Genotypes and mouse virulence of Toxoplasma gondii isolates from animals and humans in China

Observing astrocyte polarization in brains from mouse chronically infected with Toxoplasma gondii

Toxoplasma gondii (T. gondii) is a protozoan parasite that infects approximately one-third of the global human population, often leading to chronic infection. While acute T. gondii infection can cause neural damage in the central nervous system and result in toxoplasmic encephalitis, the consequences of T. gondii chronic infection (TCI) are generally asymptomatic. However, emerging evidence suggests that TCI may be linked to behavioral changes or mental disorders in hosts. Astrocyte polarization, particularly the A1 subtype associated with neuronal apoptosis, has been identified in various neurodegenerative diseases. Nevertheless, the role of astrocyte polarization in TCI still needs to be better understood. This study aimed to establish a mouse model of chronic TCI and examine the transcription and expression levels of glial fibrillary acidic protein (GFAP), C3, C1q, IL-1α, and TNF-α in the brain tissues of the mice. Quantitative real-time PCR (qRT-PCR), enzyme-linked immunosorbent assay, and Western blotting were employed to assess these levels. Additionally, the expression level of the A1 astrocyte-specific marker C3 was evaluated using indirect fluorescent assay (IFA). In mice with TCI, the transcriptional and expression levels of the inflammatory factors C1q, IL-1α, and TNF-α followed an up-down-up pattern, although they remained elevated compared to the control group. These findings suggest a potential association between astrocyte polarization towards the A1 subtype and synchronized changes in these three inflammatory mediators. Furthermore, immunofluorescence assay (IFA) revealed a significant increase in the A1 astrocytes (GFAP+C3+) proportion in TCI mice. This study provides evidence that TCI can induce astrocyte polarization, a biological process that may be influenced by changes in the levels of three inflammatory factors: C1q, IL-1α, and TNF-α. Additionally, the release of neurotoxic substances by A1 astrocytes may be associated with the development of TCI.

Plasma metagenomics reveals regional variations of emerging and re-emerging pathogens in Chinese blood donors with an emphasis on human parvovirus B19

At present, many infectious pathogens, especially emerging/re-emerging pathogens, exist in the blood of voluntary blood donors and may be transmitted through blood transfusions. However, most of Chinese blood centers only routinely screen for HBV, HCV, HIV, and syphilis. We employed metagenomic next-generation sequencing (mNGS) to investigate the microbiome in healthy voluntary blood donors to help assess blood safety in China by identifying infectious pathogens presented in donations that could lead to transfusion-acquired infections. We collected 10,720 plasma samples from voluntary blood donors from seven blood centers in different cities during 2012-2018 in China. A total of 562 GB of clean data was obtained. By analyzing the sequencing data, it was found that the most commonly identified bacteria found in the healthy blood were Serratia spp. (5.0176%), Pseudomonas spp. (0.6637%), and Burkholderia spp. (0.5544%). The principal eukaryote were Leishmania spp (1.3723%), Toxoplasma gondii (0.6352%), and Candida dubliniensis (0.1848%). Among viruses, Human Parvovirus B19 (B19V) accounts for the highest proportion (0.1490%), followed by Torque teno midi virus (0.0032%) and Torque teno virus (0.0015%). Since that B19V is a non-negligible threat to blood safety, we evaluated the positive samples for B19V tested by mNGS using quantitative polymerase chain reaction, Sanger sequencing, and phylogenetic analysis to achieve a better understanding of B19V in Chinese blood donors. Subsequently, 9 (0.07%) donations were positive for B19V DNA. The quantitative DNA levels ranged from 5.58 × 10² to 7.24 × 10⁴ IU/ml. The phylogenic analyses showed that prevalent genotypes belonged to the B19-1A subtype, which disclosed previously unknown regional variability in the B19V positivity rate. The investigation revealed that many microbes dwell in the blood of healthy donors, including some pathogens that may be dormant in the blood and only cause disease under specific conditions. Thus, investigating the range and nature of potential pathogens in the qualified donations provided a framework for targeted interventions to help prevent emerging and re-emerging infectious diseases.

