ bird flu surveillance program has focused primarily on migratory birds flying from Asia to Alaska, but new research published in December by scientists from the Smithsonian, the New York-based Consortium for Conservation Medicine and the United Kingdom’s Royal Society for the Protection of Birds reports that bird flu is most likely to be introduced to countries in the Western Hemisphere through infected poultry.

Birds migrating from Siberia are much less likely to introduce bird flu to the United States than infected wild birds flying from countries in Central and South America, which import hundreds of thousands of chickens annually from European and Asian countries where bird flu has been found.

"We need to make sure that we are preparing developing countries in this hemisphere for an outbreak of avian flu," says Peter Marra, an avian ecologist with the Smithsonian National Zoological Park’s Migratory Bird Center, who worked on the report. The research team, led by Marm Kilpatrick, a scientist at the CCM and a Smithsonian research associate, set out to identify how the disease has spread through Asia, Europe and Africa. The scientists analyzed the risk of introduction along three pathways: poultry, trade in wild birds and migrating birds.

The findings, published in the Proceedings of the National Academy of Sciences, showed that the combination of poultry trade and migratory bird movements spread H5N1 much further than it would have traveled by either of these pathways alone. The report recommends "strict controls or a ban on the importation of poultry and wild birds into the Americas and stronger enforcement to curb illegal trade." Canada, Mexico and several countries in South America regularly import hundreds of thousands of day-old chicks from other regions where bird flu is circulating, Marra says.