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===1998 US outbreak in swine===
In 1998, swine flu was found in pigs in four U.S. states. Within a year, it had spread through pig populations across the United States. Scientists found that this virus had originated in pigs as a recombinant form of flu strains from birds and humans. This outbreak confirmed that pigs can serve as a crucible where novel influenza viruses emerge as a result of the reassortment of genes from different strains.<ref>{{cite journal | author=Stephanie Desmon | url=http://www.baltimoresun.com/news/health/bal-swine-flu-strain0428,0,3165467.story | title=Expert: Swine flu virus more complex than typically seen | journal=Baltimore Sun | date=April 28, 2009}}</ref><ref>{{cite web|url=http://www.newscientist.com/blogs/shortsharpscience/2009/04/why-the-pork-industry-hates-th.html |title=Pork industry is blurring the science of swine flu - Short Sharp Science |publisher=New Scientist |date= |accessdate=2009-05-07}}</ref><ref>{{cite web|url=http://www.newscientist.com/article/mg20227063.800-swine-flu-the-predictable-pandemic.html?full=true |title=Swine flu: The predictable pandemic? - 29 April 2009 |publisher=New Scientist |date= |accessdate=2009-05-07}}</ref>