Toxoplasma gondii genotyping in AIDS patients using high resolution melt analysis (HRM analysis) in Khuzestan province, southwest Iran

Toxoplasmosis is a parasitic zoonotic disease caused by Toxoplasma gondii, a common protozoan in the Apicomplexa phylum. Several studies in Iran have demonstrated the presence of the parasite in various hosts, but no data on T. gondii genotyping in HIV patients in Khuzestan, Southwest Iran, is available. One hundred of blood samples from AIDS patients were collected and tested by real-time PCR High Resolution Melting analyses for T.gondii detection and genotyping. T. gondii was discovered in 8 out of 100 (8%) AIDS patients with dominant Type I. This study suggest that HRM method demonstrated excellent discriminating ability for T. gondii, and AIDS patients should be tested for Toxoplasma detection and genotyping to prevent parasite pathogenicity.

Iron-overload-induced ferroptosis in mouse cerebral toxoplasmosis promotes brain injury and could be inhibited by Deferiprone

Iron is a trace metal element that is essential for the survival of cells and parasites. The role of iron in cerebral toxoplasmosis (CT) is still unclear. Deferiprone (DFP) is the orally active iron chelator that binds iron in a molar ratio of 3:1 (ligand:iron) and promotes urinary iron excretion to remove excess iron from the body. The aims of this experiment were to observe the alterations in iron in brains with Toxoplasma gondii (T. gondii) acute infections and to investigate the mechanism of ferroptosis in CT using DFP. We established a cerebral toxoplasmosis model in vivo using TgCtwh3, the dominant strains of which are prevalent in China, and treated the mice with DFP at a dose of 75 mg/kg/d. Meanwhile, we treated the HT-22 cells with 100 μM DFP for half an hour and then infected cells with TgCtwh3 in vitro. A qRT-PCR assay of TgSAG1 levels showed a response to the T. gondii burden. We used inductively coupled plasma mass spectrometry, an iron ion assay kit, Western blot analysis, glutathione and glutathione disulfide assay kits, a malonaldehyde assay kit, and immunofluorescence to detect the ferroptosis-related indexes in the mouse hippocampus and HT-22 cells. The inflammatory factors interferon-γ, tumor necrosis factor-α, transforming growth factor-β, and arginase 1 in the hippocampus and cells were detected using the Western blot assay. Hematoxylin and eosin staining, electron microscopy, and the Morris water maze experiment were used to evaluate the brain injuries of the mice. The results showed that TgCtwh3 infection is followed by the activation of ferroptosis-related signaling pathways and hippocampal pathological damage in mice. The use of DFP led to ferroptosis resistance and attenuated pathological changes, inflammatory reactions and T. gondii burden of the mice, prolonging their survival time. The HT-22 cells with TgCtwh3 activated the ferroptosis pathway and was inhibit by DFP in vitro. In TgCtwh3-infected cells, inflammatory response and mitochondrial damage were severe, but these effects could be reduced by DFP. Our study elucidates the mechanism by which T. gondii interferes with the host's iron metabolism and activates ferroptosis, complementing the pathogenic mechanism of CT and further demonstrating the potential value of DFP for the treatment of CT.

LFA-1/ ICAM-1 promotes NK cell cytotoxicity associated with the pathogenesis of ocular toxoplasmosis in murine model

