By Shelby Martin
It plays out like your worst nightmare. You're faced with the fiercest, toothiest, scariest predator imaginable. All this monster wants to do is eat you up. And yet - you can't turn away. You find yourself inexplicably drawn to this monster, and you go closer, and closer...
Such is the situation with rats infected with a bizarre parasite. Toxoplasma gondii (or "toxo," as it's cheekily called) is a protozoan famously found in cat poop. The parasite is dangerous to pregnant women, but, in most humans, it seems to cause no more than flu-like symptoms. But for rats, it's a different story: the parasite can actually send them to their deaths.
Toxo can only reproduce sexually in cat intestines. (Sexy place, no?) But the parasite can live in almost any warm-blooded host, including the rat. The shortest distance from a rat to a cat is through the cat's mouth. The problem, for the parasite, is that rats are terrified of cats - even a whiff of cat urine is enough to send them squeaking for cover.
But all that changes once a rat catches toxo. Amazingly, a toxo-infected rat is actually attracted to cat urine.
The Sapolsky lab at Stanford recently studied this phenomenon. They found some toxo, they got some rats and they bought some bobcat urine. (Who knew that was commercially available?) The Sapolsky lab found that toxo-infected rats have damaging cysts on their amygdalas, the part of the brain involved in fear and anxiety. This would make sense - knock out the fear, and the rats won't run from cats.
So, are the amygdala-damaged rats completely fearless? Actually, no. It turns out the effect of toxo is astonishingly specific. The rats are still afraid of doggy smells; they are afraid of open spaces; they are leery around unknown foods. But when it comes to cat pee, they can't get enough.
Weird as toxo is, it's not particularly unique. Parasitic brainwashing happens all over the animal kingdom. The lancet fluke, Dicrocoelium dendriticum, is a protist like toxo. Unlike toxo, it's not content with only two host animals. The lancet fluke finds its way through three species in its life cycle.
Adult lancet flukes hang out inside cows. They mate in the cow's liver (another sexy place!) and send eggs off into the animal's digestive tract. An infected cow leaves fluke-laden cow pies in its wake.
Next in the lancet fluke's life cycle are snails with the munchies. Snails evidently snack on cow poo, sometimes with a lancet fluke garnish. Once inside the snail, the parasitic larvae attach themselves to the snail's digestive tract and develop into their juvenile state. The besieged snail immobilizes these invaders by wrapping them in slime. Slime balls full of flukes are excreted onto the grass, where they await their next host.
The ant is the most pitiable creature in the lancet fluke saga. To a thirsty ant, the fluke-filled slime balls are a source of moisture. The ant slurps up the slimy flukes, obliviously signing its death warrant. The lancet flukes head straight for the ant's brain.
From then on, the insect becomes restless. Instead of bedding down with its fellows at night, the ant heads for the nearest blade of grass. The erstwhile unadventurous insect clambers to the tip of a blade of grass, holds tight with its mandibles and waves in the breeze until morning. At dawn, it rejoins its nestmates on the ground.
But all is not back to normal. The very next night, the infected ant is back on that grass. This goes on until the blade of grass - along with the hapless ant - gets eaten by a cow, and the lancet fluke is back inside its favorite animal.
This is so science fiction-esque I can hardly believe it. But the mind control doesn't end with parasites. Sometimes the enemy is your boyfriend.
For example, female fruit flies have a special reason to practice safe sex. Their mate's semen contains mind-controlling compounds called accessory gland proteins. These proteins make a beeline for the female's brain, where they send her into a fit of domesticity. She refuses other suitors, even kicking them in the head if they come too close. Her days as a party girl are over, and she's ready to settle down and focus on egg-laying.
All this mind control isn't confined only to lower life forms. Toxo, the rat's nightmare, has been implicated in schizophrenia and paranoia in humans. Eighteen studies found that people with schizophrenia had higher levels of human antibodies to toxo than individuals without schizophrenia.
Of course, it is difficult to prove causation. Sadly, many people with schizophrenia are homeless, and a rougher life after the onset of their illness could explain the correlation. Still, given toxo's track record with rats, an ability to induce mental illness in humans wouldn't be entirely shocking.
Does this have implications for free will? I'm not sure. It's something to think about - that is, if the bugs in your brain will let you.
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