The known and missing links between Toxoplasma gondii and schizophrenia

Construction of Toxoplasma gondii SRS29C nucleic acid vaccine and comparative immunoprotective study of an SRS29C and SAG1 combination

Toxoplasma gondii is an intracellular protozoan parasite that infects all nucleated cells except the red blood cells. Currently, nucleic acid vaccines are being widely investigated in Toxoplasma gondii control, and several nucleic acid vaccine candidate antigens have shown good protection in various studies. The aim of this study was to construct a nucleic acid vaccine with Toxoplasma gondii SRS29C as the target gene. We explored the nucleic acid vaccine with Toxoplasma surface protein SRS29C and the combined gene of SRS29C and SAG1 and evaluated its immunoprotective effect against Toxoplasma gondii. To amplify the gene fragment and clone it to the expression vector, the recombinant plasmid pEGFP-SRS29C was constructed by PCR. Eukaryotic cells were transfected with the plasmid, and the expression of the target protein was assessed using the Western blot method. The level of serum IgG was determined via ELISA, and the splenic lymphocyte proliferation ability was detected using the CCK-8 method. The percentages of CD4+ and CD8+ T cells were measured by flow cytometry. Mice were immunised three times with single-gene nucleic acid vaccine and combination vaccine. Splenic lymphocytokine expression was determined using ELISA kits. The mice's survival time was monitored and recorded during an in vivo insect assault experiment, and the vaccine's protective power was assessed. The outcomes showed that PCR-amplification of an SRS29C gene fragment was successful. The 4,733-bp vector fragment and the 1,119-bp target segment were both recognised by double digestion. Additionally, after transfection of the recombinant plasmid pEGFP-SRS29C, Western blot examination of the extracted protein revealed the presence of a target protein strip at 66 kDa. The test results demonstrated that the IgG content in the serum of the pEGFP-SRS29C group and the co-immunization group was significantly higher than that of the PBS group and the empty vector group. The IgG potency induced by the co-immunization group was higher than that of the pEGFP-SRS29C group and the pEGFP-SAG1 group, the number of splenic lymphocyte proliferation number was higher than that of the PBS group and the empty vector group. The CD4+/CD8+ T ratio was higher than that of the PBS group and the empty vector group. The expression of IFN-γ and TNF-α in the splenocytes of the pEGFP-SRS29C group and the combined immunisation group was significantly higher following antigen stimulation. In the worm attack experiments, mice in the PBS and empty vector groups perished within 9 days of the worm attack, whereas mice in the pEGFP-SRS29C group survived for 18 days, mice in the pEGFP-SAG1 group survived for 21 days, and mice in the co-immunization group survived for 24 days. This demonstrates that the constructed Toxoplasma gondii nucleic acid vaccine pEGFP-SRS29C and the combined gene vaccine can induce mice to develop certain humoral and cellular immune responses, and enhance their ability to resist Toxoplasma gondii infection.

A review of the roles of pathogens in Alzheimer's disease

Alzheimer's disease (AD) is one of the leading causes of dementia and is characterized by memory loss, mental and behavioral abnormalities, and impaired ability to perform daily activities. Even as a global disease that threatens human health, effective treatments to slow the progression of AD have not been found, despite intensive research and significant investment. In recent years, the role of infections in the etiology of AD has sparked intense debate. Pathogens invade the central nervous system through a damaged blood-brain barrier or nerve trunk and disrupt the neuronal structure and function as well as homeostasis of the brain microenvironment through a series of molecular biological events. In this review, we summarize the various pathogens involved in AD pathology, discuss potential interactions between pathogens and AD, and provide an overview of the promising future of anti-pathogenic therapies for AD.

Correlation between toxoplasmosis and schizophrenia in Egyptian patients and its impact on dopamine serum levels

Toxoplasma gondii, a parasite infecting around one-third of the global population, has been linked to neurological disorders like schizophrenia. Abnormal dopamine levels are linked to the pathophysiology of schizophrenia, but their association remains unclear. This study aimed to investigate the relationship between T. gondii seroprevalence and dopamine serum levels in schizophrenic patients in Egypt. This case-control study included 93 patients diagnosed with schizophrenia and 93 individuals as controls. T. gondii seroprevalence was determined using an enzyme-linked immunosorbent assay (ELISA). Dopamine serum levels were measured using ELISA. Sociodemographic and clinical characteristics were also collected. The study found a higher prevalence of T. gondii IgG antibodies in patients with schizophrenia (68 %) compared to controls (46.2 %). Contact with cats, sausage consumption, and undercooked meat were identified as possible risk factors associated with T. gondii infection. The mean level of serum dopamine was significantly (P < 0.001) higher in patients with schizophrenia (115.3 Pg/ml ±31.8) compared to the control group (75.02 Pg/ml ±26.5). The study found that schizophrenic patients with T. gondii seropositivity had significantly higher dopamine serum levels (mean=145.2 ± 32.1 pg/ml) than those without T. gondii seropositivity (mean=122.5 ± 29.7 pg/ml) (p = 0.001). Logistic regression analysis revealed that T. gondii seropositivity was a significant predictor of increased dopamine serum levels in schizophrenic patients (odds ratio=3.4, 95 % confidence interval=1.8-6.4, p < 0.001). The study suggests that T. gondii seroprevalence may increase dopamine serum levels in Egyptian schizophrenic patients, potentially contributing to dopamine dysregulation in schizophrenia, but further research is needed to confirm these findings and investigate the underlying mechanisms.

A Review of Immunological and Neuropsychobehavioral Effects of Latent Toxoplasmosis on Humans

Toxoplasmosis as a zoonotic disease has a worldwide distribution and can infect a wide range of animal hosts, as well as at least one third of the world's human population. The disease is usually mild or asymptomatic in immunocompetent individuals, but dormant tissue cysts survive especially in the brain for the host lifespan, known as latent toxoplasmosis (LT). Recent studies suggest that LT can have certain neurological, immunological psychological and behavioural effects on human including schizophrenia, bipolar disorder, Alzheimer's disease, depression, suicide anxiety and sleeping disorders. LT effects are controversial, and their exact mechanisms of action is not yet fully understood. This review aims to provide an overview of the potential effects, their basic mechanisms including alteration of neurotransmitter levels, immune activation in the central nervous system and induction of oxidative stress. Additionally, beneficial effects of LT, and an explanation of the effects within the framework of manipulation hypothesis, and finally, the challenges and limitations of the current research are discussed.

Investigation of the effects of Toxoplasma gondii on behavioral and molecular mechanism in bradyzoite stage

Toxoplasma gondii is a single-celled parasite that causes a disease called toxoplasmosis. It can reach the central nervous system, but the mechanism of T. gondii disrupting the functioning of these brain regions occurs in bradyzoite stage of parasite, causing brain damage by forming tissue cysts in brain. In our study, the effects of T. gondii on locomotor activity, anxiety, learning and memory, and norepinephrine (NE), levodopa (L-DOPA), dopamine (DA) and 3,4-D-dihydroxyphenylacetic acid (DOPAC) catecholamines in amygdala, striatum, prefrontal cortex and hippocampus regions of the brain were investigated in bradyzoite stage. Twenty male Albino mice Mus musculus, 4-5 weeks old, weighing 20-25 g, were used. T. gondii inoculated to mice intraperitonealy with 48-50-hour passages of T. gondii RH Ankara strain. For intraperitoneal inoculation of mice 5x104 tachyzoites per mouse. No inoculation was made in control group (n: 20). Locomotor activity behavior in open field test (OFT), anxious behavior in elevated plus maze (EPM), and learning behavior in novel object recognition (NOR) tests were evaluated. NE, L-DOPA, DA and DOPAC were measured by HPLC in brain tissues of amygdala, striatum, prefrontal cortex and hippocampus. A decrease was observed in the locomotor activity, anxiety and learning values of the T. gondii group compared to the control group (p < 0.05). The heighten in NE and L-DOPA levels in amygdala tissue of T. gondii group compared to control group, an elevation in NE, L-DOPA, DA and DOPAC levels in striatum tissue, and an increase in levels of NE in prefrontal cortex tissue were detected in monoamine results. In hippocampus tissue, an increase was observed in DA levels, while a decrease was observed in NE, L-DOPA and DOPAC levels. In our study, it has been shown that T. gondii in bradyzoite stage reduces locomotor activity, causes learning and memory impairment, and has anxiogenic effects.

