Riddled With Life

by Marlene Zuk

I am usually such a curmudgeonly review that I delight in the opportunity to rave about this book. It’s great! For me the greatest strength of the book is the quality of the writing: Marlene Zuk really knows how to turn a cute phrase, and her humor on a subject as yucky as parasitology is knee-slapping. I very much hope to see more work from this scientist: this lady can write!

I’ll not be presenting a proper review of the book; instead, I’ll merely present some of the lessons that it taught me. First and most important is the idea that we just can’t win against the various pathogens that are always nibbling away at us. There are a few special exceptions: we appear to have achieved victory over smallpox — for the moment. While that disease has disappeared from view, we will never be absolutely certain that it’s gone forever. It’s merely gone for now.

But while we can rarely win, we can certainly prevent them from winning, and that’s the best that we can hope for. Every action we take to foil them will be countered by some evolutionary adjustment on their part to overcome our latest advance. In other words, the war against pathogens will never end; we’ll reduce the casualties we suffer, but we’ll have occasional setbacks in the form of new diseases (AIDS, SARS) and new variations on old diseases (Ebola, flu, the common cold) — which we’ll eventually respond to. Think of it this way: our weapons are devised in research laboratories around the world, but their weapons are devised through trial and error carried out trillions of times per year in the genetic peregrinations of each species of pathogen.

It’s also fascinating to discover just how many kinds of pathogens there are. There are lots of multicellular pathogens: worms, mosquitos, fleas, lice, and so on. Then there are the bacterial pathogens, of which there are zillions. Don’t forget viral pathogens, which range from the common cold to the increasing number of those involved in cancer. Lastly, prions are a completely new class of pathogen; they’re just big proteins that attack and replicate in specific cells, such as brain cells (this is where mad cow disease comes from). The parallels with human financial schemes are impressive: just as there are a zillion different ways to separate people from their money (some legal, some not), there are a zillion ways to feed more explicitly on people’s lifeblood. And the Internet provides another interesting parallel; now that it has become an important part of the human ecosystem, all sorts of pathogens are appearing, seeking to suck our digital blood.

Which reminds me of Dr. Zuk’s assault on a common belief: that pathogens always evolve to achieve a synergistic relationships with their hosts. This belief certainly makes sense: any pathogen that kills its host must necessarily die with the host, right? Well, no: a pathogen that kills its host but also achieves transmission to new hosts need not worry about killing the old host. There are lots of insects that plant their eggs inside a host, where the egg hatches and eats up the host, then bursts forth as a fully-grown adult all set to find hosts for its own eggs. There’s no reason at all why a pathogen must learn to co-exist with its host; if you’re good at what you do, you can dump the dead shell of your host and move on to a new victim, whether that victim be a bug, an animal, or a person’s finances. And don’t forget that suicide bombers advance their meme even while dying in the process.

I particularly enjoyed her tales of ghoulishly creative strategies some pathogens employ, like the fungus that infects ladybug’s brains and makes them behave in a fashion ideally suited to the reproductive advantage of the fungus — although the ladybug’s behavior also insures its own demise. However, I was saddened that she failed to include the deliciously ghoulish tale of the fungus that attacks ants and alters their brains so that they die a miserable death perfectly suited to the reproductive interests of the fungus.

There’s lots more great stuff in this book, but I’ll stop here — I’ve got this strange itchy feeling in my lower back...