Associations between Toxoplasma gondii seropositivity and psychopathological manifestations in schizophrenic patients: A single-center study from Ecuador

BACKGROUND

Schizophrenia, a complex neuropsychiatric disorder, is believed to be influenced by various factors including environmental exposures. A potential environmental factor is the infection by the obligate intracellular parasitic protozoan, Toxoplasma gondii which affects neurotransmitter levels, which could potentially exacerbate, trigger symptoms of schizophrenia or make them worst.

OBJECTIVE

To investigate the association between Toxoplasma gondii seropositivity and psychopathological presentation in persons with schizophrenia in Ecuador.

METHODS

This study was conducted at the Neuroscience Institute of Guayaquil, Ecuador. Among 368 inpatients, 104 were selected based on specific inclusion and exclusion criteria. Descriptive statistics captured patient characteristics and mental health outcomes. Logistic regression models estimated the effect of toxoplasmosis on various mental health outcomes, controlling for demographic and health-related variables.

RESULTS

86.5% of participants were seropositive for toxoplasmosis. Toxoplasma-seropositive schizophrenic patients had a lower risk of depression but a significantly higher risk of disorientation. The most prevalent mental health outcomes were Language Impairments (70.2%) and Bizarre Behavior (76.0%).

CONCLUSION

Our findings suggest that Toxoplasma gondii seropositivity may have specific effects on mental functions in schizophrenic patients, particularly reducing the risk of depression but increasing the risk of disorientation. Further studies are required to clarify these associations and the potential underlying mechanisms.

Neuroimaging investigations of dorsal stream processing and effects of stimulus synchrony in schizophrenia

Impairments in auditory and visual processing are common in schizophrenia (SP). In the unisensory realm visual deficits are primarily noted for the dorsal visual stream. In addition, insensitivity to timing offsets between stimuli are widely reported for SP. The aim of the present study was to test at the physiological level differences in dorsal/ventral stream visual processing and timing sensitivity between SP and healthy controls (HC) using MEG and a simple auditory/visual task utilizing a variety of multisensory conditions. The paradigm included all combinations of synchronous/asynchronous and central/peripheral stimuli, yielding 4 task conditions. Both HC and SP groups showed activation in parietal areas (dorsal visual stream) during all multisensory conditions, with parietal areas showing decreased activation for SP relative to HC, and a significantly delayed peak of activation for SP in intraparietal sulcus (IPS). We also observed a differential effect of stimulus synchrony on HC and SP parietal response. Furthermore, a (negative) correlation was found between SP positive symptoms and activity in IPS. Taken together, our results provide evidence of impairment of the dorsal visual stream in SP during a multisensory task, along with an altered response to timing offsets between presented multisensory stimuli.

Relationship between toxoplasmosis and schizophrenia: A review

A growing body of evidence suggests a correlation between schizophrenia and exposure to infectious agents. The majority of studied cases concerns the infection caused by T. gondii, an obligatory intracellular parasite that infects about 1/3 of the entire human population, according to the available data. The acute stage of the disease, predominantly short-lived and transient, transforms into the latent and chronic phase in which the parasite localizes within tissue cysts, mainly in the central nervous system. The chronic toxoplasmosis, primarily regarded as benign and asymptomatic, might be responsible, in light of current scientific evidence, for a vast array of neuropsychiatric symptoms. Numerous epidemiological case-control studies show a higher prevalence of T. gondii infestation in individuals with various psychiatric and behavior disorders, including schizophrenia. This paper tends to review the relevant studies that demonstrate links between schizophrenia and T. gondii infestation, of which the latter may be acquired in different developmental phases. Apart from epidemiological correlation studies, some papers on other associations were also presented, describing putative patophysiological mechanisms that might be at least partly responsible for chronic infection-induced neuromediator disturbances, together with morphological and functional alterations, e.g., low-grade neuroinflammation, which are likely to induce psychopathological symptoms. Toxoplasmosis is only one of the putative infectious agents that derange correct brain growth and differentiation, alongside genetic and environmental factors. All of them may lead eventually to schizophrenia. A better knowledge of infection mechanisms and its influence on neurobiochemical and neuropathological pathways may enable more efficient therapy and the prevention of this devastating disease.

