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

PURPOSE: Toxoplasma gondii is one of the most widespread parasites in the human population globally. Several modes of its transmission have been proposed: some are well-researched and confirmed, others remain unconfirmed. One unconfirmed hypothesis pertains to potential transmission of Toxoplasma gondii via oral sex (fellatio) in humans. A recent study found tissue cysts in the semen of men with latent toxoplasmosis. Therefore, we aimed to test the hypothesis of Toxoplasma gondii transmission through oral sex experimentally. METHODS: Eighty-two laboratory mice were orally administered semen samples from 41 men with latent toxoplasmosis. These semen samples were examined for the presence of Toxoplasma gondii DNA using PCR. RESULTS: We detected Toxoplasma gondii DNA in three of the 41 semen samples from men with latent toxoplasmosis. Oral administration of semen samples to laboratory mice did not result in parasite transmission. CONCLUSION: We have not demonstrated the transmission of Toxoplasma to mice by oral exposure to semen from infected men. While this does not conclusively rule out the possibility of such transmission in humans, the results suggest that, if it does occur, this mode of transmission is likely infrequent.

• Keywords
• Ejaculate, Fellatio, Latent toxoplasmosis, Parasitic disease, Sexual transmission, Sperm,
• MeSH
• Humans MeSH
• Disease Models, Animal MeSH
• Mice MeSH
• DNA, Protozoan genetics   MeSH
• Semen * parasitology   MeSH
• Toxoplasma * MeSH
• Toxoplasmosis * transmission   parasitology   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Male MeSH
• Mice MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• DNA, Protozoan 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

Cytomegalovirus (CMV) is the herpetic virus, which infects 45-100% people worldwide. Many reports suggest that CMV could impair cognitive functions of infected subjects. Here we searched for indices of effects of CMV on infected subjects' intelligence and knowledge. The Intelligence Structure Test I-S-T 2000 R was used to compare IQ of 148 CMV-infected and 135 CMV-free university students. Infected students expressed higher intelligence. Paradoxically, their IQ decreased with decreasing concentration of anti-CMV antibodies, which can be used, statistically, as a proxy of the time passed from the moment of infection in young subjects when the age of subjects is statistically controlled. The paradox of seemingly higher intelligence of CMV infected subjects could be explained by the presence of the subpopulation of about 5-10% CMV-positive individuals in the population of "CMV-negative students". These false negative subjects had probably not only the oldest infections and therefore the lowest concentration of anamnestic antibodies, but also the lowest intelligence among the infected students. Prevalence of CMV infection in all countries is very high, approaching sometimes 90%. Therefore, the total impact of CMV on human intelligence may be large.

• MeSH
• Biomarkers MeSH
• Cytomegalovirus Infections epidemiology   psychology   virology   MeSH
• Cytomegalovirus * MeSH
• Intelligence MeSH
• Intelligence Tests MeSH
• Cognition * MeSH
• Humans MeSH
• Public Health Surveillance MeSH
• Students * MeSH
• Case-Control Studies MeSH
• Models, Theoretical MeSH
• Universities * MeSH
• Health Knowledge, Attitudes, Practice MeSH
• Check Tag
• Humans MeSH
• Male MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Retracted Publication MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Biomarkers MeSH

Red hair is associated in women with pain sensitivity. This medical condition, and perhaps others, seems facilitated by the combination of being red-haired and female. We tested this hypothesis by questioning a large sample of Czech and Slovak respondents about the natural redness and darkness of their hair, their natural eye color, their physical and mental health (24 categories), and other personal attributes (height, weight, number of children, lifelong number of sexual partners, frequency of smoking). Red-haired women did worse than other women in ten health categories and better in only three, being particularly prone to colorectal, cervical, uterine, and ovarian cancer. Red-haired men showed a balanced pattern, doing better than other men in three health categories and worse in three. Number of children was the only category where both male and female redheads did better than other respondents. We also confirmed earlier findings that red hair is naturally more frequent in women than in men. Of the 'new' hair and eye colors, red hair diverges the most from the ancestral state of black hair and brown eyes, being the most sexually dimorphic variant not only in population frequency but also in health status. This divergent health status may have one or more causes: direct effects of red hair pigments (pheomelanins) or their by-products; effects of other genes that show linkage with genes involved in pheomelanin production; excessive prenatal exposure to estrogen (which facilitates expression of red hair during fetal development and which, at high levels, may cause health problems later in life); evolutionary recentness of red hair and corresponding lack of time to correct negative side effects; or genetic incompatibilities associated with the allele Val92Met, which seems to be of Neanderthal origin and is one of the alleles that can cause red hair.