Toxoplasma gondii: Seroprevalence and association with childhood brain tumors in Egypt

BACKGROUND

Childhood brain tumors are a significant global health challenge, yet the etiology of these tumors remains elusive. While research has identified potential risk factors, recent studies have explored the involvement of infectious agents, particularly Toxoplasma gondii (T. gondii), in brain tumor development.

METHODS

This study aimed to explore the prevalence of T. gondii infection in children diagnosed with brain tumors and to investigate the potential association between T. gondii infection and childhood brain tumors in Egypt. A total of 64 children with brain tumors and 92 healthy controls were enrolled in this study. Demographics and risk factors data were collected using structured questionnaires. Serological assay using ELISA technique was performed to detect anti-T. gondii antibodies in both cases and control groups.

RESULTS

This study revealed a significantly higher seroprevalence of T. gondii infection in brain tumor cases (62.5 %) compared to healthy controls (38 %). Furthermore, a strong association was observed between T. gondii seropositivity and childhood brain tumors (odds ratio: 2.7). Notably, the consumption of unwashed vegetables emerged as a significant risk factor for T. gondii infection in Egypt. Analysis of T. gondii seroprevalence across different subtypes of brain tumors revealed varying rates, with glioma cases displaying a striking 100 % seroprevalence.

CONCLUSIONS

These findings support the hypothesis that T. gondii infection may be a risk factor for childhood brain tumors and emphasize the need for further research in this area. The study also highlights the potential implications of control of T. gondii infection for prevention and treatment of childhood brain tumors.

Expression profiles of host miRNAs and circRNAs and ceRNA network during Toxoplasma gondii lytic cycle

Toxoplasma gondii is an opportunistic protozoan parasite that is highly prevalent in the human population and can lead to adverse health consequences in immunocompromised patients and pregnant women. Noncoding RNAs, such as microRNAs (miRNAs) and circular RNAs (circRNAs), play important regulatory roles in the pathogenesis of many infections. However, the differentially expressed (DE) miRNAs and circRNAs implicated in the host cell response during the lytic cycle of T. gondii are unknown. In this study, we profiled the expression of miRNAs and circRNAs in human foreskin fibroblasts (HFFs) at different time points after T. gondii infection using RNA sequencing (RNA-seq). We identified a total of 7, 7, 27, 45, 70, 148, 203, and 217 DEmiRNAs and 276, 355, 782, 1863, 1738, 6336, 1229, and 1680 DEcircRNAs at 1.5, 3, 6, 9, 12, 24, 36, and 48 h post infection (hpi), respectively. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses revealed that the DE transcripts were enriched in immune response, apoptosis, signal transduction, and metabolism-related pathways. These findings provide new insight into the involvement of miRNAs and circRNAs in the host response to T. gondii infection.

The interplay between toxoplasmosis and host miRNAs: Mechanisms and consequences

Toxoplasmosis is one of the highly prevalent zoonotic diseases worldwide caused by the parasite Toxoplasma gondii (T. gondii). The infection with T. gondii could pass unidentified in immunocompetent individuals; however, latent cysts remain dormant in their digestive tract, but they could be shed and excreted with feces infesting the environment. However, active toxoplasmosis can create serious consequences, particularly in newborns and infected persons with compromised immunity. These complications include ocular toxoplasmosis, in which most cases cannot be treated. Additionally, it caused many stillbirths and miscarriages. Circulating miRNAs are important regulatory molecules ensuring that the normal physiological role of various organs is harmonious. Upon infection with T. gondii, the tightly regulated miRNA profile is disrupted to favor the parasite's survival and further participate in the disease pathogenesis. Interestingly, this dysregulated profile could be useful in acute and chronic disease discrimination and in providing insights into the pathomechanisms of the disease. Thus, this review sheds light on the various roles of miRNAs in signaling pathways regulation involved in the pathogenesis of T. gondii and provides insights into the application of miRNAs clinically for its diagnosis and prognosis.

Estimations of the number people with mental diseases associated with toxoplasmosis and identification of risk factors by continent

Strong evidence exists based on metanalysis of the relationship between toxoplasmosis and many psychiatric diseases: schizophrenia, bipolar disorder, and suicidal behavior. Herein, we estimate the number of cases based on the attributable fraction due to toxoplasmosis on these diseases. The population attributable fraction of mental disease associated with toxoplasmosis was 20,4% for schizophrenia; 27,3% for bipolar disorder; and 0,29% for suicidal behavior (self-harm). The lower and upper estimated number of people with mental disease associated with toxoplasmosis was 4'816.491 and 5'564.407 for schizophrenia; 6'348.946 and 7'510.118,82 for bipolar disorder; and 24.310 and 28.151 for self-harm; for a global total lower estimated number of 11'189.748 and global total upper estimated number of 13'102.678 people with mental disease associated with toxoplasmosis for the year 2019. According to the prediction through the Bayesian model of risk factors for toxoplasmosis associated with mental disease, these varied in importance geographically; thus, in Africa, the most important risk factor was water contamination and in the European region, the cooking conditions of meats. Toxoplasmosis and mental health should be a research priority given the enormous potential impact of reducing this parasite in the general population.

Global proteomic profiling of multiple organs of cats (Felis catus) and proteome-transcriptome correlation during acute Toxoplasma gondii infection

Background

Toxoplasma gondii is a protozoan parasite which can infect almost all warm-blooded animals and humans. Understanding the differential expression of proteins and transcripts associated with T. gondii infection in its definitive host (cat) may improve our knowledge of how the parasite manipulates the molecular microenvironment of its definitive host. The aim of this study was to explore the global proteomic alterations in the major organs of cats during acute T. gondii infection.

Methods

iTRAQ-based quantitative proteomic profiling was performed on six organs (brain, liver, lung, spleen, heart and small intestine) of cats on day 7 post-infection by cysts of T. gondii PRU strain (Genotype II). Mascot software was used to conduct the student’s t-test. Proteins with P values < 0.05 and fold change > 1.2 or < 0.83 were considered as differentially expressed proteins (DEPs).

Results

A total of 32,657 proteins were identified in the six organs, including 2556 DEPs; of which 1325 were up-regulated and 1231 were down-regulated. The brain, liver, lung, spleen, heart and small intestine exhibited 125 DEPs, 463 DEPs, 255 DEPs, 283 DEPs, 855 DEPs and 575 DEPs, respectively. Gene Ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses of all proteins and DEPs in all organs showed that many proteins were enriched in binding, cell part, cell growth and death, signal transduction, translation, sorting and degradation, extracellular matrix remodeling, tryptophan catabolism, and immune system. Correlations between differentially expressed proteins and transcripts were detected in the liver (n = 19), small intestine (n = 17), heart (n = 9), lung (n = 9) and spleen (n = 3).

Conclusions

The present study identified 2556 DEPs in six cat tissues on day 7 after infection by T. gondii PRU strain, and functional enrichment analyses showed that these DEPs were associated with various cellular and metabolic processes. These findings provide a solid base for further in-depth investigation of the complex proteotranscriptomic reprogramming that mediates the dynamic interplays between T. gondii and the different feline tissues.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40249-022-01022-7.

