Immunoglobulin sub-class distribution in bipolar disorder and schizophrenia: potential relationship with latent Toxoplasma Gondii infection

The bidirectional relationship of depression and disturbances in B cell homeostasis: Double trouble

Major depressive disorder (MDD) is a recurrent, persistent, and debilitating neuropsychiatric syndrome with an increasing morbidity and mortality, representing the leading cause of disability worldwide. The dysregulation of immune systems (including innate and adaptive immune systems) has been identified as one of the key contributing factors in the progression of MDD. As the main force of the humoral immunity, B cells have an essential role in the defense against infections, antitumor immunity and autoimmune diseases. Several recent studies have suggested an intriguing connection between disturbances in B cell homeostasis and the pathogenesis of MDD, however, the B-cell-dependent mechanism of MDD remains largely unexplored compared to other immune cells. In this review, we provide an overview of how B cell abnormality regulates the progression of MMD and the potential consequence of the disruption of B cell homeostasis in patients with MDD. Abnormalities of B-cell homeostasis not only promote susceptibility to MDD, but also lead to an increased risk of developing infection, malignancy and autoimmune diseases in patients with MDD. A better understanding of the contribution of B cells underlying MDD would provide opportunities for identification of more targeted treatment approaches and might provide an overall therapeutic benefit to improve the long-term outcomes of patients with MDD.

Seroprevalence and Associated Risk Factors of Toxoplasma gondii in Patients Diagnosed with Schizophrenia: A Case-Control Cross Sectional Study

The protozoan parasite, Toxoplasma gondii, has been linked to several psychiatric disorders, including schizophrenia. The aim of this study was to assess the prevalence of T. gondii IgG antibodies and risk factors associated with seroprevalence in patients diagnosed with schizophrenia. This seroepidemiological study assessed 196 participants, divided into two groups. The study group consisted of 98 schizophrenic patients and was matched with 98 healthy blood donors. A questionnaire was used to gather information regarding potential risk factors associated with T. gondii seroprevalence. Results revealed a higher seroprevalence of T. gondii IgG antibodies in schizophrenic patients (69.39%, 68/98) when compared to healthy controls (51.02%, 50/98) (OR: 2.18; 95% CI: 1.21-3.9; p = 0.01). Patients with schizophrenia who consumed raw or undercooked meat (80.65%, 25/31) (OR: 3.75; 95% CI: 1.25-11.21, p = 0.02) and those with a lower educational level (77.59%, 45/58) (OR: 3.5; 95% CI: 1.59-7.54, p = 0.002) presented increased T. gondii seropositivity rates versus their control counterparts. Our findings indicate a high T. gondii IgG seroprevalence in patients diagnosed with schizophrenia compared to healthy blood donors. Factors associated with T. gondii seroprevalence were consumption of raw or uncooked meat and a lower educational attainment. This study provided the first data regarding the potential risk factors for toxoplasmosis in Romanian patients diagnosed with schizophrenia and may serve as a foundation for future research and the development of preventive strategies.

Immunoglobulin genes expressed in lymphoblastoid cell lines discern and predict lithium response in bipolar disorder patients

Bipolar disorder (BD) is a neuropsychiatric mood disorder manifested by recurrent episodes of mania and depression. More than half of BD patients are non-responsive to lithium, the first-line treatment drug, complicating BD clinical management. Given its unknown etiology, it is pertinent to understand the genetic signatures that lead to variability in lithium response. We discovered a set of differentially expressed genes (DEGs) from the lymphoblastoid cell lines (LCLs) of 10 controls and 19 BD patients belonging mainly to the immunoglobulin gene family that can be used as potential biomarkers to diagnose and treat BD. Importantly, we trained machine learning algorithms on our datasets that predicted the lithium response of BD subtypes with minimal errors, even when used on a different cohort of 24 BD patients acquired by a different laboratory. This proves the scalability of our methodology for predicting lithium response in BD and for a prompt and suitable decision on therapeutic interventions.

