Why is autism so common among Asians

Toxoplasmosis parasites change the synapses in the brain

Mice infected with Toxoplasma behave strangely: they lose their natural fear of cats. Magdeburg scientists had already found this out in earlier experiments. And when the rodents were presented with the smell of cat urine, they even seemed to have developed a preference for cats, the surprised researchers said.

Toxoplasmosis is caused by the pathogen Toxoplasma gondii, a unicellular parasite that is distributed worldwide. It attacks birds and mammals - including humans. However, its ultimate hosts are cats who excrete the toxoplasmosis pathogen with their feces. People can become infected while cleaning the litter box or when they come into contact with the pathogen in some other way - for example while gardening - and ingest it through their mouths. There is also danger when they eat contaminated food.

Half of all adults are infected with toxoplasma. They usually do not notice anything about this, as toxoplasmosis usually goes unnoticed. The body builds antibodies against the pathogen and is then usually immune to the disease for life. An infection rarely leads to a flu-like clinical picture with fever, fatigue, muscle pain and diarrhea.

However, once a person is infected, the parasite often remains in the organism permanently - for example in the muscle tissue or in the brain. Doctors therefore speak of a "hidden persisting" infection.

More on this: Five pathogens that can harm the unborn

The ultimate hosts of toxoplasmosis pathogens are cats - from there they can get to humans

Toxoplasmosis is dangerous for people with a weakened immune system or patients who have just had an organ transplant. Pregnant women are also at risk: if a mother was infected before pregnancy and developed immunity to toxoplasmosis, the unborn child is normally not at risk. However, if it only becomes infected during pregnancy, this can lead to retinal inflammation, developmental delays and seizures in the child or even lead to miscarriage.

Parasites affect signal transmission in the brain

Toxoplasmosis has long been known to exist. What is new, however, is how the toxoplasmosis parasite remodels the synapses in the brain. Scientists from the Institute for Inflammation and Neurodegeneration at Otto von Guericke University Magdeburg (OVGU) and the Leibniz Institute for Neurobiology (LIN) have shown that the parasite influences the metabolism in the brain of its hosts and changes the molecular composition of synapses. The results were published in the Journal of Neuroinflammation.

The parasite not only nests in the brain and muscle tissue of infected animals: "Toxoplasma gondii is absorbed by humans through digestion, gets into the bloodstream and also migrates to the brain, where it can implant itself in nerve cells for life," says Dr. Karl-Heinz Smalla from the Special Laboratory for Molecular Biological Techniques at the LIN.

The prey animal, the mouse, loses its fear of cats due to the toxosplamosis parasites

To explain the strange behavior changes in the mice, the researchers examined changes in the mouse brain - in particular the molecular composition of synapses, as they are responsible for signal processing in the brain.

In a cooperation with the Helmholtz Center for Infection Research in Braunschweig, they were able to prove that the infection changes the quantities of a total of 300 synaptic proteins in the brain. Proteins in the vicinity of glutamate-releasing excitatory synapses were particularly strongly reduced. At the same time, increased amounts of proteins were found that are involved in immune responses.

Treatment with sulfadiazine shows promise

For the treatment of toxoplasmosis infections, sulfadiazine is often used, which partially hinders the multiplication of toxoplasmas. This treatment had an effect on the examined mouse brains: "All of the examined proteins that are responsible for glutamatergic signal transmission were back in the normal range. And the inflammatory activity also decreased measurably," said the psychiatrist and neuroscientist Dr. Bjorn Schott.

Malfunction of glutamatergic synapses has been linked to depression, schizophrenia, and autism.

These findings could also be relevant for humans. "They support the assumption that Toxoplasma gondii is a risk factor for neuropsychic diseases. Malfunctions of glutamatergic synapses are associated with depression, schizophrenia and autism. Components of the immune response also show links to these diseases," said the neuroimmunologist Dr. Ildiko Rita Dunay. "This suggests that changes in the synapse may be caused by immune reactions that can lead to neuropsychiatric disorders."

