How the toxoplasmosis pathogen makes mice easier to catch

The causative agent of the toxoplasmosis cat disease generally makes mice more curious and less fearful, as a study shows. This makes them easier prey for cats.

The prevailing assumption that the pathogen manipulates mice so that they are attracted to the scent of a cat is outdated, writes a group led by Ivan Rodriguez and Dominique Soldati-Favre from the University of Geneva in “Cell Reports” trade journal.

The triggering unicellular organism Toxoplasma gondii can also affect people, especially pregnant women and people with weakened immune systems are at risk.

sense of smell-Maniupulation? No.

«For 20 years serves Toxoplasma gondii as a teaching example for a parasitic manipulation of the behavior, mainly because of the specificity of this manipulation », Rodriguez is quoted in a journal announcement. However, the investigation shows that the infection not only reduces the fear of cats, but generally changes the brain of mice considerably. This affects different behaviors.

Toxoplasma-Zellen in einer aus einem Mäusegehirn isolierten Zyste

Toxoplasma cells in a cyst isolated from a mouse brain Photo: Pierre-Mehdi Hammoudi and Damien Jacot

The researchers infected mice with the pathogen and then subjected them to the fifth to tenth week attempts. Infected mice were more curious, explored new surroundings more extensively, and were less afraid of potential predators than non-infected animals.

They spent significantly more time next to an anesthetized rat, even climbed over it and explored more intensive rooms with the smells of predators such as bobcats and foxes. They were just as interested in places with the scent of guinea pigs.

The infected mice also changed their social behavior. In a room with another mouse, a metal cube with holes, and an apple, they explored the mouse and objects alike. Uninfected mice, however, had a clear preference for the other mouse.

«Through a thorough behavioral analysis of infected mice, we show that a chronic infection with T. gondii triggers a decrease in fear, an increase in exploration behavior and a general loss of aversion to predators without specificity for cats, »the researchers write.

Manipulated Toxoplasma also human behavior?

An analysis of which areas of the brain are affected by the pathogen showed different distribution patterns, even if the visual center and other regions of the cerebral cortex were mostly affected. With genetic analyzes, Rodriguez and colleagues found increased inflammation of nerve tissue in the infected mice.

Infektionsherde in einem Mäusegehirn

foci of infection in a mouse brain Photo: UNIGE

They also demonstrated that special proteins that the pathogen produces are crucial for these inflammations. The higher the number of pathogens, the greater the changes in behavior. “Overall, the results indicate a behavioral manipulation mediated by neuronal inflammation rather than a direct disruption of certain nerve populations by the parasite,” says Rodriguez.

Da T. gondii reproduces mainly in the intestines of cats, infection via feces is possible. Mice and also farm animals such as pigs serve as an intermediate host for single-cell organisms. The parasite can get into humans through the consumption of raw meat or unwashed fruit and vegetables.

An investigation by the Robert Koch Institute (RKI) showed 2016 that more every year as 4000 pregnant women undergo toxoplasmosis and more than 300 Newborns with symptoms such as neurological problems are born.

According to the RKI, around 30 percent of people T. gondi i carry within. According to the RKI, fever, headache and muscle pain can occur in most people infected, according to the RKI.

Nevertheless, the symptoms are not comparable to those of mice, says the Geneva study director Soldati-Favre. “Even though apparently subtle changes in behavior can occur in humans, the inflammatory reactions in the human brain should never reach the same extent as in mice infected in the laboratory.” ( Stefan Parsch, dpa )