Over the past three turbulent decades, research has profoundly reshaped our understanding of chronic Toxoplasma gondii infection-traditionally regarded as harmless in immunocompetent individuals-unveiling its surprising impact on human health, performance, and behavior. This review emphasizes the effects of chronic Toxoplasma infection on physical and mental health, cognitive performance, and behavioral changes, highlighting key findings from studies investigating these domains, with a particular focus on both ultimate and proximate mechanisms underlying the observed effects. To this end, the primary focus will be on human studies; however, animal model studies will also be thoroughly considered when necessary and appropriate, to provide context and additional important information. Research demonstrates that chronic Toxoplasma infection may contribute to a broad spectrum of physical health issues. Ecological studies have revealed correlations between toxoplasmosis prevalence and increased morbidity and mortality from various conditions, including cardiovascular diseases, neurological disorders, and certain cancers. Large-scale cross-sectional studies have further shown that infected individuals report a higher incidence of numerous health complaints and diagnosed diseases, suggesting a significant impact on overall physical well-being. In addition to physical health, lifelong Toxoplasma infection (subclinical toxoplasmosis) has been implicated in cognitive impairments and behavioral changes. Studies have reported associations between infection and poorer performance in areas such as reaction time, processing speed, working memory, and executive function. Many of these behavioral changes likely relate to worsened health and a shift towards a "fast life history strategy." These cognitive deficits can have significant implications for daily functioning and performance. Furthermore, the role of Toxoplasma infection in the development or exacerbation of mental health disorders has been extensively investigated. Meta-analyses, ecological studies, and large-scale observational studies have demonstrated associations between Toxoplasma infection and an increased risk of disorders such as schizophrenia and obsessive-compulsive disorder. While the precise mechanisms underlying these associations remain under investigation, research suggests that neuroinflammation and alterations in neurotransmitter systems are likely to play a role. Far from being harmless, subclinical toxoplasmosis is increasingly recognized as a hidden factor influencing human health, behavior, and cognitive performance-with implications that extend well beyond the individual to public health at large. Further research is warranted to elucidate the complex interplay between Toxoplasma infection, host physiology, and the development of various physical, cognitive, behavioral, and mental health conditions.

• Keywords
• OCD, RhD, Rhesus D antigen, autism, evolution, intelligence, manipulation hypothesis, mental health, parasite, schizophrenia, subclinical toxoplasmosis, testosterone,
• Publication type
• Journal Article MeSH
• Review MeSH

In this article, I recount the journey of discovering the effects of latent toxoplasmosis on human psychology, behaviour, morphology, and health as I observed it from the closest perspective over the past 30+ years, during which our laboratory has been intensely focused on this research. I trace how we moved from the initial observations of differences between infected and uninfected individuals in certain personality traits to the systematic study of similar differences in behaviour, both in the laboratory and in everyday life, as well as in physiological and even morphological traits. This eventually led us to investigate the causal relationships behind these observed associations and their molecular basis. I describe some of the unexpected discoveries our research revealed - whether it was the impact of toxoplasmosis on the human sexual index, the prenatal and postnatal development, the sexual preferences and behaviour, the modulatory effect of blood Rh factor on toxoplasmosis, or the discovery of sexual transmission of toxoplasmosis. In exploring whether the toxoplasmosis-associated effects were merely side effects of an ongoing latent infection, we gradually uncovered that seemingly asymptomatic toxoplasmosis has profound (and certainly not positive) effects on the mental and physical health of infected individuals. The article also includes three separate boxes that discuss some key methodological challenges we encountered along the way, such as how to distinguish the effect of infection from mere statistical association, or how to differentiate parasitic manipulation from a simple side effect.

• Keywords
• Rh factor, Toxoplasma, behaviour, chronic toxoplasmosis, dopamine, manipulation, mental health, morbidity, parasite., personality, physical health, schizophrenia, sex ratio, testosterone,
• MeSH
• History, 20th Century MeSH
• History, 21st Century MeSH
• Humans MeSH
• Sexual Behavior MeSH
• Toxoplasmosis * psychology   physiopathology   parasitology   MeSH
• Animals MeSH
• Check Tag
• History, 20th Century MeSH
• History, 21st Century MeSH
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Historical Article MeSH
• Review MeSH

One-third of humanity harbors a lifelong infection with Toxoplasma gondii, and probably about 80% are infected with human cytomegalovirus (CMV). This study aims to delineate the associations between toxoplasmosis and cognitive abilities and compare these to the associations with CMV. We evaluated the cognitive performance of 557 students, who had been examined for Toxoplasma and CMV infections, using intelligence, memory, and psychomotor tests. The results indicated cognitive impairments in seropositive individuals for both pathogens, with variations in cognitive impact related to sex and the Rh factor. Specifically, Toxoplasma infection was associated with lower IQ in men, whereas CMV was predominantly associated with worse performance by women when testing memory and reaction speeds. Analysis of the antibody concentrations indicated that certain Toxoplasma-associated cognitive detrimental effects may wane (impaired intelligence) or worsen (impaired reaction times) over time following infection. The findings imply that the cognitive impairments caused by both neurotropic pathogens are likely due to pathological changes in the brain rather than from direct manipulative action by the parasites.