Shifting levels of peripheral inflammatory profiles as an indicator for comorbid multiple autoimmune diseases and bipolar disorder: a case report

Autoimmune diseases (AID) cause inflammatory changes in the peripheral blood, which might be a predisposing factor for the development of comorbid bipolar disorder (BD). The levels of peripheral inflammatory indicators and cytokines may also serve as potential biomarkers for predicting BD susceptibility and the efficacy of antipsychotics in patients with AID. Herein, we present the case of a 43-year-old female who has suffered from AID for over 16 years and was recently diagnosed with "bipolar and related disorder due to another medical condition".

First-episode mania after COVID-19: A case series in Iran

Background

Increasing reports of manic episodes in patients during acute infection with COVID-19 have been documented since the pandemic began, including individuals without a previous personal or family history of bipolar disorder. As infections and autoimmunity have putative roles in bipolar disorder, we aimed to document the clinical presentations, associated stressors, family aggregation patterns, and brain imaging and electroencephalographic correlates with a series of patients with episodes of mania that emerged shortly after COVID-19 infections.

Methods

We obtained all relevant clinical information from 12 patients whose first manic episode started within a month of COVID-19 infection and were treated at Rasool-e-Akram hospital and Iran psychiatric hospital, two tertiary medical centers in Tehran, Iran, in 2021.

Results

Patients had a mean age of 44. The interval between the onset of symptoms of COVID and mania ranged between 0 and 28 days (mean: 16.25, median: 14 days); it was observed to be shorter in patients with a family history of mood disorders but not in those receiving corticosteroids. Alongside a descriptive overview of our sample, we provide detailed narrative descriptions of two of the cases for illustrative purposes and discuss our observations in the context of other cases reported elsewhere and the state-of-the-art regarding infectious diseases, COVID-19, and bipolar disorder as reported in previous literature.

Conclusion

Our case series documents observational and naturalistic evidence from a dozen of cases of mania in the context of acute COVID-19, which, while limited, calls for analytical research of the phenomenon, and points at a family history of bipolar disorder and the use of corticosteroids as factors for particular focus.

Association between Toxoplasma gondii infection and psychiatric disorders: a cross-sectional study in China

Psychiatric patients have become the focus of public attention, and current research suggests a possible link between Toxoplasma gondii (T. gondii) infection and mental illness. To understand the current situation of T. gondii infection in psychiatric patients in the study area, the relationship between T. gondii infection and mental diseases, and the influence of T. gondii infection on psychiatric patients, this study examined 3101 psychiatric inpatients from 2015 to 2020. All people included in the study were tested for anti-Toxoplasma IgM antibody and anti-Toxoplasma IgG antibody. Additionally, 4040 individuals from the general population were included as controls. The chi-square test and logistic regression analysis were carried out to determine the association between psychiatric disorders and T. gondii infection. The seroprevalence of anti-Toxoplasma IgM antibody was 0.23% (7/3101) in psychiatric inpatients and 0.11% (2/1846) in the general population, and there was no significant difference (p > 0.05). The seroprevalence rate of anti-Toxoplasma IgG antibodies was 3.03% (94/3101) in psychiatric inpatients and 1.05% (23/2194) in the general population, and there was a significant difference (p < 0.01). The seroprevalence of anti-Toxoplasma IgG antibody in psychiatric inpatients was significantly different between different age groups (p < 0.01). The positivity rate of anti-Toxoplasma IgG antibodies was 5.17% (3/58) in patients with mania, 3.24% (8/247) in patients with recurrent depressive disorder, 3.54% (13/367) in patients with depression, 3.22% (39/1213) in patients with schizophrenia, 2.41% (18/748) in patients with bipolar disorder and 2.25% (2/89) in patients with dissociative disorder. Compared to the general population, patients with mania (OR = 5.149 95% CI 1.501–17.659 p = 0.009), schizophrenia (OR = 3.136 95% CI 1.864–5.275 p = 0.000), depression (OR = 3.466 95% CI 1.740–6.906 p = 0.000), recurrent depressive disorder (OR = 3.160 95% CI 1.398–7.142 p = 0.006) and bipolar disorder (OR = 2.327 95% CI 1.249–4.337 p = 0.008) were found to be significantly associated with the seroprevalence of anti-Toxoplasma IgG antibody. This study suggests that the seroprevalence of T. gondii infection in psychiatric patients was higher and that age was an influencing factor of T. gondii infection in psychiatric patients. T. gondii infection was associated with mania, schizophrenia, depression, recurrent depressive disorder and bipolar disorder.

