Your cat is friends with, or unwittingly an accomplice of a very strange parasite that has long been accused of having a peculiar effect on human behavior, known as [Toxoplasma gondii.] A number of previous studies has linked the parasite to everything from risky behavior to severe psychiatric problems, while other research has found that this mind-controlling ability is perhaps a little over-stated.
A new study – the largest study of its kind to date – has weighed on the debate and concluded that the notorious parasite has been referred to schizophrenia, although the nature of the link is unknown.
As reported in the journal Brain, Behavior, and Immunity researchers found that blood samples from over 1
The study authors concluded: “We found that individuals with a T. gondii infection had increased odds of being diagnosed with schizophrenia disorders compared to those without infection,” adding that the level of association exceeds both the genetic and most other environmental risk factors for schizophrenia to date, supporting the close relationship between T. gondii infection and schizophrenia. "Image of three tachyzoites, a developmental stage in the Toxoplasma gondii parasite life cycle. Leandro Lemgruber / University of Glasgow / Wellcome Collection (CC)
T. gondii is also known for its ability to affect the behavior of mice although it can affect the brains of most warm-blooded animals. Mice usually stay well away from the click of cat pee, understandably so, because it's a clear indication they're in the territory of their top predator. However, mice infected with the parasite appear to actively seek out a cat. In turn, the mouse acts as a vehicle for T. gondii come into contact with a cat, one of the only known animal hosts in which the parasite can sexually reproduce. Fiendishly smart, huh?
Since we are so good pals with cats, a high proportion of the population (especially in cat-loving cultures) is also infected with T. gondii as well. It is unclear how or why the parasite affects the human brain and our behavior, although some research suggests it could be due to changes in dopamine levels. It is another common trope that T. gondii is linked to increased risk of suicide and traffic accidents, perhaps because of the parasite can spark risky behavior. However, this study did not find a strong association between these factors and the parasite.
Still, that point remains relatively speculative because this study did not look for an underlying mechanism that might explain the elusive link between T. gondii and mental health problems. Nevertheless, although the case is far from settled, this study adds to the growing pile of evidence that hints at some strange link between T. gondii and mental health.