Features and Occasionals

Is a Parasite Driving Your Car?

By Diane Olson

Cruel parasites and enslaved hosts are nothing new in the insect world. There’s the fluke that forces ants to commit suicide by ungulate. The hairworm that impels grass­hoppers to drown themselves. And wasps that compel spiders to spin a special web for the larvae that will kill and eat them. But to even suggest that parasites could control human behavior has always been a taboo.

Sure, we host parasites that eat our eyeballs and cause our legs and genitals to in­flate like balloons, but no other organism can control our minds. We are, after all, masters of our domain.



Of mice and men

Meet Toxoplasma gondii (T gondii for short), the microbe that causes toxoplasmosis.

A crescent-shaped protozoan parasite, T gondii really wants to get inside a feline small intestine, which is the only place it can reproduce. To that end, it infests mice and rats and rewires their brains. Rodents infected with toxoplasmosis, while normal in all other ways, lose all fear of cats and are aroused by the scent of their urine. They become cat stalkers, begging to be eaten.

If a cat obliges, T gondii exits the mouse, enters the cat’s intestine, has sex and produces tiny, hard-walled oocysts that are shed in the cat’s feces. If the cat defecates outside, the oocysts, which can survive up to a year outside a host, are spread to other animals and taint the surrounding soil and water.

Humans are accidental hosts. We typically contract toxoplasmosis through undercooked meat, unwashed produce, raw goat milk, tainted soil or cat litter. It can also be transmitted from mother to fetus, and possibly sexually.

Worldwide, human T. gondii infection rates are around 50%, though in the U.S. only about 25% are affected. Accord­ing to a Stanford study, Parisian women have the highest infection rate, due to a predilection for cooking and consuming nearly raw meat.

Toxoplasmosis has long been recognized as dangerous to pregnant women and the immunosuppressed, as it can cause fetal brain damage and dementia. In the rest of the population, though, it was thought to be asymptomatic, aside from a brief, flu-like malaise felt in the initial phase of infection.

Turns out, that’s not the case.

Alley cats and sex kittens

Recent studies have found that in humans, as in mice, T gondii camps out in the areas of the brain that affect pleasure, fear and anxiety, cranking up the production of dopamine and altering hormone levels. In doing so, it changes the personality of its host in subtle, but significant, ways.

Weirdly enough, some of those changes differ between genders.

Infected men are more likely to dress badly, break rules, take risks, have few friends and be suspicious, jealous and morose. They also rather enjoy the smell of cat pee.

Women with toxoplasmosis, on the other hand, tend to dress well and are more outgoing, trusting and sociable. And they find the smell of cat pee highly offensive.

In both genders, T gondii hijacks the brain circuitry controlling fear, often turning it into sexual arousal. It also boosts sexual desire in both men and women, and increases their attractiveness to the opposite sex.

“In short,” says one Australian researcher, “toxoplasmosis can make men behave like alley cats and women behave like sex kittens.”

Hell on wheels

But wait, there’s more.

Toxoplasmosis also decreases attention span, lowers fear response, increases anxiety and slows reflexes. That’s likely why infected people are about 2.7 times more likely to be in a traffic accident than those who aren’t infected.

Studies also suggest that toxoplasmosis may trigger schizophrenia in genetically susceptible people, as well as increase the risk of suicide.

On the bright side, T gondii’s ability to jack up dopamine production may pave the way to curing gene-related diseases like Alzheimer’s or Parkinson’s. Or psychological problems like PTSD and social-anxiety disorder. And treating toxoplasmosis in people with schizophrenia or suicidal depression could potentially help lessen the ravages of those diseases.

If there were a treatment.

While drugs do exist to treat acute cases, there are none to cure ongoing infection. And until someone decides there’s really a need for a long-term cure, there isn’t likely to be one.

And so far, no one’s panicking.

Though perhaps all the research­ers already have toxoplasmosis and therefore are aroused, rather than frightened, by the thought of everyone on the planet being horny and fearless. Maybe they really aren’t interested in finding a cure.

Don’ts and does

Levity aside, if you’re pregnant and have flu-like symptoms, you might want to get tested. And everyone should take a few simple precautions against infection.

This does not include getting rid of your cat.

Numerous studies have concluded that living with a cat is not a significant risk factor. You’re more likely to acquire toxoplasmosis from undercooked meat, unwashed vegetables or non-purified water.

Infected cats shed the parasite only once in their life, for one to three weeks, usually when they’re young and learning to hunt. So if you have a young indoor/outdoor cat, keep tables and countertops clean and use a long-handled scooper when you clean the litter box. If you’re pregnant or immunosuppressed, have someone else clean it.

Even if you don’t have a cat, you should wear gloves when you garden, wash produce and sterilize cutting boards. And don’t eat rare meat. Especially in Paris.

Our parasite overlords

What’s most fascinating about toxoplasmosis is that it opens the door to so many profound questions.

Are you the one driving the car, choosing a mate and deciding whether or not to go out on Friday night—or is it T gondii?

How much of what we do is really controlled by other creatures?

It’s been noted that people newly infected with the flu have an increased desire to socialize, and those in the early stages of a herpes outbreak and the end stages of AIDS and syphilis intensely crave sex. Clearly, the viruses are calling the shots there, prodding their hosts to seek their own replacements.

So is free will truly a myth, not because of some divine plan, but because everything we do is done at the behest of our microscopic masters?

I don’t know, but the idea kinda turns me on.

This article was originally published on November 1, 2013.