Comments on: Evolution of the Flu Virus

By: ukko

ukko — Mon, 03 Mar 2008 10:42:55 +0000

Greg,Thanks for the reply, I would have followed up quicker but I have been down with the very virus we are discussing here. You explanation really helps, but I am still confused about why so many species of birds are susceptible. In particular when they talk about transmission from wild birds to domestic birds. I could understand duck to duck transmission but then the jump to something like chickens or turkeys seems a bit odd. Even more confusing, I also had the feeling the actual carries were smaller birds like sparrows and the like which are not waterfowl.So, I guess my question is why are so many types of birds susceptible to the same virus when movement between species in mammals is such a rare event in comparison?A big part of this is me also trying to sort out what are the real facts, issues, and mechanisms in this area and what are misperceptions I have picked up from way things are simplified in the popular media. Thanks for your help!

By: stavros

stavros — Sat, 01 Mar 2008 22:53:28 +0000

Greg, very, very interesting post! I am actually reading some stuff on biology and genetics currently (out of interest) so this post and the article came at about the right time.I still need to grasp some concepts better though 🙂

By: Greg Laden

Greg Laden — Sat, 01 Mar 2008 19:27:55 +0000

Ukko:The following answer is based on how I think this works having read quite about about influenza but not being a certified expert. So I’m pretty sure this is correct.Influenza is basically a water born virus that lives part of its life cycle in the body of birds (typically water birds). But this statement is as true as saying that primates are tropical animals that mainly eat fruit and insects. There are plenty of primates that eat mostly leaves, and a few that live well outside the tropics.So the general pattern is broken by some influenza strains that do just fine in various mammals, probably circulating among those mammal populations now and then, but it is probably only very widespread, fairly dense, and frequently interacting mammals that you find influenza at any frequency: Humans and livestock for instance.In the mean time, influenza can pass between species. One would think that it would pass more easily between closely related species and with more difficulty between distantly related species. This may be true in the very large picture (averaging over many instances) but I think most virus experts feel that influenza is largely “indifferent” in this way. Rather, there is variation among vertebrates (chordates? Tetrapods? some larger phylogenetic group) because all it really needs is the correct receptor site on a cell, and from the point of view of a virus of a particular strain, there is a small number of different receptor sites (of which a couple/few would work).So one bird virus may mutate to also be able to grow in a pig, another sub population of the same virus to grow in a human but not a pig.

By: ukko

ukko — Sat, 01 Mar 2008 15:54:02 +0000

I wonder why is it the “bird” flu and not the “mammal” flu, that is why are so many of species of birds susceptible to a given virus while the human and porcine varieties do not infect many other type of mammals?