• Keywords
• Rh factor, behavior, cognition, cytomegalovirus, intelligence, manipulation hypothesis, memory, parasite, psychomotor performance, toxoplasmosis,
• MeSH
• Cytomegalovirus Infections * immunology   epidemiology   MeSH
• Cytomegalovirus * immunology   MeSH
• Adult MeSH
• Cognition * MeSH
• Rh-Hr Blood-Group System immunology   MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Cross-Sectional Studies MeSH
• Sex Factors MeSH
• Toxoplasma * immunology   MeSH
• Toxoplasmosis * psychology   immunology   epidemiology   complications   MeSH
• Check Tag
• Adult MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Male MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Rh-Hr Blood-Group System MeSH

Human populations, especially European, are polymorphic in the RHD gene. A significant fraction of their members carry no copy of the coding section of RHD gene, which results in their Rh-negative blood type. Theoretically, this polymorphism should be unstable. Carriers of the less frequent allele are penalized by reduced fertility because of the immunization of RhD-negative mothers by their RhD-positive babies, which results in hemolytic disease of the fetus and newborn in their subsequent progeny. For about 90 years, some form of balancing selection has been suspected to sustain this polymorphism. Several recent studies showed that the RhD-positive heterozygotes express higher viability than both types of homozygotes. However, the genotype of subjects in these studies was estimated only by indirect methods. Here we compared the physical and mental health of 178 women and 86 men who were directly tested for their RHD genotype. The results showed that RhD-positive homozygotic women had worse and RhD-positive homozygotic men better physical health than RhD-negative homozygotes; the difference between RhD-negative homozygotes and heterozygotes was not significant. Our results confirmed that health of RhD-positive heterozygotes and homozygotes differ. Therefore, any result of the comparison of subjects with RhD-positive and RhD-negative phenotype depends on the heterozygote-to-homozygote ratio in the RhD-positive sample. It is, therefore, crucial to analyze the effects of RHD-genotypes, not phenotypes in future studies.

• MeSH
• Adult MeSH
• Mental Health * MeSH
• Genotype * MeSH
• Heterozygote * MeSH
• Rh-Hr Blood-Group System genetics   MeSH
• Humans MeSH
• Young Adult MeSH
• Sex Factors * MeSH
• Check Tag
• Adult MeSH
• Humans MeSH
• Young Adult MeSH
• Male MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Rh-Hr Blood-Group System MeSH
• Rho(D) antigen MeSH Browser

BACKGROUND: Latent toxoplasmosis, i.e. a lifelong infection with the protozoan parasite Toxoplasma gondii, affects about a third of the human population worldwide. In the past 10 years, numerous studies have shown that infected individuals have a significantly higher incidence of mental and physical health problems and are more prone to exhibiting the adverse effects of various diseases. METHODS: A cross-sectional internet study was performed on a population of 4499 (786 Toxoplasma-infected) participants and looked for factors which positively or negatively affect the risk of SARS-CoV-2 infection and likelihood of a severe course of COVID-19. RESULTS: Logistic regression and partial Kendall correlation controlling for sex, age, and size of the place of residence showed that latent toxoplasmosis had the strongest effect on the risk of infection (OR = 1.50) before sport (OR = 1.30) and borreliosis (1.27). It also had the strongest effect on the risk of severe course of infection (Tau = 0.146), before autoimmunity, immunodeficiency, male sex, keeping a cat, being overweight, borreliosis, higher age, or chronic obstructive pulmonary disease. Toxoplasmosis augmented the adverse effects of other risk factors but was not the proximal cause of the effect of cat-keeping on higher likelihood of COVID infection and higher severity of the course of infection because the effect of cat-keeping was also observed (and in particular) in a subset of Toxoplasma-infected respondents (Tau = 0.153). Effects of keeping a cat were detected only in respondents from multi-member families, suggesting that a cat could be a vector for the transmission of SARS-CoV-2 within a family. CONCLUSIONS: Toxoplasmosis is currently not considered a risk factor for COVID-19, and Toxoplasma-infected individuals are neither informed about their higher risk nor prioritised in vaccination programs. Because toxoplasmosis affects a large segment of the human population, its impact on COVID-19-associated effects on public health could be considerable.

