"Latent" infection with Toxoplasma gondii: association with trait aggression and impulsivity in healthy adults

An inexpensive method to measure latent toxoplasmosis and its behavioral consequences

An estimated 2.4 billion humans are affected by the protozoan Toxoplasma gondii, which causes one of the most common infections influencing human behavior and cognition. The infection and its effects are severely underresearched, because the diagnosis is costly and time-intensive, preventing widespread testing, in particular in less-than-wealthy regions. Psychological methods such as response time analysis could circumvent these problems and facilitate more intensive research. We propose a psychological diagnostic method for latent toxoplasmosis using response times, hence enabling large-scale tests of psychological, psychiatrical, and behavioral effects. A clinical trial (N = 119) showed that the method is sensitive (92 %) and specific (97 %) compared to testing for Toxoplasma IgG Antibodies (p < 0.0001, w = 0.85). A representative UK survey (N = 2020) using this method confirmed previously-hypothesized behavioral effects and uncovered previously-unknown effects of latent toxoplasmosis infections which are relevant and pervasive, both psychologically (increase in risky behaviors, depression, anxiety, and stress) and economically (decrease in yearly income of 2500 GBP; decrease in employment of 11 %).

The Legalome: Microbiology, Omics and Criminal Justice

Advances in neuromicrobiology and related omics technologies have reinforced the idea that unseen microbes play critical roles in human cognition and behaviour. Included in this research is evidence indicating that gut microbes, through direct and indirect pathways, can influence aggression, anger, irritability and antisocial behaviour. Moreover, gut microbes can manufacture chemicals that are known to compromise cognition. For example, recent court decisions in the United States and Europe acknowledge that gut microbes can produce high levels of ethanol, without consumption of alcohol by the defendants. The dismissal of driving while intoxicated charges in these cases-so-called auto-brewery syndrome-highlights the way in which microbiome knowledge will enhance the precision, objectivity and fairness of our legal systems. Here in this opinion essay, we introduce the concept of the 'legalome'-the application of microbiome and omics science to forensic psychiatry and criminal law. We argue that the rapid pace of microbial discoveries, including those that challenge ideas of free will and moral responsibility, will necessitate a reconsideration of traditional legal doctrines and justifications of retributive punishment. The implications extend beyond the courtroom, challenging us to reconsider how environmental factors-from diet to socioeconomic conditions-might shape preventative and rehabilitative efforts through their effects on the microbiome.

Toxoplasma gondii, suicidal behaviour and suicide risk factors in US Veterans enrolled in mental health treatment

Markers of chronic infection Toxoplasma gondii (Nicolle et Manceaux, 1908) have been associated with suicidal self-directed violence (SSDV). We present the results of the first study relating T. gondii IgG serology with suicide attempts and suicidal ideation in United States Veterans, known to have higher suicide rates than members of the general population. We also related T. gondii serology to SSDV risk factors, including valid and reliable measures of trait impulsivity, aggression, self-reported depression, and sleep disturbance. We recruited 407 Veterans enrolled at three Veterans Affairs Medical Centers with mean (S.D.) age = 45.6 (11.6) years; 304 men (74.7%); 203 with a history of SSDV and 204 with no history of any self-directed violence (SDV). Seropositivity and serointensity, categorised as high (top quartile) or low (lower three quartiles), were analysed in relationship to SSDV, suicidal ideation and clinical risk factors using age and gender-adjusted linear and logistic methods, after transformations and nonparametric tests when appropriate. Associations between seropositivity and SSDV and its risk factors were not significant in all groups. High serointensity, while not associated with SSDV or repeat suicide attempts, was positively associated with suicidal ideation, depression, impulsivity, and daytime dysfunction due to sleepiness (p < 0.05), but only in Veterans with a history of SSDV. In Veterans without a history of SDV, no associations were significant. These associations remained significant after adjustment for certain socioeconomic factors (i.e., income, homelessness, military rank). Including education in the model downgraded the statistical significance of suicidal ideation and depression to statistical trends, but the significance of associations with impulsivity and daytime dysfunction due to sleepiness remained. Major limitations include the cross-sectional design, overall low seropositivity within the sample, and potentially spurious results due to multiple comparisons. Thus, the results of this report need to be replicated in larger samples, ideally longitudinally.

Alterations in gut microbiota contribute to cognitive deficits induced by chronic infection of Toxoplasma gondii

Chronic infection with Toxoplasma gondii (T. gondii) emerges as a risk factor for neurodegenerative diseases in animals and humans. However, the underlying mechanisms are largely unknown. We aimed to investigate whether gut microbiota and its metabolites play a role in T. gondii-induced cognitive deficits. We found that T. gondii infection induced cognitive deficits in mice, which was characterized by synaptic ultrastructure impairment and neuroinflammation in the hippocampus. Moreover, the infection led to gut microbiota dysbiosis, barrier integrity impairment, and inflammation in the colon. Interestingly, broad-spectrum antibiotic ablation of gut microbiota attenuated the adverse effects of the parasitic infection on the cognitive function in mice; cognitive deficits and hippocampal pathological changes were transferred from the infected mice to control mice by fecal microbiota transplantation. In addition, the abundance of butyrate-producing bacteria and the production of serum butyrate were decreased in infected mice. Interestingly, dietary supplementation of butyrate ameliorated T. gondii-induced cognitive impairment in mice. Notably, compared to the healthy controls, decreased butyrate production was observed in the serum of human subjects with high levels of anti-T. gondii IgG. Overall, this study demonstrates that gut microbiota is a key regulator of T. gondii-induced cognitive impairment.

Toxoplasma gondii infection and testosterone alteration: A systematic review and meta-analyses

BACKGROUND

Toxoplasma gondii (T. gondii) is a worldwide distributed protozoan parasite which has infected a wide range of warm-blooded animals and humans. The most common form of T. gondii infection is asymptomatic (latent); nevertheless, latent toxoplasmosis can induce various alterations of sex hormones, especially testosterone, in infected humans and animals. On the other hand, testosterone is involved in behavioral traits and reproductive functions in both sexes. Hence, the purpose of this systematic review is to summarize the available evidence regarding the association between T. gondii infection and testosterone alteration.

METHODS

In the setting of a systematic review, an electronic search (any date to 10 January 2023) without language restrictions was performed using Science Direct, Web of Science, PubMed, Scopus, and Google Scholar. The PRISMA guidelines were followed. Following the initial search, a total of 12,306 titles and abstracts were screened initially; 12,281 were excluded due to the lack of eligibility criteria or duplication. Finally, 24 articles met the included criteria. A mean±standard deviation (SD) was calculated to assess the difference of testosterone between T. gondii positive and T. gondii negative humans. The possibility of publication bias was assessed using Egger's regression. P-value < 0.05 was considered statistically significant.

RESULTS

This systematic review identified 24 articles (18 studies in humans and six studies in animals). Most human studies (13 out of 19) reported an increased level of testosterone following latent toxoplasmosis in males, while three studies reported decreased levels and two studies reported an insignificant change. Eleven articles (seven datasets in males and seven datasets in females) were eligible to be included in the data synthesis. Based on the random-effects model, the pooled mean± SD of testosterone in T. gondii positive than T. gondii negative was increased by 0.73 and 0.55 units in males and females, respectively. The Egger's regression did not detect a statistically significant publication bias in males and females (p = value = 0.95 and 0.71), respectively. Three studies in male animals (rats, mice, and spotted hyenas) and two studies in female animals (mice and spotted hyenas) reported a decline in testosterone in infected compared with non-infected animals. While, one study in female rats reported no significant changes of testosterone in infected than non-infected animals. Moreover, two studies in male rats reported an increased level of testosterone in infected than non-infected animals.

CONCLUSIONS

This study provides new insights about the association between T. gondii infection and testosterone alteration and identifies relevant data gaps that can inform and encourage further studies. The consequence of increased testosterone levels following T. gondii infection could partly be associated with increased sexual behavior and sexual transmission of the parasite. On the other hand, declining testosterone levels following T. gondii infection may be associated with male reproductive impairments, which were observed in T. gondii-infected humans and animals. Furthermore, these findings suggest the great need for more epidemiological and experimental investigations in depth to understand the relationship between T. gondii infection and testosterone alteration alongside with future consequences of testosterone alteration.

