Research Article

Induction of changes in human behaviour by the parasitic protozoan Toxoplasma gondii

J. Flegra1 c1, Š. Zitkováa1, P. Kodyma2 and D. Fryntaa3

a1 Department of Parasitology, Charles University, Viničná 7, Prague 128 44, Czech Republic

a2 National Diagnostic Laboratory for Toxoplasmosis, National Institute of Public Health, Prague 110 00, Czech Republic

a3 Department of Zoology, Charles University, Viničná 7, Prague 128 44, Czech Republic


Toxoplasma gondii, the coccidian parasite, is known to induce changes in the behaviour of its intermediate hosts. The high prevalence of this parasite in the human population (20–80%) offers the opportunity of studying the influence of the parasite on human behaviour by screening of a normal population. A total of 224 men and 170 women were tested for toxoplasmosis and their personality profiles were measured by Cattell's questionnaire. Highly significant differences between Toxoplasma-infected and uninfected subjects were observed (P < 0·01). For men the factors G (low superego strength), L (protension), O (guilt proneness), and Q2 (group dependency) were positively influenced in infected subjects. For women the prevailing factors were A (affectothymia, P < 0·01), L (alaxia), O (untroubled adequacy) and Q2 (self-sufficiency). To reveal whether toxoplasmosis induces personality factor-shifts or whether certain combinations of personality factors influence the probability of acquiring Toxoplasma infection, we examined the personality profiles of 164 male patients diagnosed with acute toxoplasmosis during the past 13 years. The existence of a positive correlation between the duration of latent toxoplasmosis and the intensity of superego strength decrease (P < 0·02) suggested that the decrease of superego strength (the willingness to accept group moral standards) was induced by T. gondii infection.

(Received November 15 1995)

(Revised February 12 1996)

(Accepted February 19 1996)


c1 Corresponding author: Department of Parasitology, Faculty of Science, Charles University, Viničná 7, Prague 128 44, Czech Republic, Tel: +422 2491 5522. Fax: +422 299 713. E-mail: Flegr@mbot.cesnet.c2.