When I come home each day, my cat rarely greets me at the door. He's usually sitting upstairs, neatly composed atop a book. "How far along did you come on your novel today?" I'll ask. It's an old joke with us. He and I both know that he spent his day sleeping, eating, and chasing shadows on the patio.

At least, it's a joke to me. He doesn't understand jokes, I remind myself. Cats don't speak English. I think....

But if this is so, why do I always need to remind myself of this, post-joke? Why do I always hope the book will be open to some page beyond my bookmark? Am I starting to believe my cat can read? Am I going crazy? Is it my cat's fault?

I blame the Internet. Months ago I saw a story claiming that cats could cause schizophrenia. A parasite in their poop—was that it? Somehow this little bugger makes its way from sandbox to your brain, where it chews apart gray matter until you start hearing voices and imagining that the bus driver is tracking your movements. The idea that cats could literally drive me insane seemed too absurd, like a conspiracy to me, something cooked up by the Audubon Society, American Kennel Club, or some Internet meme-savvy pharmaceutical company.

"No, we do not accept research money from bird people, or dog people, or drug companies" says Fuller Torrey, a psychiatrist at Stanley Medical Research Institute, and one of the leading researchers behind the cat-poop-makes-you-crazy theory. His story checked out.

Torrey started investigating a parasitic cause to schizophrenia decades ago, because the prevailing theories didn't satisfy him. Torrey's sister was diagnosed with the disease back in 1957, and the doctors told the family that her condition was linked to a dysfunctional home.

Torrey grew up, went to medical school, and eventually started doing his own research, which took him past such simplistic Freudian reductions. In CT scans of twins, he noticed structural differences between healthy and schizophrenic brains. He found that in blood tests, schizophrenics' blood had high white blood cell counts—usually an indicator that a person has an infectious disease. Subsequent experiments by others confirmed these, and other clues about schizophrenia's origins.

Schizophrenia is a complicated disease, and there's no easy way to explain how it manifests. Genetics undoubtably plays a role. Schizophrenia affects about 1 percent of the population worldwide, but that rate jumps to 10 percent among people who have a parent or sibling with the disease. If the sibling is a twin, the odds leap above 40 percent.

Together, what these clues showed was not a simple psychological disease that grew from dysfunctional homes. Instead, schizophrenia is a complicated psychiatric condition with a confluence of causes. And one of these sources seems to be some sort of infectious agent.

Torrey came upon his cat hypothesis after he and a co-author looked at several decades of blood test data from schizophrenia patients, and saw that a great many of them had antibodies for the parasite Toxoplasma gondii. "It's a parasite that's been carried by felines for millions of years," says Torrey. When infected, a cat will poop or pee out millions of baby toxo cells, which can live for five years or more until they are reconstituted in the gut of a sheep, bird, rat, human, whatever. But while the parasite can infect a number of different critters, the only way it can make babies is if it finds its way back into a cat's digestive tract.

"Finds its way back" is not just a figure of speech. Research has shown that toxo-infected rats become willing prey. "One of the strongest innate behaviors in rats is the aversion to the smell of cat urine," says Joanne Webster, a zoonotic epidemiologist at Imperial College London. "Even rats that have never seen a cat have this reaction." However in experiments, Webster showed that toxo-positive rats actually sought out cat urine, putting themselves directly in the line of danger. "The toxo didn't simply dampen the reaction down, it gave the rats a fatal feline attraction," she says.

And toxo has been implicated as a mind control agent in other species. Toxo-positive sea otters swimming off the coast of California are three times more likely to be bitten by a shark than their toxo-free conspecifics. And toxo could make humans riskier behind the wheel.

But those studies came after Torrey and his co-author had developed their early hypothesis connecting toxo to schizophrenia. He believes toxo affects only infants or late-term babies that are genetically predisposed to schizophrenia. "It's like the old polio story," says Torrey. "If you get infected when you're six months old, nothing much happens. If infected at ten, you might develop polio."

The parasite causes an infection—toxoplasmosis—that triggers some hitherto unexpressed mutant stretch of the genome to epigenetically uncurl. These cause bad connections in the brain, and promote poor chemical regulation. When the person goes through puberty, these changes trigger psychotic symptoms.

Of course, not everybody's buying it. "The prevalence of cat ownership is so high relative to schizophrenia," says Tony Buffington, a semi-retired clinical cat veterinarian in Davis. Because Torrey does not account for the huge difference in number between cat-owning families with a schizophrenic member, and those without, his studies are crippled. "I think it’s important for people to put this in context," says Buffington. "The risk of developing schizophrenia from cat ownership is infinitely smaller than getting into an auto accident if you own a car."

Even if the link between the toxo and schizophrenia is real, Buffington says it's pretty unlikely that it would come from cat ownership. Cats only poop out the toxo virus once—the first time they are infected—and the time window of that happening would have to match with those early formative months in a cat-cohabiting child's life. And remember that only 1 percent of the population is schizophrenic to begin with. A pretty rare confluence.

But that doesn't rule toxo out—it just exonerates the litter box as the most likely vector. More likely is that cats who pee and poop outside pass the virus along to sheep, cows, and chickens. If undercooked, this meat could carry toxo into mommy, then umbilically into baby. House cats aren't the only kitties to blame, either. "You can also get infected by a fly that has been on cat feces and then lands on your unwashed vegetables," says Torrey. In the 1990s, a toxo outbreak occurred in Vancouver, BC. Researchers think it came from cats or cougars pooping in the city's water supply. There's been no evidence of a schizophrenia spike in Vancouver.

In the end, it'll take a lot more to prove that your cat is making you crazy—even if it's driving you crazy. "I think it’s important to emphasize that we haven't proven anything," says Torrey. "We have an association, there are lots of associations with schizophrenia." That association is enough that Torrey does not recommend cat ownership for pregnant women or families with small children. But in order to prove his hypothesis successful, he'll have to prove that toxoplasmosis medications prevent the development of schizophrenia. Which means they'd probably, eventually have to do research where they expose a bunch of children to the Toxoplasma gondii parasite. That's going to be pretty tough to get past an ethics board without a lot of animal trials.

So what's all this mean for me? Well, I'm not a baby, so my cat probably isn't making me crazy. That leaves no one but myself to blame for my crappy jokes.