An intelligent parasite that has aroused the disbelief of scientists themselves.
I have read a lot of shocking news throughout my life, but little like the one I read the other day in National Geographic magazine. The article made reference to a parasite called “Toxoplasma Gondii”, which causes Toxoplasmosis.
An evolutionary biologist of Czech origin, Jaroslav Flegr, has done a lot of research to find out more about how this protozoan affects humans. This researcher has concluded that toxoplasma gondii can control our brains, increase suicide cases, and cause mental disorders such as schizophrenia or bipolar disorder.
Toxoplasma gondii: the smart parasite
The cause of toxoplasmosis is one of the most interesting parasites on the planet, and it can affect all warm-blooded animals, including humans. Furthermore, birds and insects (flies, cockroaches) can carry the parasite and spread it widely. Cats are the only animals where the parasite produces eggs, that is why they are known as definitive hosts; in the rest of the animals they are called intermediate hosts because the parasite does not produce eggs.
Cats usually become infected when they eat undercooked and infected meat, for example, prey hunted in the wild. In order for the parasite to continue its life cycle and become an adult parasite, it must lodge in the intestines of felines. Therefore, the way to achieve this is to be ingested. And how do you achieve this? Studies suggest that the parasite has evolved in such a way that it is capable of “hacking” the neural circuits to change the behavior of rodents with such precision that they lose their fear of cats (and even become excited by their smell) so that they are easy prey for felines. We all know that mice and rats are the favorite prey of cats.
Toxoplasmosis in humans
Now, and in humans … what exactly happens? Blood tests show that toxoplasmosis, in 40% and 60% of cases, the parasite has entered the body of these people and producing the formation of antibodies. But how do people get infected? Well, in different ways:
- Eating undercooked or raw meat.
- Handling raw meat without gloves.
- Eating raw goat milk.
- Eating fresh, contaminated vegetables not washed properly.
- During gardening or on children’s playgrounds, if sands are contaminated.
- Drinking water contaminated with sporulated oocysts.
- The infection does not occur by touching or stroking the cat, but by touching land where the cats have deposited their feces, because after 24 hours after the deposition there is a risk of contagion (as long as they then put their hands in their mouth without cleaning them) .
However, very few individuals present symptoms of the disease, because with a normal immune system anyone can counteract the parasite or simply present feverish symptoms or swollen glands. Although experts claim that the major problem occurs during pregnancy. The greatest risk arises when the infection is contracted during the first months of pregnancy, presenting abortions and fetal malformations.
Toxoplasmosis causes behavioral changes in humans
Although it appears that the parasite does not cause visible symptoms in most cases, there is research that does not affirm the same. As already mentioned, one of the first scientists to be interested in toxoplasmosis and its effects in humans was Jaroslav Flegr, and he found that the changes in behavior that toxoplasmosis causes in rodents, such as changes in reaction times, lethargy or decreased fear also appear in infected humans.
In addition, Swedish scientists recently discovered that to travel throughout the body and reach the brain, toxoplasma gondii hijacks the same cells that are responsible for expelling foreign bodies, the white blood cells. Apparently, white blood cells produce a neurotransmitter that is responsible for reducing fear and anxiety in both rodents and humans.
Flegr himself, in addition, after analyzing the database of different hospital centers, discovered that an infected individual is more than twice as likely to suffer a car accident. According to Flegr, this has to do with reducing reaction time.
The relationship between toxoplasmosis and mental disorders
In 2003, Fuller Torrey, a researcher at the Stanley Medical Research Institute in Bethesda (United States), observed a relationship between schizophrenia and toxoplasma gondii. Specifically, women with high levels of the parasite were more likely to give birth to babies who could develop schizophrenia.
The hypothesis suggests that, while for most people who are infected, toxoplasma has minor effects, for others, the changes are much more exaggerated. This idea has gained strength with subsequent studies, as other work has found that antipsychotics worked as well as other drugs that were used for the treatment of this pathology, affirming, in this way, that there is a relationship between psychological disorders and infection by toxoplasma gondii.
One of the causes of the relationship between toxoplasmosis and schizophrenia has been explained by a group of scientists in the United Kingdom, who in 2009 found that the parasite has two genes for the manufacture of L-DOPA, the precursor molecule of dopamine . High levels of this neurotransmitter are associated with schizophrenia
Another study conducted by American scientists found that, among 7,440 mental health patients, there was a significant relationship between toxoplasma infection and a type of bipolar disorder in which patients suffered a greater prevalence of depressive symptoms.
Toxoplasmosis and suicide
Studies on the relationship between toxoplasmosis and psychological problems have continued and have provided surprising results. A study published in 2009 by the Journal of Nervous and Mental Disease states that there is a link between suicide and infection with this parasite. But of course this occurred in people who already have a mental illness. Similarly, another study found that countries with high rates of toxoplasmosis infection also had high suicide rates.
In Denmark, a relationship between suicide and toxoplasmosis has also been found. A joint investigation between the Danish National Hospital Registry and the Central Registry for Research in Psychiatry in Denmark found that women infected with toxoplasma were 54% more likely to attempt suicide, and were twice as likely to be successful.
In fact, these women were more likely to attempt violent suicides. But even more concerning is that the risk of a suicide attempt was positively correlated with the level of infection. Those women with the highest antibody levels were 91% more likely to attempt suicide than uninfected women. The connection between the parasite and suicide held even for women who had no history of mental illness.
- Arling TA1, Yolken RH, Lapidus M, Langenberg P, Dickerson FB, Zimmerman SA, Balis T, Cabassa JA, Scrandis DA, Tonelli LH, Postolache TT. (2009) .Toxoplasma gondii antibody titers and history of suicide attempts in patients with recurrent mood disorders. Journal of Nervous Mental Disease; 197 (12): 905-8. doi: 10.1097 / NMD.0b013e3181c29a23.
- Flegr, J. (2013) Influence of latent Toxoplasma infection on human personality, physiology and morphology: pros and cons of the Toxoplasma – human model in studying the manipulation hypothesis. Journal of Experimental Biology 216: 127-133; doi: 10.1242 / jeb.073635.
- Flegr, J. (2007) Effects of Toxoplasma on Human Behavior. Schizophrenia Bulletin. 33 (3): 757–760. doi: 10.1093 / schbul / sbl074
- National Geograpfic: ” Toxoplasmosis, new discoveries “.