Pathogens lurk in the cat's gut Toxoplasmosis parasites alter our synapses in the brain

Many people get infected: how the toxoplasmosis parasite transforms the synapses in the brain

Pets do a great job for most people. But some of the four-legged friends can transmit diseases. For example, toxoplasmosis, an infectious disease whose pathogen is often found in cat feces. Researchers have now shown in a study how the toxoplasmosis parasite rebuilds the synapses in the brain.

One of the most common infectious diseases

A few years ago, American scientists reported that some owners of cats had an increased likelihood of aggression and irascibility. For those who had been infected by Toxoplasma gondii. The worldwide single-celled parasite causes one of the most common infectious diseases, toxoplasmosis.

The single-celled parasite Toxoplasma gondii infests birds and mammals - including humans. His final hosts, however, are cats. For some people, the pathogen can be dangerous. (Image: alho007 / fotolia.com)

Unicellular parasite infests birds and mammals

The single-celled parasite Toxoplasma gondii infests birds and mammals - including humans. His final hosts, however, are cats.

Researchers from the Institute for Inflammation and Neurodegeneration at the Otto von Guericke University Magdeburg (OVGU) and the Leibniz Institute of Neurobiology (LIN) have investigated in a study how the parasite influences the metabolism in the brain of its hosts and proves that it there changes the molecular composition of synapses.

The results of the scientists were published in the journal "Journal of Neuroinflammation".

The disease usually goes unnoticed

According to a report published by the Informationsdienst Wissenschaft (idw), about 30 to 50 percent of all people have already become infected with toxoplasma during their lifetime. The over-50s even count on around 50 percent.

Most toxoplasmosis goes unnoticed and the infected do not suspect that they are affected.

"In healthy people, the infection triggers short-term cold symptoms such as chills, fever and body aches," explains Prof. Dr. med. Ildiko Rita Dunay, Director of the Institute for Inflammation and Neurodegeneration at OVGU.

"Such an infection can be dangerous for pregnant women or people with weakened immune systems. There is no therapy yet to get rid of the parasite when it attacks the brain. So once you're infected, it will last a lifetime ", says the expert.

Another problem is that toxoplasmosis in neonates often remains undetected, as experts from the Robert Koch Institute (RKI) in the journal "Scientific Reports" reported.

Parasite is absorbed by humans via digestion

The parasite nests in the muscle tissue of infected animals, but not only:

"Toxoplasma gondii is absorbed by humans via digestion, enters the bloodstream and also migrates to the brain, where it lingers for life in nerve cells," describes Dr. med. Karl-Heinz Smalla from the special laboratory Molecular Biological Techniques at the LIN.

Previous studies by other German researchers have shown that toxoplasmosis can cause severe long-term consequences in the brain.

Even scientists from Magdeburg had already found in earlier experiments with mice that there are amazing behavioral changes in animals infected with Toxoplasma gondii:

"The mice, which are the prey of cats, lost their natural fear of cats after the infection. When they presented the smell of cat urine to rodents, they even seemed to have a preference for cats, "the researchers said.

Therefore, in order to explain these behavioral changes, they investigated changes in the mouse brains - in particular the molecular composition of synapses, since these are the essential structures for signal processing in the brain.

In cooperation with the Helmholtz Center for Infection Research in Braunschweig, they were able to show that in a total of 300 synaptic proteins, the levels in the brain after a toxoplasmosis infection had changed.

In particular, proteins were particularly reduced at glutamate-releasing excitatory synapses. On the other hand, increased levels of proteins involved in immune responses have been found.

Enhanced immune response

For the treatment of toxoplasmosis infections sulfadiazine is often used, which partially inhibits the proliferation of Toxoplasmen.

The psychiatrist and neuroscientist Björn Schott explains: "We now wanted to find out how sulfadiazine treatment affects the molecular changes that occur in the brain as a result of the infection."

The result: The protein composition in the mouse brains after treatment was comparable to that of non-infected conspecifics.

"All examined proteins, which are responsible for the glutamaterge signal transmission, were again in the normal range. And also the inflammatory activity decreased measurably. "

The infection appears to result in an enhanced immune response that reduces the proteins involved in glutamate-mediated synaptic arousal, while sulfadiazine reduces toxoplasmas and thereby normalizes the immune response, thus causing synaptic protein recovery.

Findings could also be relevant to humans

These findings could also be medically relevant for humans.

"They support the suggestion that Toxoplasma gondii is a risk factor for neuropsychological disorders," said neuroimmunologist Dunay.

"Malfunction of glutamatergic synapses has been implicated in the causes of depression, schizophrenia, and autism. Also components of the immune response show references to these diseases, "explains the expert.

"This suggests that immune responses may cause synapse changes that can lead to neuropsychiatric disorders." (Ad)