Cat ownership raises the chance of severe mental illness in adulthood

Researchers at Johns Hopkins University have conducted a study wherein they discovered childhood cat ownership raises the risk of being diagnosed with severe mental illnesses later life, including schizophrenia. From Science Recorder:

"The researchers, led by Robert H. Yolken, M.D., of the Stanley Laboratory of Developmental Neurovirology at the Johns Hopkins University School of Medicine and E. Fuller Torrey of the Stanley Medical Research Institute, compared an unpublished survey on mental illness from 1982 and two later studies, which found an association between long-term childhood exposure to cats and the development of serious mental illnesses, including schizophrenia and bipolar disorder."

Granted, the link rests in exposure to cat feces, which can contain a parasite called Toxoplasma gondii. The parasite is relatively harmless to the bulk of the population, but can be devastating to those with compromised immune systems. Men and women who are immunocompromised can develop toxoplasmosis, which can, on top of raising the risk for mental illness, cause photophobia, blindness, miscarriages in pregnant women, fetal birth defects, and even death.

According to estimates by the Centers for Disease Control, as many as 60 million people in the United States may be infected with Toxoplasma gondii.

The Humane Society estimates there are about 30 to 40 million feral cats in the United States. Feral and outdoor cats have the highest chances of infection.

Studies have shown Toxoplasma gondii changes the way the brain operates, reinforcing the correlative evidence that the protozoan raises the risk for mental illness in adults. Mice infected with the protozoan permanently lose their innate fear of cats. The effect remains, even months after the presence of Toxoplasma gondii disappears in the mouse, suggesting that infection causes permanent structural changes in the brain.

Perhaps there is something to the crazy cat lady stereotype after all...