The known and missing links between Toxoplasma gondii and schizophrenia

Toxoplasma gondii, an intracellular protozoan parasite, has a striking predilection for infecting the Central Nervous System and has been linked to an increased incidence of a number of psychiatric diseases. Several in vitro and in vivo studies have shown that T. gondii infection can affect the structure, bioenergetics and function of brain cells, and alters several host cell processes, including dopaminergic, tryptophan-kynurenine, GABAergic, AKT1, Jak/STAT, and vasopressinergic pathways. These mechanisms underlying the neuropathology of latent toxoplasmosis seem to operate also in schizophrenia, supporting the link between the two disorders. Better understanding of the intricate parasite-neuroglial communications holds the key to unlocking the mystery of T. gondii-mediated schizophrenia and offers substantial prospects for the development of disease-modifying therapies.

Is there any role of latent toxoplasmosis in schizophrenia disease?

BACKGROUND

A large number of studies have hypothesized that Toxoplasma gondii is a potentially relevant etiological factor in some cases of schizophrenia. By contrast, some studies have disproved this association. The aim of this study was to investigate whether latent toxoplasmosis has any role in schizophrenia disease. Additionally, the association between T. gondii and subtypes of schizophrenia, and the impacts of toxoplasmosis on psychopathology were examined in the study.

METHODS

A total of 85 patients with schizophrenia and 60 healthy volunteers were included in this prospective study. Immunoglobulin G (IgG) antibody to T. gondii was examined by enzyme-linked immune-sorbent assay method.

RESULTS

Seropositivity rates were 43.5% for the patients with schizophrenia and 43.3% for the healthy controls (odds ratio: 1.008, 95% confidence interval: 0.517-1.964, p = 0.981).There was no significant difference in T. gondii IgG positivity between the schizophrenia and control groups with respect to sex and age. The difference in seroprevalence of T. gondii IgG antibodies among the schizophrenia subtypes was not statistically significant (p = 0.934). No significant difference was found in Positive and Negative Syndrome Subscales between Toxoplasma-infected and Toxoplasma-free patients.

CONCLUSION

In the study area with a high prevalence of T. gondii, no association between toxoplasmosis and schizophrenia was detected. These findings showed that toxoplasmosis has no role in the risk of schizophrenia disease.

Chronic Toxoplasma gondii in Nurr1-null heterozygous mice exacerbates elevated open field activity

Latent infection with Toxoplasma gondii is common in humans (approximately 30% of the global population) and is a significant risk factor for schizophrenia. Since prevalence of T. gondii infection is far greater than prevalence of schizophrenia (0.5-1%), genetic risk factors are likely also necessary to contribute to schizophrenia. To test this concept in an animal model, Nurr1-null heterozygous (+/-) mice and wild-type (+/+) mice were evaluate using an emergence test, activity in an open field and with a novel object, response to bobcat urine and prepulse inhibition of the acoustic startle response (PPI) prior to and 6 weeks after infection with T. gondii. In the emergence test, T. gondii infection significantly decreased the amount of time spent in the cylinder. Toxoplasma gondii infection significantly elevated open field activity in both +/+ and +/- mice but this increase was significantly exacerbated in +/- mice. T. gondii infection reduced PPI in male +/- mice but this was not statistically significant. Aversion to bobcat urine was abolished by T. gondii infection in +/+ mice. In female +/- mice, aversion to bobcat urine remained after T. gondii infection while the male +/- mice showed no aversion to bobcat urine. Antibody titers of infected mice were a critical variable associated with changes in open field activity, such that an inverted U shaped relationship existed between antibody titers and the percent change in open field activity with a significant increase in activity at low and medium antibody titers but no effect at high antibody titers. These data demonstrate that the Nurr1 +/- genotype predisposes mice to T. gondii-induced alterations in behaviors that involve dopamine neurotransmission and are associated with symptoms of schizophrenia. We propose that these alterations in murine behavior were due to further exacerbation of the altered dopamine neurotransmission in Nurr1 +/- mice.

