Decrease of psychomotor performance in subjects with latent 'asymptomatic'toxoplasmosis

Toxoplasma gondii is known to induce specific behavioural changes in its in termediate hosts. This is usually considered to be an evolutionary adaptati on aimed to increase the probability of transmission of the parasite into i ts definitive host, the cat, by predation. In rodents an increase of reacti on time as well as many other specific behavioural patterns have been obser ved. Here we report the results of our double blind study showing the signi ficantly 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 t hat slow and cumulative effects of latent toxoplasmosis rather than a one-s tep (and possibly transient) effect of acute toxoplasmosis disease are resp onsible for the decrease of psychomotor performance of infected subjects. T o our knowledge, this is the first study confirming the existence of such p arasite-induced changes in human behaviour that could be considered in evol utionary history of the human species as adaptive from the point of view of parasite transmission.