Question:Have other pandemic influenza viruses come from swine?
Answer: A major challenge for those of us trying to understand where pandemic influenza viruses come from when they come into humans is: "Where do they come from?" And I think the real answer to that is, "We're not sure." We do know that ancestrally all flu viruses come from the aquatic bird reservoir. So, the ducks and shorebirds that fly north and south, more or less north and south about every year, have an enormous diversity of flu viruses of all shapes and colors and flavors. And it's from that host that these viruses do sporadically jump over into other hosts, be it humans, be it pigs, be it horses or domestic poultry, such as chickens and quails.
The problem is, what is the host that these viruses are in before they get to humans? If we look back at 1918 Spanish influenza, the evidence so far points to that being an avian virus that leapt over from avians directly into humans.
The 1957 Asian flu, again, probably pigs weren't involved in that outbreak, and again probably most of those viruses, most of the genetic elements of that virus came from avians into humans.
The 1968 Hong Kong pandemic, this time we're not so sure about the role of pigs .What we do know is that their pandemic virus went into humans and pigs around about the same time. We don't know whether it went from pigs to humans or humans to pigs.
So, overall, although we're pretty sure pigs play a fairly central role in the ecology of influenza, we can't say with any certainty that they've been directly involved in any human pandemics of the past.