Metabolomic Profiling Reveals Common Metabolic Alterations in Plasma of Patients with Toxoplasma Infection and Schizophrenia

Toxoplasma gondii is an opportunistic protozoan parasite known to affect the human brain. The infection has been associated with an increased incidence of schizophrenia; however, the link between the two conditions remains unclear. This study aimed to compare the plasma metabolome of schizophrenia and non-schizophrenia subjects with or without Toxoplasma infection. Untargeted metabolomic profiling was carried out by liquid chromatography-mass spectrometry. Elevation of the α-hydroxyglutaric acid level and reduced adenosine monophosphate, inosine, hypoxanthine and xanthine were found in the subjects with either toxoplasmosis or schizophrenia alone. These results suggest that purine catabolism is a common metabolic alteration in Toxoplasma infection and schizophrenia. The roles of these metabolites on the pathogenesis of schizophrenia in relation to Toxoplasma infection warrant further studies.

Is latent Toxoplasma gondii infection associated with the occurrence of schizophrenia? A case-control study

Introduction

Neurotropic pathogens such as Toxoplasma gondii (T. gondii) which result in chronic infections in the brain are associated with mental illnesses. In view of this, a growing body of literature has revealed the possible interaction of schizophrenia and T. gondii infection.

Method

A case-control study was conducted from February 2018 to January 2019 among 47 Schizophrenia patients and 47 age and sex-matched controls. Data was collected using a structured questionnaire. Serum was used for serological analysis of anti-T. gondii IgG and IgM antibodies through chemiluminescent immunoassay. Proportions and mean with standard deviations (SD) were used as descriptive measures and variables with p-values <0.05 were considered as statistically significant and independently associated with schizophrenia.

Result

The mean ages of schizophrenia patients and controls were 29.64 ± 5.8 yrs and 30.98 ± 7.3 yrs, respectively. We found that 81.9% (77/94) of the study subjects had a positive anti-T. gondii IgG antibody. While the difference is statistically insignificant, schizophrenic patients have a marginally higher seroprevalence of toxoplasmosis than controls (87.2% vs 80.9%; p = 0.398). Schizophrenia cases who live in homes with soil floors have a significantly higher T. gondii infection as compared to those who live in homes with cement/ceramic floors (90.9% vs 33.3%; p = 0.004). Furthermore, there was a significantly lower T. gondii infection among schizophrenic cases who were taking antipsychotic medication for more than three yrs (79.3% vs 100.0%, p = 0.039). On the other hand, among all study subjects who have T. gondii infection, subjects who are addicted to khat and alcohol were about seven times more likely to develop schizophrenia (71.4% vs 47.7%, OR = 7.13, p = 0.024).

Conclusion

Our data is not sufficient to show a significant positive correlation between T. gondii infection and schizophrenia. For study subjects with T. gondii infection, addiction to khat and alcohol is one of the risk factors for schizophrenia.

Global MicroRNAs Expression Profile Analysis Reveals Possible Regulatory Mechanisms of Brain Injury Induced by Toxoplasma gondii Infection

Toxoplasma gondii (T. gondii) is an obligate intracellular parasitic protozoan that can cause toxoplasmosis in humans and other endotherms. T. gondii can manipulate the host gene expression profile by interfering with miRNA expression, which is closely associated with the molecular mechanisms of T. gondii-induced brain injury. However, it is unclear how T. gondii manipulates the gene expression of central nervous system (CNS) cells through modulation of miRNA expression in vivo during acute and chronic infection. Therefore, high-throughput sequencing was used to investigate expression profiles of brain miRNAs at 10, 25, and 50 days post-infection (DPI) in pigs infected with the Chinese I genotype T. gondii strain in this study. Compared with the control group 87, 68, and 135 differentially expressed miRNAs (DEMs) were identified in the infected porcine brains at 10, 25, and 50 DPI, respectively. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis showed that a large number significantly enriched GO terms and KEGG pathways were found, and were mostly associated with stimulus or immune response, signal transduction, cell death or apoptosis, metabolic processes, immune system or diseases, and cancers. miRNA–gene network analysis revealed that the crucial connecting nodes, including DEMs and their target genes, might have key roles in the interactions between porcine brain and T. gondii. These results suggest that the regulatory strategies of T. gondii are involved in the modulation of a variety of host cell signaling pathways and cellular processes, containing unfolded protein response (UPR), oxidative stress (OS), autophagy, apoptosis, tumorigenesis, and inflammatory responses, by interfering with the global miRNA expression profile of CNS cells, allowing parasites to persist in the host CNS cells and contribute to pathological damage of porcine brain. To our knowledge, this is the first report on miRNA expression profile in porcine brains during acute and chronic T. gondii infection in vivo. Our results provide new insights into the mechanisms underlying T. gondii-induced brain injury during different infection stages and novel targets for developing therapeutic agents against T. gondii.

Temporal transcriptomic changes in long non-coding RNAs and messenger RNAs involved in the host immune and metabolic response during Toxoplasma gondii lytic cycle

Background

Long non-coding RNAs (lncRNAs) are important regulators of various biological and pathological processes, in particular the inflammatory response by modulating the transcriptional control of inflammatory genes. However, the role of lncRNAs in regulating the immune and inflammatory responses during infection with the protozoan parasite Toxoplasma gondii remains largely unknown.

Methods

We performed a longitudinal RNA sequencing analysis of human foreskin fibroblast (HFF) cells infected by T. gondii to identify differentially expressed long non-coding RNAs (lncRNAs) and messenger RNAs (mRNAs), and dysregulated pathways over the course of T. gondii lytic cycle. The transcriptome data were validated by qRT-PCR.

Results

RNA sequencing revealed significant transcriptional changes in the infected HFFs. A total of 697, 1234, 1499, 873, 1466, 561, 676 and 716 differentially expressed lncRNAs (DElncRNAs), and 636, 1266, 1843, 2303, 3022, 1757, 3088 and 2531 differentially expressed mRNAs (DEmRNAs) were identified at 1.5, 3, 6, 9, 12, 24, 36 and 48 h post-infection, respectively. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of DElncRNAs and DEmRNAs revealed that T. gondii infection altered the expression of genes involved in the regulation of host immune response (e.g., cytokine–cytokine receptor interaction), receptor signaling (e.g., NOD-like receptor signaling pathway), disease (e.g., Alzheimer's disease), and metabolism (e.g., fatty acid degradation).

Conclusions

These results provide novel information for further research on the role of lncRNAs in immune regulation of T. gondii infection.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-05140-3.

Morphological and biochemical repercussions of Toxoplasma gondii infection in a 3D human brain neurospheres model

Background

Toxoplasmosis is caused by the parasite Toxoplasma gondii that can infect the central nervous system (CNS), promoting neuroinflammation, neuronal loss, neurotransmitter imbalance and behavioral alterations. T. gondii infection is also related to neuropsychiatric disorders such as schizophrenia. The pathogenicity and inflammatory response in rodents are different to the case of humans, compromising the correlation between the behavioral alterations and physiological modifications observed in the disease. In the present work we used BrainSpheres, a 3D CNS model derived from human pluripotent stem cells (iPSC), to investigate the morphological and biochemical repercussions of T. gondii infection in human neural cells.

Methods

We evaluated T. gondii ME49 strain proliferation and cyst formation in both 2D cultured human neural cells and BrainSpheres. Aspects of cell morphology, ultrastructure, viability, gene expression of neural phenotype markers, as well as secretion of inflammatory mediators were evaluated for 2 and 4 weeks post infection in BrainSpheres.

Results

T. gondii can infect BrainSpheres, proliferating and inducing cysts formation, neural cell death, alteration in neural gene expression and triggering the release of several inflammatory mediators.

Conclusions

BrainSpheres reproduce many aspects of T. gondii infection in human CNS, constituting a useful model to study the neurotoxicity and neuroinflammation mediated by the parasite. In addition, these data could be important for future studies aiming at better understanding possible correlations between psychiatric disorders and human CNS infection with T. gondii.

