Microscopic mind control

What would you say if I told you that parasites are infesting the brains of half the human population? Or creepier still, that these little buggers have the power to control people's behavior, making some irascible, others docile, and still others certifiably insane? You'd probably say I'd watched one too many X-Files reruns--and you'd be right--but that doesn't change the fact that it could be true.

It's easy to dismiss parasites out of hand. Unless your intestines are playing host to a parasitic colony, they seem fairly benign. But it turns out stomach upset is one of their lesser powers.

According to science writer Carl Zimmer, parasites can be downright Machiavellian.

In Return of the Puppet Masters Zimmer informs us that:

The lancet fluke . . . forces its ant host to clamp itself to the tip of grass blades, where a grazing mammal might eat it, [thus allowing the parasite] into the gut of a sheep or some other grazer . . . to complete its life cycle.

Even more disturbing, National Geographic recently reported that hairworm parasites can drive their grasshopper hosts to suicide. (Suicide Grasshoppers Brainwashed) Apparently, adult hairworms use grasshoppers as a kind of surrogate womb, implanting their eggs in the insects' bodies. I know--it's unsavory. But the real trouble starts when a baby hairworm reaches maturity and wants to strike out on its own. The only way out is to "euthanize" the grasshopper. To accomplish this, the worm pumps out a potent chemical cocktail that attacks the grasshopper's central nervous system, prompting it to head to the nearest body of water and drown itself. Once the host dies, the worm extricates itself--through the rectum. And thanks to a fairly depraved group of French biologists, you can see it here: Canal IRD.

Now that you're sufficiently grossed out, let's turn our attention back to the human mind snatchers. Anyone who's spent time around a pregnant woman has probably heard of Toxoplasma. It's a parasite people pick up from handling soil and cat litter. Scientists estimate that close to 50 percent of the world's population carries the parasite, but, until recently, they believed that Toxoplasma only posed a threat to people with weakened immune systems. Well, all that's changed now.

When scientists learned about the more bizarre aspects of parasitic behavior, they decided to take a closer look at Toxoplasma. Given that parasites were sometimes capable of manipulating their hosts, researchers wondered if Toxoplasma might be influencing human behavior. A group of scientists from Oxford University decided to infect rats with the parasite and conduct a series of tests. Why rats? It turns we have more in common with them than a talent for laughter. (Are rats laughing at us?) We also share similar brain structures. Here's a brief description of the study, courtesy of Carl Zimmer:

[Oxford] scientists studied the rats in a six-foot by six-foot [enclosed maze] . . . In each corner of the enclosure they put a nest box . . . On each of the nests they added a few drops of a particular odor. On one they added the scent of fresh straw bedding, on another the bedding from a rat's nests, on another the scent of rabbit urine, on another, the urine of a cat.

When they set healthy rats loose in the enclosure, the animals rooted around curiously and investigated the nests. But when they came across the cat odor, they shied away and never returned to that corner . . . the odor of a cat triggers a sudden shift in the chemistry of rat brains that brings on intense anxiety.

Then the researchers put Toxoplasma-carrying rats in the enclosure . . . The scent of a cat in the enclosure didn't make them anxious . . . they even took a special interest in the spot and came back to it over and over again.

So what does all this mean? It means that Toxoplasma-infected rats are drawn to cats, like lambs to the slaughter. But the findings also suggest that the parasite can impact people. Another study seems to indicate that Toxoplasma alters human personality. Interestingly, the parasite appears to affect men and women differently. Male carriers are more self-reproaching, insecure, jealous, and suspicious, while female hosts are more "outgoing and warmhearted."

Not such a bad deal for the ladies, you say? Wait till you hear the rest. Some scientists postulate that being exposed to high levels of Toxoplasma during pregnancy may "cause" or "contribute" to schizophrenia. Working off this hypothesis:

E. Fuller Torrey, of the Stanley Medical Research Institute . . . [and] the Oxford scientists . . . raised human cells in Petri dishes and infected them with Toxoplasma. Then they dosed the cells with a variety of drugs used to treat schizophrenia. Several of the drugs--most notably haloperidol--blocked the growth of the parasite.

(Return of the Puppet Masters)

Put simply, scientists now have a parasitic conspiracy theory to explain schizophrenia--or at least certain forms. (For reasons that Zimmer doesn't go in to, Toxoplasma only provides a key to understanding some strains of the disease.) To date, there's no conclusive evidence. But there's certainly enough to warrant further inquiry.

Think about it. Eradicating particular types of schizophrenia could be as simple as administering antibiotics to pregnant mothers. Amazing, no?


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