  • Like the plague! - When animals make you sick

    Bearer of the plague

    The health authorities of two counties in Arizona have struck gold in fleas: Yersinia pestis - the bubonic plague pathogen. The flea can transmit the bacteria from rodents to humans. People there now have to exercise particular caution: stay away from wild animals and protect their pets from the parasites with medication.

  • Like the plague! - When animals make you sick

    Not that unusual

    Plague cases are rare in the United States, but an average of seven human infections occur each year. It was only in June that three people were infected in New Mexico. Medically, the plague has lost its horror in developed countries. It can be treated well with antibiotics. If left untreated, however, it is often fatal.

  • Like the plague! - When animals make you sick

    Be careful, even if they look cute!

    In 2015, two visitors to Yosemite National Park fell ill with the plague. The bacteria were probably transmitted by such cute chipmunks or by squirrels. In mid-August, the park authorities closed a campsite after plague pathogens were found in two dead squirrels. There are around 300 cases of plague worldwide each year - most of them in Madagascar, DR Congo and Peru.

  • Like the plague! - When animals make you sick

    It's not just the plague that is dangerous

    There are many other diseases that can be transmitted from animals to humans - so-called zoonoses. Small children, the elderly, the sick and pregnant women in particular are at risk from infections with viruses, bacteria, fungi or parasites. Therefore, pets should be treated regularly with the necessary medication.

  • Like the plague! - When animals make you sick

    Fever thanks to kitty

    For example, cats and dogs - man's best friends - can transmit the bacterium "Campylobacter jejuni", which causes diarrhea. Cats also pass on various Bartonella bacteria that can cause fever and inflammation. And toxoplasmosis, caused by the parasite Toxoplasma gondii, can lead to dangerous complications during pregnancy.

  • Like the plague! - When animals make you sick

    Infection route through several animals

    Cowpox is a viral infection that only occurs in rural areas. Mice that live on cow pastures ingest the virus from the cattle's droppings. Then cats eat the mice and play with people in the evenings. If it gets a scratch while fighting, people become infected.

  • Like the plague! - When animals make you sick

    Sick from reptiles

    Amphibians and reptiles, on the other hand, are said to be responsible for a large number of sporadic salmonella infections in their owners. According to a study, around eleven percent of these infections in patients under the age of 21 can be traced back to animals such as iguanas, lizards, snakes or frogs.

  • Like the plague! - When animals make you sick

    Parrot disease

    Parrot disease is a zoonosis that can be particularly dangerous for children and weak people. The trigger is a type of chlamydia. It mainly meets parrots, budgies and pigeons. Humans are usually infected through the dried-up faeces of the animals. It is blown up with the dust in the air.

  • Like the plague! - When animals make you sick

    prevent diseases

    For healthy people, however, the risk is low as long as the animals are vaccinated and dewormed and hygiene rules are observed, the researchers emphasize. Nevertheless, everyone should wash their hands after a long stroke or wear gloves when cleaning the cage or terrarium.

  • Like the plague! - When animals make you sick

    Stinging danger

    But it's not just our pets that are contagious. It can happen, for example, that dangerous animals from the tropics accidentally get into temperate zones with merchandise, usually on ships. The Asian tiger mosquito, for example, transmits dengue fever.

  • Like the plague! - When animals make you sick

    Reineke Fuchs

    Until 2008 they also existed in Germany: Rabies, transmitted mainly by foxes. Large-scale vaccination campaigns have eradicated this dangerous disease. The disease was fatal for people infected with the rabies virus. Germany is now considered rabies-free.

  • Like the plague! - When animals make you sick

    All clear

    In general - this is what the researchers emphasize - outweigh the positive effects that the relationship with an animal brings with it. Small children who grow up with a dog or a bird are said to be less likely to develop allergies and respiratory infections. Dogs also ensure that we move more - and our animal friends are also good for the psyche.

    Author: Gudrun Heise, Fabian Schmidt