In her new book, “Infectious Madness,” author Harriet A. Washington explains the surprising ways mental illness can be “caught.” You’ll never look at your household pet the same way again . . .
Schizophrenia and bipolar disorder went from being rare diseases to relatively common ones in the late 19th century, writes psychiatrist E. Fuller Torrey. And during this period, he noted in his book, “The Invisible Plague: The Rise of Mental Illness from 1750 to the Present,” people also began showing cats more love.
Feline fanciers began keeping cats as pets, instead of banishing them to barns for rodent control, regarding them as Satan’s minions, and burning them to celebrate important holidays.
When England’s first cat show was held at the Crystal Palace in 1871, cat ownership had become popular in America, and at the same time, scientists recorded a sharp rise in schizophrenia rates — except among rural Hutterites, who “almost never” keep cats as pets.
Incredible as it sounds, were cats to blame?
According to much of the medical literature, yes, at least indirectly. University studies report that cats carry a zoonotic infection (one that humans can acquire from animals) that seems to cause schizophrenia.
Torrey, executive director of the influential Stanley Medical Research Institute (SMRI), suspects Toxoplasma gondii, an infectious single-celled organism that lives in the tissues of many warm-blooded animals but whose survival depends on access to cats. It can reproduce only within the stomach of a cat or closely related felid.
Although T. gondii infection has subtler effects on healthy adults, it produces serious ailments in infants and children, whose immune defenses are immature. The parasite can not only kill outright but also causes a congenital syndrome that includes deafness, retinal damage, seizures and mental retardation. It also leads to toxoplasmosis, in which flu-like symptoms are followed by an inflammation of the brain, referred to as encephalitis, and various neurological deficits.
Because T. gondii is transmitted by cats, obstetricians have long warned pregnant women not to touch litter boxes and to cook food thoroughly in order to kill any errant parasites. Now, avoiding mental illness in unborn children provides yet another reason to follow these precautions.
But Torrey and his frequent research partner Robert Yolken focused on another, biological factor: infection. They investigated the roles of the influenza, herpes simplex viruses as well as the parasite T. gondii, and other pathogens in schizophrenia, bipolar disorder and other mental disorders. Their research has helped to shift the mental-disease paradigm.
For decades, Torrey, Yolken, and other scientists abroad, including Czech parasitologist Jaroslav Flegr of Charles University, have suspected that T. gondii caused subtle changes in an infected fetus that could lead to schizophrenia 20 years later.
Later, in 2008, Yolken and Torrey published a study indicating that the peak age for becoming infected by T. gondii, between 18 and 35, coincides with the peak age of the first signs of schizophrenia. They also noted that in areas where felines are rare, the prevalence rates of both toxoplasmosis and schizophrenia are low.
But how does a cat-borne parasite dramatically change our behavior and brain function, and what purpose is served by this?
Actually, mental illness in humans serves no purpose for it: We humans are just collateral damage. The goal of T. gondii is to reach the stomach of a cat, and to achieve this, it deranges the behavior of rodents.
When people ingest T. gondii, it recruits the same neurotransmitters, which govern the behavior of both humans and rodents.
In addition to litter boxes, humans become infected when cats walk on surfaces that later hold food, which can become contaminated. Playing with cats can lead to contamination as well if you don’t wash your hands carefully before eating or placing your hands in your mouth. Outdoor cats that leave their feces on the ground also sometimes excrete into domestic animals’ feed. This adulteration results in T. gondii tissue cysts within the animals’ muscles. If humans eat this meat without cooking it thoroughly, they may become infected.
Torrey found that the most strongly positive schizophrenia correlations were not with T. gondii infections acquired in the womb but with infections that struck children and teenagers.
Why? Torrey and Yolken blame sandboxes.
“A likely mechanism for exposure in childhood is playing in the dirt of sandboxes contaminated with T. gondii oocysts,” they write, explaining that every uncovered public sandbox studied was used as a litter box by from four to 24 cats.
The connection between toxoplasmosis and schizophrenia suggests that easy preventative steps might lower schizophrenia rates, because most researchers in the field think that infection accounts for 10 to 15 percent of cases. Using gloves while cleaning litter boxes, washing hands frequently and especially before handling food, cooking food thoroughly to kill any parasites, banning cats from kitchen counters all discourage infection.
But, warns Yolken, “Preventing or treating T. gondii infection with a vaccine, on the other hand, is great idea but it is a little further down the line.”
Adapted from “Infectious Madness: The Surprising Science of How We ‘Catch’ Mental Illness” by Harriet A. Washington. Little, Brown and Company | Copyright ©2015 by Harriet A. Washington.