Infection and inflammation in schizophrenia and bipolar disorder: a genome wide study for interactions with genetic variation

Inflammation and maternal or fetal infections have been suggested as risk factors for schizophrenia (SZ) and bipolar disorder (BP). It is likely that such environmental effects are contingent on genetic background. Here, in a genome-wide approach, we test the hypothesis that such exposures increase the risk for SZ and BP and that the increase is dependent on genetic variants. We use genome-wide genotype data, plasma IgG antibody measurements against Toxoplasma gondii, Herpes simplex virus type 1, Cytomegalovirus, Human Herpes Virus 6 and the food antigen gliadin as well as measurements of C-reactive protein (CRP), a peripheral marker of inflammation. The subjects are SZ cases, BP cases, parents of cases and screened controls. We look for higher levels of our immunity/infection variables and interactions between them and common genetic variation genome-wide. We find many of the antibody measurements higher in both disorders. While individual tests do not withstand correction for multiple comparisons, the number of nominally significant tests and the comparisons showing the expected direction are in significant excess (permutation p=0.019 and 0.004 respectively). We also find CRP levels highly elevated in SZ, BP and the mothers of BP cases, in agreement with existing literature, but possibly confounded by our inability to correct for smoking or body mass index. In our genome-wide interaction analysis no signal reached genome-wide significance, yet many plausible candidate genes emerged. In a hypothesis driven test, we found multiple interactions among SZ-associated SNPs in the HLA region on chromosome 6 and replicated an interaction between CMV infection and genotypes near the CTNNA3 gene reported by a recent GWAS. Our results support that inflammatory processes and infection may modify the risk for psychosis and suggest that the genotype at SZ-associated HLA loci modifies the effect of these variables on the risk to develop SZ.

Contrasting effect of prepulse signals on performance of Toxoplasma-infected and Toxoplasma-free subjects in an acoustic reaction times test

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.

A potential association between Toxoplasma gondii infection and schizophrenia in mouse models

Schizophrenia is a serious neuropsychiatric disease of uncertain etiology, which causes human mental disorder and affects about 1% of the population. In recently years, some studies showed that some cases of schizophrenia may be associated with Toxoplasma gondii infection. In order to investigate a potential association between Toxoplasma infection and schizophrenia, we investigated the relative clinical symptom of schizophrenia such as learning and memory capability, depression and stereotypy to find some useful information by behavioral test in mouse models. Our results demonstrated that mice from Toxoplasma infection and MK-801 administration (as the model of schizophrenia) were impaired in learning and memory capability, and they had more serious depression and stereotypy compared with the control mice, especially the mice from congenital Toxoplasma infection. In addition, our results clearly showed that the number of cysts in brain tissue of congenital Toxoplasma infection mice was significantly low than in acquired Toxoplasma infected mice. Collectively, these results suggested a potential association between Toxoplasma infection and schizophrenia.

Toxoplasma gondii infection, from predation to schizophrenia: can animal behaviour help us understand human behaviour?

We examine the role of the protozoan Toxoplasma gondii as a manipulatory parasite and question what role study of infections in its natural intermediate rodent hosts and other secondary hosts, including humans, may elucidate in terms of the epidemiology, evolution and clinical applications of infection. In particular, we focus on the potential association between T. gondii and schizophrenia. We introduce the novel term 'T. gondii-rat manipulation-schizophrenia model' and propose how future behavioural research on this model should be performed from a biological, clinical and ethically appropriate perspective.

Anti-gluten immune response following Toxoplasma gondii infection in mice

Gluten sensitivity may affect disease pathogenesis in a subset of individuals who have schizophrenia, bipolar disorder or autism. Exposure to Toxoplasma gondii is a known risk factor for the development of schizophrenia, presumably through a direct pathological effect of the parasite on brain and behavior. A co-association of antibodies to wheat gluten and to T. gondii in individuals with schizophrenia was recently uncovered, suggesting a coordinated gastrointestinal means by which T. gondii and dietary gluten might generate an immune response. Here, we evaluated the connection between these infectious- and food-based antigens in mouse models. BALB/c mice receiving a standard wheat-based rodent chow were infected with T. gondii via intraperitoneal, peroral and prenatal exposure methods. Significant increases in the levels of anti-gluten IgG were documented in all infected mice and in offspring from chronically infected dams compared to uninfected controls (repetitive measures ANOVAs, two-tailed t-tests, all p≤0.00001). Activation of the complement system accompanied this immune response (p≤0.002–0.00001). Perorally-infected females showed higher levels of anti-gluten IgG than males (p≤0.009) indicating that T. gondii-generated gastrointestinal infection led to a significant anti-gluten immune response in a sex-dependent manner. These findings support a gastrointestinal basis by which two risk factors for schizophrenia, T. gondii infection and sensitivity to dietary gluten, might be connected to produce the immune activation that is becoming an increasingly recognized pathology of psychiatric disorders.

