Did This 'Swine Flu' Really Come From Pigs?

June 3, 2009 -- Question:Did this 'swine flu' virus really come from pigs?

Answer: One of the major questions we have about this particular virus that we're seeing in humans is: Where did it come from? And perhaps the best way we can get a handle on that is by actually looking at the genetic material in these viruses. And what we can tell from that if we look at the virus and the genes that go into it, a lot of these genes are very similar to viruses we've seen in North American pig populations over the last decade. There are also traces of this virus that are very similar to viruses that have been circulating in pigs in Europe and Asia.

So what we think is, somewhere these two viruses -- the virus in pigs in the Americas, the virus in pigs in Asia -- got together and formed this particular virus that's now come into humans. So the answer is, one, yes. In terms of its genetic makeup, this virus did come from pigs.

What we can't say with any certainty, however, is that this virus transmitted directly from pigs into humans. It's also possible that this virus, these two viruses got together in another host, perhaps an avian host, and then went from that avian host into humans.