This parasite could alter your behavior, and 2 billion humans already have it

Billions of parasites are present in the environment. And they can pose a danger in certain situations. In fact, more than two billion people on Earth have a parasite that alters their behavior. 

Called Toxoplasma gondii, it currently affects nearly a third of the world's population, according to the WHO. And while it has long been considered harmless to humans, studies show that it could have quite significant consequences. 

If you are unfamiliar with it, this parasite is a single-celled protozoan whose final host is the cat, and it is transmitted through close contact. However, in order to infect cats, it must pass through an intermediate host, which is often a rat or other rodent.

In this regard, tests have been carried out on mice to understand the impact of this parasite, and the results are quite worrying. Those that were infected were no longer afraid of cats, which are one of their main predators. And that's not all, because they were also attracted to the smell of cat urine.

However, humans can also serve as intermediaries through contact with contaminated cat feces, ingestion of undercooked meat or contaminated food, or, more rarely, through blood transfusions or organ transplants. And the first observations were made in the early 2000s. At that time, Czech researcher Jaroslav Flegr, from Charles University in Prague, admitted that affected humans had a more moderate change in behavior. In men, he noticed a tendency toward irritability and risk-taking. In women, he observed greater adherence to social norms.

Subsequent studies were conducted, such as one published in 2012 in the journal Schizophrenia Bulletin, which highlighted the link between this parasite and mental disorders. In 2016, a new analysis published in Acta Psychiatrica Scandinavica showed a correlation between neuropsychiatric disorders and this parasite. However, it should be noted that correlation does not imply causation, but that it may play a major role in behavior or mood.

How can this parasite affect our brain?

Toxoplasma gondii has a rather intriguing ability, as it is capable of crossing the blood-brain barrier and causing cysts to form in the brain. These cysts appear particularly in areas associated with fear, decision-making, and emotions. A study published in PLOS ONE also specified that this parasite has two genes capable of producing an enzyme similar to that which makes up dopamine, which is none other than the happiness hormone. 

However, the majority of infected people do not show any symptoms. But this parasite can be dangerous for pregnant women, due to the risk to the baby, and for people with weakened immune systems.