[Schizophenia and premorbid infections]

Schizophrenia is a disease of unknown etiology. Many authors have studied its association with infections. By meta-analysis viruses are the most studied agents, relationship with the Borna virus and human endogenous retrovirus W. Also, C. pneumoniae and C. psittaci DNA in blood are more common in patients. Finally, there is association with parasitism by T. gondii, despite the existence of publication bias. Serologically, in our environment, anti-Toxoplasma IgG may be a risk factor related to schizophrenia, and may have potential value for better diagnosis and prevention.

Toxoplasma gondii antibody titers and history of suicide attempts in patients with schizophrenia

Toxoplasma gondii (T. gondii) a widespread neurotropic parasite, has been previously associated with schizophrenia and more recently with suicidal behavior. However, no previous study has examined the association of T. gondii with suicidal behavior in schizophrenia patients. 950 individuals diagnosed with schizophrenia by SCID were recruited from the Munich area of Germany. Solid-enzyme immunoassay methods were used to measure IgG plasma antibodies to T. gondii, other neurotropic pathogens and gliadin. Logistic regression models were developed to analyze the association of T. gondii seropositivity or serointensity with history of suicidal behavior. In those younger than the median age of the sample, 38, T. gondii serointensity was associated with history of suicidal behavior (p = 0.02), while in the older patients the relationship was not significant (p = 0.21). Seropositivity was also associated with history of suicide attempt in younger patients, odds ratio 1.59 (95% CI 1.06 to 2.40), p = 0.03. Seropositivity for CMV (p = 0.22), HSV-1 (p = 0.36) and gliadin (p = 0.92) was not related to history of suicide attempt in the entire sample or any age subgroup. T. gondii serology might become, with interaction with vulnerability genes, a candidate biomarker for a subgroup of schizophrenia patients prone to attempting suicide.

Serum antibodies to Toxoplasma gondii and Herpesvidae family viruses in individuals with schizophrenia and bipolar disorder: a case-control study

BACKGROUND

Recent etiological studies for schizophrenia and bipolar disorder have focused on the protozoan Toxoplasma gondii and Herpesvirdae family viruses.

OBJECTIVE

To determine the magnitude of T. gondii, cytomegalovirus (CMV), herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2) infection in individuals with schizophrenia, bipolar disorder and healthy controls by using serologic diagnostic methods.

MATERIAL AND METHODS

Serologic diagnostic method was used to determine the prevalence and level of antibodies to T gondii, CMV HSV-1 and HSV-2 in individuals with schizophrenia, bipolar disorder, and unaffected controls recruited from Butajira, Ethiopia. The study was conducted from March to May 2009. A total of 495 serum samples were analysed for the presence and level of immunoglobulin G (IgG) to T. gondii, CMV HSV-1, and HSV-2.

RESULTS

The seroprevalence of T gondii infection was higher in individuals with schizophrenia [adjusted odds ratio = 4.7; 95% CI (1.5, 15.1)] and bipolar disorder [adjusted odds ratio = 3.0; 95% CI (1.1, 8.6)] than in unaffected controls. The level of IgG to CMV was also significantly higher in individuals with schizophrenia and bipoar disorder than in unaffected controls. Younger individuals with schizophrenia (< 25 years old) also had a significantly higher level of IgG to CMV than matched unaffected controls.

CONCLUSION

This study provides additional evidence that infection with 7T gondii and CMV may be associated with some cases of schizophrenia and bipolar disorder. Additional studies should focus on antibodies to these agents in the sera and CSF of individuals with recent-onset psychosis.

