Infection by the common parasite Toxoplasma tends to cause few obvious symptoms. But a new study published in the journal Developmental Psychology suggests that illness can cause changes in a person’s political beliefs and values, likely through an inflammatory response.
Toxoplasmosis is caused by the parasite Toxoplasma gondii and is one of the most widespread parasitic diseases in the world. Infections can be caused by situations such as eating undercooked, contaminated meat or cleaning the litter box of an infected cat. The disease most often causes no obvious symptoms in humans, but it can be dangerous for pregnant women or people with weakened immune systems.
While a Toxoplasma Infection often goes undetected, evidence suggests it increases a person’s risk for certain diseases and disorders. Study author Jaroslav Flegr and his co-authors note that an infection also appears to cause changes in personality and behavior. This is likely because the disease activates the immune system and increases certain pro-inflammatory cytokines such as IL-6. Inflammation, the authors say, has been found to affect emotional and behavioral processes.
“Our lab 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. “For the last ten years we have been studying it in the context of the stress treatment hypothesis. This hypothesis holds that infected people suffer from mild chronic stress and that the observed changes in their behavior and personality are a response to this stress. Stressed individuals switch to a more rapid life history strategy, which may affect their policy preferences. In a recent study, we looked for (and found) support for this hypothesis.”
Flegr and colleagues point out that some of the personality traits associated with toxoplasmosis may coincide with changes in political beliefs. For example, men and women infected with the disease exhibit lower conscientiousness, generosity, and novelty seeking. Parasitic infection has also been linked to anxiety disorders.
To investigate the correlation between Toxoplasma contamination and political values, the researchers distributed an online questionnaire. The analytic 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 about their mental and physical health, including the use of prescription medications, frequency of doctor visits, and the presence of anxiety, depression, phobias, and mania. They also reported whether they had been diagnosed with a mental health disorder from a list of 25 disorders. In addition, they completed a measure of political beliefs and values that assessed the four factors of Tribalism, Cultural Liberalism, Antiauthoritarianism, and Economic Equality.
According to the results, 90 men and 518 women reported being infected Toxoplasma. For women, infected with Toxoplasma was associated with worse mental and physical health and for men, it was associated with worse physical health.
The researchers then looked at the relationship between toxoplasmosis status and political beliefs. Across the entire sample, toxoplasmosis was associated with higher racialism, a construct defined by belief in one’s race 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 revealed 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.
Also only among men, toxoplasmosis was positively associated with Economic Equality, the idea of a fair and equal society. This finding was unexpected, as men with toxoplasmosis had previously been found to exhibit higher risk-taking behavior and higher entrepreneurial activity. Future research will be needed to further explore these gender differences.
“The ‘sexiest’ thing about our study is that our political views are also shaped by biological factors, including parasitic infections,” Flegr told PsyPost. “Toxoplasma it is a very widespread parasite, and therefore its prevalence (which varies dramatically between and within countries) can affect not only the political climate in different countries and different strata of the population, but also real-world politics and, consequently, history’.
“The least ‘sexy’ message of the study is this 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 major source of stress affecting not only the behavior and personality of infected individuals but also their physical and mental health and wellness. 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 in line with previous findings showing that people from areas particularly affected by parasites exhibit higher conservatism and authoritarianism. This can be explained by the parasite stress theory, which suggests that these behaviors serve to minimize contact with outsiders in order to avoid pathogen exposure. However, since the present participants came from a small area with low parasite stress, this reasoning may not hold. Instead, the authors suggest that an inflammatory response to toxoplasmosis may cause mild but chronic stress that leads to personality changes and thus changes in political attitudes.
“For now, we are only speculating about the mechanism of toxoplasmosis’ effect 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, if it affects people’s behavior during elections.”
A limitation of the study was that the sample involved a much smaller male to female ratio. This is likely because women are more likely to know about their toxoplasmosis because of the test during pregnancy.
“I’m an evolutionary biologist, the author of the theories of frozen evolution, frozen plasticity, and turbid and chemostatic selection,” added Flegr. “Studying the behavioral effects of toxoplasmosis was initially just 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 featured in the episode ‘Family Cat’ of the American animated series Family Guy in 2021.”
“However, in mapping the effects of toxoplasmosis and searching for the mechanism behind these effects, we uncovered some very disturbing evidence about the impact of latent toxoplasmosis (which is still considered clinically irrelevant by most doctors) on human health . Our highly cited 2014 paper showed that people were infected with Toxoplasma have an increased risk for many major 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 burden of the disease in Europe,” Flegr continued. “At the same time, Toxoplasma it can only be sexually reproduced in cats and can therefore be easily eradicated with appropriate veterinary vaccines. The history of latent toxoplasmosis research could well illustrate in the future that investing in basic science is the highest paying investment 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.