Ocular toxoplasmosis (OT) is one of the most common causes of posterior uveitis. However, the pathogenic mechanisms of OT have not been well elucidated. Here, we used C57BL/6 (B6) mice to establish OT by peroral infection with 20 cysts of the TgCtWh6 strain, and severe ocular damage was observed by histopathological analysis in the eyes of infected mice. RNA-sequencing results showed that infection with T. gondii increased the expression of the NK-mediated cytotoxicity gene pathway at Day 30 after ocular T. gondii infection. Both NK-cell and CD49a+ NK-cell subsets are increased in ocular tissues, and the expression levels of LFA-1 in NK cells and ICAM-1 in the OT murine model were upregulated upon infection. Furthermore, inhibition of the interaction between LFA-1 and ICAM-1 with lifitegrast, a novel small molecule integrin antagonist, inhibited the protein expression of LFA-1 and ICAM-1 in murine OT and NK cells, improved the pathology of murine OT and influenced the secretion of cytokines in the OT murine model. In conclusion, the interaction between LFA-1 and ICAM-1 plays a role in the early regulation of the CD49a+ NK-cell proportion in an OT murine model. LFA-1/ ICAM-1 may be a key molecule in the pathogenesis of OT, and may provide new insights for potential immunotherapy.

Activation of NF-κB signaling by the dense granule protein GRA15 of a newly isolated type 1 Toxoplasma gondii strain

Background

It has been reported that the NF-κB pathway, an important component of host defense system against pathogens infections, can be differentially modulated by different Toxoplasma gondii strains, depending on the polymorphism of the GRA15 protein. The recently isolated Toxoplasma strain T.gHB1 is a type 1 (ToxoDB#10) strain but shows different virulence determination mechanisms compared to the classic type 1 strains like RH (ToxoDB#10). Therefore, it is worth investigating whether the T.gHB1 strain (ToxoDB#10) affects the host NF-κB signaling pathway.

Methods

The effects of T.gHB1 (ToxoDB#10) on host NF-κB pathway were investigated in HEK293T cells. The GRA15 gene product was analyzed by bioinformatics, and its effect on NF-κB activation was examined by Western blotting and nuclear translocation of p65. Different truncations of T.gHB1 GRA15 were constructed to map the critical domains for NF-κB activation.

Results

We demonstrated that the NF-κB pathway signaling pathway could be activated by the newly identified type 1 T.gHB1 strain (ToxoDB#10) of Toxoplasma, while the classic type 1 strain RH (ToxoDB#10) did not. T.gHB1 GRA15 possesses only one transmembrane region with an extended C terminal region, which is distinct from that of classic type 1 (ToxoDB#10) and type 2 (ToxoDB#1) strains. T.gHB1 GRA15 could clearly induce IκBα phosphorylation and p65 nuclear translocation. Dual luciferase assays in HEK293T cells revealed a requirement for 194–518 aa of T.gHB1 GRA15 to effectively activate NF-κB.

Conclusions

The overall results indicated that the newly isolated type 1 isolate T.gHB1 (ToxoDB#10) had a unique GRA15, which could activate the host NF-κB signaling through inducing IκBα phosphorylation and p65 nuclear translocation. These results provide new insights for our understanding of the interaction between Toxoplasma parasites and its hosts.

Graphical Abstract

Toxoplasma gondii CDPK3 Controls the Intracellular Proliferation of Parasites in Macrophages

Interferon-γ (IFN-γ)-activated macrophages restrain the replication of intracellular parasites and disrupt the integrity of vacuolar pathogens. The growth of the less virulent type II strain of Toxoplasma gondii (such as ME49) was strongly inhibited by IFN-γ-activated murine macrophages. However, the mechanism of resistance is poorly understood. Immunity-related GTPases (IRGs) as well as guanylate-binding proteins (GBPs) contributed to this antiparasitic effect. Previous studies showed the cassette of autophagy-related proteins including Atg7, Atg3, and Atg12-Atg5-Atg16L1 complex, plays crucial roles in the proper targeting of IFN-γ effectors onto the parasitophorous vacuole (PV) membrane of Toxoplasma gondii and subsequent control of parasites. TgCDPK3 is a calcium dependent protein kinase, located on the parasite periphery, plays a crucial role in parasite egress. Herein, we show that the less virulent strain CDPK3 (ME49, type II) can enhance autophagy activation and interacts with host autophagy proteins Atg3 and Atg5. Infection with CDPK3-deficient ME49 strain resulted in decreased localization of IRGs and GBPs around PV membrane. In vitro proliferation and plaque assays showed that CDPK3-deficient ME49 strain replicated significantly more quickly than wild-type parasites. These data suggested that TgCDPK3 interacts with the host Atg3 and Atg5 to promote the localization of IRGs and GBPs around PV membrane and inhibits the intracellular proliferation of parasites, which is beneficial to the less virulent strain of Toxoplasma gondii long-term latency in host cells.