Neuropsychiatric disease and Toxoplasma gondii infection

Toxoplasma gondii infects approximately 30% of the world's population, but causes overt clinical symptoms in only a small proportion of people. In recent years, the ability of the parasite to manipulate the behaviour of infected mice and rats and alter personality attributes of humans has been reported. Furthermore, a number of studies have now suggested T. gondii infection as a risk factor for the development of schizophrenia and depression in humans. As T. gondii forms cysts that are located in various anatomical sites including the brain during a chronic infection, it is well placed anatomically to mediate these effects directly. The T. gondii genome is known to contain 2 aromatic amino acid hydroxylases that potentially could directly affect dopamine and/or serotonin biosynthesis. However, stimulation of the immune response has also recently been associated with mood and behavioural alterations in humans, and compounds designed to alter mood, such as fluoxetine, have been demonstrated to alter aspects of immune function. Herein, the evidence for T.-gondii-induced behavioural changes relevant to schizophrenia and depression is reviewed. Potential mechanisms responsible for these changes in behaviour including the role of tryptophan metabolism and the hypothalamic-pituitary-adrenal axis are discussed.

Toxocara seroprevalence in schizophrenic patients in Turkey

PURPOSE

To investigate the seroprevalence of toxocariasis in patients diagnosed as schizophrenia.

PATIENTS AND METHODS

Ninety-eight schizophrenic patients hospitalized at The Elazig Psychiatric Hospital were included in the study. Anti-Toxocara IgG and/or IgM antibodies were determined by using commercial Toxocara canis IgG and/or IgM ELISA kit.

RESULTS

Seropositivity for T. canis was detected in 45 (45.9%) of 98 patients and 2 (2.0%) of 100 control subjects the difference was statistically significant (p<0.001). The seroprevalence was 40.4% (19 cases) and 51.0% (26 cases) for female and male subjects, respectively (p=0.3). When the seropositive and seronegative schizophrenic patients were compared with respect to the age group environment they were living in, occupation period of follow up and number of hospitalizations, there were no differences between the two groups (all, p>0.05).

CONCLUSION

In conclusion, the schizophrenic state seems to present a high risk for Toxocara infection in Turkey.

Parasitosis, dopaminergic modulation and metabolic disturbances in schizophrenia: evolution of a hypothesis

Recent meta-analyses have provided a comprehensive overview of studies investigating Toxoplasma gondii antibodies in schizophrenic patients, thus attempting to clarify the potential role these infections might play in causing schizophrenia. Issues for further research have been suggested. Associations and theories that may enrich the current level of knowledge with regard to this significant subject deserve attention. Anti-parasitic agents as well as antipsychotics are effective in treating parasitosis. Both classes of drugs have been shown to exert dopaminergic activity. Parasites and human organisms have a long history of mutual contact. The effect of parasitosis on the host and the host's response to infection are undoubtedly the product of a long evolutionary process. The neurochemical background of delusions of parasitosis is potentially similar to ancient evolutionary traces of altered neurotransmission and neuropeptide gene expression caused by parasites; these include fungal and viral infections. This is very unique in medicine if a class of drugs is effective in the treatment of an illness but also cures the delusion of the same disorder as well. Furthermore, metabolic disturbances such as hyperglycemia and insulin resistance were reported several decades before the antipsychotic era. Toxoplasmosis may also be linked to insulin resistance. Schizophrenia research can benefit from understanding this evolutionary link. New chemical entities that are liable to alter neurochemical changes related to the brain's perception of the risk of predation secondary to parasites may result in new approaches for the treatment of psychosis. These findings suggest that further research is needed to clarify this evolutionary link between parasite infection and delusions of parasitosis. We believe this model may well open up new avenues of research in the discovery of drugs to counteract schizophrenia.

Effects of toxoplasma on human behavior

Although latent infection with Toxoplasma gondii is among the most prevalent of human infections, it has been generally assumed that, except for congenital transmission, it is asymptomatic. The demonstration that latent Toxoplasma infections can alter behavior in rodents has led to a reconsideration of this assumption. When infected human adults were compared with uninfected adults on personality questionnaires or on a panel of behavioral tests, several differences were found. Other studies have demonstrated reduced psychomotor performance in affected individuals. Possible mechanisms by which T. gondii may affect human behavior include its effect on dopamine and on testosterone.

