Toxoplasmosis and Schizophrenia

Cats drawn by Louis Wain during his institutionalization at Bethlem Royal Hospital

Following is an interesting article on the association between toxoplasmosis infection and schizophrenia/suicide. Read carefully, though. No one is saying that the parasite causes schizophrenia. The cat feces findings are consistent with the dominant diathesis-stress model: you inherit or are born with a certain vulnerability to mental illness and that vulnerability interacts with environmental factors (e.g., child abuse, parasitic infections, etc.) to affect the probability of a mental disorder emerging.

What would be compelling is a study of "high risk" pre-psychotic patients, e.g., the adolescent, non-schizophrenic offspring of schizophrenic parents. Test them for the T. gondii infection and treat them for it if they have it. Wait a decade or so and see if the "conversion rate" (i.e., percentage of genetically at-risk adolescents who go on to develop schizophrenia) is any different from other groups of genetically at-risk adolescents (i.e., less than 12-15%).


The Atlantic

"“Textbooks today still make silly statements that schizophrenia has always been around, it’s about the same incidence all over the world, and it’s existed since time immemorial,” [psychiatrist E. Fuller Torrey] says. “The epidemiology literature contradicts that completely.” In fact, he says, schizophrenia did not rise in prevalence until the latter half of the 18th century, when for the first time people in Paris and London started keeping cats as pets. The so-called cat craze began among “poets and left-wing avant-garde Greenwich Village types,” says Torrey, but the trend spread rapidly—and coinciding with that development, the incidence of schizophrenia soared.

Since the 1950s, he notes, about 70 epidemiology studies have explored a link between schizophrenia and T. gondii. When he and his colleague Robert Yolken, a neurovirologist at Johns Hopkins University, surveyed a subset of these papers that met rigorous scientific standards, their conclusion complemented the Prague group’s discovery that schizophrenic patients with Toxo are missing gray matter in their brains. Torrey and Yolken found that the mental illness is two to three times as common in people who have the parasite as in controls from the same region.

Human-genome studies, both scientists believe, are also in keeping with that finding—and might explain why schizophrenia runs in families. The most replicated result from that line of investigation, they say, suggests that the genes most commonly associated with schizophrenia relate to the immune system and how it reacts to infectious agents. So in many cases where the disease appears to be hereditary, they theorize, what may in fact be passed down is an aberrant or deficient immune response to invaders like T. gondii.

Epstein-Barr virus, mumps, rubella, and other infectious agents, they point out, have also been linked to schizophrenia—and there are probably more as yet unidentified triggers, including many that have nothing to do with pathogens. But for now, they say, Toxo remains the strongest environmental factor implicated in the disorder. “If I had to guess,” says Torrey, “I’d say 75 percent of cases of schizophrenia are associated with infectious agents, and Toxo would be involved in a significant subset of those.”

Just as worrisome, says Torrey, the parasite may also increase the risk of suicide. In a 2011 study of 20 European countries, the national suicide rate among women increased in direct proportion to the prevalence of the latent Toxo infection in each nation’s female population. According to Teodor Postolache, a psychiatrist and the director of the Mood and Anxiety Program at the University of Maryland School of Medicine, a flurry of other studies, several conducted by his own team, offers further support of T. gondii’s link to higher rates of suicidal behavior. These include investigations of general populations as well as groups made up of patients with bipolar disorder, severe depression, and schizophrenia, and in places as diverse as Turkey, Germany, and the Baltimore/Washington area. Exactly how the parasite may push vulnerable people over the edge is yet to be determined. Postolache theorizes that what disrupts mood and the ability to control violent impulses may not be the organism per se, but rather neurochemical changes associated with the body’s immune response to it. “As far-fetched as these ideas may sound,” says Postolache, “the American Foundation for Suicide Prevention was willing to put money behind this research.”"

Just to be clear, this is not cat schizophrenia, nor is it Cat Scratch Fever.