Association between toxoplasmosis and bipolar disorder: A systematic review and meta-analysis

BACKGROUND

The relationship between toxoplasma gondii (T. gondii) infection and bipolar disorder (BD) is poorly understood. This review explores this relationship by estimating the strength of the association between the two conditions using data from published studies.

METHODS

Following PRISMA guidelines, we performed a review and meta-analysis of published articles obtained from a systematic search of PubMed, PsycINFO, EMBASE and the Cochrane library up to January 10th, 2021. We included observational studies that compared seroprevalence of IgG class antibodies against T. gondii in patients with a diagnosis of BD with healthy controls. We excluded studies that included <10 participants in each study arm and patients with a serious concomitant medical illness. Discrepancies between the two independent researchers were resolved by consulting a third experienced researcher. Summary data were extracted from published reports. Analysis was conducted using both fixed-effects and random-effects models. The study is registered with PROSPERO number CRD42021237809.

FINDINGS

The search yielded 23 independent studies with a total of 12690 participants (4021 with BD and 8669 controls). Persons with BD had a greater odd of seropositivity with toxoplasmosis than controls, both in the fixed-effects model (OR = 1.34 [95%CI: 1.19 to 1.51]) and the random-effects model (OR = 1.69 [95%CI: 1.21 to 2.36]). No publication bias was detected but reported results showed a high heterogeneity (I2 = 84% [95%CI:77%-89%]).

INTERPRETATION

The findings support the relationship between toxoplasmosis infection and BD and suggests a need for studies designed to explore possible causal relationship. Such studies may also improve our understanding of the pathophysiology of BD and open other avenues for its treatment.

FUNDING

P.O.R. Sardegna F.S.E. 2014-2020.

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.

Neurological and Neurobehavioral Disorders Associated with Toxoplasma gondii Infection in Humans

The intracellular parasite Toxoplasma gondii is estimated to infect up to 30% of the world population, leading to lifelong chronic infection of the brain and muscle tissue. Although most latent T. gondii infections in humans have traditionally been considered asymptomatic, studies in rodents suggest phenotypic neurological changes are possible. Consequently, several studies have examined the link between T. gondii infection and diseases such as schizophrenia, epilepsy, depression, bipolar disorder, dysphoria, Alzheimer's disease, Parkinson's disease, and obsessive-compulsive disorder (OCD). To date, there is varying evidence of the relationship of T. gondii to these human neurological or neurobehavioral disorders. A thorough review of T. gondii literature was conducted to highlight and summarize current findings. We found that schizophrenia was most frequently linked to T. gondii infection, while sleep disruption showed no linkage to T. gondii infection, and other conditions having mixed support for a link to T. gondii. However, infection as a cause of human neurobehavioral disease has yet to be firmly established.

Predictive protein markers for depression severity in mood disorders: A preliminary trans-diagnostic approach study

Depression is a common symptom of many mental disorders, especially major depressive disorder (MDD) and bipolar disorder (BD). Previous studies have reported that these diseases share common pathophysiological pathways; therefore, this study elucidated whether the plasma levels of protein markers related to common depressive symptoms differed between patients with BD and those with MDD. Plasma samples of 71 patients with mood disorders and clinical manifestations were analyzed in this study. After depleting the abundant proteins, liquid chromatography-tandem mass spectrometry and label-free quantification were performed. Five proteins, viz., cholesteryl ester transfer protein (CETP), apolipoprotein D (APOD), mannan-binding lectin serine protease 2 (MASP2), Ig lambda chain V-II region BO (IGLV2-8) and Ig kappa chain V-III region NG9 (IGKV3-20) were negatively associated with the total scores of the Hamilton depression rating scale (HAM-D), after adjusting for the covariates. CETP and APOD also showed significant negative correlations with the anhedonia/retardation and guilt/agitation scores of the HAM-D. Four proteins, namely, Ig kappa chain V-II region TEW (IGKC; IGKV2D-28), Ig lambda variable 5-45 (IGLV5-45), complement factor H (CFH) and attractin (ATRN), showed significant associations with anhedonia/retardation after adjusting for covariates. Proteins that significantly correlated with the symptoms could predict the remission state of depression (area under the curve [AUC], 0.83) and anhedonia/retardation (AUC, 0.80). Bioinformatics analysis revealed that complement activation, immune response, and lipid metabolism were significantly enriched pathways. Although our study design was cross-sectional and no controls were included, protein markers identified in this preliminary study will be further investigated in our subsequent longitudinal study.

