Not for the squeamish!

Reading material: Parasite Rex. The more I learn about the various ways that living things have adapted to niches I did not even know existed, the more in awe I am of life and diversity. Tapeworms keep themselves from being pushed out of the intestines by floating along with their food for a while, then swimming back upstream. Peristalsis may vary in its intensity in different parts of the intestines, and the tapeworms deal with this by making some segments of their body swim faster while other swim more slowly. Advanced stages of sleeping sickness, an illness caused by a single-celled organism called a trypanosome, are treated with a chemical so nasty it can melt normal IV tubes. But this is the only hope once the parasite has entered the brain. Hookworms digest the walls of the intestines, releasing tissue and blood. The body protects itself by staring a series of chemical reactions which could cause the blood in the hookworm's mouth to clot, starving it:

The parasite responds with a sophistication biotechnologists can only ape. It releases molecules of its own that are precisely shaped to combine with different factors in the clotting cascade. By neutralizing them, the hookworm keeps the platelets from clumping and allows the blood to keep flowing into its mouth. Once a hookworm finishes feeding at once place, the vessels can recover and clot while the parasite moves on to a fresh bit of intestines. If the hookworm were to use some crude blood-thinner that flooded the intestines, it would turn its hosts into hemophiliacs who would quickly bleed to death and take away the hookworm's meal. A biotechnology company has isolated these molecules and is now trying to turn them into anti-clotting drugs."

Disgusting. Fascinating.

And Darwin wrote (as quoted in Parasite Rex),

I cannot persuade myself that a beneficient and omnipotent God would have designedly created the Ichneumonidae [one group of parasitic wasps] with the express intention of their feeding within the living bodies of Caterpillars.

Unlovable, yet beautiful in their diversity and complexity.

Carl Zimmer speculates that the guinea worm, which break through the flesh and come crawling out over the course of a few days, might have been the Israelites' plague of serpents described in the Bible:

They certainly plagued much of Asia and Africa. They couldn't be yanked out at one go, since they would snap in two and the remnant inside the body would die and cause a fatal infection. The universal cure for guinea worm was to rest for a week, slowly winding the worm turn by turn onto a stick to keep it alive until it had crawled free. Someone figured out this cure, someone forgotten now for perhaps thousands of years. But it may be that that person's invention was remembered in the symbol of medicine, known as the caduceus: two serpents wound around a staff.

Here's more on the origins of the staff and the serpent.

If I were teaching life science this year, I'd assign segments of this book. It's gross, which middle school kids love (actually, most people love, we just learn to hide our enthusiasm in order to seem proper and polite). If handled right, it promotes respect for these organisms - and all organisms - as wonders of nature. Too often, we stick to the "charismatic megafauna," but this is shortsighted because ALL living things play important ecological roles. The next generation needs a healthy respect for the complex interactions of species, in order to make informed decisions about medicine, environmental management, and agriculture. I'm only on chapter 2, but I believe the book explores issues of medicine and how colonization and corruption have allowed parasites to flourish even today, even when we know enough to keep outbreaks rare.