A controlled prospective study of toxoplasma gondii infection in individuals with schizophrenia: beyond seroprevalence

Toxoplasma gondii (TG) infection has been reported to be more frequent in schizophrenia. The interaction of the lifelong persisting parasite with the host's immune system involves T-cell/interferon-gamma-induced degradation of tryptophan and provides a challenge to the host well beyond a possible role in the etiology of schizophrenia. The hypothesis we tested in this study was that TG infection may be more frequent (serofrequency) and/or more intense (serointensity) in patients with schizophrenia or major depression compared with psychiatrically healthy controls. In addition, these measures are associated with the clinical course. We did a cross-sectional, prospective investigation of individuals with schizophrenia (n = 277) and major depression (n = 465) admitted to our department (2002-2005) and of healthy controls (n = 214), with all groups adjusted for age and geographic home region. Serofrequency was comparable between the groups, but serointensity was significantly higher in the patients. In individuals with schizophrenia, serointensity was significantly positively associated with C-reactive protein levels and leukocyte counts, and first-episode patients yielded significantly higher serotiters. Immunomodulatory medication was associated with decreased serotiters. In addition, the route of infection appears to differ between patients and controls. Thus, our results support increased host responses to TG infection in the patients, as well as increased titers in first-episode patients with schizophrenia; this may relate to the shifted T-helper 1/2 status described in these patients. Therefore, we suggest that TG infection, particularly in individuals with schizophrenia, is an important environmental factor in the interaction between psychiatric vulnerability, genetic background, immunomodulation, and the neurotransmitter systems.

Toxoplasma gondii in individuals with schizophrenia: association with clinical and demographic factors and with mortality

BACKGROUND

Increased rates of exposure to Toxoplasma gondii have been found in individuals with schizophrenia as compared with control groups, but the correlates of Toxoplasma exposure in schizophrenia have not been defined.

METHODS

We measured IgG class antibodies to Toxoplasma gondii in 358 individuals with schizophrenia. We correlated Toxoplasma antibody status with clinical and demographic variables and examined the effect of Toxoplasma seropositivity on mortality in a follow-up period of up to 5 years.

RESULTS

Individuals with schizophrenia who had serological evidence of Toxoplasma infection were more likely to be female but did not differ in age, race, total symptom score, or other demographic or clinical characteristics. However, we found that serological evidence of Toxoplasma was associated with a significantly increased risk of dying of natural causes during the follow-up period (Cox proportional hazard ratio of 4.70; 95% confidence interval, 1.27-17.31, P = .020) adjusted for age, gender, and other clinical and demographic variables.

CONCLUSIONS

Toxoplasma infection may confer an increased risk for mortality from natural causes in schizophrenia. An understanding of the pathogenesis of Toxoplasma infections in individuals with schizophrenia might lead to new approaches to the management of this disorder.

Early infections of Toxoplasma gondii and the later development of schizophrenia

Early exposure to several infectious agents has been associated with the later development of schizophrenia. Two recent studies assessed in utero or early postnatal exposure to Toxoplasma gondii. In one study of 63 individuals, who developed schizophrenia spectrum disorders, maternal sera obtained during pregnancy showed an increased risk (OR 2.61) of having IgG antibodies to T. gondii. In the other study of 71 individuals who developed schizophrenia, sera obtained shortly after birth also showed an increased risk (OR 1.79) of having IgG antibodies to T. gondii. Causal linking mechanisms are at present speculative but include possible direct effects of maternal IgG on the developing central nervous system (CNS) of the offspring. Additional studies are underway.

Antibodies to Toxoplasma gondii in patients with schizophrenia: a meta-analysis

Recent studies have linked infectious agents to schizophrenia. The largest number of studies has involved the analysis of Toxoplasma gondii; these studies were subjected to a meta-analysis. Published articles and abstracts were identified by searches of MEDLINE, Ovid, and Google Scholar; by a search of Chinese publications; through letters to researchers; and by visiting China. Published and unpublished controlled studies that used serological methods for measuring T. gondii antibodies to assess inpatients and/or outpatients diagnosed with schizophrenia were selected for analysis, and source documents were translated as needed. Forty-two studies carried out in 17 countries over 5 decades were identified; 23 of these (6 unpublished) met selection criteria. The combined odds ratio (OR) was 2.73 (95% confidence interval, 2.10 to 3.60; chi-square with 1 df 263; P < .000001). Seven studies that included only patients with first-episode schizophrenia (OR 2.54) did not differ significantly from 16 studies that included patients in all clinical phases (OR 2.79). The results suggest that individuals with schizophrenia have an increased prevalence of antibodies to T. gondii. This association is consistent with other epidemiological studies as well as with animal studies. Although the OR of 2.73 is modest, it exceeds that for genetic or other environmental factors identified to date and suggests that Toxoplasma is in some way associated with a large number of cases of schizophrenia. If an etiological association can be proven, it would have implications for the design of measures for the prevention and treatment of this disease.