Global profiling of protein lysine malonylation in Toxoplasma gondii strains of different virulence and genetic backgrounds

Lysine malonylation is a post-translational modification (PTM), which regulates many cellular processes. Limited information is available about the level of lysine malonylation variations between Toxoplasma gondii strains of distinct genetic lineages. Yet, insights into such variations are needed to understand the extent to which lysine malonylation contributes to the differences in the virulence and repertoire of virulence factors between T. gondii genotypes. In this study, we profiled lysine malonylation in T. gondii using quantitative liquid chromatography-tandem mass spectrometry (LC-MS/MS) and immuno-affinity purification. This analysis was performed on three T. gondii strains with distinctive pathogenicity in mice, including RH strain (type I), PRU strain (type II), and VEG strain (type III). In total, 111 differentially malonylated proteins and 152 sites were upregulated, and 17 proteins and 17 sites were downregulated in RH strain versus PRU strain; 50 proteins and 59 sites were upregulated, 50 proteins and 53 sites were downregulated in RH strain versus VEG strain; and 72 proteins and 90 sites were upregulated, and 7 proteins and 8 sites were downregulated in VEG strain versus PRU strain. Differentially malonylated proteins were involved in key processes, such as those mediating the regulation of protein metabolism, stress response, glycolysis, and actin cytoskeleton. These results reveal an association between lysine malonylation and intra-species virulence differences in T. gondii and offer a new resource for elucidating the contribution of lysine malonylation to energy metabolism and virulence in T. gondii.

Lysine malonylation has been shown to play important roles in various biological processes in Toxoplasma gondii. Here, we used quantitative liquid chromatography-tandem mass spectrometry (LC-MS/MS) and immuno-affinity purification to test the hypothesis that lysine malonylation underpins the inter-genotype differences in the virulence of T. gondii. Several up-regulated and down- regulated malonylated proteins were identified in the tachyzoites of RH (type I) strain, PRU (type II) strain, and VEG (type III) strain. Differentially regulated malonylated proteins were enriched in many biological and metabolic pathways, and were found to contribute T. gondii energy metabolism, stress response, and infectivity, suggesting the role of lysine malonylation in the regulation of T. gondii virulence. These findings expand our knowledge of lysine malonylation in T. gondii and provide more insight into the mechanisms mediating the virulence differences between T. gondii strains of different genotypes.

Unifying Virulence Evaluation in Toxoplasma gondii: A Timely Task

Toxoplasma gondii, a major zoonotic pathogen, possess a significant genetic and phenotypic diversity that have been proposed to be responsible for the variation in clinical outcomes, mainly related to reproductive failure and ocular and neurological signs. Different T. gondii haplogroups showed strong phenotypic differences in laboratory mouse infections, which provide a suitable model for mimicking acute and chronic infections. In addition, it has been observed that degrees of virulence might be related to the physiological status of the host and its genetic background. Currently, mortality rate (lethality) in outbred laboratory mice is the most significant phenotypic marker, which has been well defined for the three archetypal clonal types (I, II and III) of T. gondii; nevertheless, such a trait seems to be insufficient to discriminate between different degrees of virulence of field isolates. Many other non-lethal parameters, observed both in in vivo and in vitro experimental models, have been suggested as highly informative, yielding promising discriminatory power. Although intra-genotype variations have been observed in phenotypic characteristics, there is no clear picture of the phenotypes circulating worldwide; therefore, a global overview of T. gondii strain mortality in mice is presented here. Molecular characterization has been normalized to some extent, but this is not the case for the phenotypic characterization and definition of virulence. The present paper proposes a baseline (minimum required information) for the phenotypic characterization of T. gondii virulence and intends to highlight the needs for consistent methods when a panel of T. gondii isolates is evaluated for virulence.

