Differences among the three major strains of Toxoplasma gondii and their specific interactions with the infected host

Toxoplasma gondii genotyping from free-range chickens (Gallus gallus domesticus) in a rural area of Rio Grande do Sul, Brazil

ABSTRACT Free-range chickens may ingest oocysts of T. gondii present in the environment and consequently harbor virulent strains of this parasite in different tissues, without any clinical signs. Isolation of T. gondii through bioassays on mice and cats from naturally infected chicken tissues has been described in several countries, demonstrating the importance of free-range chickens in the transmission of this parasite. The aim of this study was the genotypic characterization of T. gondii isolates obtained from naturally infected free-range chickens in a rural area of the state of Rio Grande do Sul, Brazil. Brain and heart tissue from 12 chickens seropositive for T. gondii were processed using peptic digestion technique for parasite isolation. From 12 samples subjected to mouse bioassay, nine isolates were obtained. RFLP-PCR genotypic characterization was performed using 11 genetic markers: SAG1, 5'-3'SAG2, alt.SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1 and Apico. Genetic characterization of the isolates revealed the presence of five atypical genotypes according to ToxoDB (# 11, # 55, # 64, # 140 and # 163). Our results showed a wide genetic diversity of T. gondii in free-range chickens in this region.

Toxoplasma gondii Dense Granule Proteins 7, 14, and 15 Are Involved in Modification and Control of the Immune Response Mediated via NF-κB Pathway

Toxoplasma gondii infects almost all warm-blooded animals, including humans, leading to both cellular and humoral immune responses in the host. The virulence of T. gondii is strain specific and is defined by secreted effector proteins that disturb host immunity. Here, we focus on nuclear factor-kappa B (NFκB) signaling, which regulates the induction of T-helper type 1 immunity. A luciferase assay for screening effector proteins, including ROPs and GRAs that have biological activity against an NFκB-dependent reporter plasmid, found that overexpression of GRA7, 14, and 15 of a type II strain resulted in a strong activity. Thus, our study was aimed at understanding the involvement of NFκB in the pathogenesis of toxoplasmosis through a comparative analysis of these three molecules. We found that GRA7 and GRA14 were partially involved in the activation of NFκB, whereas GRA15 was essential for NFκB activation. The deletion of GRA7, GRA14, and GRA15 in the type II Prugniaud (Pru) strain resulted in a defect in the nuclear translocation of RelA. Cells infected with the PruΔgra15 parasite showed reduced phosphorylation of inhibitor-κBα. GRA7, GRA14, and GRA15 deficiency decreased the levels of interleukin-6 in RAW246.7 cells, and RNA-seq analysis revealed that GRA7, GRA14, and GRA15 deficiency predominantly resulted in downregulation of gene expression mediated by NFκB. The virulence of all mutant strains increased, but PruΔgra14 only showed a slight increase in virulence. However, the intra-footpad injection of the highly-virulent type I RHΔgra14 parasites in mice resulted in increased virulence. This study shows that GRA7, 14, and 15-induced host immunity via NFκB limits parasite expansion.

Pathogenesis of ocular toxoplasmosis

Ocular toxoplasmosis is a retinitis -almost always accompanied by vitritis and choroiditis- caused by intraocular infection with Toxoplasma gondii. Depending on retinal location, this condition may cause substantial vision impairment. T. gondii is an obligate intracellular protozoan parasite, with both sexual and asexual life cycles, and infection is typically contracted orally by consuming encysted bradyzoites in undercooked meat, or oocysts on unwashed garden produce or in contaminated water. Presently available anti-parasitic drugs cannot eliminate T. gondii from the body. In vitro studies using T. gondii tachyzoites, and human retinal cells and tissue have provided important insights into the pathogenesis of ocular toxoplasmosis. T. gondii may cross the vascular endothelium to access human retina by at least three routes: in leukocyte taxis; as a transmigrating tachyzoite; and after infecting endothelial cells. The parasite is capable of navigating the human neuroretina, gaining access to a range of cell populations. Retinal Müller glial cells are preferred initial host cells. T. gondii infection of the retinal pigment epithelial cells alters the secretion of growth factors and induces proliferation of adjacent uninfected epithelial cells. This increases susceptibility of the cells to parasite infection, and may be the basis of the characteristic hyperpigmented toxoplasmic retinal lesion. Infected epithelial cells also generate a vigorous immunologic response, and influence the activity of leukocytes that infiltrate the retina. A range of T. gondii genotypes are associated with human ocular toxoplasmosis, and individual immunogenetics -including polymorphisms in genes encoding innate immune receptors, human leukocyte antigens and cytokines- impacts the clinical manifestations. Research into basic pathogenic mechanisms of ocular toxoplasmosis highlights the importance of prevention and suggests new biological drug targets for established disease.

The zebrafish as a novel model for the in vivo study of Toxoplasma gondii replication and interaction with macrophages

Toxoplasma gondii is an obligate intracellular parasite capable of invading any nucleated cell. Three main clonal lineages (type I, II, III) exist and murine models have driven the understanding of general and strain-specific immune mechanisms underlying Toxoplasma infection. However, murine models are limited for studying parasite-leukocyte interactions in vivo, and discrepancies exist between cellular immune responses observed in mouse versus human cells. Here, we developed a zebrafish infection model to study the innate immune response to Toxoplasma in vivo By infecting the zebrafish hindbrain ventricle, and using high-resolution microscopy techniques coupled with computer vision-driven automated image analysis, we reveal that Toxoplasma invades brain cells and replicates inside a parasitophorous vacuole to which type I and III parasites recruit host cell mitochondria. We also show that type II and III strains maintain a higher infectious burden than type I strains. To understand how parasites are cleared in vivo, we further analyzed Toxoplasma-macrophage interactions using time-lapse microscopy and three-dimensional correlative light and electron microscopy (3D CLEM). Time-lapse microscopy revealed that macrophages are recruited to the infection site and play a key role in Toxoplasma control. High-resolution 3D CLEM revealed parasitophorous vacuole breakage in brain cells and macrophages in vivo, suggesting that cell-intrinsic mechanisms may be used to destroy the intracellular niche of tachyzoites. Together, our results demonstrate in vivo control of Toxoplasma by macrophages, and highlight the possibility that zebrafish may be further exploited as a novel model system for discoveries within the field of parasite immunity.This article has an associated First Person interview with the first author of the paper.

Effect of deletion of gra17 and gra23 genes on the growth, virulence, and immunogenicity of type II Toxoplasma gondii

The protozoan parasite Toxoplasma gondii secretes a number of dense granule proteins (GRAs) from the dense granule organelle to manipulate the host cell. Two of these effector proteins (GRA17 and GRA23) are involved in the trafficking of molecules between the parasitophorous vacuole (PV) and the host cell cytoplasm. However, their roles in establishing chronic infection remain obscured. In this study, CRISPR-Cas9 was used to delete gra17 or gra23 gene in T. gondii Pru strain (type II). The growth, the virulence, the ability to establish chronic infection, and the immunogenicity of the constructed mutant strains were investigated in Kunming mice. Pru:Δgra17 and Pru:Δgra23 mutants developed PVs with abnormal morphology and exhibited reduced growth rate, compared with the wild-type Pru strain. Deletion of gra17 abrogated acute infection and blocked cyst formation. Although the deletion of gra23 caused slight attenuation of the parasite virulence in mice, it caused a significant reduction in cyst formation. Immunization with Pru:Δgra17 induced high levels of IgG (IgG1 and IgG2a) antibodies and cytokines (interleukin-2 [IL-2], IL-10, IL-12, and interferon gamma [IFN-γ]), which conferred significant protection in mice challenged with virulent type I (RH), ToxoDB#9 (PYS) strains, or less virulent type II (Pru) strain of T. gondii. These findings show that GRA17 and GRA23 play important roles in T. gondii chronic infection and that irreversible deletion of gra17 in T. gondii type II Pru strain can be a viable option for stimulating protective immunity to T. gondii infection.