Effects of Toxoplasma gondii infection on the brain

Toxoplasma gondii, an intracellular protozoan parasite, can infect humans in 3 different ways: ingestion of tissue cysts, ingestion of oocysts, or congenital infection with tachyzoites. After proliferation of tachyzoites in various organs during the acute stage, the parasite forms cysts preferentially in the brain and establishes a chronic infection, which is a balance between host immunity and the parasite's evasion of the immune response. A variety of brain cells, including astrocytes and neurons, can be infected. In vitro studies using non-brain cells have demonstrated profound effects of the infection on gene expression of host cells, including molecules that promote the immune response and those involved in signal transduction pathways, suggesting that similar effects could occur in infected brain cells. Interferon-gamma is the essential mediator of the immune response to control T. gondii in the brain and to maintain the latency of chronic infection. Infection also induces the production of a variety of cytokines by microglia, astrocytes, and neurons, which promote or suppress inflammatory responses. The strain (genotype) of T. gondii, genetic factors of the host, and probably the route of infection and the stage (tachyzoite, cyst, or oocyst) of the parasite initiating infection all contribute to the establishment of a balance between the host and the parasite and affect the outcome of the infection.

The effect of Toxoplasma gondii on animal behavior: playing cat and mouse

A convincing body of evidence now exists to indicate that the ubiquitous protozoan Toxoplasma gondii can cause permanent behavioral changes in its host, even as a consequence of adult-acquired latent infection. Such behavioral alterations appear to be the product of strong selective pressures for the parasite to enhance transmission from its intermediate host reservoir, primarily rodent, to its feline definitive host, wherein sexual reproduction can occur and the life cycle completed. This article reviews evidence of behavioral alterations in animal hosts and considers what these may elucidate about the potential mechanisms involved and what implications such alterations could have on animal and human health.

Psychopathology in first-episode schizophrenia and antibodies to Toxoplasma gondii

OBJECTIVE

Environmental factors such as infectious agents may contribute to the psychopathology and aetiology of schizophrenia. Toxoplasma gondii (TG) is a candidate infectious agent as it is known to replicate within the human central nervous system and to alter behaviour in experimental animals.

METHOD

The relationship between antibodies to TG and psychopathological symptoms was examined in 34 first-episode patients with schizophrenia.

RESULTS

Results of regression analyses revealed that symptoms on admission, predictors of outcome, age and family history of psychiatric disease influenced the levels of antibodies to TG.

CONCLUSIONS

These results indicate that TG infections may play a role in the clinical manifestation of psychopathology in a subgroup of patients with schizophrenia.

Toxoplasma gondii and schizophrenia

Recent epidemiologic studies indicate that infectious agents may contribute to some cases of schizophrenia. In animals, infection with Toxoplasma gondii can alter behavior and neurotransmitter function. In humans, acute infection with T. gondii can produce psychotic symptoms similar to those displayed by persons with schizophrenia. Since 1953, a total of 19 studies of T. gondii antibodies in persons with schizophrenia and other severe psychiatric disorders and in controls have been reported; 18 reported a higher percentage of antibodies in the affected persons; in 11 studies the difference was statistically significant. Two other studies found that exposure to cats in childhood was a risk factor for the development of schizophrenia. Some medications used to treat schizophrenia inhibit the replication of T. gondii in cell culture. Establishing the role of T. gondii in the etiopathogenesis of schizophrenia might lead to new medications for its prevention and treatment.

