Dear Cecil: Two related questions: As a cat owner, I've been a little concerned recently about rumors that cat poop can cause schizophrenic behavior in people who are overexposed to the waste. How much truth is in this — and if there is any truth to it, what amount can possibly count as overexposure? I'm also bothered by the supposed risk to pregnant women that changing the litter box can cause — not so much to them as to the fetus, through bacteria and whatnot. If that's really true, then with a third of all Americans owning cats, why don't we see higher rates of these dreadful birth defects? Certainly some of these women must get pregnant sometime, and I doubt they all know the dangers posed to them by cleaning up what Puss left behind. What gives? Onnie in Baltimore

Cecil replies:

Buckle up, friend. This one’s bizarre.

While you’re surely right that not everyone has gotten the word, the medical profession and hopefully most women of childbearing age know that if you’re pregnant you don’t want to get near cat feces. The problem is the protozoan Toxoplasma gondii, for which cats are the principal host. The microscopic parasites reproduce in the cat’s gut, the eggs are excreted, and by a process I’m not about to describe the critters wind up in your brain and muscles, where they create tiny cysts, leading to a condition known as toxoplasmosis. Unpromising as this sounds, the symptoms of toxoplasmosis are generally mild to nonexistent in adults, which is good, because roughly a third of all humans are infected, with the rate in some tropical countries approaching 100 percent.

For some, though, things are less benign. If a woman initially becomes infected while pregnant, there’s a fair chance the T. gondii will migrate across the placenta to her unborn child, with ghastly results ranging from cerebral palsy, seizures, and mental retardation to death. Women infected prior to pregnancy don’t run the same risk, which no doubt explains why we haven’t seen an epidemic of toxo-induced birth defects — the parasite’s ubiquitousness confers a sort of immunity. I’ve seen no research suggesting there’s a threshold exposure below which there’s no danger, and in my opinion it’d be foolish to assume there is one. Besides, you’ll never get a better excuse to make somebody else clean the litter box.

Here’s where things get strange. While the link between toxoplasmosis and birth defects has long been recognized, scientists now suspect that T. gondii may cause schizophrenia too. That in itself represents a major change in thinking — till recently the assumption, based on twin studies and the like, has been that schizophrenia is transmitted genetically. No way, scoffers say: schizophrenia is so profoundly disabling that sufferers tend not to reproduce. Germs are a likelier candidate. Studies typically have found T. gondii antibodies occurring in schizophrenics at twice the rate seen in control groups.

But get this. Forty-five percent of schizophrenics tested positive in one study for both T. gondii and D-lysergic acid diethylamide, better known as LSD. To quote a recent paper: “These results support the hypothesis that T. gondii may cause schizophrenia and may do so by producing or triggering the production of an hallucinogenic chemical” (“Genes, Germs, and Schizophrenia,” Ledgerwood et al, Perspectives in Biology and Medicine, 2003). Mindful that rodents are often an intermediate host for the parasite, the authors go on to say, “Production of such a compound may have been favored by natural selection because an infected, hallucinating rodent would be more easily captured by a cat.” In other words, schizophrenia in humans may be a side effect of T. gondii‘s attempt to set cats up with a steady supply of tripping mice, the better to ensure its own reproductive success. Told you this was bizarre.

A word of caution: our authors’ impressive theoretical edifice is built on some pretty thin evidence. It’s simplistic to say T. gondii works by triggering the production of LSD — among other problems with the idea, acid mainly gives rise to visual hallucinations, whereas the delusions of schizophrenics are primarily auditory (e.g., hearing voices). No doubt genetics plays some role in schizophrenia, if only by establishing a predisposition to the condition. Still, even without the hallucinogen angle, this is a promising line of research. If germs are in fact a cause of schizophrenia, which afflicts more than two million Americans, there’s a better chance we’ll be able to come up with a method of prevention if not a cure.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.