Toxoplasma GRA15 and GRA24 are important activators of the host innate immune response in the absence of TLR11

The murine innate immune response against Toxoplasma gondii is predominated by the interaction of TLR11/12 with Toxoplasma profilin. However, mice lacking Tlr11 or humans, who do not have functional TLR11 or TLR12, still elicit a strong innate immune response upon Toxoplasma infection. The parasite factors that determine this immune response are largely unknown. Herein, we investigated two dense granule proteins (GRAs) secreted by Toxoplasma, GRA15 and GRA24, for their role in stimulating the innate immune response in Tlr11-/- mice and in human cells, which naturally lack TLR11/TLR12. Our results show that GRA15 and GRA24 synergistically shape the early immune response and parasite virulence in Tlr11-/- mice, with GRA15 as the predominant effector. Nevertheless, acute virulence in Tlr11-/- mice is still dominated by allelic combinations of ROP18 and ROP5, which are effectors that determine evasion of the immunity-related GTPases. In human macrophages, GRA15 and GRA24 play a major role in the induction of IL12, IL18 and IL1β secretion. We further show that GRA15/GRA24-mediated IL12, IL18 and IL1β secretion activates IFNγ secretion by peripheral blood mononuclear cells (PBMCs), which controls Toxoplasma proliferation. Taken together, our study demonstrates the important role of GRA15 and GRA24 in activating the innate immune response in hosts lacking TLR11.

Toxoplasma GRA15 limits parasite growth in IFNγ-activated fibroblasts through TRAF ubiquitin ligases

The protozoan parasite Toxoplasma gondii lives inside a vacuole in the host cytosol where it is protected from host cytoplasmic innate immune responses. However, IFNγ-dependent cell-autonomous immunity can destroy the vacuole and the parasite inside. Toxoplasma strain differences in susceptibility to human IFNγ exist, but the Toxoplasma effector(s) that determine these differences are unknown. We show that in human primary fibroblasts, the polymorphic Toxoplasma-secreted effector GRA15 mediates the recruitment of ubiquitin ligases, including TRAF2 and TRAF6, to the vacuole membrane, which enhances recruitment of ubiquitin receptors (p62/NDP52) and ubiquitin-like molecules (LC3B, GABARAP). This ultimately leads to lysosomal degradation of the vacuole. In murine fibroblasts, GRA15-mediated TRAF6 recruitment mediates the recruitment of immunity-related GTPases and destruction of the vacuole. Thus, we have identified how the Toxoplasma effector GRA15 affects cell-autonomous immunity in human and murine cells.

Assays to Evaluate Toxoplasma-Macrophage Interactions

The obligate intracellular protozoan parasite Toxoplasma gondii can infect any nucleated cell from a warm-blooded host. However, its interaction with host macrophages plays a critical role in shaping the immune response during infection. Therefore, assessing Toxoplasma-macrophage interactions at a cellular level is important. In this chapter, we describe assays that can be used to characterize Toxoplasma-macrophage interactions. These assays can also be used to evaluate other host-pathogen interactions. We describe multiplex approaches for measuring arginase activity, indoleamine 2,3 dioxygenase activity, cell death, and parasite growth during Toxoplasma-macrophage interactions. These assays can be used to compare how different Toxoplasma strains differ in their interaction with macrophages, and we describe how to properly assess Toxoplasma strain differences in Toxoplasma-macrophage interactions.

Evaluation of immunogenicity and protection of the Mic1-3 knockout Toxoplasma gondii live attenuated strain in the feline host

Toxoplasmosis is a zoonotic disease caused by the parasite Toxoplasma gondii. Up to a third of the global human population is estimated to carry a T. gondii infection, which can result in severe complications in immunocompromised individuals and pregnant women. Humans and animals can become infected by ingesting either tissue cysts containing T. gondii bradyzoites, from raw or undercooked meat, or sporulated oocysts from environmental sources. T. gondii oocysts are released in the faeces of cats and other felids, which are the parasite's definitive hosts, leading to environmental contamination. Therefore, vaccination of the feline host against T. gondii is an interesting strategy to interrupt the parasitic life cycle and subsequently limit contamination of intermediate hosts. With this goal in mind, we tested in cats, an attenuated live strain of T. gondii deleted for the Mic1 and Mic3 genes (Mic1-3KO) that was previously shown to be an efficient vaccine candidate in mouse and sheep models. Subcutaneous or oral vaccination routes induced a high specific antibody titer in the cat sera, indicating that the Mic1-3KO strain is immunogenic for cats. To assess protection induced by the vaccine candidate strain, we followed oocysts shedding by vaccinated cats, after oral challenge with a T. gondii wild-type strain. Surprisingly, a high antibody titer did not prevent cats from shedding oocysts from the challenge strain, regardless of the vaccination route. Our results show that the Mic1-3KO vaccine candidate is immunogenic in the feline host, is well tolerated and safe, but does not confer protection against oocysts shedding after natural infection with wild type T. gondii. This result highlights the particular relationship between T. gondii and its unique definitive host, which indicates the need for further investigations to improve vaccination strategies to limit environmental and livestock contaminations.

Sero-Epidemiological Study of Selected Zoonotic and Abortifacient Pathogens in Cattle at a Wildlife-Livestock Interface in South Africa

A cross sectional sero-epidemiological study was conducted on cattle in a communal farming area adjacent to Kruger National Park at a wildlife-livestock interface in South Africa. A total of 184 cattle were screened for exposure to 5 abortifacient or zoonotic pathogens, namely Coxiella burnetii, Toxoplasma gondii, Chlamydophila abortus, Neospora caninum, and Rift Valley fever virus (RVFV) using enzyme-linked immunosorbent assays. In addition, the virus neutralization test was used to confirm the presence of antibodies to RVFV. The seroprevalence of C. burnetii, T. gondii, C. abortus, N. caninum, and RVFV antibodies was 38.0%, 32.6%, 20.7%, 1.6%, and 0.5%, respectively, and varied between locations (p < 0.001). Seroprevalence of C. burnetii and T. gondii was highly clustered by location (intraclass correlation coefficient [ICC] = 0.57), and that of C. abortus moderately so (ICC = 0.11). Seroprevalence was not associated with sex or age for any pathogen, except for C. abortus, for which seroprevalence was positively associated with age (p = 0.01). The predominant mixed infections were C. burnetii and T. gondii (15.2%) and C. burnetii, T. gondii, and C. abortus (13.0%). The serological detection of the five abortifacient pathogens in cattle indicates the potential for economic losses to livestock farmers, health impacts to domestic animals, transmission across the livestock-wildlife interface, and the risk of zoonotic transmission. This is the first documentation of T. gondii infection in cattle in South Africa, while exposure to C. burnetii, C. abortus, and N. caninum infections is being reported for the first time in cattle in a wildlife-livestock interface in the country.

Role of the kynurenine pathway and the endocannabinoid system as modulators of inflammation and personality traits

BACKGROUND

Kynurenine pathway metabolites and endocannabinoids both exert potent regulatory effects on the immune system, but the relationship between these molecules is unknown. The role of these immunobiological mediators in emotionality and personality traits is not previously characterized.

