Answers:
While it is still unknown, it is currently thought that the flu virus jump from birds to humans.
swine are thought to be the vector that allowed the flu to intervene from birds to humans as swine own receptors on their cell that are indistinguishable as both birds and humans receptors.
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According to Wikipedia, "One proposal is that the virus strain originate at Fort Riley, Kansas, by two genetic mechanism — genetic drift and antigenic shift — contained by virus within poultry and swine which the fort bred for local consumption. But evidence from a recent restoration of the virus suggests that it jump directly from birds to humans, short traveling through swine."
Studies hold shown that it is similar to modern bird flu which is why nearby is so much concern nearly it.
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