Parasite Rex.
2000. Carl Zimmer. The Free Press,
New York. 298 pp., hardbound. $26.
If
there were an annual award for the nonfiction book with the
greatest “Yuck Factor,” Carl Zimmer’s Parasite
Rex would win in a landslide. Consider this juicy description
of the intestinal habitat of tapeworms: “Tapeworms live
in surging tides of half-digested food, blood, and bile, driven
by the intestine’s endless peristalsis.” A sort
of internal Perfect Storm.
And listen to this vignette from the author’s visit with a parasitologist: “Just before my arrival, Brooks and his assistants had opened up a deer and found a dozen species living in or on it, including nematodes that live only in the deer’s Achilles tendon and flies that lay their eggs in the deer’s nose. (Brooks calls these last ones the snot bots.)” Then there is the tale of a blood fluke that drills its way into a victim’s capillary, pushes into a vein, rides blood surges into the lungs, swims out of the lungs to an artery, and “may tour its host’s entire body three times until it finally comes to rest in the liver.” And that’s just the beginning of the horror flick showing inside a human body near you.
Parasites are anything that lives on or in another living thing, usually at the expense of that living thing. They can be viruses, bacteria, fungi, plants, or animals. It turns out most living creatures are parasites of one sort or another. In fact, every single cell in every single organism other than viruses, bacteria, and blue-green algae, contains a former parasite called mitochondria, which basically fuel life. Similarly, plants’ photosynthesizing chloroplasts are remnants of ancient parasitic bacteria.
While these ancient parasitic relationships seem to have turned out for the best, at least from our point of view, most do not. Parasites can bring pain, disfiguration, malnutrition, and death. Some scary parasites enslave their victims, manipulating their behavior and making zombies of the hapless hosts.
A barnacle, Sacculina, parasitizes crabs big time. A female Sacculina burrows into a crab and sprouts roots that ultimately engulf the entire body of the crab, even wrapping around its eyestalks; it lives on nutrients sucked from the crab’s blood. And then it gets worse. Soon a male or two joins the female and they begin producing thousands and thousands of new Sacculina. The poor crab stops growing, stops mating, stops doing anything but eating to feed the parasite and taking care of the Sacculina’s multitudinous larvae as if they were its own. Even male crabs are tricked into being doting moms. As Zimmer puts it, “. . . they control their hosts, becoming in effect their new brain, and turning them into new creatures.”
Carl Zimmer is an award-winning science journalist, so for all the yuckiness in Parasite Rex he weaves a fascinating, scientifically accurate, and up-to-the-minute story about these often bizarre life forms and the sometimes equally bizarre defenses that their hosts mount against them. To tell this story, he travels from a primitive clinic in dusty rural Sudan to gleaming American laboratories, and from life’s origin in some past primeval soup to life’s possible future if the “human parasite” continues to wreak such havoc with the planet. His writing is clear and colorful, replete with amazing similes, such as “a piece of pig flesh with Trichinella running through it like a night of shooting stars.”
Nicer is this: “To sum up what scientists have learned about the immune system since [1879] is like trying to reproduce the Sistine Chapel in crayon.” Zimmer is too modest. He paints a masterful picture of the intricacies of the immune system and why it works—and doesn’t work—against various parasites.
Human bodies may host a large array of parasites, Zimmer reports, more than 1.4 billion people carry roundworm, another 1.3 billion support hookworm, and another billion have whipworm, to list just a few of the scourges we’re susceptible to.
Malaria kills millions of people each year—one every 12 seconds. The disease is caused by the parasite Plasmodium, which is carried by various species of mosquitoes. While we tend to blame the bloodsucking mosquitoes, it seems they are as much victims of this killer as we are. Once it gets into a mosquito, Plasmodium first makes the insect less likely to seek a blood meal—no sense increasing the risk of a death-swat that would squash both parasite and host. But then, after the Plasmodium reproduces and its “young” are ready to seek new hosts, it makes the mosquito both hungrier and less able to keep blood flowing in any particular bite. This forces the mosquito to pierce more potential hosts, thus spreading the Plasmodium more effectively.
Parasites also influence our behavior, although not to the extent of making us zombies (or is some parasite only leading us to believe not?). While an adult guinea worm is content to stay in the home it finds in a human leg (after a circuitous trip from a human mouth), juvenile guinea worms must escape from the leg and get into water, to find their intermediate crustacean host. So juveniles, unlike adults, provoke a massive immune response that creates a burning blister. To relieve the pain, people are prone to put their abscessing leg into a cool pond—whereupon the young worms swim to freedom. The good news is that this parasite can be foiled through simple measures like teaching people to keep their infected legs out of pools. As a result, the guinea worm may soon be eradicated.
Today Americans are mostly free from such horrors, thanks to advances in medicine, good sanitation and hygiene, and various kinds of pest control. But as Zimmer makes abundantly clear, parasites have a way of outwitting their hosts. They evolve new tricks almost as quickly as we learn to thwart the old ones. So our future could be as buggy as our past. Prepare yourself: Read Parasite Rex, then share it with your favorite pre-teen, who will find enough good parts to keep friends and family grossed out for weeks.
--Susan Lumpkin
Parasite Rex is available at The National Zoo Bookstore, or you may order it from The National Zoo Store Online at http://store.fonz.org.
ZooGoer 29(6) 2000. Copyright 2000 Friends of the National
Zoo. All rights reserved.