METHODS

Interleukin-6 (IL-6), 2-arachidonoylglycerol (2-AG) and picolinic acid (PIC) were measured in the plasma of physically healthy individuals who had history of mood, anxiety, and personality disorders (n = 96) or who had no history of any psychiatric disorder (n = 56) by DSM-5 Criteria. Dimensional assessments of personality were performed using the Eysenck Personality Questionnaire (EPQ) and the Tridimensional Personality Questionnaire (TPQ).

RESULTS

Plasma IL-6 levels were significantly associated with plasma 2-AG levels and plasma PIC levels across all subjects. PIC levels were also negatively associated with 2-AG levels across all subjects, independent of IL-6 levels. In our analysis of the biological determinants of personality factors, we identified significant associations between IL-6 and novelty seeking assessment, and between PIC and neuroticism assessment.

CONCLUSIONS

These data provide evidence of a biological link between metabolites of the kynurenine pathway, the endocannabinoid system and IL-6 and suggest that these factors may influence personality traits.

Zombie bugs? Manipulation of kissing bug behavior by the parasite Trypanosoma cruzi

The parasite manipulation hypothesis states that the parasite modifies host's behavior thereby increasing the probability that the parasite will pass from an intermediate host to its final host. We used the kissing bugs Triatoma pallidipennis and T. longipennis and two isolates of the Trypanosoma cruzi parasite (Chilpancingo and Morelos) to test these ideas. These insects are intermediate hosts of this parasite, which is the causal agent of Chagas disease. The Chilpancingo isolate is more pathogenic than the Morelos isolate, in the bugs. We expected that infected bugs would be more active and likely at detecting human-like odors. Given the differences in pathogenicity between isolates, we expected the Chilpancingo isolate to induce these effects more strongly and lead to higher parasite number than the Morelos isolate. Finally, infected bugs would gain less mass (a mechanism thought to increase bite rate, and thus transmission) than non-infected bugs. Having determined that both isolate haplotypes belong to the Tc1a group, we found that: (a) young instars of both species were more active and likely to detect human odor when they were infected, regardless of the isolate; (b) there was no difference in parasite abundance depending on isolate; and, (c) infected bugs did not end up with less weight than uninfected bugs. These results suggest that T. cruzi can manipulate the bugs, which implies a higher risk to contract Chagas disease than previously thought.

Genetic characterization of Toxoplasma gondii in Iranian HIV positive patients using multilocus nested-PCR-RFLP method

The aim of the present study was to investigate the prevalence and genotyping of Toxoplasma gondii in Iranian human immunodeficiency virus (HIV)-positive patients using multilocus-nested polymerase chain reaction restriction fragment length polymorphism (Mn-PCR-RFLP). A total of 102 serum samples obtained from infected patients were collected from the laboratory centres in northern Iran. Anti-T. gondii antibodies and deoxyribonucleic acid (DNA) detection were accomplished by an enzyme-linked immunosorbent assay and PCR. The Mn-PCR-RFLP method was used for the genotyping of T. gondii. Overall, 68.6% (70/102) and 11.7% (12/102) of the individuals were tested positive for anti-T. gondii immunoglobulin G and T. gondii DNA, respectively. Complete genotyping was performed on 10/12 (83.3%) PCR-positive samples. Accordingly, the samples were classified as genotype #1 (type II clonal; n = 3, 30%), genotype #2 (type III clonal; n = 2, 20%), genotype #10 (type I clonal; n = 2, 20%), genotype #27 (type I variant; n = 1, 10%), genotype #35 (type I variant; n = 1, 10%) and genotype #48 (type III variant; n = 1, 10%). The results were indicative of the high frequency of the type I and type I variant of T. gondii strains in HIV-positive patients in northern Iran. Given the high prevalence of T. gondii and frequency of pathogenic types (pathogen in laboratory mice) in the patients, special measures should be taken to prevent the possible increased incidence of encephalitis by T. gondii.

Global Lysine Crotonylation and 2-Hydroxyisobutyrylation in Phenotypically Different Toxoplasma gondii Parasites

Toxoplasma gondii is a unicellular protozoan parasite of the phylum Apicomplexa. The parasite repeatedly goes through a cycle of invasion, division and induction of host cell rupture, which is an obligatory process for proliferation inside warm-blooded animals. It is known that the biology of the parasite is controlled by a variety of mechanisms ranging from genomic to epigenetic to transcriptional regulation. In this study, we investigated the global protein posttranslational lysine crotonylation and 2-hydroxyisobutyrylation of two T. gondii strains, RH and ME49, which represent distinct phenotypes for proliferation and pathogenicity in the host. Proteins with differential expression and modification patterns associated with parasite phenotypes were identified. Many proteins in T. gondii were crotonylated and 2-hydroxyisobutyrylated, and they were localized in diverse subcellular compartments involved in a wide variety of cellular functions such as motility, host invasion, metabolism and epigenetic gene regulation. These findings suggest that lysine crotonylation and 2-hydroxyisobutyrylation are ubiquitous throughout the T. gondii proteome, regulating critical functions of the modified proteins. These data provide a basis for identifying important proteins associated with parasite development and pathogenicity.

Inter- and intra-genotype differences in induced cystogenesis of recombinant strains of Toxoplasma gondii isolated from chicken and pigs

The ability to differentiate from the proliferative (tachyzoite) to the latent (bradyzoite) stage of isolates of Toxoplasma gondii recombinant genotypes (I/II/III and I/III) and reference strains from a clonal line (RH and ME49) was investigated in this study. Two isolates from chicken (#114 and #277; ToxoDB) and 3 from pigs (#114; ToxoDB) were the subjects for evaluation. The isolates were grown in cell culture under 2 different conditions: culture medium at pH 7.0 (neutral, without stress induction) or pH 8.0 (alkaline, stress inducing). After 4 days, the cultures were fixed and the events resulting from infection and induction were labeled. T. gondii cysts were labeled using Dolichos biflorus-FITC lectin (DBL-cysts) and free tachyzoites or vacuolar were labeled using an anti-T. gondii polyclonal antibody followed by an Alexa 594-conjugated secondary antibody (DBL-negative structures compatible with parasite structures - lysis plaques or vacuole). Differences in DBL-cysts formation in vitro in response to exogenous stress were observed between recombinant genotype isolates and the typical genotypes. The differences in conversion rates and the patterns of lysis plate production between genotype I/III isolates (#114) indicate that care should be taken when extrapolating the in vitro phenotypic characteristics of parasites from the same genotype.

Toxoplasma gondii-induced host cellular cell cycle dysregulation is linked to chromosome missegregation and cytokinesis failure in primary endothelial host cells

Toxoplasma gondii is a zoonotic and intracellular parasite with fast proliferating properties leading to rapid host cell lysis. T. gondii modulates its host cell on numerous functional levels. T. gondii was previously reported to influence host cellular cell cycle and to dampen host cell division. By using primary endothelial host cells, we show for the first time that T. gondii tachyzoite infections led to increased host cell proliferation and to an enhanced number of multi-nucleated host cells. As detected on DNA content level, parasite infections induced a G2/M cell cycle arrest without affecting expression of G2-specific cyclin B1. In line, parasite-driven impairment mainly concerned mitotic phase of host cells by propagating several functional alterations, such as chromosome segregation errors, mitotic spindle alteration and blockage of cytokinesis progression, with the latter most likely being mediated by the downregulation of the Aurora B kinase expression.

iTRAQ-Based Global Phosphoproteomics Reveals Novel Molecular Differences Between Toxoplasma gondii Strains of Different Genotypes