DNA hydrolysing IgG catalytic antibodies: an emerging link between psychoses and autoimmunity

It is not uncommon to observe autoimmune comorbidities in a significant subset of patients with psychotic disorders, namely schizophrenia (SCZ) and bipolar disorder (BPD). To understand the autoimmune basis, the DNA abyzme activity mediated by serum polyclonal IgG Abs were examined in psychoses patients, quantitatively, by an in-house optimized DNase assay. A similar activity exhibited by IgG Abs from neuropsychiatric-systemic lupus erythematosus (NP-SLE) patients was used as a comparator. Our data revealed that the IgG DNase activity of SCZ was close to that of NP-SLE and it was twofold higher than the healthy controls. Interestingly, the association between DNase activity with PANSS (positive, general and total scores) and MADRS were noted in a subgroup of SCZ and BPD patients, respectively. In our study group, the levels of IL-6 and total IgG in BPD patients were higher than SCZ and healthy controls, indicating a relatively inflammatory nature in BPD, while autoimmune comorbidity was mainly observed in SCZ patients.

Bipolar disorders

Bipolar disorders are a complex group of severe and chronic disorders that includes bipolar I disorder, defined by the presence of a syndromal, manic episode, and bipolar II disorder, defined by the presence of a syndromal, hypomanic episode and a major depressive episode. Bipolar disorders substantially reduce psychosocial functioning and are associated with a loss of approximately 10-20 potential years of life. The mortality gap between populations with bipolar disorders and the general population is principally a result of excess deaths from cardiovascular disease and suicide. Bipolar disorder has a high heritability (approximately 70%). Bipolar disorders share genetic risk alleles with other mental and medical disorders. Bipolar I has a closer genetic association with schizophrenia relative to bipolar II, which has a closer genetic association with major depressive disorder. Although the pathogenesis of bipolar disorders is unknown, implicated processes include disturbances in neuronal-glial plasticity, monoaminergic signalling, inflammatory homoeostasis, cellular metabolic pathways, and mitochondrial function. The high prevalence of childhood maltreatment in people with bipolar disorders and the association between childhood maltreatment and a more complex presentation of bipolar disorder (eg, one including suicidality) highlight the role of adverse environmental exposures on the presentation of bipolar disorders. Although mania defines bipolar I disorder, depressive episodes and symptoms dominate the longitudinal course of, and disproportionately account for morbidity and mortality in, bipolar disorders. Lithium is the gold standard mood-stabilising agent for the treatment of people with bipolar disorders, and has antimanic, antidepressant, and anti-suicide effects. Although antipsychotics are effective in treating mania, few antipsychotics have proven to be effective in bipolar depression. Divalproex and carbamazepine are effective in the treatment of acute mania and lamotrigine is effective at treating and preventing bipolar depression. Antidepressants are widely prescribed for bipolar disorders despite a paucity of compelling evidence for their short-term or long-term efficacy. Moreover, antidepressant prescription in bipolar disorder is associated, in many cases, with mood destabilisation, especially during maintenance treatment. Unfortunately, effective pharmacological treatments for bipolar disorders are not universally available, particularly in low-income and middle-income countries. Targeting medical and psychiatric comorbidity, integrating adjunctive psychosocial treatments, and involving caregivers have been shown to improve health outcomes for people with bipolar disorders. The aim of this Seminar, which is intended mainly for primary care physicians, is to provide an overview of diagnostic, pathogenetic, and treatment considerations in bipolar disorders. Towards the foregoing aim, we review and synthesise evidence on the epidemiology, mechanisms, screening, and treatment of bipolar disorders.

