I have read many shocking news items in my life, but few like the one I read the other day in the National Geographic . The article referred 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 protozoon affects human beings. This researcher has concluded that toxoplasma gondii can control our brains, increase cases of suicide and cause mental disorders such as schizophrenia or bipolar disorder.

Toxoplasma gondii: the intelligent parasite

The cause of toxoplasmosis is one of the most interesting parasites on the planet, and can affect all warm-blooded animals, including humans. In addition, birds and insects (flies, cockroaches) can carry the parasite and spread it widely. Cats are the only animals where the parasite produces eggs, so 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 are usually infected when they eat undercooked and infected meat, for example, prey that has been hunted in their habitat . In order for the parasite to continue its life cycle and develop into an adult parasite, it must be hosted in the intestines of cats. Therefore, the way to achieve this is to be ingested. And how does it achieve this? Studies suggest that the parasite has evolved in such a way that it is able to “hack” into the neural circuits to change the behavior of rodents with such precision that they lose their fear of cats (and even become aroused by their smell) so that they become easy prey for cats. We all know that mice and rats are the favorite prey of cats.

Toxoplasmosis in humans

Now, what exactly happens in humans? Blood tests show that toxoplasmosis, in 40% to 60% of cases the parasite has entered the body of these people and produced 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’s milk.
  • Eating contaminated fresh vegetables that have not been properly washed.
  • During gardening or on children’s playgrounds if the sand is contaminated.
  • Drinking water contaminated with sporulated oocysts.
  • Infection does not occur by touching or stroking the cat, but by touching soil where cats have deposited their feces, because after 24 hours after deposition there is a risk of infection (provided that you then put your hands in your mouth without cleaning them).

However, very few individuals have symptoms of the disease , because with a normal immune system anyone can counteract the parasite or simply have feverish symptoms or swollen glands. Although experts say the major problem occurs during pregnancy. The greatest risk arises when the infection is contracted during the early months of pregnancy, leading to miscarriages 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 claim the same. As mentioned above, one of the first scientists to take an interest in toxoplasmosis and its effects on humans was Jaroslav Flegr, and he found that the changes in behaviour 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 in order 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. White blood cells appear to produce a neurotransmitter that reduces fear and anxiety in both rodents and humans.

Flegr himself, after analyzing the database of different hospitals, found that an infected individual is more than twice as likely to suffer a car accident. According to Flegr, this has to do with the reduction in 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 link between schizophrenia and toxoplasma gondii . Specifically, that women with high levels of the parasite were more likely to give birth to babies who might 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 another paper has found that antipsychotics worked just as well as other drugs used to treat this condition, thus affirming that there is a relationship between psychological disorders and toxoplasma gondii infection .

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 by U.S. 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 suffer a greater prevalence of depressive symptoms.

Toxoplasmosis and suicide

Studies on the relationship between toxoplasmosis and psychological problems have continued and have yielded 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 by this parasite. But, of course, this is true for people who already have a mental illness. Similarly, another study found that countries with high rates of toxoplasmosis infection also had high rates of suicide

In Denmark, a link has also been found between suicide and toxoplasmosis . A joint investigation between the Danish National Hospital Register and the Danish Central Register of Psychiatric Research found that women infected with toxoplasma were 54% more likely to attempt suicide, and were twice as likely to succeed.

In fact, these women were more likely to attempt violent suicides. But even more worrisome is that the risk of attempted suicide correlated positively 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 remained even for women who had no history of mental illness.

Bibliographic references:

  • Arling TA1, Yolken RH, Lapidus M, Langenberg P, Dickerson FB, Zimmerman SA, Balis T, Cabassa JA, Scrandis DA, Tonelli LH, Postolache TT 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”.