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T. gondii infects, proliferates and induce cysts formation in neurospheres.

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T. gondii infection induces neural cell death in neurospheres.

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T. gondii infection promotes alteration in neural gene expression in neurospheres.

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T. gondii infection promotes release of inflammatory mediators in neurospheres.

Interaction Between the Complement System and Infectious Agents - A Potential Mechanistic Link to Neurodegeneration and Dementia

As part of the innate immune system, complement plays a critical role in the elimination of pathogens and mobilization of cellular immune responses. In the central nervous system (CNS), many complement proteins are locally produced and regulate nervous system development and physiological processes such as neural plasticity. However, aberrant complement activation has been implicated in neurodegeneration, including Alzheimer's disease. There is a growing list of pathogens that have been shown to interact with the complement system in the brain but the short- and long-term consequences of infection-induced complement activation for neuronal functioning are largely elusive. Available evidence suggests that the infection-induced complement activation could be protective or harmful, depending on the context. Here we summarize how various infectious agents, including bacteria (e.g., Streptococcus spp.), viruses (e.g., HIV and measles virus), fungi (e.g., Candida spp.), parasites (e.g., Toxoplasma gondii and Plasmodium spp.), and prion proteins activate and manipulate the complement system in the CNS. We also discuss the potential mechanisms by which the interaction between the infectious agents and the complement system can play a role in neurodegeneration and dementia.

Quantitative Peptidomics of Mouse Brain After Infection With Cyst-Forming Toxoplasma gondii

Toxoplasma gondii is an obligate intracellular parasite capable of establishing persistent infection within the host brain and inducing severe neuropathology. Peptides are important native molecules responsible for a wide range of biological functions within the central nervous system. However, peptidome profiling in host brain during T. gondii infection has never been investigated. Using a label-free peptidomics approach (LC–MS/MS), we identified a total of 2,735 endogenous peptides from acutely infected, chronically infected and control brain samples following T. gondii infection. Quantitative analysis revealed 478 and 344 significantly differentially expressed peptides (DEPs) in the acute and chronic infection stages, respectively. Functional analysis of DEPs by Gene Ontology suggested these DEPs mainly originated from cell part and took part in cellular process. We also identified three novel neuropeptides derived from the precursor protein cholecystokinin. These results demonstrated the usefulness of quantitative peptidomics in determining bioactive peptides and elucidating their functions in the regulation of behavior modification during T. gondii infection.

Toxoplasma gondii induces metabolic disturbances in the hippocampus of BALB/c mice

Toxoplasma gondii can cross the blood-brain barrier and infect different regions of the brain including the hippocampus. In the present study, we examined the impact of Toxoplasma gondii infection on the metabolism of the hippocampus of female BALB/c mice compared to control mice using ultra-high-performance liquid chromatography-tandem mass spectrometry. Multivariate analysis revealed significant differences between infected and control hippocampi and identified 25, 82, and 105 differential metabolites (DMs) in the infected hippocampi at 7, 14, and 21 days post-infection (dpi), respectively. One DM (sphingosyl-phosphocholine in the sphingolipid metabolism pathway) and 11 dysregulated pathways were detected at all time points post-infection, suggesting their important roles in the neuropathogenesis of T. gondii infection. These pathways were related to neural activity, such as inflammatory mediator regulation of TRP channels, retrograde endocannabinoid signaling, and arachidonic acid metabolism. Weighted correlation network analysis and receiver operating characteristic analysis identified 33 metabolites significantly associated with T. gondii infection in the hippocampus, and 30 of these were deemed as potential biomarkers for T. gondii infection. This study provides, for the first time, a global view of the metabolic perturbations that occur in the mouse hippocampus during T. gondii infection. The potential relevance of the identified metabolites and pathways to the pathogenesis of cognitive impairment and psychiatric disorders are discussed.

Toxoplasma gondii, Herpesviridae and long-term risk of transition to first-episode psychosis in an ultra high-risk sample

BACKGROUND

Ultra high-risk (UHR) criteria were introduced to identify people at imminent risk of developing psychosis. To improve prognostic accuracy, additional clinical and biological risk factors have been researched. Associations between psychotic disorders and infections with Toxoplasma gondii and Herpesviridae have been found. It is unknown if exposure to those pathogens increases the risk of transition to psychosis in UHR cohorts.

METHODS

We conducted a long-term follow-up of 96 people meeting UHR criteria, previously seen at the Personal Assessment and Crisis Evaluation (PACE) clinic, a specialized service in Melbourne, Australia. Transition to psychosis was assessed using the Comprehensive Assessment of the At-Risk Mental State (CAARMS) and state public mental health records. The relationship between IgG antibodies to Herpesviridae (HSV-1, HSV-2, CMV, EBV, VZV) and Toxoplasma gondii and risk for transition was examined with Cox regression models.

RESULTS

Mean follow-up duration was 6.46 (±3.65) years. Participants who transitioned to psychosis (n = 14) had significantly higher antibody titers for Toxoplasma gondii compared to those who did not develop psychosis (p = 0.03). After adjusting for age, gender and year of baseline assessment, seropositivity for Toxoplasma gondii was associated with a 3.6-fold increase in transition hazard in multivariate Cox regression models (HR = 3.6; p = 0.036). No significant association was found between serostatus for Herpesviridae and risk of transition.

CONCLUSIONS

Exposure to Toxoplasma gondii may contribute to the manifestation of positive psychotic symptoms and increase the risk of transitioning to psychosis in UHR individuals.

Toxoplasma gondii infection and the risk of adult glioma in two prospective studies

Toxoplasma gondii (T gondii) is a common parasite that shows affinity to neural tissue and may lead to the formation of cysts in the brain. Previous epidemiologic studies have suggested an association between glioma and increased prevalence of T gondii infection, but prospective studies are lacking. Therefore, we examined the association between prediagnostic T gondii antibodies and risk of glioma in two prospective cohorts using a nested case-control study design. Cases and matched controls were selected from the American Cancer Society's Cancer Prevention Study-II Nutrition Cohort (CPSII-NC) (n = 37 cases and 74 controls) and the Norwegian Cancer Registry's Janus Serum Bank (Janus) (n = 323 cases and 323 controls). Blood samples collected prior to diagnosis were analyzed for antibodies to two T gondii surface antigens (p22 and sag-1), with individuals considered seropositive if antibodies to either antigen were detected. Conditional logistic regression was used to calculate odds ratios (OR) and 95% confidence intervals (95% CI) for each cohort. In both cohorts, a suggestive increase in glioma risk was observed among those infected with T gondii (OR: 2.70; 95% CI: 0.96-7.62 for CPSII-NC; OR: 1.32, 95% CI: 0.85-2.07 for Janus), particularly among participants with high antibody titers specific to the sag-1 antigen (CPSII-NC OR: 3.35, 95% CI: 0.99-11.38; Janus OR: 1.79, 95% CI: 1.02-3.14). Our findings provide the first prospective evidence of an association between T gondii infection and risk of glioma. Further studies with larger case numbers are needed to confirm a potential etiologic role for T gondii in glioma.

Additive effect of glutathione S-transferase T1 active genotype and infection with Toxoplasma gondii for increasing the risk of schizophrenia

PURPOSE

To determine if Toxoplasma gondii (T. gondii) infection may play a role in the development of schizophrenia in genetically susceptible persons with regard to genes encoding glutathione S-transferase T1 (GSTT1) and M1 (GSTM1).

METHODS

A total of 78 cases with psychiatric diagnosis of schizophrenia were compared with 91 healthy controls. For detection of IgG antibodies, enzyme-linked immunosorbent assay was used. Genotyping of GSTM1 and GSTT1 was performed by multiplex PCR. Chi-square and logistic regression were used for statistical analyses.