Association between exposure to toxoplasmosis and major psychiatric disorders: a systematic review

Objective:

To assess the association between exposure to toxoplasmosis and major psychiatric disorders through a systematic review of the literature.

Methods:

The literature review was performed in the MEDLINE, SciELO, and PsycINFO databases. To evaluate the quality of the studies included in the review, the Newcastle-Ottawa Scale was used.

Results:

Thirty-one studies were included, and the majority found an association between exposure to toxoplasmosis and schizophrenia or bipolar disorder (58.3 and 54.5% of the included papers, respectively), but not major depressive disorder. We found no significant difference in mean quality scores between studies that corroborated and contradicted the association hypothesis for either schizophrenia or bipolar disorder. All included papers were considered at least satisfactory according to the Newcastle-Ottawa Scale (total scores ≥ 6 out of 9).

Conclusion:

Although there was no association between exposure to toxoplasmosis and major depressive disorder, the results indicate an association with both bipolar disorder and schizophrenia, despite their heterogeneity. Further studies should be performed with more specific variables so that the nature of these relationships can be elucidated.

Comparison of serum protein profiles between major depressive disorder and bipolar disorder

BACKGROUND

Major depressive disorder and bipolar disorder are prevalent and debilitating psychiatric disorders that are difficult to distinguish, as their diagnosis is based on behavioural observations and subjective symptoms. Quantitative protein profile analysis might help to objectively distinguish between these disorders and increase our understanding of their pathophysiology. Thus, this study was conducted to compare the peripheral protein profiles between the two disorders.

METHODS

Serum samples were collected from 18 subjects with major depressive disorder and 15 subjects with bipolar disorder. After depleting abundant proteins, liquid chromatography-tandem mass spectrometry (LC-MS/MS) and label-free quantification were performed. Data-dependent acquisition data were statistically analysed from the samples of 15 subjects with major depressive disorder and 10 subjects with bipolar disorder who were psychotropic drug-free. Two-sided t-tests were performed for pairwise comparisons of proteomes to detect differentially-expressed proteins (DEPs). Ingenuity Pathway Analysis of canonical pathways, disease and functions, and protein networks based on these DEPs was further conducted.

RESULTS

Fourteen DEPs were significant between subjects with major depressive disorder and those with bipolar disorder. Ras-related protein Rab-7a (t = 5.975, p = 4.3 × 10^- 6) and Rho-associated protein kinase 2 (t = 4.782, p = 8.0 × 10^- 5) were significantly overexpressed in subjects with major depressive disorder and Exportin-7 (t = -4.520, p = 1.5 × 10^- 4) was significantly overexpressed in subjects with bipolar disorder after considering multiple comparisons. Bioinformatics analysis showed that cellular functions and inflammation/immune pathways were significantly different.

CONCLUSIONS

Ras-related protein Rab-7a, Rho-associated protein kinase 2, and Exportin-7 were identified as potential peripheral protein candidates to distinguish major depressive disorder and bipolar disorder. Further large sample studies with longitudinal designs and validation processes are warranted.

Toxoplasma gondii: How an Amazonian parasite became an Inuit health issue

Toxoplasma gondii is a protozoan parasite that originated in the Amazon. Felids (mammals in the cat family) are the only definitive hosts. These animals shed large numbers of infectious oocysts into the environment, which can subsequently infect many intermediate hosts, including birds, mammals and, possibly, fish. Human T. gondii seroprevalence is high in some parts of the Canadian Arctic and is associated with adverse health consequences among Inuit population. Since the range of felids does not extend to the Arctic, it is not immediately obvious how this parasite got from the Amazon to the Arctic. The objectives of this overview are to summarize the health impacts of T. gondii infection in Inuit in Canada's North and to consider how this infection could have reached them. This article reviews the prevalence of T. gondii infection in terrestrial and marine animals in the Canadian Arctic and discusses their potential role in the foodborne transmission of this parasite to humans. Two distribution factors seem plausible. First, felids in more southern habitats may release infectious oocysts into waterways. As these oocysts remain viable for months, they can be transported northward via rivers and ocean currents and could infect Arctic fish and eventually the marine mammals that prey on the fish. Second, migratory terrestrial and marine intermediate hosts may be responsible for carrying T. gondii tissue cysts to the Arctic, where they may then pass on the infection to carnivores. The most likely source of T. gondii in Inuit is from consumption of traditionally-prepared country foods including meat and organs from intermediate hosts, which may be consumed raw. With climate change, northward migration of felids may increase the prevalence of T. gondii in Arctic wildlife.

