Higher Extraversion and Lower Conscientiousness in Humans Infected with Toxoplasma

Toxoplasmosis is associated with specific differences in the personality of infected subjects relative to non‐infected subjects. These differences are usually considered to be a side effect of the manipulative activity of the parasite aimed to increase the probability of its transmission from the intermediate host to the definitive host by predation. The personality of infected subjects was studied mostly using the Cattell's questionnaire. However, this questionnaire is now considered outdated and has been mostly substituted with the Neuroticism–Extraversion–Openness Personality Inventory—Revised (NEO‐PI‐R) questionnaire in clinical practice. Here, we searched for the association between toxoplasmosis and the personality by screening a population of students with the NEO‐PI‐R questionnaire. We found that Toxoplasma‐infected male and female students had significantly higher extraversion and lower conscientiousness. The conscientiousness negatively correlated with the length of infection in men, which suggested that the toxoplasmosis associated differences were more probably the result of slow cumulative changes induced by latent toxoplasmosis, rather than transient side effect of acute Toxoplasma infection. The existence of this correlation also supported (but of course not proved) the hypothesis that Toxoplasma infection influenced the personality, rather than the hypothesis that the personality influenced the probability of the infection. Copyright © 2011 John Wiley & Sons, Ltd.