It’s Taking Over My Brain!

The following article is from Uncle John’s Factastic Bathroom Reader.

As you may recall from your eighth-grade biology class, protozoa are single-celled creatures. Here’s something your teacher probably didn’t cover: There’s a protozoan that can alter what you think, feel, and do. It may sound like science fiction… but it’s not.


Imagine this plot for a movie: A trusted pet helps a race of microscopic invaders enter your body. Once inside, they affect your brain. You might start taking more risks and become more outgoing, or you might become paranoid. Strange smells, repugnant to most people, might suddenly give you great pleasure. And there’s a chance of blindness, insanity, and death.

Fairly ordinary science fiction, right? Nope. Because the invaders, protozoa known as Toxoplasma gondii, are real. What’s worse, they’ve already infected billions of people— maybe even some of your friends, neighbors, family members… and you.


Ironically, all that T. gondii want is to find their way inside a susceptible cat so they can wake up from suspended animation, break out of their protective shells, and start to reproduce. They can only do this in the lining of a cat’s intestines, but when they do, they launch huge quantities of their spawn with each load of cat poop. And time is urgent, because they have only a few weeks before the cat’s immune system surrounds and neutralizes them.

(Image credit: Ke Hu and John M. Murray)

Once outside of their host, the newly encapsulated protozoa go into a state of suspended animation. They can remain that way for weeks, months, or years— alive and ready, no matter how much the cat poop gets trampled, turned into compost, spread on crops, or eaten by scavengers. They wait patiently, hoping to get inside another cat.

They have evolved certain strategies to do that: one is by packaging themselves inside a slow, easy-to-catch mouse. (Seriously.) But mice are rarely that slow— they’re usually fast, smart, and very cautious about avoiding cats. The protozoa make them easier for cats to catch by a kind of mind control, which not only affects mice, but other unsuspecting mammals as well… including humans.


(Image credit: Gennaro Visciano)

Of course there’s no guarantee that a cat will see, chase, or catch a toxoplasma-laden mouse. So T. gondii have evolved to tilt the balance to the cat’s favor. They do that by altering the mouse’s body chemistry. After the protozoa invade a mouse’s body, they migrate to its muscles and into its brain. After a short sickness, the mouse’s immune system combats the invaders by permanently encasing them in cysts throughout the mouse’s body, where they go into suspended animation again.

Here’s how the protozoa fight back: they produce certain chemicals from inside the cysts, notably dopamine and a brain messenger called GABA. When those powerful chemicals are released by protozoa trapped in or near the brain, they cause the mice to act in ways that greatly increase their chance of being eaten by cats. For one, the mice, which usually avoid anything that smells like cat urine, suddenly become attracted to it, so they seek it out. Infected mice also act less fearful, move around in a way that makes them more visible to cats, and hang out in open spaces instead of creeping around its dark corners. All of these behaviors are essentially a huge “EAT ME” sign for cats on the prowl. The mice do get eaten, and the protozoa, released from their cysts during digestion, find themselves exactly where they want to be.


It’s not just mice and cats. Some other mammals— including humans— and some birds can be infected, too. They experience the short, flulike sickness, the migrating of the protozoa into muscles and brain, and the surprising changes in the way the brain acts and reacts.

Studies have found that people infected with toxoplasma exhibit slower response times and have higher rates of schizophrenia, OCD, mood disorders, and depression, but a reduced level of fear, anxiety, and sexual arousal. Strangely, there’s also a gender difference: infected men are somewhat more likely to be rule-breakers, introverted, oblivious to fashion and social cues, suspicious, and attracted to the scent of cat urine. Infected women, by contrast, are more likely to be rule-followers, extroverted, stylish, promiscuous, sensitive to others’ opinions, trusting, and repulsed by the smell of cat urine. Infected men and women are both more likely to be neurotic— prone to guilt, self-doubt, and insecurity— and more accident-prone: infected drivers and pedestrians were found to be almost three times more likely to be involved in a traffic accident.

Another odd effect: latent toxoplasmosis may also have contributed to wine and perfume production. It’s estimated that 45 percent of the French are infected, and two of France’s trademark products unwittingly exploit the fact that infected men are attracted to the scent of cat urine. One is Chanel No. 5, which reportedly mixes floral scents with those of peelike sexual hormones from the African civet. The other is sauvignon blanc wine, which contains a chemical byproduct that’s similar to a pheromone in cat urine. (Believe it or not, “cat pee” is a common, and usually favorable, description in wine reviews.)


Most people who get infected don’t even know it, or at most feel vaguely sick for a week or two before their immune systems kick in. Afterward, when the infection goes into its latent stage, victims will likely exhibit only a few fairly subtle behavioral changes. However, people who are most vulnerable to the condition— babies and people with suppressed immune systems— can get seriously ill when first infected, with damage to their internal organs, brain, and eyes.

However, your best bet is to avoid getting infected in the first place. You can get toxoplasmosis from undercooked meat, unwashed vegetables, and contaminated water, or from being born to a mother who is in the two-week active infection stage, before her immune system neutralizes the protozoa. In North America, toxoplasmosis often comes in on little cat feet and is contracted through handling cat feces, which is why doctors recommend that pregnant women and people with compromised immune systems avoid contact with cat litter boxes.

Does this mean you should give away your cat? No. Indoor cats don’t usually get the parasite; outdoor cats can pass it along for only about three weeks of their lives, usually just to the point when they’re old enough to begin hunting. Then, as with humans, they become permanently immune to getting an active case of toxoplasmosis again.

It does, however, mean that you should wash vegetables and cook meat well to kill the parasite. And one more word of warning: don’t flush cat poop down the toilet. Marine birds and mammals can get toxoplasmosis from sewage and rain runoff. A study of dead sea otters in California found that 13 percent were killed by T. gondii protozoa.


There is no cure for the dormant stage of infection yet. If the protozoa are inside you now, they’ll likely stay there until you die. The good news is that the effects, if any, are usually pretty subtle. It might be possible to manage even the mental effects that are more troublesome: experiments in infected mice found that dopamine-blocking drugs brought their behavior back to normal. And if there’s any comfort in knowing that you’ve got company, studies estimate that 10– 20 percent of Americans, and up to half of all people on Earth, have it. In fact, more people worldwide are infected with toxoplasma than are connected to the Internet.


The article above is reprinted with permission from Uncle John’s Factastic Bathroom Reader. The 28th volume of the series is chock-full of fascinating stories and facts, and comes in both the Kindle version and paper with a classy cloth cover.

Since 1988, the Bathroom Reader Institute had published a series of popular books containing irresistible bits of trivia and obscure yet fascinating facts. If you like Neatorama, you'll love the Bathroom Reader Institute's books - go ahead and check 'em out!

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