Genetic disruption of dopamine β-hydroxylase dysregulates innate responses to predator odor in mice

In rodents, exposure to predator odors such as cat urine acts as a severe stressor that engages innate defensive behaviors critical for survival in the wild. The neurotransmitters norepinephrine (NE) and dopamine (DA) modulate anxiety and predator odor responses, and we have shown previously that dopamine β-hydroxylase knockout (Dbh -/-), which reduces NE and increases DA in mouse noradrenergic neurons, disrupts innate behaviors in response to mild stressors such as novelty. We examined the consequences of Dbh knockout on responses to predator odor (bobcat urine) and compared them to Dbh-competent littermate controls. Over the first 10 min of predator odor exposure, controls exhibited robust defensive burying behavior, whereas Dbh -/- mice showed high levels of grooming. Defensive burying was potently suppressed in controls by drugs that reduce NE transmission, while excessive grooming in Dbh -/- mice was blocked by DA receptor antagonism. In response to a cotton square scented with a novel "neutral" odor (lavender), most control mice shredded the material, built a nest, and fell asleep within 90 min. Dbh -/- mice failed to shred the lavender-scented nestlet, but still fell asleep. In contrast, controls sustained high levels of arousal throughout the predator odor test and did not build nests, while Dbh -/- mice were asleep by the 90-min time point, often in shredded bobcat urine-soaked nesting material. Compared with controls exposed to predator odor, Dbh -/- mice demonstrated decreased c-fos induction in the anterior cingulate cortex, lateral septum, periaqueductal gray, and bed nucleus of the stria terminalis, but increased c-fos in the locus coeruleus and medial amygdala. These data indicate that relative ratios of central NE and DA signaling coordinate the type and valence of responses to predator odor.

Toxoplasma gondii infection in people with schizophrenia is related to higher hair glucocorticoid levels

Introduction

Toxoplasma gondii (TG) is a common protozoan parasite infecting approximately one third of the human population. Animal studies have shown that this parasite can manipulate its host behavior. Based on this, human studies have assessed if TG can be involved in mental health disorders associated with important behavioral modifications such as schizophrenia. However, results have been discrepant. Given that TG has a strong impact on fear and risk-taking processes in animal studies and that fear and risk-taking behaviors are associated with the human stress response, we tested whether glucocorticoid biomarkers (salivary and hair) differ in people with schizophrenia and controls as a function of TG status.

Methods

We measured TG antibodies in blood samples, as well as salivary and hair glucocorticoid levels in 226 people with schizophrenia (19.9% women, mean age = 39 years old) and 129 healthy individuals (controls) (45.7% women, mean age = 41 years old).

Results

The results showed that people with schizophrenia infected with TG presented significantly higher hair glucocorticoid concentrations than non-infected people with schizophrenia. This effect was not found in control participants. No effect was observed for salivary glucocorticoid levels. Additionally, there were no associations between TG infection and positive psychotic symptoms nor impulsivity.

Discussion

These results show that people with schizophrenia present high levels of hair glucocorticoid levels only when they are infected with TG. Further studies performed in populations suffering from other mental health disorders are needed to determine if this effect is specific to schizophrenia, or whether it is generalized across mental health disorders.

Genetic disruption of dopamine β-hydroxylase dysregulates innate responses to predator odor in mice

In rodents, exposure to predator odors such as cat urine acts as a severe stressor that engages innate defensive behaviors critical for survival in the wild. The neurotransmitters norepinephrine (NE) and dopamine (DA) modulate anxiety and predator odor responses, and we have shown previously that dopamine β-hydroxylase knockout (Dbh -/-), which reduces NE and increases DA in mouse noradrenergic neurons, disrupts innate behaviors in response to mild stressors such as novelty. We examined the consequences of Dbh knockout (Dbh -/-) on responses to predator odor (bobcat urine) and compared them to Dbh-competent littermate controls. Over the first 10 min of predator odor exposure, controls exhibited robust defensive burying behavior, whereas Dbh -/- mice showed high levels of grooming. Defensive burying was potently suppressed in controls by drugs that reduce NE transmission, while excessive grooming in Dbh -/- mice was blocked by DA receptor antagonism. In response to a cotton square scented with a novel "neutral" odor (lavender), most control mice shredded the material, built a nest, and fell asleep within 90 min. Dbh -/- mice failed to shred the lavender-scented nestlet, but still fell asleep. In contrast, controls sustained high levels of arousal throughout the predator odor test and did not build nests, while Dbh -/- mice were asleep by the 90-min time point, often in shredded bobcat urine-soaked nesting material. Compared with controls exposed to predator odor, Dbh -/- mice demonstrated decreased c-fos induction in the anterior cingulate cortex, lateral septum, periaqueductal gray, and bed nucleus of the stria terminalis, but increased c-fos in the locus coeruleus and medial amygdala. These data indicate that relative ratios of central NE and DA signaling coordinate the type and valence of responses to predator odor.

Genetic diversity of Toxoplasma gondii in South America: occurrence, immunity, and fate of infection

Toxoplasma gondii is an intracellular parasite with a worldwide distribution. Toxoplasma gondii infections are of great concern for public health, and their impact is usually most severe in pregnant women and their foetuses, and in immunocompromised individuals. Displaying considerable genetic diversity, T. gondii strains differ widely according to geographical location, with archetypal strains predominantly found in the Northern Hemisphere and non-archetypal (atypical) strains, with highly diverse genotypes, found mainly in South America. In this review, we present an overview of the identification and distribution of non-archetypal strains of T. gondii. Special attention is paid to the strains that have been isolated in Brazil, their interaction with the host immunological response, and their impact on disease outcomes. The genetic differences among the strains are pivotal to the distinct immunological responses that they elicit. These differences arise from polymorphisms of key proteins released by the parasite, which represent important virulence factors. Infection with divergent non-archetypal strains can lead to unusual manifestations of the disease, even in immunocompetent individuals.

Toxoplasma gondii, a plea for a thorough investigation of its oncogenic potential

It is estimated that 30 % of the world's population harbours the parasite Toxoplasma gondii, particularly in the brain. Beyond its implication in potentially severe opportunistic or congenital infections, this persistence has long been considered as without consequence. However, certain data in animals and humans suggest that this carriage may be linked to various neuropsychiatric or neurodegenerative disorders. The hypothesis of a potential cerebral oncogenicity of the parasite is also emerging. In this personal view, we will present the epidemiological arguments in favour of an association between toxoplasmosis and cerebral malignancy, before considering the points that could underlie a potential causal link. More specifically, we will focus on the brain as the preferred location for T. gondii persistence and the propensity of this parasite to interfere with the apoptosis and cell cycle signalling pathways of their host cell.

Pharmacological Mechanism of Ketamine in Suicidal Behavior Based on Animal Models of Aggressiveness and Impulsivity: A Narrative Review

Around 700,000 people die from suicide each year in the world. Approximately 90% of suicides have a history of mental illness, and more than two-thirds occur during a major depressive episode. Specific therapeutic options to manage the suicidal crisis are limited and measures to prevent acting out also remain limited. Drugs shown to reduce the risk of suicide (antidepressants, lithium, or clozapine) necessitate a long delay of onset. To date, no treatment is indicated for the treatment of suicidality. Ketamine, a glutamate NMDA receptor antagonist, is a fast-acting antidepressant with significant effects on suicidal ideation in the short term, while its effects on suicidal acts still need to be demonstrated. In the present article, we reviewed the literature on preclinical studies in order to identify the potential anti-suicidal pharmacological targets of ketamine. Impulsive-aggressive traits are one of the vulnerability factors common to suicide in patients with unipolar and bipolar depression. Preclinical studies in rodent models with impulsivity, aggressiveness, and anhedonia may help to analyze, at least in part, suicide neurobiology, as well as the beneficial effects of ketamine/esketamine on reducing suicidal ideations and preventing suicidal acts. The present review focuses on disruptions in the serotonergic system (5-HT_B receptor, MAO-A enzyme), neuroinflammation, and/or the HPA axis in rodent models with an impulsive/aggressive phenotype, because these traits are critical risk factors for suicide in humans. Ketamine can modulate these endophenotypes of suicide in human as well as in animal models. The main pharmacological properties of ketamine are then summarized. Finally, numerous questions arose regarding the mechanisms by which ketamine may prevent an impulsive-aggressive phenotype in rodents and suicidal ideations in humans. Animal models of anxiety/depression are important tools to better understand the pathophysiology of depressed patients, and in helping develop novel and fast antidepressant drugs with anti-suicidal properties and clinical utility.

