Chapter 16

THE WEALTHY DISEASE

Some more thoughts on the goodness of parasites ...

Meet Crohn's disease, a nasty ailment of the digestive system. It gives you the runs and causes severe pain in your stomach, and there's no known way to cure it. No matter what foods you eat, the pain of Crohn's won't stop. The disease keeps its victims awake night after night and is strong enough to drive many into a deep depression.

People who get Crohn's often suffer their entire lives. The symptoms may go away for a few years but invariably return in all their destructive glory. There is no escape.

So what kind of parasite causes Crohn's?

Hah, fooled you! Unlike all the other diseases in this book, Crohn's is not caused by parasites. Quite the opposite. It is probably caused by the absence of parasites.

Say what now? Well, no one knows for sure, but here's what some scientists have noticed:

Crohn's disease didn't exist before the 1930s, when members of a few wealthy families in New York City got it. As time passed, the disease spread to the rest of the United States. It always started in rich neighborhoods first, only making its way into the bad parts of town much later. It took until the 1970s to reach the poorest parts of our country.

These days, Crohn's is on the march across the world. In the 1980s, it appeared in Japan, just when a lot of Japanese were starting to get really rich. Lately it's been making its way through South Korea, in the wake of that country's economic boom.

And guess what? It still doesn't exist anywhere in the third world. Poor people never get Crohn's disease. And this has led many scientists to think that Crohn's results from the most common sign of a rich society: clean water.

That's right: clean water.

You see, most of the invaders of our guts come from dirty water. If you drink clean water your whole life, you'll have a lot fewer parasites. But that can actually be a problem. Your immune system has evolved to expect parasites in your stomach. And when no parasites show up, your immune defenses can get kind of ... twitchy. Sort of like a night watchman with nothing to do, drinking too much coffee and cleaning his gun again and again.

So when your twitchy, understimulated immune system detects the slightest little stomach bug, it launches into emergency mode and goes looking for a hookworm to kill. Unfortunately, there are no hookworms inside you, because your water supply is cleaner than at any time in human history. (Which you thought was a good thing.)

But your immune defenses have to do something, so they attack your digestive system, tearing it to pieces.

Lucky you.

We humans have lived with our parasites for a long time, evolving alongside them, walking hand in hand down the generations. So maybe it's not surprising that when we get rid of them all at once, strange things happen. Our bodies freak out in the absence of our little friends.

So the next time you're eating a rare steak and start worrying about parasites, just remember: All those worms and worts and other little creatures trying to wriggle down your throat can't be all bad.

They've been making us their home for a long, long time.