To gain insights into differences in the virulence among T. gondii strains at the post-translational level, we conducted a quantitative analysis of the phosphoproteome profile of T. gondii strains belonging to three different genotypes. Phosphopeptides from three strains, type I (RH strain), type II (PRU strain) and ToxoDB#9 (PYS strain), were enriched by titanium dioxide (TiO2) affinity chromatography and quantified using iTRAQ technology. A total of 1,441 phosphopeptides, 1,250 phosphorylation sites and 759 phosphoproteins were detected. In addition, 392, 298, and 436 differentially expressed phosphoproteins (DEPs) were identified in RH strain when comparing RH/PRU strains, in PRU strain when comparing PRU/PYS strains, and in PYS strain when comparing PYS/RH strains, respectively. Functional characterization of the DEPs using GO, KEGG, and STRING analyses revealed marked differences between the three strains. In silico kinase substrate motif analysis of the DEPs revealed three (RxxS, SxxE, and SxxxE), three (RxxS, SxxE, and SP), and five (SxxE, SP, SxE, LxRxxS, and RxxS) motifs in RH strain when comparing RH/PRU strains, in PRU strain when comparing PRU/PYS, and in PYS strain when comparing PYS/RH strains, respectively. This suggests that multiple overrepresented protein kinases including PKA, PKG, CKII, IKK, and MAPK could be involved in such a difference between T. gondii strains. Kinase associated network analysis showed that ROP5, ROP16, and cell-cycle-associated protein kinase CDK were the most connected kinase peptides. Our data reveal significant changes in the abundance of phosphoproteins between T. gondii genotypes, which explain some of the mechanisms that contribute to the virulence heterogeneity of this parasite.

Human GBP1 is a microbe-specific gatekeeper of macrophage apoptosis and pyroptosis

The guanylate binding protein (GBP) family of interferon-inducible GTPases promotes antimicrobial immunity and cell death. During bacterial infection, multiple mouse Gbps, human GBP2, and GBP5 support the activation of caspase-1-containing inflammasome complexes or caspase-4 which trigger pyroptosis. Whether GBPs regulate other forms of cell death is not known. The apicomplexan parasite Toxoplasma gondii causes macrophage death through unidentified mechanisms. Here we report that Toxoplasma-induced death of human macrophages requires GBP1 and its ability to target Toxoplasma parasitophorous vacuoles through its GTPase activity and prenylation. Mechanistically, GBP1 promoted Toxoplasma detection by AIM2, which induced GSDMD-independent, ASC-, and caspase-8-dependent apoptosis. Identical molecular determinants targeted GBP1 to Salmonella-containing vacuoles. GBP1 facilitated caspase-4 recruitment to Salmonella leading to its enhanced activation and pyroptosis. Notably, GBP1 could be bypassed by the delivery of Toxoplasma DNA or bacterial LPS into the cytosol, pointing to its role in liberating microbial molecules. GBP1 thus acts as a gatekeeper of cell death pathways, which respond specifically to infecting microbes. Our findings expand the immune roles of human GBPs in regulating not only pyroptosis, but also apoptosis.

The One Health Approach to Toxoplasmosis: Epidemiology, Control, and Prevention Strategies

One Health is a collaborative, interdisciplinary effort that seeks optimal health for people, animals, plants, and the environment. Toxoplasmosis, caused by Toxoplasma gondii, is an intracellular protozoan infection distributed worldwide, with a heteroxenous life cycle that practically affects all homeotherms and in which felines act as definitive reservoirs. Herein, we review the natural history of T. gondii, its transmission and impacts in humans, domestic animals, wildlife both terrestrial and aquatic, and ecosystems. The epidemiology, prevention, and control strategies are reviewed, with the objective of facilitating awareness of this disease and promoting transdisciplinary collaborations, integrative research, and capacity building among universities, government agencies, NGOs, policy makers, practicing physicians, veterinarians, and the general public.

Acute Toxoplasma gondii infection alters the number of neurons and the proportion of enteric glial cells in the duodenum in Wistar rats

BACKGROUND

Toxoplasma gondii infection can occur through the ingestion of raw meat that contains tissue cysts or food that contains oocysts. Through the ingestion of oocysts, the parasite crosses the intestinal barrier, where the enteric nervous system is located. The objective was to investigate the kinetics of neuronal and glial responses during acute T. gondii infection.

METHODS

We used 45 Wistar rats that were divided into a control group and infected groups that were evaluated at 6, 12, 24, 48, 72 hours, 7 days, 10 days, and 15 days after infection. The rats received 5000 sporulated oocysts of the parasite orally. To detect neurons and enteric glia cells, the myenteric and submucosal plexuses of the duodenum underwent double-labeling immunohistochemical techniques to evaluate HuC/HuD and S100, HuC/HuD and ChAT, and HuC/HuD and nNOS.

KEY RESULTS

We observed a reduction of the total neuron population in the submucosal plexus 72 hours after infection. Cholinergic neurons decreased in the submucosal plexus 15 days after infection, and nitrergic neurons decreased in the myenteric plexus 72 hours after infection. A decrease in the number of glial cells was observed 7 days after infection in the submucosal plexus, and an increase in the enteric glial cell (EGC)/neuron ratio was found in both plexuses 48 hours after infection.

CONCLUSIONS AND INFERENCES

We found decrease of neurons and increase in the EGC/neuron ratio in both plexuses caused by acute T. gondii infection, with major alterations 72 hours after oral infection. The number of cholinergic neurons decreased in the submucosal plexus, and the number of nitrergic neurons decreased in the myenteric plexus. A decrease in the number of enteric glial cells was observed in the submucosal plexus, and an increase in the enteric glial cell/neuron ratio was observed in both ganglionate plexuses of the duodenum.

Advances in the Development of Anti-Toxoplasma gondii Vaccines: Challenges, Opportunities, and Perspectives

Important progress has been made in understanding how immunity is elicited against Toxoplasma gondii - a complex pathogen with multiple mechanisms of immune evasion. Many vaccine candidates have been tested using various strategies in animal models. However, none of these strategies has delivered as yet, and important challenges remain in the development of vaccines that can eliminate the tissue cysts and/or fully block vertical transmission. In this review, we provide an overview of the current understanding of the host immune response to T. gondii infection and summarize the key limitations for the development of an effective, safe, and durable toxoplasmosis vaccine. We also discuss how the successes and failures in developing and testing vaccine candidates have provided a roadmap for future vaccine development.

Brazilian strains of Toxoplasma gondii are controlled by azithromycin and modulate cytokine production in human placental explants

BACKGROUND

Toxoplasma gondii is a protozoan parasite that causes congenital toxoplasmosis by transplacental transmission. Parasite strains are genetically diverse and disease severity is related to the genotype. In Uberlândia city, Brazil, two virulent strains were isolated: TgChBrUD1 and TgChBrUD2. Congenital toxoplasmosis is more prevalent in South America compared to Europe, and more often associated with severe symptoms, usually as a result of infection with atypical strains.

METHODS

Considering that T. gondii has shown high genetic diversity in Brazil, the effectiveness of traditional treatment may not be the same, as more virulent strains of atypical genotypes may predominate. Thus, the aim of this study were to evaluate the Brazilian strain infection rate in human villous explants and the azithromycin efficacy with regard to the control of these strains compared to traditional therapy. Villi were infected with RH, ME49, TgChBrUD1 or TgChBrUD2 strains and treated with azithromycin, spiramycin or a combination of pyrimethamine plus sulfadiazine. The villous viability was analyzed by LDH assay and morphological analysis. Parasite proliferation, as well as production of cytokines was analyzed by qPCR and ELISA, respectively. Statistical analysis was performed using the GraphPad Prism 5.0.