Chronic Toxoplasma gondii infection contributes to perineuronal nets impairment in the primary somatosensory cortex

Toxoplasma gondii is able to manipulate the host immune system to establish a persistent and efficient infection, contributing to the development of brain abnormalities with behavioral repercussions. In this context, this work aimed to evaluate the effects of T. gondii infection on the systemic inflammatory response and structure of the primary somatosensory cortex (PSC). C57BL/6 and BALB/c mice were infected with T. gondii ME49 strain tissue cysts and accompanied for 30 days. After this period, levels of cytokines IFN-γ, IL-12, TNF-α and TGF-β were measured. After blood collection, mice were perfused and the brains were submitted to immunohistochemistry for perineuronal net (PNN) evaluation and cyst quantification. The results showed that C57BL/6 mice presented higher levels of TNF-α and IL-12, while the levels of TGF-β were similar between the two mouse lineages, associated with the elevated number of tissue cysts, with a higher occurrence of cysts in the posterior area of the PSC when compared to BALB/c mice, which presented a more homogeneous cyst distribution. Immunohistochemistry analysis revealed a greater loss of PNN labeling in C57BL/6 animals compared to BALB/c. These data raised a discussion about the ability of T. gondii to stimulate a systemic inflammatory response capable of indirectly interfering in the brain structure and function.

Back to the Future: The Role of Infections in Psychopathology. Focus on OCD

OBJECTIVE

Recently, there has been a resurgence of interest in the relationship between infections and psychopathology, given the increasing data on the neurotropism and neurological/psychiatric morbidity of the SARS-COV2 virus, responsible for the current worldwide pandemic. Although the majority of observations were those obtained in mood and schizophrenic disorders, a few data are also available on the presence of bacterial or viral infections in patients suffering from obsessive-compulsive disorder (OCD). Therefore, given the limited information, the present paper aimed at reviewing the most updated evidence of infections in neuropsychiatric disorders and their possible mechanisms of actions, with a narrow focus on microbes in OCD.

METHOD

This paper is a narrative review. The databases of PubMed, Scopus, Embase, PsycINFO and Google Scholar were accessed to research and collect English language papers published between 1 January 1980 and 31 December 2021. The data on PANDAS/PANS and those observed during severe brain infections were excluded.

RESULTS

Several pathogens have been associated with an increased risk to develop a broad spectrum of neuropsychiatric conditions, such as schizophrenia, mood disorders, autism, attention-deficit/hyperactivity disorder, anorexia nervosa, and post-traumatic stress disorder. Some evidence supported a possible role of infections also in the pathophysiology of OCD. Infections from Herpes simplex virus 1, Borna disease virus, Group A-Beta Hemolytic Streptococcus, Borrelia spp., and Toxoplasma gondii were actually found in patients with OCD. Although different mechanisms have been hypothesized, all would converge to trigger functional/structural alterations of specific circuits or immune processes, with cascade dysfunctions of several other systems.

CONCLUSIONS

Based on the current evidence, a possible contribution of different types of microbes has been proposed for different neuropsychiatric disorders including OCD. However, the currently available literature is meager and heterogeneous in terms of sample characteristics and methods used. Therefore, further studies are needed to better understand the impact of infectious agents in neuropsychiatric disorders. Our opinion is that deeper insights in this field might contribute to a better definition of biological underpinnings of specific clinical pictures, as well as to promote psychiatric precision medicine, with treatments based on altered pathological pathways of single patients. This might be particularly relevant in OCD, a disorder with a high proportion of patients who are resistant or do not respond to conventional therapeutic strategies.

Le Petit Machiavellian Prince: Effects of Latent Toxoplasmosis on Political Beliefs and Values

Humans infected by Toxoplasma gondii express no specific symptoms but manifest higher incidence of many diseases, disorders and differences in personality and behavior. The aim of this study was to compare the political beliefs and values of Toxoplasma-infected and Toxoplasma-free participants. We measured beliefs and values of 2315 responders via an online survey (477 Toxoplasma-infected) using the Political Beliefs and Values Inventory (PI34). This study showed Toxoplasma-infected and Toxoplasma-free participants of our cross-sectional study differed in three of four factors of PI34, scoring higher in Tribalism and lower in Cultural liberalism and Anti-Authoritarianism. We found sex differences in political beliefs associated with Toxoplasma infection. Infected women scored higher in tribalism and lower in cultural liberalism, compared with the Toxoplasma-free control group, while infected men scored higher in economic equity. These results fit with sexual differences in behavior and attitude observed after toxoplasmosis infection. Controlling for the effect of worse physical health and mental health had little impact, suggesting that impaired health did not cause these changes. Rather than adaptation to prevalence of parasites, as suggested by parasite-stress theory, the differences might be side-effects of long-term mild inflammatory reaction. However, to get clear picture of the mild inflammation effects, more research focused on different infectious diseases is needed.

The emerging paradigm of calcium homeostasis as a new therapeutic target for protozoan parasites

Calcium channels (CCs), a group of ubiquitously expressed membrane proteins, are involved in many pathophysiological processes of protozoan parasites. Our understanding of CCs in cell signaling, organelle function, cellular homeostasis, and cell cycle control has led to improved insights into their structure and functions. In this article, we discuss CCs characteristics of five major protozoan parasites Plasmodium, Leishmania, Toxoplasma, Trypanosoma, and Cryptosporidium. We provide a comprehensive review of current antiparasitic drugs and the potential of using CCs as new therapeutic targets. Interestingly, previous studies have demonstrated that human CC modulators can kill or sensitize parasites to antiparasitic drugs. Still, none of the parasite CCs, pumps, or transporters has been validated as drug targets. Information for this review draws from extensive data mining of genome sequences, chemical library screenings, and drug design studies. Parasitic resistance to currently approved therapeutics is a serious and emerging threat to both disease control and management efforts. In this article, we suggest that the disruption of calcium homeostasis may be an effective approach to develop new anti-parasite drug candidates and reduce parasite resistance.

Association between Toxoplasma gondii Infection in Brain and a History of Depression in Suicide Decedents: A Cross-Sectional Study

We assessed the association between Toxoplasma gondii (T. gondii) infection of the central nervous system and suicide correlates in suicide decedents. Eighty-seven decedents who died by suicide received in a forensic setting for medico-legal autopsies in Mexico City were studied. Two samples of brain (amygdala and prefrontal cortex) from each decedent were examined for detection of T. gondii using immunohistochemistry. Correlates of suicide including a history of previous suicide attempts, co-morbid mental disorder, consumption of alcohol or tobacco, irritability and aggression, economic problems, presence of drugs or alcohol in blood and suicide method were obtained and analyzed for their association with T. gondii infection. T. gondii immunohistochemistry was positive in prefrontal cortex sections in 6 decedents and in an amygdala section in one decedent. Thus, the prevalence of T. gondii infection in brain in suicide victims was 8.0% (7/87). Bivariate and logistic regression analysis of suicide correlates showed that only a history of depression was associated with T. gondii infection of the brain in suicide victims (OR: 12.00; 95% CI: 2.26–63.46; p = 0.003). Our results provide evidence that T. gondii infection in brain is associated with a history of depression in suicide decedents.

Cross-sectional association of Toxoplasma gondii exposure with BMI and diet in US adults

Toxoplasmosis gondii exposure has been linked to increased impulsivity and risky behaviors, which has implications for eating behavior. Impulsivity and risk tolerance is known to be related with worse diets and a higher chance of obesity. There is little known, however, about the independent link between Toxoplasma gondii (T. gondii) exposure and diet-related outcomes. Using linear and quantile regression, we estimated the relationship between T. gondii exposure and BMI, total energy intake (kcal), and diet quality as measured by the Health Eating Index-2015 (HEI) among 9,853 adults from the 2009–2014 National Health and Nutrition Examination Survey. Previous studies have shown different behavioral responses to T. gondii infection among males and females, and socioeconomic factors are also likely to be important as both T. gondii and poor diet are more prevalent among U.S. populations in poverty. We therefore measured the associations between T. gondii and diet-related outcomes separately for men and women and for respondents in poverty. Among females <200% of the federal poverty level Toxoplasmosis gondii exposure was associated with a higher BMI by 2.0 units (95% CI [0.22, 3.83]) at median BMI and a lower HEI by 5.05 units (95% CI [-7.87, -2.24]) at the 25^th percentile of HEI. Stronger associations were found at higher levels of BMI and worse diet quality among females. No associations were found among males. Through a detailed investigation of mechanisms, we were able to rule out T. gondii exposure from cat ownership, differing amounts of meat, and drinking water source as potential confounding factors; environmental exposure to T. gondii as well as changes in human behavior due to parasitic infection remain primary mechanisms.

Toxoplasmosis gondii (T. gondii) is a parasite that infects over 10 percent of the US population. T. gondii infection can cause serious health problems for some people, but most infections remain undiagnosed and subclinical. When an individual is infected, T. gondii can chronically reside in muscle and central nervous system (including brain) tissue. Previous studies have found that individuals with prior exposure to T. gondii may engage in more risky and impulsive behaviors, and risk tolerance and impulsivity may be related with individual’s diet. Our study examines whether individuals with T. gondii exposure have higher body mass index (BMI) and worse diets. We further discuss and test for alternative explanations that prevent us from establishing a causal relationship between T. gondii and BMI/diet. Overall, our results show that T. gondii exposure is related with higher BMI and worse diets among lower-income females in the US. Our results uncover a novel correlate of BMI and diets, and suggest the importance of investigating the broader public health impacts of chronic T. gondii infection.

