Infection from the common parasite Toxoplasma tends to produce few apparent symptoms. But a new study published in the journal Evolutionary Psychology suggests that the disease can spur changes in a person’s political beliefs and values, most likely through an inflammatory reaction.
Toxoplasmosis is caused by the parasite Toxoplasma gondii and is one of the most prevalent parasitic diseases in the world. Infections can spur from situations like consuming uncooked, contaminated meat or cleaning the litter box of an infected cat. The disease most often produces no obvious symptoms in humans but can be dangerous for pregnant women or people with compromised immune systems.
While a Toxoplasma infection often goes unnoticed, evidence suggests it increases a person’s risk of certain diseases and disorders. Study author Jaroslav Flegr and his co-authors note that an infection seems to also induce personality and behavioral changes. This is likely because the disease activates the immune system and increases certain proinflammatory cytokines like IL-6. Inflammation, the authors say, has been found to influence emotional and behavioral processes.
“Our laboratory has been studying the effects of latent toxoplasmosis on human (and rodent) behavior and personality since 1992,” said Flegr, a professor at Charles University in Prague. “In the last ten years, we have been studying it in the context of the stress-coping hypothesis. 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. Stressed people switch to a faster life history strategy, which may affect their policy preferences. In a recent study, we sought (and found) support for this hypothesis.”
Flegr and colleagues point out that some of the personality traits associated with toxoplasmosis might coincide with changes in political beliefs. For example, men and women infected with the disease demonstrate lower conscientiousness, generosity, and novelty-seeking. The parasitic infection has also been linked to anxiety disorders.
To investigate the association between Toxoplasma infection and political values, the researchers distributed an online questionnaire. The analytic sample included only participants who reported having been tested for toxoplasmosis and who 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 various questions related to their mental and physical health, including use of prescription drugs, 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 which assessed the four factors of Tribalism, Cultural Liberalism, Anti-authoritarianism, and Economic Equity.
According to the results, 90 men and 518 women reported being infected with Toxoplasma. For women, being infected with Toxoplasma was associated with worse mental and physical health, and for men, it was associated with worse physical health.
The researchers next looked at the association between toxoplasmosis status and political beliefs. Across the entire 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 uncovered significant gender differences. Among men only, toxoplasmosis status was no longer associated with Tribalism. The authors say this lack of significant effect may be driven by the smaller number of male participants.
Also among men only, toxoplasmosis was positively associated with Economic Equity, the idea of a fair and equal society. This finding was unexpected since men with toxoplasmosis have previously been found to show higher risk-taking behavior and higher entrepreneurship activity. Future research will be needed to further investigate these gender differences.
“The most ‘sexy’ takeaway from our study is that our political views are also shaped by biological factors, including parasitic infections,” Flegr told PsyPost. “Toxoplasma is a very widespread parasite, and therefore its prevalence (which varies dramatically 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, history.”
“The less ‘sexy’ message of the study is that Toxoplasma gondii, which is the source of long-term infection in 30% of the human population in both 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 and well-being. Consequently, much greater efforts should be made to find a Toxoplasma vaccine and a method of treatment for lifelong latent toxoplasmosis.”
The researchers said their results are largely aligned with past findings showing that people from areas particularly affected by parasites demonstrate higher conservatism and authoritarianism. This might be explained by the parasite-stress theory which suggests that these attitudes serve to minimize contact with outsiders in order to avoid pathogen exposure. However, since the current participants came from a small region with low parasitic stress, this reasoning may not hold. Instead, the authors suggest that an inflammatory reaction to toxoplasmosis might cause mild yet chronic stress that leads to personality changes, and thus, changes in political attitudes.
“At present, we are only speculating about 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 is currently assumed. We also do not know how universal the observed phenomena are and how strong their influence is on people’s actual behavior, for example, whether it affects the behavior of people during elections.”
A limitation of the study was that the sample involved a much smaller ratio of men to women. This is likely because women are more likely to know their toxoplasmosis status due to testing during pregnancy.
“I am an evolutionary biologist, the author of the theories of frozen evolution, frozen plasticity, and turbidostatic and chemostatic selection,” Flegr added. “The study of the behavioral effects of toxoplasmosis was originally only my scientific hobby. It sounds funny that a tiny parasite could affect our personality, sexual preferences, or political beliefs. For this reason, our team’s work was awarded the Ig Nobel Prize in 2014 and was also introduced in the episode ‘Family Cat’ of the U.S. animated series Family Guy in 2021.”
“However, in the course of mapping the effects of toxoplasmosis and searching for the mechanism behind these effects, we uncovered some very disturbing facts about the impact of latent toxoplasmosis (which even today is considered clinically irrelevant by most doctors) on 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 the prevalence of toxoplasmosis between countries explain 23% of the variability in the overall burden of disease in Europe,” Flegr continued. “At the same time, Toxoplasma can only reproduce sexually in cats and can therefore be easily eradicated by appropriate veterinary vaccines. The story of latent toxoplasmosis research could nicely illustrate in the future that investment in basic science is the investment with the greatest return ever.”
The study, “Le Petit Machiavellian Prince: Effects of Latent Toxoplasmosis on Political Beliefs and Values”, was authored by Robin Kopecky, Lenka Příplatová, Silvia Boschetti, Konrad Talmont-Kaminski, and Jaroslav Flegr.
