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Common parasite infection Toxoplasma tends to produce few noticeable symptoms. But a new study published in the journal Evolutionary Psychology suggests that the disease can cause changes in a person’s beliefs and political values, most likely through an inflammatory reaction.

Toxoplasmosis is caused by the parasite Toxoplasma gondii and is one of the most common parasitic diseases in the world. Infections can arise from situations such as eating raw, contaminated meat or cleaning an infected cat’s litter box. The disease most often produces no obvious symptoms in men, but can be dangerous for pregnant women or people with weakened immune systems.

While a Toxoplasma infection often goes unnoticed, evidence suggests it increases a person’s risk of certain diseases and disorders. Author of the study Jaroslav Flegr and his co-authors note that an infection also seems to induce personality and behavioral changes. This is likely because the disease activates the immune system and increases certain pro-inflammatory cytokines like IL-6. According to the authors, inflammation influences emotional and behavioral processes.

“Our laboratory has been studying the effects of latent toxoplasmosis on the behavior and personality of humans (and rodents) since 1992,” said Flegr, a professor at Charles University in Prague. “For the past ten years, we have been studying it within the framework of the hypothesis of adaptation to stress. This hypothesis posits that infected humans suffer from mild chronic stress and that the observed changes in their behavior and personality are a response to this stress. People under stress move to a life story strategy more quickly, which may affect their political preferences. In a recent study, we sought (and found) support for this hypothesis.

Flegr and his colleagues point out that some of the personality traits associated with toxoplasmosis could coincide with changes in political beliefs. For example, men and women infected with the disease show less conscientiousness, generosity, and novelty-seeking. Parasitic infection has also been linked to anxiety disorders.

To study the association between Toxoplasma infection and political values, the researchers distributed an online questionnaire. The analytical sample included only participants who reported having been tested for toxoplasmosis and were therefore able to report their status. This resulted in a sample of 2,315 Czech residents – 1,848 women and 467 men.

Participants were asked a variety of questions related to their mental and physical health, including prescription drug use, frequency of doctor visits, and presence of anxiety, depression, phobias, and mania. They also indicated whether they had been diagnosed with a mental health disorder from a list of 25 disorders. Additionally, they completed a measure of political beliefs and values ​​that assessed the four factors of tribalism, cultural liberalism, anti-authoritarianism, and economic equity.

According to the results, 90 men and 518 women said they had been infected with Toxoplasma. For women, being infected with Toxoplasma was associated with poorer mental and physical health, and for men, it was associated with poorer physical health.

The researchers then examined the association between toxoplasmosis status and political beliefs. Across the sample, toxoplasmosis was associated with higher tribalism, a construct defined by loyalty to one’s tribe and an ‘us versus them’ mentality. Toxoplasmosis was also associated with lower cultural liberalism and lower anti-authoritarianism.

When the researchers analyzed this separately for men and women, they found significant gender differences. Among men only, toxoplasmosis status was no longer associated with tribalism. The authors say this lack of a significant effect may be due to the smaller number of male participants.

Among men, too, toxoplasmosis was positively associated with economic equity, the idea of ​​a just and egalitarian society. This finding was unexpected as men with toxoplasmosis have previously been found to show higher risk behavior and higher entrepreneurial activity. Future research will be needed to further investigate these gender differences.

“The ‘sexiest’ finding from our study is that our political opinions are also shaped by biological factors, including parasitic infections,” Flegr told PsyPost. “Toxoplasma is a very widespread parasite, and therefore its prevalence (which varies greatly between and within countries) can influence not only the political climate in different countries and different social strata of the population, but also real-world politics and, consequently , the story.

“The less ‘sexy’ message of the study is that Toxoplasma gondii, which is the long-term source of infection in 30% of the human population in developed and developing countries, is likely to be a significant source of stress that affects not only the behavior and personality of infected people, but also their physical and mental health. health and wellbeing. Therefore, much greater efforts should be made to find a Toxoplasma vaccine and a method of treating latent toxoplasmosis for life.

The researchers said their results are broadly aligned with previous findings showing that people from areas particularly affected by parasites exhibit higher conservatism and authoritarianism. This could be explained by the parasitic stress theory which suggests that these attitudes serve to minimize contact with strangers in order to avoid exposure to pathogens. However, since the current participants came from a small region with low parasite stress, this reasoning may not hold. Instead, the authors suggest that an inflammatory reaction to toxoplasmosis could cause mild but chronic stress that results in personality changes, and therefore shifts in political attitudes.

“At present, we are only speculating on the mechanism of the impact of toxoplasmosis on our political beliefs and values,” Flegr explained. “If our stress management hypothesis is correct, then latent toxoplasmosis is a much more powerful health-related factor than currently assumed. We also don’t know how universal the observed phenomena are and how strong their influence is on people’s actual behavior, for example, whether it affects people’s behavior in elections.

A limitation of the study was that the sample had a much lower ratio of males to females. This is likely because women are more likely to know their toxoplasmosis status due to testing done during pregnancy.

“I am an evolutionary biologist, the author of the theories of frozen evolution, frozen plasticity, and turbidostatic and chemostatic selection,” Flegr added. “Studying the behavioral effects of toxoplasmosis was originally just my scientific hobby. It seems funny that a little parasite can affect our personality, our sexual preferences or our political beliefs. For this reason, our team’s work was awarded the Ig Nobel Prize in 2014 and was also featured in the “Family Cat” episode of the American animated series Family Guy in 2021.”

“However, in the course of mapping the effects of toxoplasmosis and investigating the mechanism behind these effects, we discovered some very disturbing facts about the impact of latent toxoplasmosis (which even today is considered clinically irrelevant by most physicians) to human health. Our highly cited 2014 paper showed that people infected with Toxoplasma have an increased risk of many important diseases and disorders, including ischemic heart disease, certain cancers and epilepsy.

“In fact, differences in toxoplasmosis prevalence between countries explain 23% of the variability in the overall disease burden in Europe,” Flegr continued. “At a time, Toxoplasma can reproduce sexually only in cats and can therefore be easily eradicated by appropriate veterinary vaccines. The history of latent toxoplasmosis research may well illustrate in the future that investing in basic science is the most profitable investment ever.

The study, “The Machiavellian Little Prince: effects of latent toxoplasmosis on beliefs and political valueswas written by Robin Kopecky, Lenka Příplatová, Silvia Boschetti, Konrad Talmont-Kaminski and Jaroslav Flegr.