Toxoplasma gondii seropositivity in patients with depressive and anxiety disorders

Introduction

Toxoplasma gondii (T. gondii) is an obligate intracellular parasite that is estimated to be carried by one-third of the world population. Latent T. gondii infection has been linked to several neuropsychiatric mood disorders and behaviors. The aim of the present study was to examine whether T. gondii seropositivity is associated with affective disorders, as well as with aggression reactivity and suicidal thoughts.

Methods

In the Netherlands Study of Depression and Anxiety (NESDA), T. gondii antibodies were assessed in patients with current depressive (n ​= ​133), anxiety (n ​= ​188), comorbid depressive and anxiety (n ​= ​148), and remitted disorders (n ​= ​889), as well as in healthy controls (n ​= ​373) based on DSM-IV criteria. Seropositivity was analyzed in relation to disorder status, aggression reactivity and suicidal thoughts using multivariate analyses of covariance and regression analyses.

Results

Participants were on average 51.2 years (SD ​= ​13.2), and 64.4% were female. Seropositivity was found in 673 participants (38.9%). A strong positive association between T. gondii seropositivity and age was observed. No significant associations were found between T. gondii seropositivity and disorder status, aggression reactivity and suicidal thoughts. The adjusted odds ratio (OR) for any remitted disorder versus controls was 1.13 (95% CI: 0.87-1.49), and for any current disorder versus controls was 0.94 (95% CI: 0.69-1.28).

Conclusions

No evidence was found for a relationship between affective disorders and T. gondii infection in the current sample.

Three genetic-environmental networks for human personality

Phylogenetic, developmental, and brain-imaging studies suggest that human personality is the integrated expression of three major systems of learning and memory that regulate (1) associative conditioning, (2) intentionality, and (3) self-awareness. We have uncovered largely disjoint sets of genes regulating these dissociable learning processes in different clusters of people with (1) unregulated temperament profiles (i.e., associatively conditioned habits and emotional reactivity), (2) organized character profiles (i.e., intentional self-control of emotional conflicts and goals), and (3) creative character profiles (i.e., self-aware appraisal of values and theories), respectively. However, little is known about how these temperament and character components of personality are jointly organized and develop in an integrated manner. In three large independent genome-wide association studies from Finland, Germany, and Korea, we used a data-driven machine learning method to uncover joint phenotypic networks of temperament and character and also the genetic networks with which they are associated. We found three clusters of similar numbers of people with distinct combinations of temperament and character profiles. Their associated genetic and environmental networks were largely disjoint, and differentially related to distinct forms of learning and memory. Of the 972 genes that mapped to the three phenotypic networks, 72% were unique to a single network. The findings in the Finnish discovery sample were blindly and independently replicated in samples of Germans and Koreans. We conclude that temperament and character are integrated within three disjoint networks that regulate healthy longevity and dissociable systems of learning and memory by nearly disjoint sets of genetic and environmental influences.

Environmental Risk Factors for Schizophrenia and Bipolar Disorder and Their Relationship to Genetic Risk: Current Knowledge and Future Directions

Schizophrenia (SZ) and bipolar disorder (BD) are severe psychiatric disorders which result from complex interplay between genetic and environmental factors. It is well-established that they are highly heritable disorders, and considerable progress has been made identifying their shared and distinct genetic risk factors. However, the 15-40% of risk that is derived from environmental sources is less definitively known. Environmental factors that have been repeatedly investigated and often associated with SZ include: obstetric complications, infections, winter or spring birth, migration, urban living, childhood adversity, and cannabis use. There is evidence that childhood adversity and some types of infections are also associated with BD. Evidence for other risk factors in BD is weaker due to fewer studies and often smaller sample sizes. Relatively few environmental exposures have ever been examined for SZ or BD, and additional ones likely remain to be discovered. A complete picture of how genetic and environmental risk factors confer risk for these disorders requires an understanding of how they interact. Early gene-by-environment interaction studies for both SZ and BD often involved candidate genes and were underpowered. Larger samples with genome-wide data and polygenic risk scores now offer enhanced prospects to reveal genetic interactions with environmental exposures that contribute to risk for these disorders. Overall, although some environmental risk factors have been identified for SZ, few have been for BD, and the extent to which these account for the total risk from environmental sources remains unknown. For both disorders, interactions between genetic and environmental risk factors are also not well understood and merit further investigation. Questions remain regarding the mechanisms by which risk factors exert their effects, and the ways in which environmental factors differ by sex. Concurrent investigations of environmental and genetic risk factors in SZ and BD are needed as we work toward a more comprehensive understanding of the ways in which these disorders arise.

Potential linkage between Toxoplasma gondii infection and physical education scores of college students

Objective

Toxoplasma gondii is a worldwide protozoan parasite that could infect virtually all warm-blooded animals, including humans. Our study aimed to investigate the prevalence of T. gondii infection in college students at Anhui province, China and to assess risk factors for T. gondii infection in college students. Moreover, growing studies demonstrated the association between T. gondii infection and host behavioral changes. We also studied the linkage between T. gondii and physical education (PE) scores of college students.

Methods

A total of 2704 serum samples of medical school students attending physical education lessons were collected from September 2017 to September 2019 and evaluated for T. gondii IgG antibodies using an enzyme-linked immunosorbent assay (ELISA). Questionnaires and statistical analysis were used to determine the risk factors for T. gondii infection. We also analysed PE scores of T. gondii -infected students and T. gondii-uninfected students.

Results

The overall seroprevalence of T. gondii was 11.5%. The main risk factors related to T. gondii infection in college students were cat in the household and gardening or agriculture activity. Furthermore, in the basketball group and the soccer group, scores of T. gondii seropositive students were significantly higher than those of seronegative students, while in other sports there was no difference between scores of T. gondii-infected students and T. gondii uninfected students.

Conclusion

This is the first report of T. gondii seroprevalence in college students in Anhui province, China.

Latent Toxoplasma gondii infections are associated with elevated biomarkers of inflammation and vascular injury

BACKGROUND

Toxoplasma gondii is a protozoan parasite that infects cats as definitive hosts and other warm-blooded animals including humans as intermediate hosts. It forms infectious cysts in the brain, muscle and other tissues establishing life-long latent infection. Approximately 10% of the US population is infected. While latent infections are largely asymptomatic, they are associated with neurological deficits and elevated risks of neuropsychiatric diseases.

METHODS

This cross-sectional epidemiological study investigated associations of T. gondii infections with biomarkers of inflammation and vascular injury: soluble intercellular adhesion molecule 1 (ICAM-1), soluble vascular cell adhesion molecule 1 (VCAM-1), C-reactive protein (CRP), and serum amyloid A (SAA). Serum samples from 694 adults in the Raleigh-Durham-Chapel Hill, North Carolina metropolitan area were tested for IgG antibody response to T. gondii, and for the above biomarkers using commercially available assays.

RESULTS

T. gondii seroprevalence rate in this sample was 9.7%. Seropositivity was significantly associated with 11% (95% confidence limits 4, 20%) greater median levels of VCAM-1 (p = 0.003), and marginally significantly with 9% (1, 17%), and 36% (1, 83%) greater median levels of ICAM-1, and CRP, respectively (p = 0.04 for each) after adjusting for sociodemographic and behavioral covariates, while the 23% (- 7, 64%) adjusted effect on SAA was not statistically significant (p = 0.15).

CONCLUSIONS

Latent infections with T. gondii are associated with elevated biomarkers of chronic inflammation and vascular injury that are also known to be affected by ambient air pollution.

Correlation of Suicidal Thoughts and Toxoplasmosis in Patients With Depression

Objective

We investigated the correlation between serum anti-Toxplasma gondii IgG and suicidal thoughts in depressive patients.

Methods

Depressive patients with (n = 100) and without (n = 100) suicidal thoughts along with 100 healthy control subjects were recruited for this study. In all three groups, a semi-structured clinical interview form called Structured Clinical Interview for DSM-IV (Diagnostic and Statistical Manual of Mental Disorders) Axis-I Disorder (SCID-I), Hamilton Depression Rating Scale (HAMD), suicidal behavior scale, and a sociodemographic data form were completed. Sera from all participants were taken, and anti-toxoplasma IgG was measured by Enzyme Linked Immunosorbent Assay (ELISA)-Chemiluminescent Microparticle Immunoassay. Statistical analysis of the data was performed.

