Wednesday, June 08, 2005

A new take on infectious disease


Ewald began in typical evolutionary terrain, studying hummingbirds and other creatures visible to the naked eye. It was on a 1977 field trip to study a species called Harris's sparrow in Kansas that a bad case of diarrhoea laid him up for a few days and changed the course of his career. The more he meditated on how Darwinian principles might apply to the organisms responsible for his distress - asking himself, for instance, what impact treating the diarrhoea would have on the vast populations of bacteria evolving within his intestine - the more obsessed he became. Was his diarrhoea a strategy used by the pathogen to spread itself, he wondered, or was it a defence employed by the host - his body - to flush out the invader? If he curbed the diarrhoea with medication, would he be benefiting the invader or the host?

Some people think it's scary to have these time bombs in our bodies," Ewald says, 'but it's also encouraging - because if it's a disease organism, then there's probably something we can do about it. The textbooks say, In 1900 most people died of infectious diseases, and today most people don't die of infectious disease; they die of cancer and heart disease and Alzheimers and all these things. Well, in ten years I think the textbooks will have to be rewritten to say, "Throughout history most people have died of infectious disease, and most people continue to die of infectious disease."


This is a classic case of Famous First Words: "That's funny. I wonder ..." Lots os scientific discoveries start about like this.

We've had diarrhea for a long time and now someone actually thought about it.

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