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The current H5N1 HPAI virus is a subtype of influenza type A viruses and was first isolated from South African terns in 1961. The current outbreak started in late 2003 and early 2004 in eight countries in Asia. While originally reported as controlled, since June 2004 new outbreaks of H5N1 have reappeared. Migratory and smuggled birds are likely to be responsible for the spread of H5N1. The infected birds shed large quantities of virus in their feces, and exposure to infected droppings or to environments contaminated by the virus is common. It is anticipated that H5N1 will continue to spread along the migratory pathways of wild birds. Most human infections have occurred in rural areas where freely-roaming small poultry flocks are kept.
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