Results

The serum anti-toxoplasma IgG levels of patients with suicidal thoughts were significantly higher than those without suicidal thoughts and the controls, which were 80.04 ± 40.66, 78 ± 14.82, and 19.98 ± 14.65, respectively, p < 0.001. There was no correlation between toxoplasma IgG and HAMD score in patients lacking suicidal thoughts (r = -0.112, p = 0.463).

Conclusion

This study shows a correlation between seropositivity for anti-Toxoplasma gondii IgG and depression with suicidal thoughts.

Toxoplasma gondii and Psychopathology: Latent Infection Is Associated with Interpersonal Sensitivity, Psychoticism, and Higher Testosterone Levels in Men, but Not in Women

Objective

The ability of parasites to hijack the nervous system, manipulating the host’s physiology and behavior in ways that enhance the parasite’s fitness while damaging host fitness, is a topic of ongoing research interest in evolutionary biology, but is largely overlooked in mental health research. Nevertheless, recent evidence has shown that Toxoplasma gondii infection can change host testosterone levels and influence the development of some psychiatric disorders. Here, we tested this hypothesis in a mixed sample of 213 non-clinical subjects.

Methods

Participants (nmales = 108, nfemales = 105) provided 5 ml of blood to quantify testosterone levels and Toxoplasma gondii antibodies. The Symptom Checklist-90-Revised was used to assess psychopathological symptoms.

Results

The results showed that Toxoplasma-infected men had higher testosterone levels and scored higher in Interpersonal Sensitivity and Psychoticism symptoms than non-infected men. Toxoplasma-infected women did not differ from control women.

Conclusions

Framed in an evolutionary framework, the findings suggest that the elevated testosterone levels and the expression of psychopathological symptoms can be seen as the result of the manipulation exerted by Toxoplasma gondii either to reach its definitive host or to increase its spread. Future research can benefit from integrating insights from evolutionary biology and parasite-host interactions with physiology, immunology, and mental health to develop a better understanding of mental health etiology.

Toxoplasma gondii, Suicidal Behavior, and Intermediate Phenotypes for Suicidal Behavior

Within the general literature on infections and suicidal behavior, studies on Toxoplasma gondii (T. gondii) occupy a central position. This is related to the parasite's neurotropism, high prevalence of chronic infection, as well as specific and non-specific behavioral alterations in rodents that lead to increased risk taking, which are recapitulated in humans by T. gondii's associations with suicidal behavior, as well as trait impulsivity and aggression, mental illness and traffic accidents. This paper is a detailed review of the associations between T. gondii serology and suicidal behavior, a field of study that started 15 years ago with our publication of associations between T. gondii IgG serology and suicidal behavior in persons with mood disorders. This "legacy" article presents, chronologically, our primary studies in individuals with mood disorders and schizophrenia in Germany, recent attempters in Sweden, and in a large cohort of mothers in Denmark. Then, it reviews findings from all three meta-analyses published to date, confirming our reported associations and overall consistent in effect size [ranging between 39 and 57% elevation of odds of suicide attempt in T. gondii immunoglobulin (IgG) positives]. Finally, the article introduces certain links between T. gondii and biomarkers previously associated with suicidal behavior (kynurenines, phenylalanine/tyrosine), intermediate phenotypes of suicidal behavior (impulsivity, aggression) and state-dependent suicide risk factors (hopelessness/dysphoria, sleep impairment). In sum, an abundance of evidence supports a positive link between suicide attempts (but not suicidal ideation) and T. gondii IgG (but not IgM) seropositivity and serointensity. Trait impulsivity and aggression, endophenotypes of suicidal behavior have also been positively associated with T. gondii seropositivity in both the psychiatrically healthy as well as in patients with Intermittent Explosive Disorder. Yet, causality has not been demonstrated. Thus, randomized interventional studies are necessary to advance causal inferences and, if causality is confirmed, to provide hope that an etiological treatment for a distinct subgroup of individuals at an increased risk for suicide could emerge.

Parasite infection disrupts escape behaviours in fish shoals

Many prey species have evolved collective responses to avoid predation. They rapidly transfer information about potential predators to trigger and coordinate escape waves. Predation avoidance behaviour is often manipulated by trophically transmitted parasites, to facilitate their transmission to the next host. We hypothesized that the presence of infected, behaviourally altered individuals might disturb the spread of escape waves. We used the tapeworm Schistocephalus solidus, which increases risk-taking behaviour and decreases social responsiveness of its host, the three-spined stickleback, to test this hypothesis. Three subgroups of sticklebacks were placed next to one another in separate compartments with shelter. The middle subgroup contained either uninfected or infected sticklebacks. We confronted an outer subgroup with an artificial bird strike and studied how the escape response spread through the subgroups. With uninfected sticklebacks in the middle, escape waves spread rapidly through the entire shoal and fish remained in shelter thereafter. With infected sticklebacks in the middle, the escape wave was disrupted and uninfected fish rarely used the shelter. Infected individuals can disrupt the transmission of flight responses, thereby not only increasing their own predation risk but also that of their uninfected shoal members. Our study uncovers a potentially far-reaching fitness consequence of grouping with infected individuals.

A history of juvenile mild malaria exacerbates chronic stress-evoked anxiety-like behavior, neuroinflammation, and decline of adult hippocampal neurogenesis in mice

Children residing in high malaria transmission regions are particularly susceptible to malaria. This early-life window is also a critical period for development and maturation of the nervous system, and inflammatory insults during this period may evoke a persistent increase in vulnerability for psychopathology. We employed a two-hit model of juvenile mild malaria and a two-week chronic unpredictable mild stress (CUMS) regime, commencing 60 days post-parasite clearance, to assess whether a history of juvenile infection predisposed the mice towards mood-related behavioral alterations and neurocognitive deficits. We showed that adult mice with a history of juvenile malaria (A-H/JMAL) exhibited heightened CUMS-associated anxiety-like behavior, with no observable change in cognitive behavior. In contrast, mice with a history of adult malaria did not exhibit such enhanced stress vulnerability. At baseline, A-H/JMAL mice showed increased activated microglia within the hippocampal dentate gyrus subfield. This was accompanied by a decrease in proliferating neuronal progenitors, with total number of immature hippocampal neurons unaltered. This neuroinflammatory and neurogenic decline was further exacerbated by CUMS. At day-14 post-CUMS, hippocampi of A-H/JMAL mice showed significantly higher microglial activation, and a concomitant decrease in progenitor proliferation and number of immature neurons. Taken together, these results suggest that a history of juvenile mild malaria leaves a neuroinflammatory mark within the hippocampal niche, and this may contribute to a heightened stress response in adulthood. Our findings lend credence to the idea that the burden of malaria in early-life results in sustained CNS changes that could contribute to increased vulnerability to adult-onset neuronal insults.

Catastrophic consequences: can the feline parasite Toxoplasma gondii prompt the purrfect neuroinflammatory storm following traumatic brain injury?

Traumatic brain injury (TBI) is one of the leading causes of morbidity and mortality worldwide; however, treatment development is hindered by the heterogenous nature of TBI presentation and pathophysiology. In particular, the degree of neuroinflammation after TBI varies between individuals and may be modified by other factors such as infection. Toxoplasma gondii, a parasite that infects approximately one-third of the world’s population, has a tropism for brain tissue and can persist as a life-long infection. Importantly, there is notable overlap in the pathophysiology between TBI and T. gondii infection, including neuroinflammation. This paper will review current understandings of the clinical problems, pathophysiological mechanisms, and functional outcomes of TBI and T. gondii, before considering the potential synergy between the two conditions. In particular, the discussion will focus on neuroinflammatory processes such as microglial activation, inflammatory cytokines, and peripheral immune cell recruitment that occur during T. gondii infection and after TBI. We will present the notion that these overlapping pathologies in TBI individuals with a chronic T. gondii infection have the strong potential to exacerbate neuroinflammation and related brain damage, leading to amplified functional deficits. The impact of chronic T. gondii infection on TBI should therefore be investigated in both preclinical and clinical studies as the possible interplay could influence treatment strategies.

