Toxoplasmas (Toxoplasma gondii) are parasitic feline protists that, in some cases, can be transmitted to other animals, including humans in contact with infected domestic cats. The development of toxoplasmosis occurs mainly in the tissues of the nervous system and seriously affects the behavior of the hosts - at least rodents. Experiments have repeatedly shown that infected mice and rats are much less afraid of cat odor.
This influence is realized due to epigenetic changes in neurons caused by T. gondii. It is believed to facilitate reproduction and spread of the parasite. However, biologists from the University of Geneva have found that the fearlessness of infected mice is not limited to cats alone. In an article accepted for publication in the journal Cell Reports, Dominique Soldati-Favre and his colleagues note that such animals were much more free to explore open spaces, which are usually avoided.
In addition, such mice reacted much more calmly to the experimenter's hand, which is usually feared, and did not even fall into a stupor if an anesthetized rat, the most important and terrible enemy of mice, was placed in the cage. Finally, compared with uninfected animals, Toxoplasma carriers spent more time examining odors - not only of the harmless guinea pig, but also of the fox.
Moreover, the authors demonstrated a correlation between the severity of "fearless" behavior and the number of T. gondii cysts in the brain tissues of animals. All this, according to scientists, refutes the idea that Toxoplasma makes rodents more tolerant of felines: we are talking about a general decrease in anxiety and a weakening of reactions to stress factors.
It is worth remembering that toxoplasmosis is widespread in humans, transmitted through pets, and in general is not too dangerous for us. At the same time, experiments on mice have generated a lot of speculation about the effect of the parasite on human behavior and an increase in the host's propensity to take risks. There is no unequivocal evidence for this phenomenon, but the new work of Swiss scientists, having discovered the wide effect of Toxoplasma on rodent anxiety, strengthens the position of this very controversial hypothesis.