RESULTS

The treatments were not toxic and TgChBrUD1 infected villi showed a higher parasite burden compared with others strains. Treatments significantly reduced the intracellular proliferation of T. gondii, regardless of the strain. TgChBrUD1-infected villi produced a larger amount of MIF, IL-6 and TGF-β1 compared with other infected villi. Azithromycin treatment increased MIF production by RH- or TgChBrUD2-infected villi, but in ME49- or TgChBrUD1-infected villi, the MIF production was not altered by treatment. On the other hand, azithromycin treatment induced lower IL-6 production by ME49- or TgChBrUD1-infected villi.

CONCLUSIONS

Azithromycin treatment was effective against T. gondii Brazilian strains compared with conventional treatment. Also, the TgChBrUD1 strain replicated more in villi and modulated important cytokines involved in parasite control, showing that different strains use different strategies to evade the host immune response and ensure their survival.

A Double-Edged Sword: Complement Component 3 in Toxoplasma gondii Infection

Sprague Dawley rats and Kunming (KM) mice are artificially infected with type II Toxoplasma gondii strain Prugniaud (Pru) to generate toxoplasmosis, which is a fatal disease mediated by T. gondii invasion of the central nervous system (CNS) by unknown mechanisms. The aim is to explore the mechanism of differential susceptibility of mice and rats to T. gondii infection. Therefore, a strategy of isobaric tags for relative and absolute quantitation (iTRAQ) is established to identify differentially expressed proteins (DEPs) in the rats' and the mice's brains compared to the healthy groups. In KM mice, which is susceptible to T. gondii infection, complement component 3 (C3) is upregulated and the tight junction (TJ) pathway shows a disorder. It is presumed that T. gondii-stimulated C3 disrupts the TJ of the blood-brain barrier in the CNS. This effect allows more T. gondii passing to the brain through the intercellular space.

Systematic review and meta-analysis of variation in Toxoplasma gondii cyst burden in the murine model

Toxoplasma gondii is an obligate intracellular protozoan parasite that infects approximately 30% of the population of the United States, with worldwide distribution. The chronic (latent) infection, mediated by the bradyzoite parasite life stage, has attracted attention due to possible links to host behavioral alteration and psychomotor effects. Mice are a common model organism for studying the chronic stage, as they are natural hosts of infection. Notably, published studies demonstrate vast ranges of measured cyst burden within the murine brain tissue. The inconsistency of measured cyst burden within and between experiments makes interpretation of statistical significance difficult, potentially confounding studies of experimental anti-parasitic approaches. This review analyzes variation in measured cyst burden in a wide array of experimental mouse infections across published literature. Factors such as parasite infection strain, mouse strain, mode of infection, and infectious dose were all examined. The lowest variation in measured cyst burden occurred with the commonly available Balb/c and CBA mice undergoing infection by the ME49 strain of T. gondii. A summary of cyst variation and average cyst counts in T. gondii mouse models is presented, which may be useful for designing future experiments.

The Influence of Parasite Infections on Host Immunity to Co-infection With Other Pathogens

Parasites have evolved a wide range of mechanisms that they use to evade or manipulate the host's immune response and establish infection. The majority of the in vivo studies that have investigated these host-parasite interactions have been undertaken in experimental animals, especially rodents, which were housed and maintained to a high microbiological status. However, in the field situation it is increasingly apparent that pathogen co-infections within the same host are a common occurrence. For example, chronic infection with pathogens including malarial parasites, soil-transmitted helminths, Mycobacterium tuberculosis and viruses such as HIV may affect a third of the human population of some developing countries. Increasing evidence shows that co-infection with these pathogens may alter susceptibility to other important pathogens, and/or influence vaccine efficacy through their effects on host immune responsiveness. Co-infection with certain pathogens may also hinder accurate disease diagnosis. This review summarizes our current understanding of how the host's immune response to infection with different types of parasites can influence susceptibility to infection with other pathogenic microorganisms. A greater understanding of how infectious disease susceptibility and pathogenesis can be influenced by parasite co-infections will enhance disease diagnosis and the design of novel vaccines or therapeutics to more effectively control the spread of infectious diseases.

Chronic Toxoplasma gondii Infection Induces Anti-N-Methyl-d-Aspartate Receptor Autoantibodies and Associated Behavioral Changes and Neuropathology

Anti-NMDA receptor (NMDAR) autoantibodies have been postulated to play a role in the pathogenesis of NMDAR hypofunction, which contributes to the etiology of psychotic symptoms. Toxoplasma gondii is a pathogen implicated in psychiatric disorders and associated with elevation of NMDAR autoantibodies. However, it remains unclear whether parasite infection is the cause of NMDAR autoantibodies. By using mouse models, we found that NMDAR autoantibody generation had a strong temporal association with tissue cyst formation, as determined by MAG1 antibody seroreactivity (r = 0.96; P < 0.0001), which is a serologic marker for the cyst burden. The presence of MAG1 antibody response, but not T. gondii IgG response, was required for NMDAR autoantibody production. The pathogenic relevance of NMDAR autoantibodies to behavioral abnormalities (blunted response to amphetamine-triggered activity and decreased locomotor activity and exploration) and reduced expression of synaptic proteins (the GLUN2B subtype of NMDAR and PSD-95) has been demonstrated in infected mice. Our study suggests that NMDAR autoantibodies are specifically induced by persistent T. gondii infection and are most likely triggered by tissue cysts. NMDAR autoantibody seroreactivity may be a novel pathological hallmark of chronic toxoplasmosis, which raises questions about NMDAR hypofunction and neurodegeneration in the infected brain.

Toxoplasma gondii: Biological Parameters of the Connection to Schizophrenia

It is increasingly evident that the brain is not truly an immune privileged site and that cells of the central nervous system are sensitive to the inflammation generated when the brain is fighting off infection. Among the many microorganisms that have access to the brain, the apicomplexan protozoan Toxoplasma gondii has been one of the most studied. This parasite has been associated with many neuropsychiatric disorders including schizophrenia. This article provides a comprehensive review of the status of Toxoplasma research in schizophrenia. Areas of interest include (1) the limitations and improvements of immune-based assays to detect these infections in humans, (2) recent discoveries concerning the schizophrenia-Toxoplasma association, (3) findings of Toxoplasma neuropathology in animal models related to schizophrenia pathogenesis, (4) interactions of Toxoplasma with the host genome, (5) gastrointestinal effects of Toxoplasma infections, and (6) therapeutic intervention of Toxoplasma infections.

Chitosan Microsphere Used as an Effective System to Deliver a Linked Antigenic Peptides Vaccine Protect Mice Against Acute and Chronic Toxoplasmosis

Multiple antigenic peptide (MAP) vaccines have advantages over traditional Toxoplasma gondii vaccines, but are more susceptible to enzymatic degradation. As an effective delivery system, chitosan microspheres (CS) can overcome this obstacle and act as a natural adjuvant to promote T helper 1 (Th1) cellular immune responses. In this study, we use chitosan microparticles to deliver multiple antigenic epitopes from GRA10 (G10E), containing three dominant epitopes. When G10E was entrapped within chitosan microparticles (G10E-CS), adequate peptides for eliciting immune response were loaded in the microsphere core and this complex released G10E peptides stably. The efficiency of G10E-CS was detected both in vitro, via cell culture, and through in vivo mouse immunization. In vitro, G10E-CS activated Dendritic Cells (DC) and T lymphocytes by upregulating the secretion of costimulatory molecules (CD40 and CD86). In vivo, Th1 biased cellular and humoral immune responses were activated in mice vaccinated with G10E-CS, accompanied by significantly increased production of IFN-γ, IL-2, and IgG, and decreases in IL-4, IL-10, and IgG1. Immunization with G10E-CS conferred significant protection with prolonged survival in mice model of acute toxoplasmosis and statistically significant decreases in cyst burden in murine chronic toxoplasmosis. The results from this study indicate that chitosan microspheres used as an effective system to deliver a linked antigenic peptides is a promising strategy for the development of efficient vaccine against T. gondii.