RESULTS

A higher frequency of the GSTT1 active gene in schizophrenic patients was observed. When risk categories based on the combination of T. gondii status and GSTs polymorphisms were compared, risk of schizophrenia increased in T. gondii positive/GSTT1 absent subjects (OR = 4.75, p = 0.05) compared with T. gondii negative/GSTT1 absent group. When T. gondii positive subjects had the GSTT1 active genotype, the risk increased linearly (OR = 10.20, p < 0.001). Odds ratio in T. gondii positive groups were almost the same in combination with the GSTM1 active genotype (OR = 4.45, p = 0.003) or null genotype (OR = 4.37, p = 0.006).

CONCLUSIONS

Our results showed an additive effect for T. gondii and GSTT1 active genotype as risk factors for schizophrenia in Iranian population. This is a small pilot study and replicating the study with larger groups of patients in multinational investigation to clarify these findings is recommended.

Seroepidemiology of Toxoplasma gondii infection in people with alcohol consumption in Durango, Mexico

The seroepidemiology of infection with Toxoplasma gondii (T. gondii) in alcohol consumers is largely undeveloped. In light of this, we sought to determine the seroprevalence of T. gondii infection in alcohol consumers in Durango, Mexico, and the association of T. gondii seroprevalence with characteristics of the population studied. Anti-T. gondii IgG and IgM antibodies were searched in sera of participants using commercially available enzyme immunoassays. Bivariate and logistic regression analyses were then used to determine the association between T. gondii infection and the characteristics of the population studied. Of the 1544 people studied (mean age: 39.4±14.0 years), 173 (11.2%) tested positive for anti-T. gondii IgG antibodies. We were able to test 167 of the 173 anti-T. gondii IgG positive sera for anti-T. gondii IgM antibodies. Fifty-five (32.9%) of these 167 serum samples were positive for anti-T. gondii IgM antibodies. Bivariate analysis showed that visual impairment, history of surgery, and hepatitis were negatively associated with T. gondii IgG seropositivity (P<0.05). In women, seropositivity to T. gondii was positively associated with a history of pregnancy (P<0.05). Logistic regression analysis showed that T. gondii seropositivity was associated with the variables consumption of armadillo meat (OR = 2.33; 95% CI: 1.04–5.22; P = 0.03), and the use of latrines for elimination of excretes (OR = 2.27; 95% CI: 1.07–4.80; P = 0.03); and high (>150 IU/ml) anti-T. gondii IgG antibodies were associated with consumption of both armadillo meat (OR = 2.25; 95% CI: 1.01–5.02; P = 0.04) and crowding at home (OR = 1.63; 95% CI: 1.02–2.61; P = 0.03). We found a distinct T. gondii seroprevalence in people with alcohol consumption from those previously found in population groups in the region. This is the first study that illustrates the association between high anti-T. gondii antibodies and crowding in Mexico, and the second study on the association between T. gondii infection and consumption of armadillo meat and the use of latrines in this country. We conclude that epidemiology of T. gondii infection in people with alcohol consumption deserves further investigation.

Transcriptomic Profiling of Mouse Brain During Acute and Chronic Infections by Toxoplasma gondii Oocysts

Infection by the protozoan Toxoplasma gondii can have a devastating impact on the structure and function of the brain of the infected individuals, particularly immunocompromised patients. A systems biology view of the brain transcriptome can identify key molecular targets and pathways that mediate the neuropathogenesis of cerebral toxoplasmosis. Here, we performed transcriptomic analysis of the brain of mice infected by T. gondii Pru strain oocysts at 11 and 33 days post-infection (dpi) compared to uninfected (control) mice using RNA sequencing (RNA-seq). T. gondii altered the expression of 936 and 2,081 transcripts at 11 and 33 dpi, respectively, and most of these were upregulated in the infected brains. Gene Ontology (GO) enrichment and pathway analysis showed that immune response, such as interferon-gamma (IFN-γ) responsive genes were strongly affected at 11dpi. Likewise, differentially expressed transcripts (DETs) related to T cell activation, cytokine production and immune cell proliferation were significantly altered at 33 dpi. Host-parasite interactome analysis showed that some DETs were involved in immune signaling, metabolism, biosynthesis-related processes and interspecies interaction. These findings should increase knowledge of the mouse brain transcriptome and the changes in transcriptional regulation and downstream signaling pathways during acute and chronic T. gondii infections.

Global profiling of lysine 2-hydroxyisobutyrylome in Toxoplasma gondii using affinity purification mass spectrometry

Lysine 2-hydroxyisobutyrylation (K_hib) is a recently discovered and evolutionarily conserved form of protein post-translational modification (PTM) found in mammalian and yeast cells. Previous studies have shown that K_hib plays roles in the activity of gene transcription and K_hib-containing proteins are closely related to the cellular metabolism. In this study, a global K_hib-containing analysis using the latest databases (ToxoDB 46, 8322 sequences, downloaded on April 16, 2020) and sensitive immune-affinity enrichment coupled with liquid chromatography-tandem mass spectrometry was performed. A total of 1078 K_hib modification sites across 400 K_hib-containing proteins were identified in tachyzoites of Toxoplasma gondii RH strain. Bioinformatics and functional enrichment analysis showed that K_hib-modified proteins were associated with various biological processes, such as ribosome, glycolysis/gluconeogenesis, and central carbon metabolism. Interestingly, many proteins of the secretory organelles (e.g., microneme, rhoptry, and dense granule) that play roles in the infection cycle of T. gondii were found to be K_hib-modified, suggesting the involvement of K_hib in key biological process during T. gondii infection. We also found that histone proteins, key enzymes related to cellular metabolism, and several glideosome components had K_hib sites. These results expanded our understanding of the roles of K_hib in T. gondii and should promote further investigations of how K_hib regulates gene expression and key biological functions in T. gondii.

Toxoplasma infection induces microglia-neuron contact and the loss of perisomatic inhibitory synapses

Infection and inflammation within the brain induces changes in neuronal connectivity and function. The intracellular protozoan parasite, Toxoplasma gondii, is one pathogen that infects the brain and can cause encephalitis and seizures. Persistent infection by this parasite is also associated with behavioral alterations and an increased risk for developing psychiatric illness, including schizophrenia. Current evidence from studies in humans and mouse models suggest that both seizures and schizophrenia result from a loss or dysfunction of inhibitory synapses. In line with this, we recently reported that persistent T. gondii infection alters the distribution of glutamic acid decarboxylase 67 (GAD67), an enzyme that catalyzes GABA synthesis in inhibitory synapses. These changes could reflect a redistribution of presynaptic machinery in inhibitory neurons or a loss of inhibitory nerve terminals. To directly assess the latter possibility, we employed serial block face scanning electron microscopy (SBFSEM) and quantified inhibitory perisomatic synapses in neocortex and hippocampus following parasitic infection. Not only did persistent infection lead to a significant loss of perisomatic synapses, it induced the ensheathment of neuronal somata by myeloid-derived cells. Immunohistochemical, genetic, and ultrastructural analyses revealed that these myeloid-derived cells included activated microglia. Finally, ultrastructural analysis identified myeloid-derived cells enveloping perisomatic nerve terminals, suggesting they may actively displace or phagocytose synaptic elements. Thus, these results suggest that activated microglia contribute to perisomatic inhibitory synapse loss following parasitic infection and offer a novel mechanism as to how persistent T. gondii infection may contribute to both seizures and psychiatric illness.

