Decrease of psychomotor performance in subjects with latent ‘asymptomatic’ toxoplasmosis

J.  HAVLÍCEK  a1, Z.  GAŠOVÁ  a2, A. P.  SMITH  a3, K.  ZVÁRA  a4 and J.  FLEGR  a1 c1
a1 Department of Parasitology, Faculty of Science, Charles University, Vinicná 7, 128 44 Prague, Czech Republic
a2 Institute of Haematology and Blood Transfusion, U nemocnice 1, 120 00 Prague, Czech Republic
a3 Centre for Occupational and Health Psychology, School of Psychology, Cardiff University, UK
a4 Department of Probability and Statistics, Faculty of Mathematics and Physics, Charles University, Sokolovská 83, 186 00, Prague 8, Czech Republic

Article author query
havlicek j   [PubMed][Google Scholar] 
gasova z   [PubMed][Google Scholar] 
smith a   [PubMed][Google Scholar] 
zvara k   [PubMed][Google Scholar] 
flegr j   [PubMed][Google Scholar] 


Toxoplasma gondii is known to induce specific behavioural changes in its intermediate hosts. This is usually considered to be an evolutionary adaptation aimed to increase the probability of transmission of the parasite into its definitive host, the cat, by predation. In rodents an increase of reaction time as well as many other specific behavioural patterns have been observed. Here we report the results of our double blind study showing the significantly longer reaction times of 60 subjects with latent toxoplasmosis in comparison with those of 56 controls. Moreover, the existence of a positive correlation between length of infection and mean reaction time suggested that slow and cumulative effects of latent toxoplasmosis rather than a one-step (and possibly transient) effect of acute toxoplasmosis disease are responsible for the decrease of psychomotor performance of infected subjects. To our knowledge, this is the first study confirming the existence of such parasite-induced changes in human behaviour that could be considered in evolutionary history of the human species as adaptive from the point of view of parasite transmission.

(Received July 24 2000)
(Revised November 13 2000)
(Accepted November 15 2000)

Key Words: manipulation hypothesis; parasite; human; reaction times; Toxoplasma gondii; behaviour; evolution.

c1 Corresponding author: Department of Parasitology, Faculty of Science, Charles University, Vinicná 7, Prague 128 44, Czech Republic. Tel: + 4202 21953289. Fax: + 4202 24919704. E-mail: