Toxoplasma and Borrelia infections directly linked to personality, independent of health deterioration

New research in Parasitological folia provides proof that certain latent infections, particularly in Toxoplasma gondii And Borrelia spp., are directly linked to personality traits without being mediated by an overall deterioration in health status. This research challenges the previous belief that the behavioral changes observed in infected individuals were simple side effects of compromised health.

Toxoplasma gondii And Borrelia spp. are two microorganisms known for their intriguing and sometimes insidious impacts on human health. Toxoplasma gondii, a protozoan parasite, infects a wide range of hosts, including humans, primarily through contaminated undercooked meat, contaminated water, or contact with infected cat feces. In most healthy adults, this infection often goes unnoticed or may cause mild flu-like symptoms.

Borrelia spp., on the other hand, are a group of bacteria best known for causing Lyme disease, transmitted to humans through the bites of infected ticks. Early signs of infection may include a characteristic target-shaped rash and flu-like symptoms, which may progress to more serious neurological or heart problems if left untreated. Similar to Toxoplasma, Borrelie can also persist in the body long after initial infection, leading to chronic symptoms even in treated individuals.

Previous research has linked Toxoplasma gondii with various psychiatric disorders, such as schizophrenia, and changes in behavior and personality traits, such as increased risk-taking and aggression. Similarly, although less is known about the long-term behavioral effects of Borrelie infections, emerging evidence suggests potential impacts on cognitive functions and mental health, long after the acute infection phase has resolved.

In their new study, led by Professor Jaroslav Flegr of Charles University in Prague, the researchers sought to determine whether changes in behavior and health associated with Toxoplasma And Borrelie infections are direct effects of the pathogens themselves or simple consequences of the deterioration in health they cause.

The study included data from 4,942 women and 2,820 men who responded to an online survey, which was announced on social media platforms such as Facebook and Twitter. The average age of women was around 43 years old and that of men around 40 years old. Among these participants, 24% of women and 12% of men reported having tested positive for Toxoplasma gondii. For Borrelie infections, 41.6% of women and 30.7% of men reported testing positive.

To assess cognitive and personality traits, various psychometric tests were included in the survey. These included the Cattell 16PF test and a modified Meili test to assess memory and intelligence. For psychomotor performance, the researchers used the Stroop test, which measures cognitive flexibility and processing speed. Personality traits were assessed using the Ten-Item Personality Inventory and the Czech version of the Three-Domain Disgust Scale, which included measures for pathogen disgust, sexual disgust, moral disgust and an additional scale for injury disgust.

The results indicated that individuals infected with Toxoplasma gondii were more likely to experience a range of health problems, consistent with previous studies suggesting a link between Toxoplasma infection and various health complications, including psychiatric disorders. Likewise, participants with Borrelie Infections reported poorer physical health than their uninfected counterparts, although the impact on mental health was less pronounced than that of Toxoplasma.

The researchers found that infection status was associated with changes in several behavioral traits. Both Toxoplasma And Borrelie the infections were linked to personality differences, including lower conscientiousness and changes in traits linked to the Dark Triad – Machiavellianism, narcissism and psychopathy. Especially, Toxoplasma-positive individuals demonstrated lower Machiavellianism scores, and Toxoplasma-positive women scored lower on narcissism.

Additionally, researchers identified differences in disgust sensitivity, with infected individuals showing altered reactions to pathogen and injury disgust scenarios. There was a negative correlation between Toxoplasma gondii infection and disgust from both pathogens and injuries, suggesting that higher levels of these disgust responses could protect against infection

Interestingly, the study also found that these infections were linked to cognitive functions, as demonstrated by tasks such as the Stroop test. Toxoplasma-infected individuals showed prolonged reaction times and lower accuracy in their responses, suggesting a direct impact on the speed and accuracy of cognitive processing.

One of the most crucial aspects of the results was that the observed changes in personality and cognitive functions were not influenced by the health status of the individuals. This was demonstrated by statistical analyzes showing that controlling for physical and mental health did not diminish the association between infection status and behavioral changes. This directly contradicts the hypothesis that the behavioral effects observed in infected individuals are only side effects of poor health caused by the infection.

But do Toxoplasma gondii And Borrelia spp. Are infections responsible for observed differences in personality and cognitive functions? It’s still not clear.

The cross-sectional nature of the study limits the ability to draw causal conclusions from the data. Although researchers attempted to control for several variables, there could still be unmeasured confounding factors that affect both the likelihood of infection and the outcomes studied. For example, certain behavioral traits could make individuals more susceptible to these infections rather than being a consequence of them.

“Our results suggest that the behavioral effects of latent toxoplasmosis and borreliosis are direct effects of the infections rather than secondary effects of poor health of infected subjects,” the researchers concluded. “However, it should be emphasized that neither trajectory analysis nor any other statistical method can conclusively confirm the validity of a model. …For example, no statistical method can determine whether the positive association between intelligence and Toxoplasma Or Borrelie HIV positivity is the result of a positive effect (direct or indirect) of higher intelligence on the risk of infection or vice versa. Only an experimental study, unfeasible for ethical reasons, could distinguish these two fundamentally different models.”

The study “Parasitic manipulation or side effects? The effects of the former Toxoplasma gondii and Borrelia spp. infections on human personality and cognitive performance are not mediated by impaired health,” was written by Jaroslav Flegr, Jana Ullmann and Jan Toman.