Ultra Performance Liquid Chromatography-Tandem Mass Spectrometry-Based Metabolomics Reveals Metabolic Alterations in the Mouse Cerebellum During Toxoplasma gondii Infection

Toxoplasma gondii is a protozoan parasite with a remarkable neurotropism. We recently showed that T. gondii infection can alter the global metabolism of the cerebral cortex of mice. However, the impact of T. gondii infection on the metabolism of the cerebellum remains unknown. Here we apply metabolomic profiling to discover metabolic changes associated with T. gondii infection of the mouse cerebellum using ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Multivariate statistics revealed differences in the metabolic profiles between the infected and control mouse groups and between the infected mouse groups as infection advanced. We also detected 10, 22, and 42 significantly altered metabolites (SAMs) in the infected cerebellum at 7, 14, and 21 days post infection (dpi), respectively. Four metabolites [tabersonine, arachidonic acid (AA), docosahexaenoic acid, and oleic acid] were identified as potential biomarker or responsive metabolites to T. gondii infection in the mouse cerebellum. Three of these metabolites (AA, docosahexaenoic acid, and oleic acid) play roles in the regulation of host behavior and immune response. Pathway analysis showed that T. gondii infection of the cerebellum involves reprogramming of amino acid and lipid metabolism. These results showcase temporal metabolomic changes during cerebellar infection by T. gondii in mice. The study provides new insight into the neuropathogenesis of T. gondii infection and reveals new metabolites and pathways that mediate the interplay between T. gondii and the mouse cerebellum.

Transcriptome Profiling of Toxoplasma gondii-Infected Human Cerebromicrovascular Endothelial Cell Response to Treatment with Monensin

Central to the progression of cerebral toxoplasmosis is the interaction of Toxoplasma gondii with the blood-brain barrier (BBB) endothelial cells. In the present work, we tested the hypothesis that inhibition of Wnt pathway signalling by the monovalent ionophore monensin reduces the growth of T. gondii infecting human brain microvascular endothelial cells (hBMECs) or microglial cells. The anti-parasitic effect of monensin (a Wnt signalling inhibitor) on the in vitro growth of T. gondii tachyzoites was investigated using two methods (Sulforhodamine B staining and microscopic parasite counting). The monensin inhibited T. gondii growth (50% inhibitory concentration [IC₅₀] = 0.61 μM) with a selective index = 8.48 when tested against hBMECs (50% cytotoxic concentration [CC₅₀] = 5.17 μM). However, IC₅₀ of monensin was 4.13 μM with a SI = 13.82 when tested against microglia cells (CC₅₀ = 57.08 μM), suggesting less sensitivity of microglia cells to monensin treatment. The effect of T. gondii on the integrity of the BBB was assessed by the transendothelial electrical resistance (TEER) assay using an in vitro human BBB model. The results showed that T. gondii infection significantly decreased hBMECs' TEER resistance, which was rescued when cells were treated with 0.1 µM monensin, probably due to the anti-parasitic activity of monensin. We also investigated the host-targeted effects of 0.1 µM monensin on global gene expression in hBMECs with or without T. gondii infection. Treatment of hBMECs with monensin did not significantly influence the expression of genes involved in the Wnt signalling pathway, suggesting that although inhibition of the Wnt signalling pathway did not play a significant role in T. gondii infection of hBMECs, monensin was still effective in limiting the growth of T. gondii. On the contrary, monensin treatment downregulated pathways related to steroids, cholesterol and protein biosynthesis and their transport between endoplasmic reticulum and Golgi apparatus, and deregulated pathways related to cell cycle and DNA synthesis and repair mechanisms. These results provide new insight into the host-modulatory effect of monensin during T. gondii infection, which merits further investigation.

Associations of mental disorders and neurotropic parasitic diseases: a meta-analysis in developing and emerging countries

BACKGROUND

Although they are declining worldwide, neurotropic parasitic diseases are still common in developing and emerging countries. The aim of this study was to estimate the pooled prevalence and pooled association measures of comorbidities between mental disorders (anxiety, depression, bipolar disorder, and schizophrenia) and neurotropic parasitic diseases (malaria, cysticercosis, toxoplasmosis, human African trypanosomiasis, Chagas disease, and human toxocariasis) in developing and emerging countries.

METHODS

As the first meta-analysis on this topic, this study was performed in accordance with PRISMA guidelines. The protocol was registered in PROSPERO (N°CRD42017056521). The Medline, Embase, Lilacs, and Institute of Epidemiology and Tropical Neurology databases were used to search for articles without any restriction in language or date. We evaluated the quality of studies independently by two investigators using the Downs and Black assessment grid and pooled estimates using the random-effects method from CMA (Comprehensive Meta Analysis) Version 3.0.

RESULTS

In total, 18 studies published between 1997 and 2016 met our inclusion criteria. We found that the prevalence of anxiety and depression in people suffering from Chagas disease and/or neurocysticercosis was 44.9% (95% CI, 34.4-55.9). In 16 pooled studies that included 1782 people with mental disorders and 1776 controls, toxoplasmosis and/or toxocariasis were associated with increased risk of schizophrenia and/or bipolar disorders (odds ratio = 2.3; 95% CI, 1.7-3.2). Finally, toxocariasis and/or toxoplasmosis were associated with an increased risk of the onset of schizophrenia (odds ratio = 2.4; 95% CI, 1.7-3.4).

CONCLUSION

Our pooled estimates show that the associations between diseases studied are relatively high in developing and emerging countries. This meta-analysis supports the hypothesis that toxoplasmosis could be the cause of schizophrenia. These findings could prove useful to researchers who want to further explore and understand the associations studied.

Development of an in vitro system to study the developmental stages of Toxoplasma gondii using a genetically modified strain expressing markers for tachyzoites and bradyzoites

Toxoplasma gondii, the agent of toxoplasmosis, is an intracellular parasite that can infect a wide range of vertebrate hosts. Toxoplasmosis causes severe damage to immunocompromised hosts and its treatment is mainly based on the combination of pyrimethamine and sulfadiazine, which causes relevant side effects primarily observed in AIDS patients, including bone marrow suppression and hematological toxicity (pyrimethamine) and/or hypersensitivity and allergic skin reactions (sulfadiazine). Thus, it is important to investigate new compounds against T. gondii, particularly those that may act on bradyzoites, which are present in cysts during the chronic disease phase. We propose an in vitro model to simultaneously study new candidate compounds against the two main causative stages of Toxoplasma infection in humans, using the EGS-DC strain that was modified from a type I/III strain (EGS), isolated from a case of human congenital toxoplasmosis in Brazil and engineered to express markers for both stages of development. One feature of this strain is that it presents tachyzoite and bradyzoite in the same culture system and in the same host cell under normal culture conditions. Additionally, this strain presents stage-specific fluorescent protein expression, allowing for easy identification of both stages, thus making this strain useful in different studies. HFF cells were infected and after 4 and 7 days post infection the cells were treated with 10 μM of pyrimethamine or atovaquone, for 48 or 72 h. We used high-throughput screening to quantify the extent of parasite infection. Despite a reduction in tachyzoite infection caused by both treatments, the atovaquone treatment reduced the bradyzoite infection while the pyrimethamine one increased it. Ultrastructural analysis showed that after treatment with both drugs, parasites displayed altered mitochondria. Fluorescence microscopy of cells labeled with MitoTracker CMXRos showed that the cysts present inside the cells lost their mitochondrial membrane potential. Our results indicate that this experimental model is adequate to simultaneously analyze new active compounds against tachyzoite and bradyzoite forms.

Impaired social behaviour and molecular mediators of associated neural circuits during chronic Toxoplasma gondii infection in female mice

Toxoplasma gondii (T. gondii) is a neurotropic parasite that is associated with various neuropsychiatric disorders. Rodents infected with T. gondii display a plethora of behavioural alterations, and Toxoplasma infection in humans has been strongly associated with disorders such as schizophrenia, in which impaired social behaviour is an important feature. Elucidating changes at the cellular level relevant to neuropsychiatric conditions can lead to effective therapies. Here, we compare changes in behaviour during an acute and chronic T. gondii infection in female mice. Further, we notice that during chronic phase of infection, mice display impaired sociability when exposed to a novel conspecific. Also, we show that T. gondii infected mice display impaired short-term social recognition memory. However, object recognition memory remains intact. Using c-Fos as a marker of neuronal activity, we show that infection leads to an impairment in neuronal activation in the medial prefrontal cortex, hippocampus as well as the amygdala when mice are exposed to a social environment and a change in functional connectivity between these regions. We found changes in synaptic proteins that play a role in the process of neuronal activation such as synaptophysin, PSD-95 and changes in downstream substrates of cell activity such as cyclic AMP, phospho-CREB and BDNF. Our results point towards an imbalance in neuronal activity that can lead to a wider range of neuropsychiatric problems upon T. gondii infection.

