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SWINE FLU 豬流感!!!

Main article: 2009 swine flu outbreak

The origins of the new swine influenza strain involved in the 2009 swine flu outbreak remain unknown. One theory is that Asian and European strains traveled to Mexico in migratory birds or in people, then combined with North American strains in Mexican pig factory farms before jumping over to farm workers.[32] The Mexican health agency acknowledged that the original disease vector of the virus may have been flies multiplying in manure lagoons of pig farms near Perote, Veracruz, owned by Granjas Carroll,[33] a subsidiary of Smithfield Foods.[34] The strain is a reassortment of several strains of influenza A virus subtype H1N1 that are, separately, endemic in humans and in swine. Preliminary genetic characterization found that the hemagglutinin (HA) gene was similar to that of swine flu viruses present in U.S. pigs since 1999, but the neuraminidase (NA) and matrix protein (M) genes resembled versions present in European swine flu isolates. Viruses with this genetic makeup had not previously been found to be circulating in humans or pigs, but there is no formal national surveillance system to determine what viruses are circulating in pigs in the U.S.[12]