An international group of scientists suggests a relationship between toxoplasmosis and the tendency to undertake
A common theme in stories that blend science fiction with terror is that of the alien capable of controlling a person’s mind for his own purposes. Although these are fantasy stories, we can observe things similar in nature. We all know of the existence of parasites, living creatures that live on another or inside: the tapeworms, ticks or the protozoan that causes malaria are some common examples. These parasites, like the rest of the living beings, need to survive and reproduce. Those who do it better become, after several generations, more abundant than those who reproduce less; This is the basis of natural selection, the main engine of evolution on our planet.
In this context, some parasites have evolved to modify the behavior of their hosts to help them complete their life cycle, even at the cost of their lives. Some chilling examples of this phenomenon are:
Dicrocoelium Dendriticum: A flat worm that breeds in the liver of ruminants, but frequently infects ants. The worm affects the behavior of the ant to climb a blade of grass and anchor to it with its jaws, increasing the chances that a cow or another ruminant will accidentally eat it.
Spinochordodes tellinii: A worm that lives in the water, but whose larvae develop inside insects such as crickets and grasshoppers. Once the larva complete its development, it drives its host to jump to nearby water bodies, where the adult worm leaves the insect’s body.
Ophiocordyceps unilateralis: A fungus that infects the body of ants and, when the infection has progressed enough, makes them cling to a high floor in a cool and humid place and stay there until they die. Meanwhile, the fungus creates fruitful bodies that emerge from the ant’s body and release their spores, which thanks to the humidity conditions and the height of the plant will have a better chance of spreading and germinating.
Although these extreme examples mainly affect animals with relatively simple nervous systems such as insects, the more complex animals are not spared. A very common example, and the protagonist of this article, is the Toxoplasma gondii. Toxoplasma is a single-celled organism that needs to live within the cells of other living beings. Although it can infect and reproduce asexually within almost any hot-blooded animal, sexual reproduction, the key phase of its life cycle, can only occur in the body of a cat. Toxoplasma is reproduced within intestinal cells and releases a large number of «eggs» (actually sleeping forms of the parasite) that come out of the body along with the feces.
In this way, any animal that contacts feces of a cat affected by Toxoplasma can be infected in turn and become a carrier. This includes human animals, and it is estimated that about one-third of the world’s population has traces of the parasite in their bodies. In Chile, the percentage is somewhat higher and different studies give an estimate of 35 to 40%. Toxoplasma infection is mostly asymptomatic; Most people go through a short flu-like stage and then their immune system keeps the parasite under control. The two major risk groups are those individuals with immunosuppression (e.g. AIDS-affected people) and developing fetuses. Congenital toxoplasmosis, which is the disorder that results from the transmission of Toxoplasma from the mother to the fetus through the placenta, can cause major malformations in the developing fetus, and that is why it is recommended that pregnant women take measures Preventive as to avoid contact with cats and eat the meat well cooked.
However, despite the absence of obvious and harmful symptoms of toxoplasma infection, this parasite presents a particularly disturbing facet. As we discussed before, parasites evolve to optimize their access to those conditions that allow them to complete their life cycle. For Toxoplasma this means getting to the inside of a cat and, like other parasites, throughout its evolutionary history has developed the ability to manipulate its hosts to achieve their goals. This manifests itself very clearly in a very common type of host, usually living with cats and has «privileged» access to their digestive system: domestic rodents such as rats and mice. It is a well-known thing that Toxoplasma infection affects the behavior of these animals. For example, infected rats have been found to be attracted to cat-urine-smelling places instead of avoiding them, as healthy animals do.
More generally, toxoplasma-infected rodents are more active, show less aversion to the new, and have worse reaction times with the result that, for example, they fall into traps more frequently than uninfected animals. Rats with toxoplasmosis presenting these behaviors have unusually high levels of the neurotransmitter dopamine, and their behavior can be reversed to non-infected rats both by the application of drugs against Toxoplasma as Using dopamine antagonists, which reduce their activity in the brain. Molecular studies carried out years later confirmed that the sleeping forms of the parasite are capable of increasing the release of dopamine in brain cells, which gives us a plausible mechanism for the changes exerted on the host.
Toxoplasmosis in humans
So we have a parasite that infects 30% of the human population, and we know that it is capable of influencing the behavior of mammals. Knowing this, we have an interesting and quite disturbing question: can Toxoplasma influence the behavior of infected humans in the same way as in domestic rodents? The evidence that exists for now points to the fact that, despite the lack of obvious physical symptoms, the latent infections of toxoplasma have effects on the human brain. This is not something completely unexpected, since a parasite that enters a human body will do the same as if it enters a rat or a mouse: to create latent intracellular forms that if they are in the brain increase the metabolism of dopamine.
One of the most studied effects is the relationship between Toxoplasma infection and schizophrenia: high dopamine levels in some parts of the brain found in toxoplasma-infected rodents are similar to those found in people with Schizophrenia, and dopamine antagonist drugs that reverse abnormal behavior in rats are used to treat people with schizophrenia. In addition, the proportion of schizophrenic people affected by Toxoplasma is approximately 2.7 times greater than in people without schizophrenia, a correlation stronger than that of all known genetic and environmental factors.
