Disease Eradication, Part I - An Introduction

(Abandoned smallpox hospital in New York - photo credit: Ralph Hockens)

Eradication, Part I - An Introduction

In his first annual letter, Bill Gates discussed the eradication of polio and committed 255 million dollars to the cause. Britain and Germany will give another $280 million. The Gates Foundation commitment to polio eradication is interesting, in part because eradication is still a somewhat controversial goal.

Eradication is controversial because it's an expensive and difficult goal. Some cost models argue that controlling, rather than eradicating, diseases, is a better goal. Control can be achieved in a country or region, rather than worldwide.  On the other hand, eradication is final, and is of untold benefit to future generations.

There are only three diseases that the WHO has called to eradicate - smallpox, Dracunculiasis (guinea worm) and polio. That is because there aren't that many diseases which are good candidates for eradication. Anything that also affects animals is out of the question, because we can't vaccinate every wild animal in the world. (that is one reason avian influenza is so scary.) So is anything with a very long incubation period. Of the three, only smallpox has actually been eradicated.

Smallpox was the easy one. It affected the developed world as well as the developing world, so donors had self-interest in working toward eradication. It wasn't dependent on donations for the public good. It had a reliable vaccine which didn't require special refrigeration and needed only a single dose to be effective. It also had very visible effects, so sophisticated laboratory diagnosis wasn't needed to detect it.

Polio and Guinea Worm will not be so easy. Polio is much more contagious than smallpox, and its vaccine occasionally causes outbreaks of the virus. Only one in 200 cases can found through early detection. Guinea worm disease is caused by water infected with nematodes (skinny worms ranging from microscopic to about two inches long), and it's controlled through provision of clean filtered water or well water. You treat people infected with guinea worm, but thus far no attempts have been made to eliminate it from the water supply.

One note on eradication - it should not be confused with elimination. (Bill Gates seems to use the words interchangably, but he is being imprecise.) Eradiction means gone gone gone from the earth and not infecting people ever again. Elimination means no longer a public health threat. So you could eliminate polio in one place, like we have in the US, but still have the occasional case crop up and be quickly identified and treated.

This is the first of three posts. In the next two posts, I will discuss the arguments against eradication and those in favor.