Characterisation of susceptibility of chicken macrophages to infection with Toxoplasma gondii of type II and III strains

Toxoplasma gondii is known to be able to infect any nucleated cell including immune cells like macrophages. In addition, it is assumed that macrophages serve as trojan horse during distribution in hosts. The underlying causes of parasite host interaction remain yet not fully understood. The aim of the present study was to investigate susceptibility of chicken macrophages to infection with T. gondii and the process of infection in avian cells in comparison to cells of mammalian origin. Primary avian blood monocyte-derived macrophages were infected with tachyzoites of type II (ME49) and III (NED) strains. Long term observations of parasite replication in primary macrophages were compared to data obtained in an avian macrophage cell line (HD11) and a standard cultivation mammalian cell line (VERO). Furthermore, we assessed the immune response of the primary macrophages by long-term investigation of gene expression of IL-1 beta, IL-12p40, Lipopolysaccharide induced TNF-alpha factor (LITAF) and inducible nitric oxide synthase (iNOS) comparing viable and heat-inactivated tachyzoites of the ME49 strain. Albeit, we found no differences between both strains, replication of tachyzoites in avian primary macrophages was significantly different from immortalized cell lines HD11 and VERO. The crucial period of parasite replication was between 8 and 24 h post-infection coinciding with the upregulation of gene expression of cytokines and iNOS revealing an active macrophage response at this period. Gene expression in macrophages was higher after infection with viable tachyzoites than by exposure of cells to heat-inactivated tachyzoites. Hence, we conclude that the process of penetration is pivotal for host cell response to the parasite both in avian as in mammalian cells.

Toward detection of toxoplasmosis from urine in mice using hydro-gel nanoparticles concentration and parallel reaction monitoring mass spectrometry

Diagnosis of clinical toxoplasmosis remains a challenge, thus limiting the availability of human clinical samples. Though murine models are an approximation of human response, their definitive infection status and tissue availability make them critical to the diagnostic development process. Hydrogel mesh nanoparticles were used to concentrate antigen to detectable levels for mass spectrometry. Seven Toxoplasma gondii isolates were used to develop a panel of potential peptide sequences for detection by parallel reaction monitoring (PRM) mass spectrometry. Nanoparticles were incubated with decreasing concentrations of tachyzoite lysate to explore the limits of detection of PRM. Mice whose toxoplasmosis infection status was confirmed by quantitative real-time PCR had urine tested by PRM after hydrogel mesh concentration for known T. gondii peptides. Peptides from GRA1, GRA12, ROP4, ROP5, SAG1, and SAG2A proteins were detected by PRM after nanoparticle concentration of urine, confirming detection of T. gondii antigen in the urine of an infected mouse.

Could age and aging change the host response to systemic parasitic infections? A systematic review of preclinical evidence

The impact of age and aging in the evolution of systemic parasitic infections remains poorly understood. We conducted a systematic review from preclinical models of Chagas disease, leishmaniasis, malaria, sleeping sickness and toxoplasmosis. From a structured and comprehensive search in electronic databases, 29 studies were recovered and included in the review. Beyond the characteristics of the experimental models, parasitological and immunological outcomes, we also discussed the quality of current evidence. Our findings indicated that throughout aging, parasitemia and mortality were consistently reduced in Chagas disease and malaria, but were similar or increased in leishmaniasis and highly variable in toxoplasmosis. While a marked humoral response in older animals was related to the anti-T. cruzi protective phenotype, cellular responses mediated by a polarized Th1 phenotype were associated with a more effective defense against Plasmodium infection. Conversely, in leishmaniasis, severe infections and high mortality rates were potentially related to attenuation of humoral response and an imbalance between Th1 and Th2 phenotypes. Due to the heterogeneous parasitological outcomes and limited immunological data, the role of aging on toxoplasmosis evolution remains unclear. From a detailed description of the methodological bias, more controlled researches could avoid the systematic reproduction of inconsistent and poorly reproducible experimental designs.

Genotyping of polymorphic effectors of Toxoplasma gondii isolates from China

Background

Toxoplasma gondii is an opportunistic protozoan apicomplexan and obligate intracellular parasite that infects a wide range of animals and humans. Rhoptry proteins 5 (ROP5), ROP16, ROP18 and dense granules 15 (GRA15) are the important effectors secreted by T. gondii which link to the strain virulence for mice and modulate the host’s response to the parasite. Little has been known about these molecules as well as GRA3 in type Chinese 1 strains that show polymorphism among strains of archetypical genotypes. This study examined the genetic diversity of these effectors and its correlated virulence in mice among T. gondii isolates from China.

Results

Twenty-one isolates from stray cats were detected, of which 15 belong to Chinese 1, and 6 to ToxoDB #205. Wh6 isolate, a Chinese 1 strain, has an avirulent phenotype. PCR-RFLP results of ROP5 and ROP18 presented few variations among the strains. Genotyping of GRA15 and ROP16 revealed that all the strains belong to type II allele except Xz7 which carries type I allele. ROP16 amino acid alignment at 503 locus demonstrated that 17 isolates are featured as type I or type III (ROP16_I/III), and the other 4 as type II (ROP16_II). The strains investigated may be divided into four groups based on GRA3 amino acid alignment, and all isolates of type Chinese 1 belong to the μ-1 allele except Wh6 which is identical to type II strain.

Conclusions

PCR-RFLP and sequence alignment analyses of ROP5, ROP16, ROP18, GRA3, and GRA15 in T. gondii revealed that strains with the same genotype may have variations in some of their key genes. GRA3 variation exhibited by Wh6 strain may be associated with the difference in phenotype and pathogenesis.

Electronic supplementary material

The online version of this article (10.1186/s13071-017-2527-4) contains supplementary material, which is available to authorized users.

Integrative transcriptome and proteome analyses define marked differences between Neospora caninum isolates throughout the tachyzoite lytic cycle

Neospora caninum is one of the main causes of transmissible abortion in cattle. Intraspecific variations in virulence have been widely shown among N. caninum isolates. However, the molecular basis governing such variability have not been elucidated to date. In this study label free LC-MS/MS was used to investigate proteome differences between the high virulence isolate Nc-Spain7 and the low virulence isolate Nc-Spain1H throughout the tachyzoite lytic cycle. The results showed greater differences in the abundance of proteins at invasion and egress with 77 and 62 proteins, respectively. During parasite replication, only 19 proteins were differentially abundant between isolates. The microneme protein repertoire involved in parasite invasion and egress was more abundant in the Nc-Spain1H isolate, which displays a lower invasion rate. Rhoptry and dense granule proteins, proteins related to metabolism and stress responses also showed differential abundances between isolates. Comparative RNA-Seq analyses during tachyzoite egress were also performed, revealing an expression profile of genes associated with the bradyzoite stage in the low virulence Nc-Spain1H isolate. The differences in proteome and RNA expression profiles between these two isolates reveal interesting insights into likely mechanisms involved in specific phenotypic traits and virulence in N. caninum.

SIGNIFICANCE

The molecular basis that governs biological variability in N. caninum and the pathogenesis of neosporosis has not been well-established yet. This is the first study in which high throughput technology of LC-MS/MS and RNA-Seq is used to investigate differences in the proteome and transcriptome between two well-characterized isolates. Both isolates displayed different proteomes throughout the lytic cycle and the transcriptomes also showed marked variations but were inconsistent with the proteome results. However, both datasets identified a pre-bradyzoite status of the low virulence isolate Nc-Spain1H. This study reveals interesting insights into likely mechanisms involved in virulence in N. caninum and shed light on a subset of proteins that are potentially involved in the pathogenesis of this parasite.