Another effect similar to those found in rodents is the deterioration of reaction times, which among other things results in a higher risk of traffic accidents and labor for infected people. On the other hand, in a similar way to those found in rodents, some studies have found that Toxoplasma infection increases impulsivity and the tendency to take risks. In general, these changes are subtle and difficult to measure; The results vary according to the studies, the used groups of people and the administered tests, a common problem when studying the relationship of the human personality with external factors.
However, some studies hypothesize that these trends, weak when looked at on a personal level, can have greater and clearer effects when looked at at the level of large populations. This is the case of the study presented here, published by Stefanie K. Johnson and collaborators in Proceedings of the Royal Society B. Based on the idea that Toxoplasma infection increases impulsivity and increases the tendency to take risks, raised the Hypothesis that a latent infection would increase the tendency to devote to business in individuals, and that this would have a reflex at the social level. To check the effects of toxoplasmosis at the individual level, they took saliva samples from 1495 students to determine the presence of Toxoplasma antibodies, indicating that there is a latent infection.
These data of presence or absence of infection were crossed with the career chosen by the students. They did the same procedure of sampling between 197 attendees to events related to entrepreneurship, noting who had started their own company in the past. Of the students, 22% were positive for toxoplasma antibodies. This proportion remained stable in non-business-related careers, while business careers rose to 31%. In this way, the possibilities of choosing a business career were 1.4 times greater in those infected by toxoplasma than in those without infecting. This trend was even clearer when examining subdisciplines in business: The proportion of Toxoplasma infected was 1.7 times greater in those related to the creation and management of companies than in others considered less risky, As for example accounting. The proportion remained consistent among professionals attending entrepreneurship events: Toxoplasma infected had a chances 1.8 times greater than having started a successful business.
So at the individual level we find a fairly consistent correlation between being infected with Toxoplasma and the taste for lives with high risk and reward. This is already quite surprising, although consistent with the biology of the parasite, but the study goes a little further. His hypothesis is that this individual-level tendency can translate into something observable on a larger scale. To this end, they examined the relationship between the prevalence of Toxoplasma infection and the entrepreneurial activity data collected in an economic database generated by an international consortium of universities. The results, replicated using different types of analyses, suggest that in those countries with higher prevalence of latent toxoplasmosis there is a greater intention to undertake, more entrepreneurial activity in general and fewer people who do not undertake for fear of Failure.
The results shown in this study are striking. When this happens, it is important to consider whether they are trustworthy. This study is correlational, that means that only shows a relationship between factors: increases the prevalence of infection, raises the enterprise. However, nothing assures us that one thing is causing the other, entrepreneurship activity may be influenced by many factors, and perhaps one of them will make people more inclined to undertake and also more likely to contract the parasite, Like eating raw meat. Nevertheless, the results are solid, there is no candidate factor to be causing both things at once, and the effects are consistent with what we know of the parasite. Finally, there is already an earlier study that found negative relationships between the prevalence of toxoplasmosis and the cultural confidence and institutional quality of the countries studied, a result consistent with more neurotic behavior, another of the Effects observed in people infected with Toxoplasma.
Although we still have years of study to determine the exact way in which Toxoplasma influences us, the scopes of these results are fascinating. We have a very common micro-organism around the world that can influence people’s character and cause measurable effects on the culture and economy of a society. Although it seems disturbing in principle, there is no need to be alarmed. The human personality is affected by a multitude of factors that drive it in different directions, and the presence or absence of Toxoplasma is only one of them. Remember that these effects result in slight trends at the statistical level, and in a person given any effect of Toxoplasma can be countered by other factors. On a social and economic level, the results are more interesting, the economic models are based on many occasions on rational behaviors against things like the relationship between risk and reward, but what if we have whole societies in which the attitude is the risk biased due to a high prevalence of toxoplasma? Will sociologists of the future have to incorporate Toxoplasma and perhaps other microorganisms into their models and studies? Could this be a labor revolution for biologists and physicians, who will be in demand as advisors to politicians and economists?
Jokes and speculations aside, and finally, this type of study and its results highlight two things as important as horror stories about parasites and mind control. The first is the importance of interdisciplinary work: These studies are the result of gathering studies of economics and biology, something that is generally not very common, but in this case has taught us something new and fascinating about this world and ourselves. The second is the perspective that gives us this. For the parasite we are not different from a rat or a mouse, and the effect it has on us is similar. In the end it is important to remember that, through many airs, we are animals and we are integrated into an ecosystem of living beings that influence and influence us in turn.
Original article: https://royalsocietypublishing.org/doi/abs/10.1098/rspb.2018.0822
Toxoplasma increases dopamine metabolism: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0023866
Other relations between Toxoplasma and culture: https://link.springer.com/article/10.1007/s10887-013-9089-x
* This article emerges from the content alliance between the counter and the Interdisciplinary center of Neuroscience of Valparaiso