• Keywords
• COVID-19, Cat, Pets, Risk factors, SARS-CoV-2, Symptoms, Zoonosis,
• MeSH
• COVID-19 epidemiology   parasitology   physiopathology   MeSH
• Incidence MeSH
• Humans MeSH
• Cross-Sectional Studies MeSH
• Surveys and Questionnaires MeSH
• Risk Factors MeSH
• Social Media * MeSH
• Severity of Illness Index MeSH
• Toxoplasma immunology   pathogenicity   MeSH
• Toxoplasmosis complications   MeSH
• Check Tag
• Humans MeSH
• Male MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Geographicals
• Czech Republic epidemiology   MeSH
• Slovakia epidemiology   MeSH

Factors which indicate lower life expectancy also induce switching to a faster life strategy, that is, a higher investment in current reproduction at the expense of future reproduction and body maintenance. We tested a hypothesis according to which impairment of individual health serves as a signal for switching to a faster life strategy using online-gathered data from 32,911 subjects. Worse health was associated with lower age at menarche and earlier initiation of sexual life in women and higher sexual desire and earlier reproduction in both sexes. Individuals with worse health also exhibited lower sexual activity, lower number of sexual partners, and lower total number of children. These results suggest that impaired health shifts individuals towards a faster life strategy but also has a negative (physiological) effect on behaviours related to sexual life. Signs of a faster life strategy were also found in Rh-negative men in good health, indicating that even just genetic predisposition to worse health could serve as a signal for switching to a faster life strategy. We suggest that improved public health in developed countries and the resulting shift to a slower life strategy could be the ultimate cause of the phenomenon of demographic transition.

• MeSH
• Adult MeSH
• Libido physiology   MeSH
• Middle Aged MeSH
• Humans MeSH
• Menarche physiology   MeSH
• Young Adult MeSH
• Reproduction physiology   MeSH
• Sexual Behavior physiology   MeSH
• Age Factors MeSH
• Health Status MeSH
• Life History Traits MeSH
• Check Tag
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Young Adult MeSH
• Male MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

BACKGROUND: Since its discovery in the 1930s, the effects of Rh phenotype on human health and wellbeing, with the exception of the effects of Rh-negativity of a mother on the risk of hemolytic anemia of Rh-positive children, has only rarely been studied. In the last few years, however, several studies have shown that Rh-negative subjects have worse health and performance in certain tests than their Rh-positive peers. Nothing is known about the effect of Rh phenotype on the quality of life of subjects as measured by a standard instrument. METHODS: We hereby analyzed the data of 1768 male (24% Rh-negative) and 3759 female participants (23% Rh-negative) of an anonymous internet study using the partial Kendall test with the age and the population of the hometown of subjects controlled. RESULTS: The results showed that the Rh-negative women, but not men, scored worse in wellbeing measured with the WHO-BREFF. The Rh-negative men scored worse in mental health-related variables and in their reported economic situation and the Rh-negative women scored better in physical health-related variables. Both the Rh-negative men and women reported higher sexual activity than their Rh-positive peers. CONCLUSIONS: The effects of the Rh phenotype were significant after the correction for multiple tests. However, they were usually weaker and less numerous than those of smoking, consuming alcohol, and high body mass index, which were used as a sort of internal control.

• MeSH
• Adult MeSH
• Mental Health * MeSH
• Phenotype * MeSH
• Fertility * MeSH
• Body Mass Index MeSH
• Rh-Hr Blood-Group System metabolism   MeSH
• Libido * MeSH
• Humans MeSH
• Surveys and Questionnaires MeSH
• Sexual Behavior * MeSH
• Check Tag
• Adult MeSH
• Humans MeSH
• Male MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Rh-Hr Blood-Group System MeSH

BACKGROUNDS: The prevalence of toxoplasmosis is higher in schizophrenics than in the general population. It has been suggested that certain symptoms of schizophrenia, including changes in olfactory functions, are in fact symptoms of toxoplasmosis that can be easily detected in schizophrenics only due to the increased prevalence of toxoplasmosis in this population. Schizophrenics have impaired identification of odors and lower sensitivity of odor detection, however, no information about these parameters of non-schizophrenic Toxoplasma-infected subjects is available. METHODS: Here we searched for differences in olfactory functions between 62 infected and 61 noninfected non-schizophrenic subjects using the case-controls experimental design. RESULTS: The infected men scored better than the non-infected controls in the standard odor-identification test. The infected women rated all smells as more intensive while the infected men rated nearly all smells as less intensive. Infected women rated the pleasantness of the smell of the cat urine as higher than the non-infected women and the opposite was true for the men-in contrast, higher pleasantness of odor in infected men and lower in infected women were observed and described in the 2011 study. Toxoplasmosis, Rh, and toxoplasmosis-Rh interaction were not associated with the rated pleasantness of the smell of other stimuli. However, our sample contained only 17 Rh negative men and 30 Rh negative women. Therefore, all results concerning the main effects of Rh factor and the interaction with Rh factor must be considered only preliminary. CONCLUSIONS: Our results suggest that latent toxoplasmosis is associated with changes in the olfactory functions in humans; however, the observed changes differ from those observed in schizophrenics.