GRA24-Based DNA Vaccine Prolongs Survival in Mice Challenged With a Virulent Toxoplasma gondii Strain

Toxoplasma gondii causes infections in a wide range of intermediate hosts and remains a threatening disease worldwide because of the lack of effective drugs and vaccines. Dense granule protein 24 (GRA24) is a novel essential virulence factor that is transferred into the nucleus of host cells from the parasitophorous vacuole to regulate gene expression. In the present study, bioinformatic analysis showed that GRA24 had a high score for B-cell and T-cell epitopes compared with surface antigen 1 (SAG1), which has been studied as a promising vaccine candidate. As a DNA vaccine, pVAX1-GRA24 was injected intramuscularly into BALB/c mice and the induced immune response was evaluated. pVAX1-GRA24 induced high levels of a mixed Th1/Th2 cytokines at 6 weeks after immunization. Antibody determinations, cytokines [interferon gamma (IFN-γ), interleukin (IL)-12, IL-4, IL-10], antigen-specific lymphocyte proliferation, CD4+ and CD8+ T lymphocytes, and cytotoxic T lymphocyte activity showed that mice immunized with pVAX1-GRA24 produced specific humoral and cellular immune responses. The expression levels of interferon regulatory factor 8 (IRF8), nuclear factor kappa B (NF-κB), and T-Box 21 (T-bet) were significantly higher in the pVAX1-GRA24 immunization group than in the control groups. Survival times were prolonged significantly (24.6 ± 5.5 days) in the mice immunized with pVAX1-GRA24 compared with the mice in the control groups, which died within 7 days of T. gondii challenge (p < 0.05). The results of the present study showed that pVAX1-GRA24 induced a T. gondii-specific immune response and thus represents a promising candidate vaccine to treat toxoplasmosis.

A Case-Control Seroprevalence Study on the Association Between Toxoplasma gondii Infection and Bipolar Disorder

Background and Aims: Infection with the parasite Toxoplasma gondii has been associated with bipolar disorder in several countries other than Mexico. Therefore, we sought to determine the association between seropositivity to T. gondii and bipolar disorder in a Mexican population. Methods: We performed an age- and gender-matched case-control study of 66 patients with bipolar disorder (WHO International Classification of Diseases, 10th Revision code: F31) and 396 subjects without this disorder from the general population. Anti-Toxoplasma immunoglobulin G (IgG) and IgM antibodies were determined using commercially available enzyme-linked immunoassays. Results: Six (9.1%) of the 66 patients with bipolar disorder and 22 (5.6%) of the 396 controls had anti-T. gondii IgG antibodies (odds ratio [OR] = 1.7; 95% confidence interval [CI] = 0.66-4.36; P = 0.26). Stratification by gender and age did not show a difference in seroprevalence between cases and controls. The frequency of high (> 150 international units/ml) anti-T. gondii IgG levels was similar in cases (n = 2) and in controls (n = 12) (OR = 1.0; 95% CI = 0.21-4.57; P = 1.00). Stratification by International Classification of Diseases, 10th Revision F31 codes showed that patients with F31.3 code had a higher seroprevalence of T. gondii infection than their age- and gender-matched controls (OR = 16.4; 95% CI = 1.25-215.09; P = 0.04). None of the six anti-T. gondii IgG-seropositive patients with bipolar disorder and 4 (18.2%) of the 22 anti-T. gondii IgG-seropositive controls had anti-T. gondii IgM antibodies (P = 0.54). Conclusions: Our results suggest that T. gondii seropositivity is not associated with bipolar disorder in general. However, a specific type of bipolar disorder (F31.3) might be associated with T. gondii seropositivity. Further research to elucidate the role of T. gondii infection in bipolar disorder is needed.