http://theweek.com/articles/731238/concept-schizophrenia-dying

“Indeed, one past error has been to mistake a path for the path or, more commonly, to mistake a back road for a motorway. For example, based on their work on the parasite Toxoplasma gondii, which is transmitted to humans via cats, researchers E. Fuller Torrey and Robert Yolken have argued that “the most important etiological agent [cause of schizophrenia] may turn out to be a contagious cat.” It will not.

Toxoplasma gondii — likely a cause of ‘schizophrenia’, unlikely the most important | (Kateryna Kon/Shutterstock/Courtesy The Conversation)

Evidence does suggest that exposure to Toxoplasma gondii when young can increase the odds of someone being diagnosed with schizophrenia. However, the size of this effect involves less than a twofold increase in the odds of someone being diagnosed with schizophrenia. This is, at best, comparable to other risk factors, and probably much lower.

For example, suffering childhood adversity, using cannabis, and having childhood viral infections of the central nervous system, all increase the odds of someone being diagnosed with a psychotic disorder (such as schizophrenia) by around two to threefold. More nuanced analyses reveal much higher numbers.

««Compared with non-cannabis users, the daily use of high-potency, skunk-like cannabis is associated with a fivefold increase in the odds of someone developing psychosis. Compared with someone who has not suffered trauma, those who have suffered five different types of trauma (including sexual and physical abuse) see their odds of developing psychosis increase more than fiftyfold.”

http://theweek.com/articles/731238/concept-schizophrenia-dying