The alien in your head. When a parasite takes control of the body

Recent research shows that some parasites are able to control humans like a puppet. Our brain has become a target for the protozoan parasite Toxoplasma gondii, for example. It can manipulate human behaviour, even leading its host to death.

The motorcyclist was entering a curve at 190 km/h. His knee was almost touching the asphalt. Suddenly the motorcycle skidded, collapsed on the road, and the man driving it flipped several times. He died on the spot. For the police the case was clear: the traffic pirate himself was to blame for the accident. However, this death hid a secret that only came to light at the hospital.

– When a hospital receives organs for transplantation taken from a motorcyclist, doctors should test them for Toxoplasma gondii in particular. This parasite is extremely common in accident victims – explains prof. Robert Sapolsky, a neurosurgeon at Stanford University. This was also the case of the aforementioned traffic pirate who lost control of his vehicle and died. After examining his corpse, doctors found parasites not only in his kidneys but also in his brain – which is not at all uncommon among the infected.

But what does Toxoplasma gondii do in the human body? The hosts of this protozoan are mostly domestic cats. It only uses us as an intermediate station to travel from one animal to another. The parasite measures only a few micrometers, penetrates the intestinal wall and enters the body cells with the blood. There it not only reproduces, but also begins to reprogram the person – for this purpose it takes over the brain. – Under the influence of Toxoplasma gondii men become more impulsive and prone to risks, explains Prof. Sapolsky. – Hence the many traffic accidents caused by speeding. Among the fatalities are three to four times as many people infected with the parasite as healthy people.

Professor Jaroslav Flegr knows very well how the invasion of this protozoan affects humans. In the early 1980s, as a student, he noticed that his behavior had changed dramatically: out of the blue, he began to run through the streets in front of cars and to criticize communism without words – the latter punishable in Czechoslovakia by years in prison. After a medical examination, he found out that he was a victim of Toxoplasma gondii.

The alien in your head. When a parasite takes control of the body

Today, Professor Jaroslav Flegr, a parasitologist from Charles University in Prague, deals with this protozoan parasite professionally. – Analyses show that one third of the world’s population is infected with this parasite and controlled by it, says the scientist. In some regions of Latin America even 95% of the population is infected. In the majority, the immune system is able to kill the intruder. What if it doesn’t work out? – Men become jealous and risk-taking, while women become more open and polite,” explains Prof. Flegr. – Also suicidal people, depressed people and people suffering from schizophrenia often turn out to be carriers of the parasite.

The alien in your head. When a parasite takes control of the body

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But what does Toxoplasma gondii do to our brain? – It has incredible abilities! – believes Prof. Sapolsky. – First of all, it can simply destroy the nerve pathways in our head. This occurs in the amygdala, the fear center. The possible consequences are surprising: we stop being afraid of situations in which we are in danger, and put our lives at risk without a second thought. – Second, the parasite has two versions of the TYH gene, responsible for the production of dopamine. This compound enables a sense of happiness. Toxoplasma gondii can produce dopamine and deliver it directly to the nucleus accumbens, part of the brain’s reward system.

As a result, people find pleasure in life-threatening activities and devote themselves to extreme sports, for example. – The parasite really can make us do the stupidest things, against our instinct for self-preservation. This protozoan knows more about the neurobiology of fear than the 25,000 neurologists who have specialized in the subject for years.

The alien in your head. When a parasite takes control of the body

Destroying the parasite is difficult but possible, especially when it is in its free life phase (not being a cyst). This is the power of antipsychotic drugs or antibiotics, for example. It is also possible to inhibit the effects of its presence, for example, by administering substances that block the action of dopamine.

However, there is an institution that would like to conduct research on the potential benefits of the protozoan – the US military. – The impact of the parasite on humans is well known. It does not surprise me at all that the army is fascinated by it – admits Prof. Sapolsky.

– Toxoplasma gondii prompts people to expose themselves to incredibly dangerous situations that any healthy person would avoid. For now, we don’t know what exactly the military’s research is aimed at. What is certain, however, is that carriers of this disease can be among the bravest warriors in the world, ready to make great sacrifices and take any risk. Do the generals want to “create” fearless soldiers by secretly infecting healthy men with Toxoplasma gondii? This would be neither the first nor the last illegal Army experiment in history.

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