• MeSH
• Eye Color * MeSH
• Hair Color * MeSH
• Humans MeSH
• Sex Factors * MeSH
• Health Status * MeSH
• Check Tag
• Humans MeSH
• Male MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Geographicals
• Czech Republic MeSH
• Slovakia MeSH

BACKGROUND: A recent study performed on 1.3 million patients showed a strong association between being bitten by a cat and probability of being diagnosed with depression. Authors suggested that infection with cat parasite Toxoplasma could be the reason for this association. METHOD: A cross sectional internet study on a non-clinical population of 5,535 subjects was undertaken. RESULTS: The subjects that reported having been bitten by a dog and a cat or scratched by a cat have higher Beck depression score. They were more likely to have visited psychiatrists, psychotherapists and neurologists in past two years, to have been previously diagnosed with depression (but not with bipolar disorder). Multivariate analysis of models with cat biting, cat scratching, toxoplasmosis, the number of cats at home, and the age of subjects as independent variables showed that only cat scratching had positive effect on depression (p = 0.004). Cat biting and toxoplasmosis had no effect on the depression, and the number of cats at home had a negative effect on depression (p = 0.021). CONCLUSIONS: Absence of association between toxoplasmosis and depression and five times stronger association of depression with cat scratching than with cat biting suggests that the pathogen responsible for mood disorders in animals-injured subjects is probably not the protozoon Toxoplasma gondii but another organism; possibly the agent of cat-scratched disease - the bacteria Bartonella henselae.

• MeSH
• Bartonella henselae physiology   MeSH
• Depression microbiology   MeSH
• Cats MeSH
• Humans MeSH
• Multivariate Analysis MeSH
• Cat-Scratch Disease microbiology   MeSH
• Cross-Sectional Studies MeSH
• Dogs MeSH
• Animals MeSH
• Check Tag
• Cats MeSH
• Humans MeSH
• Male MeSH
• Dogs MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

Rhesus-positive and Rhesus-negative persons differ in the presence-absence of highly immunogenic RhD protein on the erythrocyte membrane. The biological function of the RhD molecule is unknown. Its structure suggests that the molecular complex with RhD protein transports NH3 or CO2 molecules across the erythrocyte cell membrane. Some data indicate that RhD positive and RhD negative subjects differ in their tolerance to certain biological factors, including, Toxoplasma infection, aging and fatique. Present cross sectional study performed on 3,130 subjects) showed that Rhesus negative subjects differed in many indices of their health status, including incidences of many disorders. Rhesus negative subjects reported to have more frequent allergic, digestive, heart, hematological, immunity, mental health, and neurological problems. On the population level, a Rhesus-negativity-associated burden could be compensated for, for example, by the heterozygote advantage, but for Rhesus negative subjects this burden represents a serious problem.

• MeSH
• Child MeSH
• Adult MeSH
• Genetic Predisposition to Disease MeSH
• Incidence MeSH
• Rh-Hr Blood-Group System genetics   MeSH
• Middle Aged MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Polymorphism, Genetic MeSH
• Cross-Sectional Studies MeSH
• Aged, 80 and over MeSH
• Aged MeSH
• Age Distribution MeSH
• Health Status MeSH
• Check Tag
• Child MeSH
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Male MeSH
• Aged, 80 and over MeSH
• Aged 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

BACKGROUND: Past research linked Toxoplasma gondii (TG) infection in humans with neurological and mental disorders (e.g., schizophrenia, Alzheimer's disease and attention disorders), irregularities of the dopaminergic and testosterone system, and increased likelihood of being involved in traffic accidents. METHODOLOGY/PRINCIPAL FINDINGS: We test for an association between TG infection and financial decision-making (DM) using a case-control design in a sample of female Czech students (n = 79). We estimate each subject's risk attitude and loss aversion using an experimental economic task involving real monetary incentives. We find no significant evidence that either measure of decision-making is associated with TG infection. CONCLUSION: We were unable to find evidence of an association between TG infection and financial decision-making in females.

• MeSH
• Adult MeSH
• Financial Management * MeSH
• Rh-Hr Blood-Group System genetics   immunology   MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Risk-Taking * MeSH
• Decision Making MeSH
• Sex Factors MeSH
• Case-Control Studies MeSH
• Toxoplasmosis complications   diagnosis   MeSH
• Check Tag
• Adult MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Rh-Hr Blood-Group System MeSH
• Rho(D) antigen MeSH Browser

