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The exact role that migratory birds have played and will play in the spread of avian flu is still uncertain. What remains undisputed is that millions of cases of H5N1, along with nearly every instance of transmission to humans, have been traced to domestic poultry. Regardless of the level of risk posed by avian migration, human trade -- and illegal trafficking -- of birds can foment the spread of avian flu. While domestic birds are limited in their ability to move themselves over large distances, they are easily transported -- in small and large numbers, by hand or by truck -- from town to town, city to city, and nation to nation. The map indicates prominent land trade routes in Southeast Asia, including regions that have seen outbreaks of H5N1. What is clear on the map is that the overwhelming majority of human cases have occured along these trade corridors.
If the trade and associated transport of birds is a key factor in the spread of avian flu, land routes are not the only potential sources for spreading the virus. In 2004, Indonesia became the first country outside of the Southeast Asian mainland to report cases of H5N1. While it is certainly possible that migrating birds may have carried the virus to Indonesia, the government there has not been aggressive in culling domestic chicken flocks or imposing biosecurity measures to limit the movement of infected chickens, so trade is likely to play a role in the spread of the disease within Indonesia.
Another factor that must be considered is the trade in contraband animals. In December 2003, six ducks smuggled into Taiwan from mainland China were found to be infected with H5N1. Perhaps even more alarming for Western observers, in October 2004, customs officials in Brussels seized two live birds -- both rare eagles -- from a man's suitcase. The smuggler had flown to Brussels from Bangkok, by way of Vienna. The birds tested positive for H5N1.
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Sources: Asian Development Bank; Australasian Wader Study Group; World Organization for Animal Health; World Health Organization; Food and Agriculture Organization of the United Nations; Recombinomics, Inc.; Wildlife Conservation Society; NEW SCIENTIST; ProMed
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Intro - Read a briefing on the dangers posed by avian influeza and the challenges nations must overcome in order to fight against it.
Photo Essay - Learn more about influenza and science's sruggle against it.
Filmmaker Notes - Go behind the scenes with producer Micah Fink.
Interactive Map - Get the facts about the AIDS pandemic in sub-Saharan Africa.
Interactive Challenge - Test your knowledge of AIDS in Africa.
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