Neuroprotective role of resveratrol mediated by purinergic signalling in cerebral cortex of mice infected by Toxoplasma gondii

The central nervous system of the intermediate host plays a central role in lifelong persistence of Toxoplasma gondii as well as the pathogenesis of congenital toxoplasmosis and reactivated infection in immunocompromised individuals. The purinergic system has been implicated in a wide range of immunological pathways for controlling intracellular responses to pathogens, including T. gondii. In the present study, we investigated the effect of resveratrol (RSV) on ectonucleotidases, adenosine deaminase (ADA), and purinergic receptors during chronic infection by T. gondii. For this study, Swiss mice were divided into control (CTL), resveratrol (RSV), infected (INF), and INF+RSV groups. The animals were orally infected with the VEG strain and treated with RSV (100 mg/kg, orally). Ectonucleotidase activities, P2X₇, P2Y₁, A1, and A_2A purinergic receptor density, ROS, and thiobarbituric acid reactive substances levels were measured in the cerebral cortex of mice. T. gondii infection increased NTPDase and reduced ADA activities. Treatment with RSV also affected enzymes hydrolysing extracellular nucleotides and nucleosides. Finally, RSV affected P1 and P2 purinergic receptor expression during T. gondii infection. Overall, RSV-mediated beneficial changes in purinergic signalling and oxidative stress, possibly improving cerebral cortex homeostasis in T. gondii infection.

Infection during childhood and the risk of violent criminal behavior in adulthood

Infections during brain development appear to contribute to cognitive impairment and aggressive behavior, as well as to a number of developmental mental disorders closely associated with violent criminal behavior. Yet, no study has thus far ever investigated whether infections during brain development increases the risk of violent criminality later in life. In this population-based cohort study, about 2.2 million individuals born in Sweden between the years 1973 and 1995 were included in an effort to estimate the association between infections during childhood (registered ICD-10 diagnoses of infections incurred before the age of 14 years) and violent criminal behavior (registered convictions for a violent crime between the ages of 15 and 38 years, prior to December 31, 2011). After inclusion of several sociodemographic parameters, risks of violent criminal behavior conferred by childhood infections - expressed as hazard ratios (HRs) and 95% confidence intervals (CIs) - were calculated by means of Cox regression. Mediation analyses were performed to explore the effect of psychiatric disorders on the association between infections during childhood and violent criminality. Results revealed a modest, yet significant, association between an infection during childhood and violent criminality later in life (adjusted HR 1.14, 95% CI 1.12-1.16). Infections during the first year of life and infections in the central nervous system were associated with the highest risks of subsequent violent criminality (adjusted HR 1.20, 95% CI 1.18-1.23, and adjusted HR 1.17, 95% CI 1.08-1.26, respectively). The association was partly mediated by the presence of a psychiatric disorder. In summary, independent of a wide range of covariates, our results suggest that infections during brain development could be part of the genesis of violent criminal behavior.

[Toxoplasmosis and behavioural changes (French translation of the article)]

Nearly one-third of the planet's population is affected by T. gondii infection. In ophthalmology, toxoplasmosis is even considered to be the most common cause of posterior uveitis of infectious origin. Humans are only an intermediate host, and T. gondii needs to infect cats for its sexual reproduction. All the elements increasing the risk of predation by the definitive host are then favourable to the parasite. Numerous experimental animal model studies have shown that T. gondii infection is associated with predatory risk behaviours such as an attraction of infected mice to cat urine. Infection with the parasite is associated with a demethylation of the promoters of certain genes in the cerebral amygdala of the intermediate hosts, modifying dopaminergic circuits associated with fear. Similarly, T. gondii has been linked to behavioural changes in humans. Toxoplasma infection is classically associated with the frequency of schizophrenia, suicide attempts or "road rage." A more recent study shows that toxoplasma infection prevalence was a consistent, positive predictor of entrepreneurial activity. Fear of failure would be less important in infected individuals, who are more willing than others to start their own business. These elements shed interesting light on behaviours and their possible relationship with toxoplasmosis, which is generally considered benign in adults.

Interaction of Toxoplasma gondii infection and elevated blood lead levels on children's neurobehavior

A chronic infection caused by Toxoplasma gondii was considered asymptomatic in immunologically healthy humans, but results from animal and epidemiological studies led to a reconsideration of this assumption. The objective of this study was to evaluate the seroprevalence of T. gondii infection and its possible effects on the behavior of school-aged children in Bahia, Brazil. Serum anti-body determinations were performed by Enzyme-linked Immunosorbent Assay (ELISA). Blood lead levels (BLL) were measured by graphite furnace atomic absorption spectrometry (GFAAS). The evaluation of a child's behavior was assessed using the Child Behavior Check List (CBCL). Multivariate models applying logistic regression were used to test the association of chronic T. gondii infection and BLL with behavioral outcomes in children. Seroprevalence for anti-T. gondii IgG antibody was 43.7 % (95 %-CI: 35.8-51.9). Significant associations between chronic T. gondii infection and total behavioral problems (OR = 2.50; 95 %-CI: 1.06-5.88), internalizing spectrum problems (OR = 4.35; 95 %-CI: 1.11-17.14) and rule breaking (OR = 2.61; 95 %-CI: 1.12-6.05) were observed. A possible interaction between toxoplasmosis prevalence and lead exposure was detected. Children with above the median BLL and positive for IgG anti-T. gondii showed a 5.51-fold increase (95 %-CI: 1.75-17.38) in the chance of displaying disobedient behavior. The results suggest that T. gondii infection may be contributing to the high indices of behavioral changes. Moreover, these findings are the first evidence for a possible interaction between chronic T. gondii infection and elevated blood lead levels on children's neurobehavior.

Latent Toxoplasmosis Effects on Rodents and Humans: How Much is Real and How Much is Media Hype?

Toxoplasma gondii is a ubiquitous, intracellular protozoan parasite with a broad range of intermediate hosts, including humans and rodents. In many hosts, T. gondii establishes a latent long-term infection by converting from its rapidly dividing or lytic form to its slowly replicating and encysting form. In humans and rodents, the major organ for encystment is the central nervous system (CNS), which has led many to investigate how this persistent CNS infection might influence rodent and human behavior and, more recently, neurodegenerative diseases.

Toxoplasma gondii is a ubiquitous, intracellular protozoan parasite with a broad range of intermediate hosts, including humans and rodents. In many hosts, T. gondii establishes a latent long-term infection by converting from its rapidly dividing or lytic form to its slowly replicating and encysting form. In humans and rodents, the major organ for encystment is the central nervous system (CNS), which has led many to investigate how this persistent CNS infection might influence rodent and human behavior and, more recently, neurodegenerative diseases. Given the interest in this topic, here we seek to take a global approach to the data for and against the effects of latent T. gondii on behavior and neurodegeneration and the proposed mechanisms that might underlie behavior modifications.

Toxoplasmosis in a Cohort of Italian Patients With Bipolar and Psychotic Disorders: How Infection May Affect Clinical Features?

This study investigated the seroprevalence of Toxoplasma gondii in a cohort of 101 Italian inpatients affected by mood or schizophrenia-spectrum disorders and compared clinical features between seronegative and seropositive subjects. Patients diagnosed according to DSM-5 criteria underwent clinical assessments and blood collection to test parasite-specific IgG/IgM serum levels. Twenty-eight patients (27.7%) had IgG anti-T. gondii, and none had IgM antibodies. We found higher prevalence rate in patients aged 40 years or older, as compared with younger. No significant association was detected between T. gondii and a specific diagnostic category; however, bipolar disorder (BD)-II showed the highest positivity rate (40.9%). The seropositive status was significantly associated with a lower presence of psychotic symptoms, higher number of total episodes of predominant excitatory polarity, longer illness duration, and lower severity of current episode, particularly anxiety, depressive, and withdrawal/retardation symptoms. These preliminary results seem to point out an association between chronic toxoplasmosis and a specific subtype of BD.

Toxoplasmosis and behavioural changes

Nearly one-third of the planet's population is affected by Toxoplasma gondii infection. In ophthalmology, toxoplasmosis is even considered to be the most common cause of posterior uveitis of infectious origin. Humans are only an intermediate host and T. gondii needs to infect cats for its sexual reproduction. All the elements increasing the risk of predation by the definitive host are then favourable to the parasite. Numerous experimental animal model studies have shown that T. gondii infection is associated with predatory risk behaviours such as an attraction of infected mice to cat urine. Infection with the parasite is associated with a demethylation of the promoters of certain genes in the cerebral amygdala of the intermediate hosts, modifying dopaminergic circuits associated with fear. Similarly, T. gondii has been linked to behavioural changes in humans. Toxoplasma infection is classically associated with the frequency of schizophrenia, suicide attempts or "road rage". A more recent study shows that toxoplasma infection prevalence was a consistent, positive predictor of entrepreneurial activity. Fear of failure would be less important in infected individuals, who are more willing than others to start their own business. These elements shed interesting light on behaviours and their possible relationship with toxoplasmosis, which is generally considered benign in adults.

