Thursday, August 18, 2005

Evolution matters

I kept meaning to write this up, but A Voyage to Arcturus reminded me to get on with it. Avian influenza is getting closer and closer to the tipping point into a global pandemic, and WorldChanging asks Can We Out-Collaborate a Pandemic?

Here's the problem, nicely summarized in this Seattle P-I piece. Right now, this strain of influenza has killed a bunch of chickens and geese and such, and a few dozen people. It's so virulent right now that it kills people too fast for them to pass it on to others.

In many studies of the spread of disease, what people find is that virulence (the rate at which a disease manifests and kills the host) declines with time, while infectivity (the probability of infection given a fixed amount of contact) increases. Both are evolutionary responses. An overly virulent disease doesn't spread, so any variation in virulence tends to result in selection for less virulence, at least up to a point. Infectivity will increase for the same selective reasons. That's evolution at work.

Scientists have found this exact pattern in the ducks of Southeast Asia. The virus is less virulent and more infective now than it was a couple years ago. Less virulent strains will keep jumping to chickens and on to humans, and at some point, there's every reason to believe that that transmission will result in the most deadly global pandemic in history.

Don't get frightened. After all, it might not happen. But if it does, scientists estimate that 50 million will die worldwide, 2.2 million in the US alone. Probably all in a year or so.

This is not the same flu you're used to. A 24-hour flu is probably a mild case of food poisoning, and the annual flu people get shots for is a fluffy bunny compared to the avian flu, H5N1.

As I understand it, this virus is more closely related to the Spanish flu that killed so many in 1918-1919. Our understanding of the dynamics of a new flu pandemic is directly related to our understanding of that pandemic, an understanding driven in part by phylogenetic similarities of the two strains.

What's the solution? Part of it is ramping up production of H5 antigen and H5N1 vaccine, or stockpiling anti-viral drugs. As this article from Perspectives in Health points out:

But a vaccine is no magic solution. We probably can't make and distribute enough vaccine for most of the world. And what if there is no pandemic? Or what if the virus mutates or drifts a lot, and the vaccine proves minimally useful? Is this really a good use of scarce health dollars, especially in developing countries? Maybe we should stockpile antiviral drugs. But they're expensive, and who knows how well they will work against the actual pandemic strain that arises? The worst response to the stockpiling dilemma is also the most tempting: Stockpile only a little vaccine and some antivirals and imply that you have enough. Some officials are already engaging in this kind of overreassurance. The risk communication answer: Share the dilemma and let the public help you decide.
They also suggest making plans for how you'd manage the changed world of a flu pandemic.

The other thing to do is write letters to your congresscritters, and state and federal leaders to express your concern and encourage them to make sure the public health network is strong enough in the US. A strong system of effective monitoring and the capacity to intervene rapidly to prevent an outbreak could save millions, and prevent the global depression some financial analysts expect to follow an H5N1 pandemic.

We can see this coming, the thing to do is to prevent it from being as bad as it could be.

For more information, check the Flu Wiki.