Antibodies to infectious agents in individuals with recent onset schizophrenia

We investigated the levels of antibodies to infectious agents in the serum and cerebral spinal fluids (CSFs) of individuals with recent onset schizophrenia and compared these levels to those of controls without psychiatric disease. We found that untreated individuals with recent onset schizophrenia had significantly increased levels of serum and CSF IgG antibody to cytomegalovirus and Toxoplasma gondii as compared to controls. The levels of serum IgM class antibodies to these agents were not increased. Untreated individuals with recent onset schizophrenia also had significantly lower levels of serum antibody to human herpesvirus type 6 and varicella zoster virus as compared to controls. Levels of antibodies to herpes simplex virus type 1, herpes simplex virus type 2, and Epstein Barr virus, and did not differ from cases and controls. We also found that treatment status had a major effect on the levels of antibodies in this population. Individuals who were receiving treatment had lower levels of antibodies to cytomegalovirus and Toxoplasma gondii, and higher levels of serum antibodies to human herpesvirus type 6 as compared to untreated individuals. The level of antibodies to Toxoplasma and human herpesvirus type 6 measured in treated individuals did not differ from the levels measured in controls. In the case of cytomegalovirus, the levels of CSF antibodies in treated individuals did not differ from those of controls, while the level of serum IgG antibodies to CMV remained slightly greater than controls in this population. Our studies indicate that untreated individuals with recent onset schizophrenia have altered levels of antibodies to cytomegalovirus, Toxoplasma gondii, and human herpesvirus type 6 while the levels of these antibodies in treated individuals with recent onset schizophrenia are similar to those of controls. These findings indicate that infectious agents may play a role in the etiopathogenesis of some cases of schizophrenia.

Herpesviruses and Toxoplasma gondii in orbital frontal cortex of psychiatric patients

Herpes simplex virus (HSV), Epstein-Barr virus (EBV), cytomegalovirus (CMV), and human herpesvirus-6 (HHV-6) are viruses capable of establishing latency. All of these infect the CNS and have been detected in human postmortem brains. Toxoplasma gondii is a protozoan organism which can reactivate in the brains of previously infected immunocompromised individuals. To screen for the presence of herpesviruses and T. gondii in postmortem orbital frontal brain samples from patients with schizophrenia, affective disorders, and controls, we used nested-polymerase chain reaction (n-PCR)/sequencing. We identified HHV-6B sequences in 2/51 postmortem brain samples but no sequences from other herpesviruses. We did not detect sequences of T. gondii in the postmortem brains. Additional studies including ones directed at the sensitive detection of viral nucleic acids in multiple brain regions should be directed at confirming or excluding a role for viruses and protozoa in the etiology of these disorders.

Genes, germs, and schizophrenia: an evolutionary perspective

Literature on schizophrenia and other mental illnesses has emphasized the compatibility of evidence with genetic causation without adequately considering alternative hypotheses of disease causation. Although some studies from the mid-20th century reported associations between certain pathogens and schizophrenia, only recently has the possibility of infectious causation of schizophrenia again become an active focus of research. Infectious causation of schizophrenia is still, however, generally regarded as less well demonstrated than genetic causation. This article evaluates the evidence that has been used to support genetic and infectious causation. Our consideration of infectious causation focuses on the protozoan Toxoplasma gondii but also assesses other pathogens that may contribute to the development of some of the illnesses currently categorized as schizophrenia. Although evidence generally accepted as demonstrating genetic causation can be readily explained by hypotheses of infectious causation, some of the evidence implicating infectious causation cannot be similarly explained by genetic causation. This asymmetry indicates that a scientific approach to the causation of schizophrenia needs to put a greater emphasis on tests that distinguish hypotheses of genetic causation from those of infectious causation.

The schizophrenia-rheumatoid arthritis connection: infectious, immune, or both?

Schizophrenia and rheumatoid arthritis share an impressive number of similarities. Both are chronic, relapsing diseases of unknown etiology. Both became prominent in the early 19th century and have prevalences of approximately 1% in North America and Europe. Both run in families, have pairwise concordance rates of approximately 30% among monozygotic twins, and are more common among individuals born in urban areas. For both diseases, studies have reported greater exposure to cats in childhood than in controls. Both diseases have been associated with similar class II HLA antigens. Both have also been suspected of having infectious etiology, with similar agents--retroviruses, herpesviruses including EBV, and Toxoplasma gondii--having been associated in some cases. Since there is also a well-documented inverse correlation between these two diseases, it is possible that they share a common infectious and/or immune etiology and that once a person gets one of the diseases then they are relatively immune to the other.