Uncovering the complex genetics of human character

Human personality is 30-60% heritable according to twin and adoption studies. Hundreds of genetic variants are expected to influence its complex development, but few have been identified. We used a machine learning method for genome-wide association studies (GWAS) to uncover complex genotypic-phenotypic networks and environmental interactions. The Temperament and Character Inventory (TCI) measured the self-regulatory components of personality critical for health (i.e., the character traits of self-directedness, cooperativeness, and self-transcendence). In a discovery sample of 2149 healthy Finns, we identified sets of single-nucleotide polymorphisms (SNPs) that cluster within particular individuals (i.e., SNP sets) regardless of phenotype. Second, we identified five clusters of people with distinct profiles of character traits regardless of genotype. Third, we found 42 SNP sets that identified 727 gene loci and were significantly associated with one or more of the character profiles. Each character profile was related to different SNP sets with distinct molecular processes and neuronal functions. Environmental influences measured in childhood and adulthood had small but significant effects. We confirmed the replicability of 95% of the 42 SNP sets in healthy Korean and German samples, as well as their associations with character. The identified SNPs explained nearly all the heritability expected for character in each sample (50 to 58%). We conclude that self-regulatory personality traits are strongly influenced by organized interactions among more than 700 genes despite variable cultures and environments. These gene sets modulate specific molecular processes in brain for intentional goal-setting, self-reflection, empathy, and episodic learning and memory.

Uncovering the complex genetics of human temperament

Experimental studies of learning suggest that human temperament may depend on the molecular mechanisms for associative conditioning, which are highly conserved in animals. The main genetic pathways for associative conditioning are known in experimental animals, but have not been identified in prior genome-wide association studies (GWAS) of human temperament. We used a data-driven machine learning method for GWAS to uncover the complex genotypic-phenotypic networks and environmental interactions related to human temperament. In a discovery sample of 2149 healthy Finns, we identified sets of single-nucleotide polymorphisms (SNPs) that cluster within particular individuals (i.e., SNP sets) regardless of phenotype. Second, we identified 3 clusters of people with distinct temperament profiles measured by the Temperament and Character Inventory regardless of genotype. Third, we found 51 SNP sets that identified 736 gene loci and were significantly associated with temperament. The identified genes were enriched in pathways activated by associative conditioning in animals, including the ERK, PI3K, and PKC pathways. 74% of the identified genes were unique to a specific temperament profile. Environmental influences measured in childhood and adulthood had small but significant effects. We confirmed the replicability of the 51 Finnish SNP sets in healthy Korean (90%) and German samples (89%), as well as their associations with temperament. The identified SNPs explained nearly all the heritability expected in each sample (37-53%) despite variable cultures and environments. We conclude that human temperament is strongly influenced by more than 700 genes that modulate associative conditioning by molecular processes for synaptic plasticity and long-term memory.

The complex genetics and biology of human temperament: a review of traditional concepts in relation to new molecular findings

Recent genome-wide association studies (GWAS) have shown that temperament is strongly influenced by more than 700 genes that modulate associative conditioning by molecular processes for synaptic plasticity and long-term learning and memory. The results were replicated in three independent samples despite variable cultures and environments. The identified genes were enriched in pathways activated by behavioral conditioning in animals, including the two major molecular pathways for response to extracellular stimuli, the Ras-MEK-ERK and the PI3K-AKT-mTOR cascades. These pathways are activated by a wide variety of physiological and psychosocial stimuli that vary in positive and negative valence and in consequences for health and survival. Changes in these pathways are orchestrated to maintain cellular homeostasis despite changing conditions by modulating temperament and its circadian and seasonal rhythms. In this review we first consider traditional concepts of temperament in relation to the new genetic findings by examining the partial overlap of alternative measures of temperament. Then we propose a definition of temperament as the disposition of a person to learn how to behave, react emotionally, and form attachments automatically by associative conditioning. This definition provides necessary and sufficient criteria to distinguish temperament from other aspects of personality that become integrated with it across the life span. We describe the effects of specific stimuli on the molecular processes underlying temperament from functional, developmental, and evolutionary perspectives. Our new knowledge can improve communication among investigators, increase the power and efficacy of clinical trials, and improve the effectiveness of treatment of personality and its disorders.

Suicide and suicide risk

Although recent years have seen large decreases in the overall global rate of suicide fatalities, this trend is not reflected everywhere. Suicide and suicidal behaviour continue to present key challenges for public policy and health services, with increasing suicide deaths in some countries such as the USA. The development of suicide risk is complex, involving contributions from biological (including genetics), psychological (such as certain personality traits), clinical (such as comorbid psychiatric illness), social and environmental factors. The involvement of multiple risk factors in conveying risk of suicide means that determining an individual's risk of suicide is challenging. Improving risk assessment, for example, by using computer testing and genetic screening, is an area of ongoing research. Prevention is key to reduce the number of suicide deaths and prevention efforts include universal, selective and indicated interventions, although these interventions are often delivered in combination. These interventions, combined with psychological (such as cognitive behavioural therapy, caring contacts and safety planning) and pharmacological treatments (for example, clozapine and ketamine) along with coordinated social and public health initiatives, should continue to improve the management of individuals who are suicidal and decrease suicide-associated morbidity.

Toxoplasma gondii Serointensity and Seropositivity: Heritability and Household-Related Associations in the Old Order Amish

Toxoplasma gondii (T. gondii) is an intracellular parasite infecting one third of the world's population. Latent T. gondii infection has been associated with mental illness, including schizophrenia and suicidal behavior. T. gondii IgG antibody titers were measured via ELISA. The heritability of T. gondii IgG was estimated using a mixed model that included fixed effects for age and sex and random kinship effect. Of 2017 Old Order Amish participants, 1098 had positive titers (54.4%). The heritability for T. gondii serointensity was estimated to be 0.22 (p = 1.7 × 10-8 and for seropositivity, it was estimated to be 0.28 (p = 1.9 × 10-5). Shared household environmental effects (i.e., household effects) were also determined. Household effects, modeled as a random variable, were assessed as the phenotypic covariance between any two individuals who had the same current address (i.e., contemporaneous household), and nuclear household (i.e., the phenotypic covariance between parents and children only, not other siblings or spouses). Household effects did not account for a significant proportion of variance in either T. gondii serointensity or T. gondii seropositivity. Our results suggest a significant familial aggregation of T. gondii serointensity and seropositivity with significant heritability. The shared household does not contribute significantly to family aggregation with T. gondii, suggesting that there are possible unmeasured non-household shared and non-shared environmental factors that may play a significant role. Furthermore, the small but significant heritability effects justify the exploration of genetic vulnerability to T. gondii exposure, infection, virulence, and neurotropism.

Relationship between Toxoplasma gondii seropositivity and depression in children and adolescents

Identification of the structural causes of depression is important for the treatment process, and toxoplasmosis may be related to psychiatric disorders. The aim of this study was to evaluate the relationship between Toxoplasma gondii (T. gondii) seropositivity and depression in children and adolescents. This case-control study included 37 children and adolescents aged 11-18 years diagnosed with depression who were followed by the Manisa Celal Bayar University Child and Adolescent Mental Health Service and 36 children and adolescents aged 11-18 years with no history of depressive episodes or psychiatric disorder treated by the Pediatric Outpatient Department. The T. gondii serology of these two groups was evaluated and compared. There were no statistically significant age or sex differences between the 37 participants with depression and the 36 healthy controls. Eight patients and two controls were seropositive for T. gondii, a statistically significant difference (p = 0.046). Seropositivity was significantly higher in patients with suicidal ideation (p = 0.005) than in those without suicidal ideation. The seropositivity of seven of the nine participants who attempted suicide was significantly higher (p < 0.001) than that of participants who did not. Thus, T. gondii infection may affect the predisposition for and severity of depression.

Genome-wide association study in two populations to determine genetic variants associated with Toxoplasma gondii infection and relationship to schizophrenia risk

T. gondii (TOXO) infects over one billion people worldwide, yet the literature lacks a Genome Wide Association Study (GWAS) focused on genetic variants controlling the persistence of TOXO infection. To identify putative T. gondii susceptibility genes, we performed a GWAS using IgG seropositivity as the outcome variable in a discovery sample (n = 790) from an Ashkenazi dataset, and a second sample of predominately African Americans (The Grady Trauma Project, n = 285). We also performed a meta-analyses of the 2 cohorts. None of the SNPs in these analyses was statistically significant after Bonferroni correction for multiple comparisons. In the Ashkenazi population, the gene region of CHIA (chitinase) showed the most nominally significant association with TOXO. Prior studies have shown that the production of chitinase by macrophages in the brain responding to TOXO infection is crucial for controlling the burden of T. gondii cysts. We found a surprising number of genes involved in neurodevelopment and psychiatric disorders among our top hits even though our outcome variable was TOXO infection. In the meta-analysis combining the Ashkenazi and Grady Trauma Project samples, there was enrichment for genes implicated in schizophrenia spectrum disorders (p < .05). Upon limiting our sample to those without mental illness, two schizophrenia related genes (CNTNAP2, GABAR2) still had significant TOXO-associated variants at the p < .05 level, but did not pass the genome wide significance threshold after correction for multiple comparisons. Using Ingenuity Systems molecular network analysis, we identified molecular nodes suggesting that while different genetic variants associated with TOXO in the two population samples, the molecular pathways for TOXO susceptibility nevertheless converged on common pathways. Molecular nodes in these common pathways included NOTCH1, CD44, and RXRA. Prior studies show that CD44 participates in TOXO-induced immunopathology and that RXRA is instrumental in regulating T-helper immune responses. These data provide new insights into the pathophysiology of this common neurotropic parasite.

