Findings in Folia Parasitologica highlight connection between certain infections, and personality traits, independent of overall health.
These results challenge the long-standing assumption that behavioral changes associated with such infections are merely secondary effects of compromised physical well-being.
Toxoplasma gondii, a protozoan parasite, is recognized for its subtle yet significant effects on human health. Transmission typically occurs through consumption of undercooked contaminated meat, exposure to contaminated water, or contact with infected cat feces. In adults with robust immune systems, this infection often remains asymptomatic or presents with mild flu-like symptoms.
Borrelia spp., a bacterial group responsible for Lyme disease, is transmitted via bites from infected ticks. Early symptoms may include a distinctive bull’s-eye rash and general malaise, which, if untreated, can advance to severe neurological or cardiac complications. Similar to Toxoplasma gondii, Borrelia spp. is capable of persisting in the host, potentially leading to chronic conditions even after treatment.
The findings revealed an increased likelihood of various health issues among those infected with Toxoplasma gondii, consistent with earlier research linking this infection to numerous health complications, including psychiatric disorders. Participants with Borrelia infections reported poorer physical health compared to those without the infection, although the effects on mental health appeared less significant when compared to Toxoplasma.
Associations were observed between infection status and changes in behavioral traits. Both Toxoplasma gondii and Borrelia infections were linked to alterations in personality characteristics, including reduced conscientiousness and shifts in traits connected to the Dark Triad—Machiavellianism, narcissism, and psychopathy. Notably, individuals positive for Toxoplasma gondii scored lower on Machiavellianism, with Toxoplasma-positive women showing reduced scores in narcissism.
Differences in disgust sensitivity were also identified. Altered reactions to pathogen and injury disgust scenarios were observed among infected participants. A negative correlation between Toxoplasma gondii infection and both pathogen and injury disgust was noted, suggesting that heightened disgust sensitivity might serve as a protective factor against infection.
Cognitive functions were similarly impacted, as shown in tasks such as the Stroop test. Prolonged reaction times and reduced precision were evident among Toxoplasma-infected individuals, indicating a direct influence of the infection on processing speed and accuracy.
Previous studies have associated Toxoplasma gondii infection with various psychiatric disorders, including schizophrenia, and with changes in behavior and personality traits, such as heightened risk-taking and aggression. Although the long-term behavioral impacts of Borrelia infections remain less understood, emerging research indicates potential effects on cognitive functions and mental health that persist well beyond the acute phase of infection.
In a new investigation led by Professor Jaroslav Flegr from Charles University in Prague, an effort was made to determine whether behavioral and health changes linked to Toxoplasma gondii and Borrelia infections are direct consequences of the pathogens or secondary effects of any health deterioration caused by the infections.
The Study
The research analyzed data collected from 4,942 women and 2,820 men through an online survey promoted on social media platforms such as Facebook and Twitter. The participants had an average age of approximately 43 years for women and 40 years for men. Among these individuals, positive test results for Toxoplasma gondii were reported by 24% of women and 12% of men. Positive test results for Borrelia infections were reported by 41.6% of women and 30.7% of men.
Cognitive and personality traits were assessed using a comprehensive range of psychometric tools. These included the Cattell 16PF test and a modified Meili test to evaluate memory and intelligence. Cognitive flexibility and processing speed were measured using the Stroop test. Personality traits were evaluated with the Ten Item Personality Inventory and the Czech adaptation of the Three Domain Disgust Scale, which encompassed pathogen disgust, sexual disgust, moral disgust, and an additional measure of injury disgust.
The Results
A key aspect of the findings revealed that changes in personality and cognitive functions were not influenced by the physical or mental health of the individuals. Statistical analyses demonstrated that controlling for overall health did not weaken the connection between infection status and behavioral changes. This challenges the notion that such behavioral effects are simply secondary to health deterioration caused by the infections.
The question remains whether Toxoplasma gondii and Borrelia spp. infections directly lead to these observed differences in personality and cognitive function. Definitive conclusions cannot yet be drawn.
The study’s cross-sectional design limits the ability to establish causation. Despite efforts to account for multiple variables, unmeasured factors may still influence both infection risk and behavioral outcomes. For instance, certain preexisting behavioral traits might increase susceptibility to these infections rather than being outcomes of the infections themselves.
“Our results suggest that the behavioral effects of latent toxoplasmosis and borreliosis are direct effects of the infections rather than side effects of impaired health of the infected subjects. However, it should be emphasised that neither path 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 Borrelia seropositivity is the result of a positive (direct or indirect) effect of higher intelligence on the risk of infection or vice versa. Only an experimental study, which is not feasible for ethical reasons, could distinguish between these two fundamentally different models.”
https://doi.org/10.14411/fp.2023.020
Abstract
Bacteria Borrelia burgdorferi s. l. and even more the protist Toxoplasma gondii Nicolle et Manceaux, 1908, are known to affect the behaviour and mental health of their animal and human hosts. Both pathogens infect a significant fraction of human population, both are neurotropic and survive in the host’s body for a long time. While latent infections were thought to be clinically asymptomatic, recent studies suggest otherwise, revealing adverse effects on human health. It was hypothesised that the specific behavioural effects of these pathogens may be side effects of general health impairments in infected individuals. This hypothesis was tested using about one hour-long survey consisting of questionnaires and performance tests on a cohort of 7,762 members of the internet population. Results showed that individuals infected with T. gondii reported worse physical and mental health, and those infected with Borrelia spp. reported worse physical health than uninfected controls. Furthermore, infected and noninfected individuals differed in several personality traits, including conscientiousness, pathogen disgust, injury disgust, Machiavellianism, narcissism, tribalism, anti-authoritarianism, intelligence, reaction time, and precision. While the majority of behavioural effects associated with Borrelia infection were similar to those associated with Toxoplasma infection, some differences were observed, such as performance in the Stroop test. Path analyses and nonparametric partial Kendall correlation tests showed that these effects were not mediated by impaired health in infected individuals, contradicting the side effects hypothesis.