Comparative proteomic analysis of virulent and avirulent strains of Toxoplasma gondii reveals strain-specific patterns

Research exploring the proteome of Toxoplasma gondii oocysts has gained momentum over the past few years. However, little is known about the oocyst's protein repertoires that contribute to differential virulence among T. gondii strains. Here, we used isobaric tag for relative and absolute quantitation-based proteomic analysis of oocysts of two T. gondii strains exhibiting the virulent PYS (ToxoDB#9) phenotype versus the less virulent PRU (Type II, ToxoDB#1) phenotype. Our aim was to determine protein expression patterns that contribute to the virulence of a particular phenotype. A total of 2,551 proteins were identified, of which 374 were differentially expressed proteins (DEPs) (|log2 fold change| ≥ 0.58 and P < 0.05). DEPs included 192 increased and 182 decreased proteins. Gene Ontology and KEGG pathway analyses revealed a large number of DEPs enriched in various metabolic processes. Protein interaction network analysis using STRING identified inosine monophosphate dehydrogenase (IMPDH), Bifunctional GMP synthase/glutamine amidotransferase protein, Glucose-6-phosphate 1-dehydrogenase, and Citrate synthase as the top four hubs. Of the 22 virulence proteins commonly expressed in the oocysts of the two strains, 13 and 2 proteins were increased in PYS strain and PRU strain, respectively. Also, 10 and 3 of the 22 identified oocyst wall proteins showed higher expression in oocysts of PRU strain and PYS strain, respectively. These findings revealed new proteomic differences in the oocysts of T. gondii strains of different genotypic backgrounds.

Azithromycin treatment is able to control the infection by two genotypes of Toxoplasma gondii in human trophoblast BeWo cells

Trophoblast infection by Toxoplasma gondii plays a pivotal role in the vertical transmission of toxoplasmosis. Here, we investigate whether the antibiotic therapy with azithromycin, spiramycin and sulfadiazine/pyrimethamine are effective to control trophoblast infection by two Brazilian T. gondii genotypes, TgChBrUD1 or TgChBrUD2. Two antibiotic protocols were evaluated, as follow: i) pre-treatment of T. gondii-tachyzoites with selected antibiotics prior trophoblast infection and ii) post-treatment of infected trophoblasts. The infection index/replication and the impact of the antibiotic therapy on the cytokine milieu were characterized. It was observed that TgChBrUD2 infection induced lower infection index/replication as compared to TgChBrUD1. Regardless the therapeutic protocol, azithromycin was more effective to control the trophoblast infection with both genotypes when compared to conventional antibiotics. Azithromycin induced higher IL-12 production in TgChBrUD1-infected cells that may synergize the anti-parasitic effect. In contrast, the effectiveness of azithromycin to control the TgChBrUD2-infection was not associated with the IL-12 production. BeWo-trophoblasts display distinct susceptibility to T. gondii genotypes and the azithromycin treatment showed to be more effective than conventional antibiotics to control the T. gondii infection/replication regardless the parasite genotype.

Molecular detection and genetic characterization of Toxoplasma gondii in farmed raccoon dogs (Nyctereutes procyonoides) in Shandong province, eastern China

Toxoplasma gondii is a successful opportunistic parasite, affecting a wide range of vertebrate animals and humans. Genetic diversity of T. gondii in raccoon dogs (Nyctereutes procyonoides) is of great importance to understand the transmission of T. gondii in the environment. However, no information is available about the distribution of genetic diversity of T. gondii infection in raccoon dogs. This study was conducted to estimate the prevalence and genetic characterization of T. gondii from raccoon dogs in Shandong province, eastern China. A total of 314 brain tissue samples of raccoon dogs were collected and genomic DNA was extracted and assayed for T. gondii infection using semi-nested PCR targeting B1 gene. The positive DNA samples were typed at 10 genetic markers (SAG1, SAG2(5'+3' SAG2, alter.SAG2), SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, and Apico) by multiplex multilocus nested polymerase chain reaction-restriction fragment length polymorphism (Mn- PCR-RFLP) technology. Thirty-five (11.15%) of 314 DNA samples were detected positive. Only six samples were completely typed at all genetic loci, and these samples represented ToxoDB genotype#9. Two sample were typed at 9 genetic loci and one was typed at 8 genetic loci, all of them represented Type I. To our knowledge, this is the first report of genetic characterization of T. gondii in raccoon dogs in China. These results revealed the existence of genetic diversity of T. gondii in raccoon dogs in China. These data provided base-line information for controlling T. gondii infection in raccoon dogs.

Toxoplasma gondii: Laboratory Maintenance and Growth

Toxoplasma gondii is a highly successful apicomplexan protozoan capable of infecting any warm-blooded animal worldwide. In humans, Toxoplasma infections are life-long, with approximately one-third of the world's population chronically infected. Although normally controlled by the host immune system, T. gondii infection can lead to a variety of clinical outcomes in individuals with immature or suppressed immune systems. After penetrating the intestine, parasites rapidly disseminate throughout the body and stimulate production of the cytokines interleukin (IL)-12, IL-18, and interferon (IFN)-γ by immune cells. These cytokines play a key role in host resistance to T. gondii by promoting a strong Th1 response. Recent reports show that gut commensal bacteria can act as molecular adjuvants during T. gondii infection. Thus, T. gondii is an excellent model system to study host-pathogen interactions. This unit outlines the protocols for in vitro and in vivo maintenance and growth of T. gondii. © 2017 by John Wiley & Sons, Inc.

Mechanisms and pathways of Toxoplasma gondii transepithelial migration

Toxoplasma gondii is a ubiquitous parasite and a prevalent food-borne parasitic pathogen. Infection of the host occurs principally through oral consumption of contaminated food and water with the gastrointestinal tract being the primary route for entry into the host. To promote infection, T. gondii has evolved highly specialized strategies for rapid traversal of the single cell thick intestinal epithelial barrier. Parasite transmigration via the paracellular pathway between adjacent cells enables parasite dissemination to secondary sites of infection where chronic infection of muscle and brain tissue is established. It has recently been proposed that parasite interactions with the integral tight junction (TJ) protein occludin influences parasite transmigration of the intestinal epithelium. We review here the emerging mechanisms of T. gondii transmigration of the small intestinal epithelium alongside the developing role played in modulating the wider TJ-associated proteome to rewire host cell regulatory systems for the benefit of the parasite.

Host and Toxoplasma gondii genetic and non-genetic factors influencing the development of ocular toxoplasmosis: A systematic review

Toxoplasmosis is a cosmopolitan infection caused by the apicomplexan parasite Toxoplasma gondii. This infectious disease is widely distributed across the world where cats play an important role in its spread. The symptomatology caused by this parasite is diverse but the ocular affectation emerges as the most important clinical phenotype. Therefore, we conducted a systematic review of the current knowledge of ocular toxoplasmosis from the genetic diversity of the pathogen towards the treatment available for this infection. This review represents an update to the scientific community regarding the genetic diversity of the parasite, the genetic factors of the host, the molecular pathogenesis and its association with disease, the available diagnostic tools and the available treatment of patients undergoing ocular toxoplamosis. This review will be an update for the scientific community in order to encourage researchers to deploy cutting-edge investigation across this field.