BACKGROUND: About 30% of people on Earth have latent toxoplasmosis. Infected subjects do not express any clinical symptoms, however, they carry dormant stages of parasite Toxoplasma for the rest of their life. This form of toxoplasmosis is mostly considered harmless, however, recent studies showed its specific effects on physiology, behaviour and its associations with various diseases, including psychiatric disorders such as schizophrenia. Individuals who suffer from schizophrenia have about 2.7 times higher prevalence of Toxoplasma-seropositivity than controls, which suggests that some traits characteristic of schizophrenic patients, including the sex difference in schizophrenia onset, decrease of grey matter density in specific brain areas and modification of prepulse inhibition of startle reaction could in fact be caused by toxoplasmosis for those patients who are Toxoplasma-seropositive. METHODOLOGY/PRINCIPAL FINDINGS: We measured the effect of prepulse inhibition/facilitation of the startle reaction on reaction times. The students, 170 women and 66 men, were asked to react as quickly as possible to a startling acoustic signal by pressing a computer mouse button. Some of the startling signals were without the prepulse, some were 20 msec. preceded by a short (20 msec.) prepulse signal of lower intensity. Toxoplasma-seropositive subjects had longer reaction times than the controls. Acoustic prepulse shorted the reaction times in all subjects. This effect of prepulse on reaction times was stronger in male subjects and increased with the duration of infection, suggesting that it represented a cumulative effect of latent toxoplasmosis, rather than a fading out after effect of past acute toxoplasmosis. CONCLUSIONS: Different sensitivity of Toxoplasma-seropositive and Toxoplasma-seronegative subjects on effect of prepulses on reaction times (the toxoplasmosis-prepulse interaction) suggested, but of course did not prove, that the alternations of prepulse inhibition of startle reaction observed in schizophrenia patients probably joined the list of schizophrenia symptoms that are in fact caused by latent toxoplasmosis.

• MeSH
• Adult MeSH
• Humans MeSH
• Young Adult MeSH
• Reaction Time MeSH
• Schizophrenic Psychology MeSH
• Schizophrenia immunology   parasitology   physiopathology   MeSH
• Sex Factors MeSH
• Toxoplasma physiology   MeSH
• Toxoplasmosis immunology   parasitology   physiopathology   psychology   MeSH
• Reflex, Startle physiology   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

BACKGROUND: Toxoplasmosis, one of the most common zoonotic diseases worldwide, can induce various hormonal and behavioural alterations in infected hosts, and its most common form, latent toxoplasmosis, influences the course of pregnancy. Autoimmune thyroid diseases (AITD) belong to the well-defined risk factors for adverse pregnancy outcomes. The aim of this study was to investigate whether there is a link between latent toxoplasmosis and maternal AITD in pregnancy. METHODS: Cross-sectional study in 1248 consecutive pregnant women in the 9-12th gestational weeks. Serum thyroid-stimulating hormone (TSH), thyroperoxidase antibodies (TPOAb), and free thyroxine (FT4) were assessed by chemiluminescence; the Toxoplasma status was detected by the complement fixation test (CFT) and anti-Toxoplasma IgG enzyme-linked immunosorbent assay (ELISA). RESULTS: Overall, 22.5% of the women were positive for latent toxoplasmosis and 14.7% were screened positive for AITD. Women with latent toxoplasmosis had more often highly elevated TPOAb than the Toxoplasma-negative ones (p = 0.004), and latent toxoplasmosis was associated with decrease in serum TSH levels (p = 0.049). Moreover, we found a positive correlation between FT4 and the index of positivity for anti-Toxoplasma IgG antibodies (p = 0.033), which was even stronger in the TPOAb-positive Toxoplasma-positive women, (p = 0.014), as well as a positive correlation between FT4 and log2 CFT (p = 0.009). CONCLUSIONS: Latent toxoplasmosis was associated with a mild increase in thyroid hormone production in pregnancy. The observed Toxoplasma-associated changes in the parameters of AITD are mild and do not seem to be clinically relevant; however, they could provide new clues to the complex pathogenesis of autoimmune thyroid diseases.

• MeSH
• Autoimmune Diseases epidemiology   etiology   MeSH
• Autoantibodies blood   immunology   MeSH
• Adult MeSH
• Thyroid Hormones blood   MeSH
• Immunoglobulin G blood   immunology   MeSH
• Pregnancy Complications epidemiology   etiology   MeSH
• Middle Aged MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Thyroid Diseases epidemiology   etiology   MeSH
• Antibodies, Protozoan blood   immunology   MeSH
• Cross-Sectional Studies MeSH
• Risk Factors MeSH
• Pregnancy MeSH
• Toxoplasmosis complications   diagnosis   MeSH
• Pregnancy Outcome MeSH
• Check Tag
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Pregnancy MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Geographicals
• Czech Republic epidemiology   MeSH
• Names of Substances
• Autoantibodies MeSH
• Thyroid Hormones MeSH
• Immunoglobulin G MeSH
• Antibodies, Protozoan MeSH