Metabolomic signature of mouse cerebral cortex following Toxoplasma gondii infection

BACKGROUND

The protozoan parasite Toxoplasma gondii infects and alters the neurotransmission in cerebral cortex and other brain regions, leading to neurobehavioral and neuropathologic changes in humans and animals. However, the molecules that contribute to these changes remain largely unknown.

METHODS

We have investigated the impact of T. gondii infection on the overall metabolism of mouse cerebral cortex. Mass-spectrometry-based metabolomics and multivariate statistical analysis were employed to discover metabolomic signatures that discriminate between cerebral cortex of T. gondii-infected and uninfected control mice.

RESULTS

Our results identified 73, 67 and 276 differentially abundant metabolites, which were involved in 25, 37 and 64 pathways at 7, 14 and 21 days post-infection (dpi), respectively. Metabolites in the unsaturated fatty acid biosynthesis pathway were upregulated as the infection progressed, indicating that T. gondii induces the biosynthesis of unsaturated fatty acids to promote its own growth and survival. Some of the downregulated metabolites were related to pathways, such as steroid hormone biosynthesis and arachidonic acid metabolism. Nine metabolites were identified as T. gondii responsive metabolites, namely galactosylsphingosine, arachidonic acid, LysoSM(d18:1), L-palmitoylcarnitine, calcitetrol, 27-Deoxy-5b-cyprinol, L-homophenylalanine, oleic acid and ceramide (d18:1/16:0).

CONCLUSIONS

Our data provide novel insight into the dysregulation of the metabolism of the mouse cerebral cortex during T. gondii infection and have important implications for studies of T. gondii pathogenesis.

Monitoring of kynurenine pathway metabolites, neurotransmitters and their metabolites in blood plasma and brain tissue of individuals with latent toxoplasmosis

The aim of the presented work was to develop a highly sensitive, accurate and rapid analytical method for the determination of concentration levels of tryptophan and its metabolites of kynurenine catabolic pathway, as well as neurotransmitters and their metabolites in complex biological matrices (brain tissue and blood plasma). The developed analytical method consists of analytes separation from the biological matrices by protein precipitation (blood plasma) or solvent extraction (brain tissue), derivatization of the analytes and their detection by high-performance liquid chromatography combined with mass spectrometry. Individual steps of the whole process were optimized and the method was validated in the terms of selectivity, linearity (R²≥0.980), precision (RSD ≤ 13.3%), recovery (≥82.0%), limit of detection (1.8 ng/mL of blood plasma, 2.2 pg/mg of brain tissue) and limit of quantification (2.5 ng/mL of blood plasma, 2.8 pg/mg of brain tissue). The method was subsequently verified by an animal study, where the concentration levels of the analytes in biological matrices (blood plasma and brain tissue) of T. gondii - infected rats and control animals were compared. All the data obtained from the animal study were statistically evaluated. Increased concentration levels of kynurenine catabolic pathway metabolites (e.g. kynurenine, 3-hydroxykynurenine, quinolinic acid) were observed in the case of T. gondii - infected rats in contrast to the control group. The opposite effect was determined in the case of serotonin and its metabolite 5-hydroxyindoleacetic acid, where higher concentration levels were found in blood plasma of healthy subjects. Finally, Principal Component Analysis (PCA) was utilized for a score plot formation. PCA score plots have demonstrated the similarities of individuals within each group and the differences among the groups.

Efficient genome engineering of Toxoplasma gondii using the TALEN technique

Background

Aromatic amino acid hydroxylase 2 (AAH2) is a bradyzoite-specific upregulated protein that may alter host behaviour by altering the host dopaminergic pathway. To better understand the role of the parasite’s AAH2 in host-parasite interactions, we generated an AAH2 fluorescent marker strain of T. gondii using the TALEN technique.

Methods

We generated an AAH2 fluorescent marker strain of T. gondii, which was designated PRU/AAH2-eGFP, using the TALEN technique. This strain stably expressed pyrimethamine resistance for screening and expressed enhanced green fluorescent protein (eGFP)-tagged AAH2 in the bradyzoite stage. The bradyzoite conversion of PRU/AAH2-eGFP was observed both in vitro and in vivo. The fluorescence localization of AAH2 in mouse models of chronic infection was observed by a Bruker in vivo imaging system.

Results

Transgenic T. gondii was successfully generated by the TALEN system. The eGFP-tagged AAH2 could be detected by in vivo imaging.

Conclusions

This study verified the feasibility of using TALEN technology for T. gondii research and provided an in vivo imaging method for in vivo research of bradyzoite-stage proteins.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3378-y) contains supplementary material, which is available to authorized users.

Negative Effects of Latent Toxoplasmosis on Mental Health

Infection by the parasite Toxoplasma, which affects about 33% of world population, is associated with an increased risk of several mental health disorders, the most strongly with schizophrenia. It is unknown whether schizophrenia is associated with this infection the most strongly, or whether this association has just been the most intensively studied for historical reasons. We used the data from 6,367 subjects tested for toxoplasmosis who took part in an internet survey to search for associations of these infections with 24 mental health disorders and evidence of otherwise impaired mental health. The typical symptom associated with toxoplasmosis was anxiety, and the typical toxoplasmosis-associated disorders were autism (OR = 4.78), schizophrenia (OR = 3.33), attention deficit hyperactivity disorder (OR = 2.50), obsessive compulsive disorder (OR = 1.86), antisocial personality disorder (OR = 1.63), learning disabilities (OR = 1.59), and anxiety disorder (OR = 1.48). Toxoplasmosis could play a substantial role in the etiopathogenesis of mental health disorders and its association with schizophrenia is the second strongest association, after autism.

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.

From inflammatory reactions to neurotransmitter changes: Implications for understanding the neurobehavioral changes in mice chronically infected with Toxoplasma gondii

Toxoplasma gondii is a protozoan parasite that can cause a latent infection in the central nervous system, leading to neurobehavioral abnormalities in the host. However, the mechanism underlying these changes remains relatively unexplored. In this study, we detected behavioral changes, pathological injury, secretion of neurotransmitters and related signal pathway in mice infected by T. gondii using behavioral test, histopathology, immunofluorescence staining, western blotting, HPLC and real time PCR. Mice showed neurobehavioral disturbances two months after infection with T. gondii. Histopathology revealed the activation of astrocytes and microglia, apoptosis of neurons and decreases in synapses in the brain of infected mice. Excessive secretion of cytokines and chemokines was detected in the brains of mice infected by T. gondii compared to uninfected mice. Furthermore, T. gondii infection led to abnormalities in neurotransmitters and the activation of NF-κB and dopamine (DA) signaling pathways in the infected mice. In conclusion, excessive activation of the inflammation in the brain could induce neuronal apoptosis in mice chronically infected with T. gondii. Dysregulation of the dopaminergic neurotransmitter could provide an explanation of neurobehavioral disorders in infected hosts.