Presence of Toxoplasma gondii infection in brain as a potential cause of risky behavior: a report of 102 autopsy cases

Toxoplasmosis was linked to impairment in brain function, encompassing a wide range of behavioral and neuropsychiatric changes. Currently, the precise localization of Toxoplasma gondii in the human brain is limited and the parasite DNA was not found in population-based screening of autopsy cases. The aim of proposed study was to identify the presence of parasite DNA within the brain and its association with risky behavior and alcohol consumption in postmortem examination. Preliminarily, 102 cases with certain circumstances of death at time of forensic autopsy was included. Due to high risk of bias, the females were excluded from the analysis and final study group consists 97 cases divided into three groups: risky behavior, inconclusively risky behavior, and control group. The obtained tissue samples for Nested PCR covered four regions of the brain: symmetric left/right and anterior/posterior horns of lateral ventricles comprising lining ependyma and hippocampus. The second type of material comprised blood evaluated for antibodies prevalence using ELISA and alcohol concentration using HS-GC-FID. Analysis demonstrated 16.5% prevalence concerning the parasite DNA presence in examined brain tissue samples without specific distribution and association with age at death or days after death until an autopsy was performed. Results have shown correlation between occurrence of risky behavior leading to death and higher proportions of positive parasite DNA presence within the brain. Correlation was not observed between parasite DNA presence and excessive alcohol consumption. Conducted screening demonstrated correlation between parasite DNA presence in the brain with risky behavior and provided new information on possible effects of latent toxoplasmosis.

What is the natural measurement unit of temperament: single traits or profiles?

There is fundamental doubt about whether the natural unit of measurement for temperament and personality corresponds to single traits or to multi-trait profiles that describe the functioning of a whole person. Biogenetic researchers of temperament usually assume they need to focus on individual traits that differ between individuals. Recent research indicates that a shift of emphasis to understand processes within the individual is crucial for identifying the natural building blocks of temperament. Evolution and development operate on adaptation of whole organisms or persons, not on individual traits or categories. Adaptive functioning generally depends on feedback among many variable processes in ways that are characteristic of complex adaptive systems, not machines with separate parts. Advanced methods of unsupervised machine learning can now be applied to genome-wide association studies and brain imaging in order to uncover the genotypic-phenotypic architecture of traits like temperament, which are strongly influenced by complex interactions, such as genetic epistasis, pleiotropy and gene-environment interactions. We have found that the heritability of temperament can be nearly fully explained by a large number of genetic variants that are unique for multi-trait profiles, not single traits. The implications of this finding for research design and precision medicine are discussed.This article is part of the theme issue 'Diverse perspectives on diversity: multi-disciplinary approaches to taxonomies of individual differences'.

Moderation of the relationship between Toxoplasma gondii seropositivity and trait impulsivity in younger men by the phenylalanine-tyrosine ratio

Previously, we reported that Toxoplasma gondii (T. gondii)-seropositivity is associated with higher impulsive sensation seeking in younger men. As dopaminergic and serotonergic signaling regulate impulsivity, and as T. gondii directly and indirectly affects dopaminergic signaling and induces activation of the kynurenine pathway leading to the diversion of tryptophan from serotonin production, we investigated if dopamine and serotonin precursors or the tryptophan metabolite kynurenine interact with the T. gondii-impulsivity association. In 950 psychiatrically healthy participants, trait impulsivity scores were related to T. gondii IgG seropositivity. Interactions were also identified between categorized levels of phenylalanine (Phe), tyrosine (Tyr), Phe:Tyr ratio, kynurenine (Kyn), tryptophan (Trp) and Kyn:Trp ratio, and age and gender. Only younger T. gondii-positive men with a high Phe:Tyr ratio, were found to have significantly higher impulsivity scores. There were no significant associations in other demographic groups, including women and older men. No significant effects or interactions were identified for Phe, Tyr, Kyn, Trp, or Kyn:Trp ratio. Phe:Tyr ratio, therefore, may play a moderating role in the association between T. gondii seropositivity and impulsivity in younger men. These results could potentially lead to individualized approaches to reduce impulsivity, based on combined demographic, biochemical and serological factors.

Biomolecular Changes and Cortical Neurodegenerative Lesions in Trichinella Spiralis Infected BALB/c Mice: A Preliminary Study Elucidating a Potential Relationship Between Systemic Helminthic Infections and Idiopathic Parkinson's

Idiopathic Parkinson's (IP) is a neurodegenerative disease that is suspected to be due to exposure to infections during early life. Toxoplasmosishas been the only suspected parasitic infection in IP (Celik et al., 2010). Recently, some non-central nervous system bacterial and viral infections have been incriminated in IP (Çamcı & Oğuz, 2016). So in the current study, we tried to explore if the systemic inflammatory reactions triggered by some helminths like Trichinella spiralis can induce Parkinsonian lesions in the brain, especially that the cerebral complications have been reported in 10-20% of Trichinella spiralis infected patients . An experimental study was designed to assess the neurodegenerative and biomolecular changes that may occur in Trichinella spiralis infected BALB/C mice in comparison to rotenone induced PD model and apparently healthy ones. The motor affection was significantly lesser in the Trichinella infected mice than the Parkinson's model, but when the catalepsy score was calculated (through the grid and bar tests) it was found to be significantly higher in the infected mice than in the healthy ones. A significant increase in the blood advanced oxidative protein products (AOPP), IFN-γ, TGF-β, and brain DNA fragmentation was also detected in the Trichinella spiralis infected mice. After histopathological examination, a significant increase in the cortical apoptotic neurons and Lewy's body were observed in the Trichinella infected and the rotenone induced Parkinson's model sections. A significant decrease in the immunohistochemical expression of the tyrosine hydroxylase expression in the brain sections and the ELISA measured dopamine level in the brain homogenate was also reported in the infected mice group. This study findings may collectively suggest that the systemic inflammatory reactions and the oxidative stresses associated with some systemic helminthic infections like trichinellosis are possible to precipitate neurodegenerative lesions and biomolecular changes in the brain , and manifest with IPD later in life.

Toxoplasmosis: A pathway to neuropsychiatric disorders

Toxoplasma gondii is an obligate intracellular parasite that resides, in a latent form, in the human central nervous system. Infection with Toxoplasma drastically alters the behaviour of rodents and is associated with the incidence of specific neuropsychiatric conditions in humans. But the question remains: how does this pervasive human pathogen alter behaviour of the mammalian host? This fundamental question is receiving increasing attention as it has far reaching public health implications for a parasite that is very common in human populations. Our current understanding centres on neuronal changes that are elicited directly by this intracellular parasite versus indirect changes that occur due to activation of the immune system within the CNS, or a combination of both. In this review, we explore the interactions between Toxoplasma and its host, the proposed mechanisms and consequences on neuronal function and mental health, and discuss Toxoplasma infection as a public health issue.

Toxoplasma gondii infection and behavioral outcomes in humans: a systematic review

Studies suggest that the protozoan Toxoplasma gondii can disturb human behavior. This study aimed to systematically review the scientific literature on the possible associations between Toxoplasma gondii infection and neurobehavioral abnormalities in humans. We reviewed and summarized the studies published since 1990. The descriptors used were related to T. gondii infection and behavioral outcomes in humans; the main databases of the medical literature were accessed. The results of eight original articles published between 1994 and 2016 were evaluated and described. The most common serological method was the enzyme immunoassay. Most of the researchers used validated instruments for behavioral evaluation. Seven studies reported some association between the prevalence of anti-T. gondii antibodies and some altered behavioral aspects in adult humans; these studies focused on adult population in Europe and the USA. The most reported behavioral deviations are related to greater impulsivity and aggressiveness. There are very few studies on this subject, which present some limitations for inference and conclusions: most were cross-sectional studies, with a small sample size and in similar populations. Investigations with a larger sample size of different population groups should be performed to evaluate multiple factors.