2023-04-30 12:41:00
All pregnant women have already heard of it, serological screening being compulsory for them in France. Toxoplasmosis, a fairly common and often benign disease – except for fetuses, hence this increased monitoring of future mothers – comes from a parasite that is often linked to cats, for the simple and good reason that it is a very frequent guest. How dangerous is it? Should you get rid of your feline? We disentangle the true from the false.
Let’s first recall what we are talking about: toxoplasma gondii, a microscopic parasite which can develop in the muscles and brains of all warm-blooded animals, and which often affects small animals, such as mice and birds, which have the particularity… of being the prey of cats.
Once ingested, the toxoplasmas will develop in the intestine of this one, and be eliminated via the stools. If the soiled grass is ingested by cows, for example, the meat of the latter will then be contaminated, and the man who will eat it with it… Ditto for fruits and vegetables in contact with soil soiled by cat feces .
The manipulated mouse brain
How dangerous is it? In 2013, four biologists from the University of California at Berkeley published a amazing discovery and worrying. Mice infected with toxoplasma gondii lose their innate and very marked aversion for their feline predators! In some cases, this behavioral change persists even after a parasite, when the infection-related inflammation becomes undetectable. “It is possible that t. gondii causes a permanent change in the brain during an acute infection,” the researchers conclude.
However, humans are, like mice, intermediate hosts of t. gondii. Between a third and a half of the world’s human population is infected with the parasite, which lodges in our brain cells. In 2016 he was estimated that around 32% of the adult French population was affected, the vast majority of the time in a latent form causing no apparent symptoms.
Could it be that behavioral changes also occur in humans infected with the parasite? That we have, like mice, developed tendencies favorable to the reproduction of t. gondii, for example an attraction to the company of cats?
It is well and truly demonstrated that t. gondii subtly influences our immune system, allowing it to thrive in our body without significantly affecting our health. “The tight regulation of the inflammatory reaction makes it possible to avoid that too weak a response leads to the death of the host, or that too strong a response prevents invasion”, explain the researchers who contributed to the understanding of this phenomenon, authors of a article appeared in the journal Cell in 2016.
Poorly understood correlations with aggression
More controversially, other researchers establish a link between toxoplasmosis and certain psychiatric disorders, in particular schizophrenia, bipolar disorders, or certain aggressive tendencies. A 2015 study points, for example, to a higher than average prevalence of toxoplasmosis in people with schizophrenia and obsessive-compulsive disorders.
But, at present, there is no scientific consensus on the mechanisms behind this apparent correlation. The same year, a study published in PLOS One also concluded the opposite, from a sample of 837 New Zealanders, 28% of whom tested positive for the disease.
“Correlation is not causation, and it is certainly not a reason to get rid of your cats, declared Royce Lee, professor of psychiatry and behavioral neurosciences at the University of Chicago, co-author himself in 2016 of ‘a study on the link between toxoplasmosis and aggression. We do not yet understand the mechanisms involved: it could be an increased inflammatory response, direct modulation of the brain by the parasite, or even reverse causation, whereby aggressive individuals tend to have more cats or eat more undercooked meat. »
Real danger for fetuses and immunocompromised
It is therefore impossible, at present, to assert that toxoplasmosis has a significant influence on our mental health… or that it is responsible for our veneration for tomcats. However, infection with this parasite is not always without danger. People infected during or just before pregnancy can transmit the parasite to the fetus, which is at risk of developing nervous system and eye diseases. Nearly 3,000 cases of congenital toxoplasmosis have thus been diagnosed since surveillance was introduced in 2007 by the National reference center on toxoplasmosis.
The disease is sometimes fatal for immunocompromised people (suffering from AIDS, cancer or transplant recipients), because it can reactivate previously acquired infections. ANSES recommends that these categories of the population adopt simple preventive measures. Since the parasite can be present in raw or undercooked meat, oysters, clams and mussels, as well as on insufficiently rinsed vegetables or fruits, it is recommended to wash your hands often when preparing these foods and to clean them. cook enough.
If you live with a cat, it is advisable to wash its litter box daily with boiling water, as parasites may be found in its excrement. And of course, the fear of toxoplasmosis should never motivate the abandonment of his pet.
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