Your cat might be driving you crazy
"What research says about cats: they're selfish, unfeeling, environmentally harmful creatures."
Updated by Joseph Stromberg Oct 16, 2014. Written in the Vox Tuesday February 10, 2015.
A cyst filled with Toxoplasma gondii parasites, as seen in a mouse brain. (Jitinder P. Dubey)
Finally, there's the weird, unsettling connection between cats, a parasite called Toxoplasma gondii, and litter boxes.This parasite can infect pretty much any sort of animal — including humans — but it can only sexually reproduce when inside the intestines of cats. In order to get there, it's been found to alter the behavior of infected rodents, making them less fearful of predators. In other words, when T. gondii gets picked up by a mouse, it increases the chance that the mouse will get eaten by a cat, so the parasite can reproduce once again.
This may seem bizarre enough, but over the past few years, some scientists have begun to suspect that the parasites alter human behavior in a similar way. Humans often pick up T. gondii from handling cats' litter boxes (because the parasites can be found in their feces), and there's an increasing amount of evidence that the resulting long-term, latent infection can subtly change a person's personality over time.
When parasites found in cat litter infect humans, they seem to subtly change personality over time
Of course, we're not rodents, so the parasites aren't successful in getting us eaten by cats. But the actual consequences are just as troubling. People who have been infected have greater rates of neuroticism and schizophrenia, and have slower reflex times in lab experiments. As a result, it seems, they get into traffic accidents more often. There's evidence that they have higher rates of suicide. All this, it seems, are unintended results of the parasite's ability to alter a mouse's brain to increase the chance of predation.
Now, everyone who owns a cat doesn't get infected by T. gondii, and there are other ways of getting the parasite (like eating undercooked meat). And the infection itself doesn't seem to cause these behavioral changes in everyone — they just occur at slightly higher rates among the millions of people worldwide who are infected.
Still, if you needed one more reason not to house an animal that doesn't love you, manipulates your emotions to get food, and helps to eradicate endangered species, it's a pretty damn good one.
Further reading: Kathleen McAuliffe's eye-opening article in the Atlantic: How Your Cat Is Making You Crazy
Further viewing: 3 ways society gives an unfair advantage to good-looking people
Update: This article previously stated the original estimate that cats kill 1.4 to 3.7 billion birds annually but didn't note the subsequent criticism of that number.
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- Science of Everyday Life
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Toxoplasma gondii antibody titers and history of suicide attempts in patients with recurrent mood disorders.
Arling TA1, Yolken RH, Lapidus M, Langenberg P, Dickerson FB, Zimmerman SA, Balis T, Cabassa JA, Scrandis DA, Tonelli LH, Postolache TT.
Abstract
Toxoplasma
gondii (T.gondii) is an obligate intracellular protozoan parasite
infecting one-third of the world population, residing relatively
silently in the brain of the immunocompetent host. We hypothesized that
T.gondii seropositivity and serointensity are associated with having a
history of attempting suicide and, in those attempting suicide, a
greater number of attempts. T.gondii seropositivity and antibody titers
were compared between (a) patients with recurrent mood disorders with
history of suicide attempt (99 individuals) versus (b) patients with
recurrent mood disorders without history of suicide attempt (119
individuals), and (c) healthy controls (39 individuals). Diagnosis was
made using the Structured Clinical Interview for DSM-IV. Statistical
methods included chi square, analysis of variance, and linear and
logistic regression analyses. Suicide attempters had higher T.gondii
antibody titers than nonsuicide attempters (p = 0.004). The logistic
regression analysis revealed a predictive association between titers of
anti- T.gondii antibodies and history of suicide attempt with OR = 1.55
(1.14-2.12), p = 0.006. No significant relationship was found between
T.gondii seropositivity and suicide attempt status, number of prior
suicide attempts, and recurrent mood disorder diagnosis. Although
preliminary and bearing replication, this is the first report, to our
knowledge, of an association between attempting suicide and T. gondii.
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