• MeSH
• Adult MeSH
• Cats MeSH
• Rh-Hr Blood-Group System metabolism   MeSH
• Humans MeSH
• Young Adult MeSH
• Urine MeSH
• Odorants MeSH
• Schizophrenia metabolism   parasitology   physiopathology   MeSH
• Case-Control Studies MeSH
• Toxoplasma pathogenicity   MeSH
• Toxoplasmosis metabolism   physiopathology   MeSH
• Animals MeSH
• Check Tag
• Adult MeSH
• Cats MeSH
• Humans MeSH
• Young Adult MeSH
• Male MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Rh-Hr Blood-Group System MeSH

Several recent studies have demonstrated the association of cat-related injuries with major depression and with depressiveness in the general population. It was suggested that cat-scratch disease, the infection with the bacterium Bartonella henselae, can be responsible for the observed association. However, no direct evidence for the role of the Bartonella infection in this association has been published until now. In this preregistered case-controls study performed on 250 healthy subjects tested earlier for the presence of anti-Toxoplasma IgG antibodies, we searched for the positive association between presence of anamnestic anti-Bartonella IgG antibodies and depressiveness measured with Beck II inventory, depression subscale of neuroticism measured with N-70 questionnaire, and self-reported health problems. We found that that Bartonella seropositivity was positively correlated with Beck depression only in Toxoplasma-seronegative men and negatively correlated with health in Toxoplasma-seronegative women. Bartonella seropositivity expressed protective effects against Toxoplasma seropositivity-associated increased neuroticism in men while Toxoplasma-seropositivity expressed protective effects against Bartonella seropositivity-associated health problems in women. A comparison of the patterns of association of mental and physical health problems with Bartonella seropositivity and with reported cat-related injury suggests that different factor, possibly infection with different pathogen transmitted by cat related-injuries than the B. henselae, is responsible for the observed association of cat related-injuries with depressiveness and major depression. The existence of complex interactions between Bartonella seropositivity, Toxoplasma seropositivity, and sex also suggest that the effect of symbionts on the host's phenotype must by always studied in the context of other infections, and separately for men and women.

• Keywords
• Bartonella, Toxoplasma, animal-related injuries, bartonellosis, cat-scratch disease, depressiveness, major depression, toxoplasmosis,
• Publication type
• Journal Article MeSH

BACKGROUND: Toxoplasma, a protozoan parasite of cats, infects many species of intermediate and paratenic hosts, including about one-third of humans worldwide. After a short phase of acute infection, the tissue cysts containing slowly dividing bradyzoites are formed in various organs and toxoplasmosis proceeds spontaneously in its latent form. In immunocompetent subjects, latent toxoplasmosis was considered asymptomatic. However, dozens of studies performed on animals and humans in the past twenty years have shown that it is accompanied by a broad spectrum of specific behavioural, physiological and even morphological changes. In human hosts, the changes often go in the opposite direction in men and women, and are mostly weaker or non-existent in Rh-positive subjects. METHODS: Here, we searched for the indices of lower endurance of the infected subjects by examining the performance of nearly five hundred university students tested for toxoplasmosis and Rh phenotype in two tests, a weight holding test and a grip test. RESULTS: The results confirmed the existence of a negative association of latent toxoplasmosis with the performance of students, especially Rh-negative men, in these tests. Surprisingly, but in an accordance with some already published data, Toxoplasma-infected, Rh-positive subjects expressed a higher, rather than lower, performance in our endurance tests. DISCUSSION: Therefore, the results only partly support the hypothesis for the lower endurance of Toxoplasma infected subjects as the performance of Rh-positive subjects (representing majority of population) correlated positively with the Toxoplasma infection.

• MeSH
• Physical Endurance * MeSH
• Immunoglobulin G blood   MeSH
• Immunoglobulin M blood   MeSH
• Rh-Hr Blood-Group System blood   MeSH
• Humans MeSH
• Young Adult MeSH
• Antibodies, Protozoan blood   MeSH
• Hand Strength * MeSH
• Toxoplasma immunology   MeSH
• Toxoplasmosis physiopathology   MeSH
• Check Tag
• Humans MeSH
• Young Adult MeSH
• Male MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Immunoglobulin G MeSH
• Immunoglobulin M MeSH
• Rh-Hr Blood-Group System MeSH
• Antibodies, Protozoan MeSH