Marlene Zuk Mentioned in Today's NYT Natalie Angier Column

From The New York Times, June 26, 2007

In Parasite Survival, Ploys to Get Help From a Host
By NATALIE ANGIER

Not long ago, my daughter proposed a way she could earn some extra cash beyond her weekly allowance. Would I give her a quarter, she wanted to know, every time she cleaned the cat box?

Twenty-five cents to clean the cat box? I squealed with unconcealed joy. Truly we’d hit commensal pay dirt here. She had fiscal motivation, and I could use the olfactory vacation.

But then I read a few items about Toxoplasma gondii, the parasitic protozoa that can be lurking in cat scat, and I changed my mind. I told my daughter that she should skip the litter patrol and try cleaning the refrigerator instead.

I’m not normally a fluttering, overprotective mother, and I know that the risk of contracting the toxoplasma pathogen or any serious infectious illness from the cat box is tiny. Still, we’re talking parasites here, and parasitism is an evolutionary force to be reckoned with, a source of nearly bottomless cunning and breathtaking bio-inventiveness.

Predators want to kill you and eat you right there on the veldt. Parasites, by contrast, want to keep you alive, the better to serve as a parasite paradise, a cozy haven where they can grow at their own pace, suckle on your moist, nourishing tissues, multiply their numbers and finally, one way or another, pass those numbers along. Toxoplasma, it seems, is a member of a particularly insidious genus of parasite, which seek perpetuity by controlling their hapless hosts’ minds. So maybe I’m hyperventilating here, but if any mind in my house is to be monkeyed with, I would really prefer it be mine.

Driving toxoplasma’s specific virulence is its two-stage life cycle and its shifting definition of a suitable host. The amoebalike protozoa begins its days as an asexual opportunist, its eggs able to hatch and grow in the body of any warm-blooded host — cat, rat, bat, buffalo, crow, human: practically any homeotherm unfortunate enough to harbor or have incidentally ingested the little eggs will do.

Come the parasite’s second, sexual stage, though, and it gets fussy. To mingle with others of its kind and produce the next generation of eggs, toxoplasma must find its way to the gastrointestinal tract of a cat. Wild or domestic, tabby or puma, no matter — just as long as it is feline. And this demand for a particular end-stage host, this stipulation that the protozoa migrate to the perfect sexual staging ground no matter what its natal home may have been, serves as the sort of evolutionary pressure known to give rise to chilling parasite ploys.

Consider the case of the thorny-headed worm, which Marlene Zuk, a biology professor at the University of California, Riverside, describes in her fascinating new book, “Riddled With Life.” The parasitic worm spends its childhood growing in the belly of a pill bug, a small terrestrial crustacean that feeds on detritus and dry leaves and, occasionally, worm eggs scattered therein. But on reaching parasitic puberty, the worm requires a very different environment: an avian digestive tract. The worm wants the pill bug to be eaten by a bird. Fine: many birds will eat pill bugs if given the chance. But the worm has a tight schedule to keep, and it can’t afford to wait around and hope some industrious starling discovers its tasty crustacean housing. After all, a pill bug normally spends the sunlit hours when diurnal birds are about coiled away like a petite armadillo, often beneath some unpeckable tree stump or stone.

For more, please click here.