Deciphering the Draft Genome of Toxoplasma gondii RH Strain

Toxoplasmosis is a widespread parasitic infection by Toxoplasma gondii, a parasite with at least three distinct clonal lineages. This article reports the whole genome sequencing and de novo assembly of T. gondii RH (type I representative strain), as well as genome-wide comparison across major T. gondii lineages. Genomic DNA was extracted from tachyzoites of T. gondii RH strain and its identity was verified by PCR and LAMP. Subsequently, whole genome sequencing was performed, followed by sequence filtering, genome assembly, gene annotation assignments, clustering of gene orthologs and phylogenetic tree construction. Genome comparison was done with the already archived genomes of T. gondii. From this study, the genome size of T. gondii RH strain was found to be 69.35Mb, with a mean GC content of 52%. The genome shares high similarity to the archived genomes of T. gondii GT1, ME49 and VEG strains. Nevertheless, 111 genes were found to be unique to T. gondii RH strain. Importantly, unique genes annotated to functions that are potentially critical for T. gondii virulence were found, which may explain the unique phenotypes of this particular strain. This report complements the genomic archive of T. gondii. Data obtained from this study contribute to better understanding of T. gondii and serve as a reference for future studies on this parasite.

Besnoitia besnoiti lytic cycle in vitro and differences in invasion and intracellular proliferation among isolates

Background

Bovine besnoitiosis, caused by the protozoan Besnoitia besnoiti, reduces productivity and fertility of affected herds. Besnoitiosis continues to expand in Europe and no effective control tools are currently available. Experimental models are urgently needed. Herein, we describe for the first time the kinetics of standardised in vitro models for the B. besnoiti lytic cycle. This will aid to study the pathogenesis of the disease, in the screening for vaccine targets and drugs potentially useful for the treatment of besnoitiosis.

Methods

We compared invasion and proliferation of one B. tarandi (from Finland) and seven B. besnoiti isolates (Bb-Spain1, Bb-Spain2, Bb-Israel, Bb-Evora03, Bb-Ger1, Bb-France, Bb-Italy2) in MARC-145 cell culture. Host cell invasion was studied at 4, 6, 8 and 24 h post infection (hpi), and proliferation characteristics were compared at 24, 48, 72, 96, 120, and 144 hpi.

Results

In Besnoitia spp., the key parameters that determine the sequential adhesion-invasion, proliferation and egress steps are clearly distinct from those in the related apicomplexans Toxoplasma gondii and Neospora caninum. Besnoitia spp. host cell invasion is a rather slow process, since only 50 % of parasites were found intracellular after 3–6 h of exposure to host cells, and invasion still took place after 24 h. Invasion efficacy was significantly higher for Bb-France, Bb-Evora03 and Bb-Israel. In addition, the time span for endodyogeny to take place was as long as 18–35 h. Bb-Israel and B. tarandi isolates were most prolific, as determined by the tachyzoite yield at 72 hpi. The total tachyzoite yield could not be predicted neither by invasion-related parameters (velocity and half time invasion) nor by proliferation parameters (lag phase and doubling time (dT)). The lytic cycle of Besnoitia was asynchronous as evidenced by the presence of three different plaque-forming tachyzoite categories (lysis plaques, large and small parasitophorous vacuoles).

Conclusions

This study provides first insights into the lytic cycle of B. besnoiti isolates and a standardised in vitro model that allows screening of drug candidates for the treatment of besnoitiosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1405-9) contains supplementary material, which is available to authorized users.

Host Mitochondrial Association Evolved in the Human Parasite Toxoplasma gondii via Neofunctionalization of a Gene Duplicate

In Toxoplasma gondii, an intracellular parasite of humans and other animals, host mitochondrial association (HMA) is driven by a gene family that encodes multiple mitochondrial association factor 1 (MAF1) proteins. However, the importance of MAF1 gene duplication in the evolution of HMA is not understood, nor is the impact of HMA on parasite biology. Here we used within- and between-species comparative analysis to determine that the MAF1 locus is duplicated in T. gondii and its nearest extant relative Hammondia hammondi, but not another close relative, Neospora caninum. Using cross-species complementation, we determined that the MAF1 locus harbors multiple distinct paralogs that differ in their ability to mediate HMA, and that only T. gondii and H. hammondi harbor HMA⁺ paralogs. Additionally, we found that exogenous expression of an HMA⁺ paralog in T. gondii strains that do not normally exhibit HMA provides a competitive advantage over their wild-type counterparts during a mouse infection. These data indicate that HMA likely evolved by neofunctionalization of a duplicate MAF1 copy in the common ancestor of T. gondii and H. hammondi, and that the neofunctionalized gene duplicate is selectively advantageous.

Variation detection based on next-generation sequencing of type Chinese 1 strains of Toxoplasma gondii with different virulence from China

BACKGROUND

Toxoplasma gondii is an intracellular protozoan that affects most species of endothermic animals including humans with a great infection rate. The vertical transmission of T. gondii causes abortion, constituting a serious threat to humans and leading to great losses in livestock production. Distinct from population structure of T. gondii in North America and Europe, Chinese 1 (ToxoDB #9) is a dominant genotype prevalent in China. Among the isolates of Chinese 1, the Wh3 and Wh6 have different virulence and pathogenicity in mice. However, little has been known about their difference at the genomic level. Thus the next-generation sequencing (NGS) approach was used to discover the association of the phenotypical variations with the genome sequencing data and the expression and polymorphisms of the key effectors.

RESULTS

We successfully sequenced the genome of Chinese 1 strains of Wh3 and Wh6. The average sequencing depths were 63.91 and 63.61 for Wh3 and Wh6, respectively. The variations of both isolates were identified in comparison with reference genome of type I GT1 strain. There were 505,645 and 505,856 SNPs, 30,658 and 30,004 indels, 4661 and 2320 SVs, and 1942 and 3080 CNVs for Wh3 and Wh6, respectively. In target search variations of particular factors of T. gondii, the dense granule protein 3 (GRA3) and rhoptry neck protein 3 (RON3) were found to have 35 SNPs, 2 indels and 89 SNPs, 6 indels, respectively. GRA3 and RON3 were both found to have higher expression levels in less virulent Wh6 than in virulent Wh3. Both strains of type Chinese 1 share polymorphic GRA15II and ROPI/III with type I, II, and III strains.

CONCLUSIONS

Sequencing of the two strains revealed that genome structure of Chinese 1 and type I strains has considerable genomic variations. Sequencing and qRT-PCR analyses of 26 effectors displayed a remarkable variation that may be associated with phenotype and pathogenic differences.

Role of CD4+ Foxp3+ Regulatory T Cells in Protection Induced by a Live Attenuated, Replicating Type I Vaccine Strain of Toxoplasma gondii

Vaccination with the live attenuated Toxoplasma gondii Mic1.3KO strain induced long-lasting immunity against challenge with Toxoplasma gondii type I and type II strains. The involvement of regulatory T cells (Tregs) in the protection mechanism was investigated. Intraperitoneal injection of Mic1.3KO induced a weak and transient influx of CD4(+) Foxp3(+) T regulatory cells followed by recruitment/expansion of CD4(+) Foxp3(-) CD25(+) effector cells and control of the parasite at the site of infection. The local and systemic cytokine responses associated with this recruitment of Tregs were of the TH1/Treg-like type. In contrast, injection of RH, the wild-type strain from which the vaccinal strain is derived, induced a low CD4(+) Foxp3(+) cell influx and uncontrolled multiplication of the parasites at this local site, followed by death of the mice. The associated local and systemic cytokine responses were of the TH1/TH17-like type. In addition, in vivo Treg induction in RH-infected mice with interleukin-2 (IL-2)/anti-IL-2 complexes induced control of the parasite and a TH1/Treg cytokine response similar to the response after Mic1.3KO vaccination. These results suggest that Tregs may contribute to the protective response after vaccination with Mic1.3KO.