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Influenza has been making the news recently - bird 'flu is spreading Westwards from Asia, and comparisons are being made to the 1918 Spanish 'flu epidemic that killed around 50 million people.
The 1918 influenza outbreak has popped up during my research a few times, most notably in the work of Sattenspiel and colleagues into its dynamics in the Canadian subarctic (The Hudson Bay Trading Company kept detailed accounts of the movement of people and influenza, which has provided the raw material for a small network study). There has for some time been speculation about the nature of the virus which caused the 1918 pandemic, and it has recently been sequenced in its totality[1]. It has subsequently been created in a laboratory, and demonstrated to be highly lethal in mice[2]. There has been some debate as to whether publishing the full sequence and then actually building a very similar virus was sound or not, but the scientific consensus seems to be that it was; I agree with that, so I won't say anything more on it for now.
What is significant about this work is that it suggests a hypothesis about the origin of the 1918 strain, as distinct from the pandemic strains from 1957 and 1968 (which were substantially less serious). The 1918 strain killed far more people than these other pandemic strains, and was proportionally far more dangerous to otherwise healthy 20-40 year-olds. Specifically, it appears to have arisen by direct evolution of an highly pathogenic avian influenza strain, rather than by assortment of genes between avian and human strains infecting the same host (as is thought to be the case for the 1957 and 1968 strains).
What of the current H5N1 bird 'flu, then? In the human cases, viruses isolated have had some of the same changes that the 1918 strain did, suggesting that this virus may be making similar evolutionary changes to those the 1918 strain did to enable it to become highly infectious between humans; current cases are largely thought to have been the result of birds (or bird waste) infecting humans. The concern that the current H5N1 strain may make the evolutionary step to being readily transmissible between humans is understandable, therefore.
Unfortunately, it is impossible to say if, never mind when, this change might occur, nor indeed how dangerous the resulting virus would be. Global travel patterns would certainly contribute to its rapid dissemination across the world, but it may yet become less pathogenic to humans whilst evolving to become more transmissible between them. The WHO is encouraging governments to prepare for the worst, and rightly so, but only time will tell how bad it will be (if it happens at all)...
[1] Taubenberger et al, Nature 437, 889-893 (2005)
[2] Tumpey et al, Science 310, 77-80 (2005)
The 1918 influenza outbreak has popped up during my research a few times, most notably in the work of Sattenspiel and colleagues into its dynamics in the Canadian subarctic (The Hudson Bay Trading Company kept detailed accounts of the movement of people and influenza, which has provided the raw material for a small network study). There has for some time been speculation about the nature of the virus which caused the 1918 pandemic, and it has recently been sequenced in its totality[1]. It has subsequently been created in a laboratory, and demonstrated to be highly lethal in mice[2]. There has been some debate as to whether publishing the full sequence and then actually building a very similar virus was sound or not, but the scientific consensus seems to be that it was; I agree with that, so I won't say anything more on it for now.
What is significant about this work is that it suggests a hypothesis about the origin of the 1918 strain, as distinct from the pandemic strains from 1957 and 1968 (which were substantially less serious). The 1918 strain killed far more people than these other pandemic strains, and was proportionally far more dangerous to otherwise healthy 20-40 year-olds. Specifically, it appears to have arisen by direct evolution of an highly pathogenic avian influenza strain, rather than by assortment of genes between avian and human strains infecting the same host (as is thought to be the case for the 1957 and 1968 strains).
What of the current H5N1 bird 'flu, then? In the human cases, viruses isolated have had some of the same changes that the 1918 strain did, suggesting that this virus may be making similar evolutionary changes to those the 1918 strain did to enable it to become highly infectious between humans; current cases are largely thought to have been the result of birds (or bird waste) infecting humans. The concern that the current H5N1 strain may make the evolutionary step to being readily transmissible between humans is understandable, therefore.
Unfortunately, it is impossible to say if, never mind when, this change might occur, nor indeed how dangerous the resulting virus would be. Global travel patterns would certainly contribute to its rapid dissemination across the world, but it may yet become less pathogenic to humans whilst evolving to become more transmissible between them. The WHO is encouraging governments to prepare for the worst, and rightly so, but only time will tell how bad it will be (if it happens at all)...
[1] Taubenberger et al, Nature 437, 889-893 (2005)
[2] Tumpey et al, Science 310, 77-80 (2005)
(no subject)
Would you mind if I link to this in my journal?
Also, respect for having scholarly footnotes to an lj post :)
(no subject)
If you have comment-email turned on, then me commenting like this will remind you.
(no subject)
Now that's cunning, I didn't think of that.
Much thank yous for permission :)