Risk Assessment of Human Toxoplasmosis Associated with the Consumption of Pork Meat in Italy

Toxoplasmosis is a cosmopolitan disease and has a broad range of hosts, including humans and several wild and domestic animals. The human infection is mostly acquired through the consumption of contaminated food and pork meat has been recognized as one of the major sources of transmission. There are, however, certain fundamental differences between countries; therefore, the present study specifically aims to evaluate the exposure of the Italian population to Toxoplasma gondii through the ingestion of several types of pork meat products habitually consumed in Italy and to estimate the annual number of human infections within two subgroups of the population. A quantitative risk assessment model was built for this reason and was enriched with new elements in comparison to other similar risk assessments in order to enhance its accuracy. Sensitivity analysis and two alternative scenarios were implemented to identify the factors that have the highest impact on risk and to simulate different plausible conditions, respectively. The estimated overall average number of new infections per year among adults is 12,513 and 92 for pregnant women. The baseline model showed that almost all these infections are associated with the consumption of fresh meat cuts and preparations (mean risk of infection varied between 4.5 × 10^-5 and 5.5 × 10^-5 ) and only a small percentage is due to fermented sausages/salami. On the contrary, salt-cured meat products seem to pose minor risk but further investigations are needed to clarify still unclear aspects. Among all the considered variables, cooking temperature and bradyzoites' concentration in muscle impacted most the risk.

The association between toxoplasma and the psychosis continuum in a general population setting

Toxoplasma gondii infection is associated with increased risk for psychosis. However, the possible association between T. gondii and psychotic-like symptoms in the general adult population is unknown. We investigated whether T. gondii is associated with psychotic-like symptoms and psychosis diagnoses using data from Health 2000, a large cross-sectional health survey of the Finnish general population aged 30 and above. Seropositivity to toxoplasma was defined as a cutoff of 50IU/ml of IgG antibodies. Lifetime psychotic-like symptoms were identified with section G of the Composite International Diagnostic Interview, Munich version (M-CIDI). Symptoms were considered clinically relevant if they caused distress or help-seeking or there were at least three of them. Lifetime psychotic disorders were screened from the sample and were diagnosed with DSM-IV using SCID-I interview and information from medical records. All data were available for 5906 participants. We adjusted for variables related to T. gondii seropositivity (age, gender, education, region of residence, cat ownership, and C-reactive protein measuring inflammation) in regression models. We found that T. gondii seropositivity was significantly associated with clinically relevant psychotic-like symptoms (OR 1.77, p=0.001) and with the number of psychotic-like symptoms (IRR=1.55, p=0.001). The association between toxoplasma and diagnosed psychotic disorders did not reach statistical significance (OR 1.45 for schizophrenia). In a large sample representing the whole Finnish adult population, we found that serological evidence of toxoplasma infection predicted psychotic-like symptoms, independent of demographic factors and levels of C-reactive protein. Toxoplasma infection may be a risk factor for manifestation of psychotic-like symptoms.

Fetomaternal and Pediatric Toxoplasmosis

Toxoplasmosis is one of the most important causes of foodborne illnesses and inflammatory complications, as well as congenital disorders. Promiscuous Toxoplasma is transmitted by contaminated food and animal produce, water, vegetations, fruits and sexually through semen. Toxoplasma infects nucleated cells with a unique tropism for muscles and central nervous system and a mind bugging malicious effect. Pregnant women with acute or reactivated toxoplasmosis can transmit Toxoplasma via transplacental to the fetus. The severity of congenital toxoplasmosis depends on the gestation period, as infection in early pregnancy causes more severe consequences. Congenital toxoplasmosis complications include miscarriage, encephalitis, neurological retardation, mental illnesses, auditory and visual inflammatory disorders, cardiovascular abnormalities, and pains. Current therapies are inefficient for congenital and chronic toxoplasmosis or have severe side effects with life threatening complications. There is an urgent need for effective and safe therapeutic modalities to treat complications of toxoplasmosis and effective vaccines to eliminate the infectious agent. This investigation will discuss pathogenesis of feto-maternal, congenital and pediatric toxoplasmosis, the current available therapies in practice, and explore those therapeutic modalities in experimental stages for promising future trials.

Potential Sabotage of Host Cell Physiology by Apicomplexan Parasites for Their Survival Benefits

Plasmodium, Toxoplasma, Cryptosporidium, Babesia, and Theileria are the major apicomplexan parasites affecting humans or animals worldwide. These pathogens represent an excellent example of host manipulators who can overturn host signaling pathways for their survival. They infect different types of host cells and take charge of the host machinery to gain nutrients and prevent itself from host attack. The mechanisms by which these pathogens modulate the host signaling pathways are well studied for Plasmodium, Toxoplasma, Cryptosporidium, and Theileria, except for limited studies on Babesia. Theileria is a unique pathogen taking into account the way it modulates host cell transformation, resulting in its clonal expansion. These parasites majorly modulate similar host signaling pathways, however, the disease outcome and effect is different among them. In this review, we discuss the approaches of these apicomplexan to manipulate the host–parasite clearance pathways during infection, invasion, survival, and egress.

Brains and Brawn: Toxoplasma Infections of the Central Nervous System and Skeletal Muscle

Toxoplasma gondii is a widespread parasitic pathogen that infects over a third of the world's population. Following an acute infection, the parasite can persist within its mammalian host as intraneuronal or intramuscular cysts. Cysts will occasionally reactivate, and - depending on the host's immune status and site of reactivation - encephalitis or myositis can develop. Because these diseases have high levels of morbidity and can be lethal, it is important to understand how Toxoplasma traffics to these tissues, how the immune response controls parasite burden and contributes to tissue damage, and what mechanisms underlie neurological and muscular pathologies that toxoplasmosis patients present with. This review aims to summarize recent important developments addressing these critical topics.

Toxoplasma gondii and schizophrenia: a review of published RCTs

Over the last 60 years, accumulating evidence has suggested that acute, chronic, and maternal Toxoplasma gondii infections predispose to schizophrenia. More recent evidence suggests that chronically infected patients with schizophrenia present with more severe disease. After acute infection, parasites form walled cysts in the brain, leading to lifelong chronic infection and drug resistance to commonly used antiparasitics. Chronic infection is the most studied and closely linked with development and severity of schizophrenia. There are currently four published randomized controlled trials evaluating antiparasitic drugs, specifically azithromycin, trimethoprim, artemisinin, and artemether, in patients with schizophrenia. No trials have demonstrated a change in psychopathology with adjunctive treatment. Published trials have either selected drugs without evidence against chronic infection or used them at doses too low to reduce brain cyst burden. Furthermore, trials have failed to achieve sufficient power or account for confounders such as previous antipsychotic treatment, sex, age, or rhesus status on antiparasitic effect. There are currently no ongoing trials of anti-Toxoplasma therapy in schizophrenia despite ample evidence to justify further testing.

Reexamining Chronic Toxoplasma gondii Infection: Surprising Activity for a "Dormant" Parasite

PURPOSE OF REVIEW

Despite over a third of the world's population being chronically infected with Toxoplasma gondii, little is known about this largely asymptomatic phase of infection. This stage is mediated in vivo by bradyzoites within tissue cysts. The absence of overt symptoms has been attributed to the dormancy of bradyzoites. In this review, we reexamine the conventional view of chronic toxoplasmosis in light of emerging evidence challenging both the nature of dormancy and the consequences of infection in the CNS.

RECENT FINDINGS

New and emerging data reveal a previously unrecognized level of physiological and replicative capacity of bradyzoites within tissue cysts. These findings have emerged in the context of a reexamination of the chronic infection in the brain that correlates with changes in neuronal architecture, neurochemistry, and behavior that suggest that the chronic infection is not without consequence.

SUMMARY

The emerging data driven by the development of new approaches to study the progression of chronic toxoplasma infection reveals significant physiological and replicative capacity for what has been viewed as a dormant state. The emergence of bradyzoite and tissue cyst biology from what was viewed as a physiological "black box" offers exciting new areas for investigation with direct implications on the approaches to drug development targeting this drug-refractory state. In addition, new insights from studies on the neurobiology on chronic infection reveal a complex and dynamic interplay between the parasite, brain microenvironment, and the immune response that results in the detente that promotes the life-long persistence of the parasite in the host.