How Different Is This Swine Flu Virus From Bird Flu?

June 3, 2009 -- Question:How different is the swine flu virus from bird flu?

Answer: In the last decade we've really had two major circulating forms of virus that we're particularly concerned about from the public health front -- that is the avian flu, or bird flu, and the swine H1N1 virus. And one of the questions that comes up is how similar are these two viruses? And in terms of the influenza world, they really are at opposite spectrums -- both in terms of how these viruses behave and the host of which they're in.

So, the bird flu virus on one hand -- the H5N1 avian flu circulating in poultry and wild bird populations of the world -- that particular virus has a very high level of intrinsic pathogenicity. What I mean by that is, when it tends to infect a host, particularly a mammalian host, it causes very severe disease.

With this virus, the swine H1N1 virus, this particular virus -- as far as we know doesn't circulate widely in avian hosts.

It really is a mammalian-adapted virus, and certainly, what we know about at least the appearance of this particular strain, they don't cause a lot disease in their hosts -- fairly benign infections similar to what we're seeing in humans.

So, bird flu and swine flu, they're again both influenza A viruses, but in terms of their genetic makeup, in terms of their biology, in terms of how they behave, they're very, very different beasts.