Toxoplasma gondii infection as a risk factor for osteoporosis: a case-control study

Background

More than one-third of the total world population is infected by Toxoplasma gondii (T. gondii). T. gondii has been linked to various diseases, such as cancer, mental disorders, type 2 diabetes mellitus (T2DM), etc. However, the effects of T. gondii infection on the risk of osteoporosis are unclear. Our study aimed to uncover evidence to determine whether patients exposed to T. gondii have an increased or decreased risk of osteoporosis in people with abnormal bone mineral density (BMD) by using case–control study.

Methods

A total of 729 patients, including 316 osteopenia and 413 osteoporosis patients of Han Chinese ancestry were selected in the study. Their blood samples were collected and the levels of specific IgG antibodies against T. gondii were measured using ELISA assay. We obtained some information about the patients from the medical record that included demographic indexes and clinical data. A logistic regression analysis was used to evaluate the effects of T. gondii infection on femur osteoporosis, lumbar osteoporosis and compound osteoporosis. Potential interaction was analyzed using multifactor dimensionality reduction software 1.0.0 (MDR 1.0.0).

Results

113 positive patients with T. gondii infections have been detected, including 80 cases of osteoporosis and 33 cases of osteopenia, the infection rates of T. gondii were 19.37% (80/413) and 10.44% (33/316), respectively. The patients with T.gondii infections were at a 2.60 times higher risk of suffering from compound osteoporosis than those without T. gondii infections (OR = 2.60, 95% CI 1.54–4.39, P < 0.001), but not associated with femur osteoporosis (OR = 1.01, 95% CI 0.43–2.34, P = 0.989) and lumbar osteoporosis (OR = 0.84, 95% CI 0.34–2.07, P = 0.705) after adjusting for the covariates. Moreover, a significantly higher risk of compound osteoporosis in the individuals with all two factors (T. gondii infection, Female) was observed compared with reference group (without T. gondii infection, male) under the interaction model (OR = 11.44, 95%CI = 5.44–24.05, P < 0.001). And the individuals with all two factors (T. gondii infection, over 70 years) exhibited a 8.14-fold higher possibility of developing compound osteoporosis compared with reference group (without T. gondii infection, under 70 years) (OR = 8.14, 95% CI 3.91–16.93, P < 0.001). We further stratified by age and sex, and found that women with T. gondii infection was more likely to develop compound osteoporosis than those without infection(OR = 3.12, 95% CI  1.67–5.81, P < 0.001), but we not found the association between T. gondii infection and compound osteoporosis in males (OR = 1.36, 95% CI 0.37–4.94, P = 0.645).

Conclusions

T. gondii infection is a risk factor for osteoporosis, especially compound osteoporosis. Meanwhile, it is very necessary for patients with osteoporosis to further diagnose and treat T. gondii infection, especially women.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05257-z.

Investigation of Toxoplasma gondii in wastewater and surface water in the Qinghai-Tibet Plateau, China using real-time PCR and multilocus genotyping

Toxoplasma gondii is a protozoan parasite, causing one of the most prevalent parasitic infections in the world. In the present study water sources of the Qinghai-Tibet Plateau (QTP), China, where the hygienic infrastructure is still developing, were investigated. A total of 214 water samples of 10 L volume, were collected from wastewater treatment plants (WWTPs), a slaughterhouse and rivers. The samples were filtered and then analysed using real-time PCR and multilocus genotyping. T. gondii DNA was found in four (1.9%) samples representing T. gondii type I; in one of them T. gondii-like oocysts were also confirmed microscopically. The approximate level of contamination of positive samples ranged between 30 and 2300 T. gondii sporozoites. The results of this study confirmed that T. gondii is present in wastewater in the greater metropolitan area of Xining and a neighbouring county. Contamination of wastewater at this level constitutes rather a moderate source of Toxoplasma infections in humans and animals. It suggests, however, a link between environmental exposure of animals, meat processing facilities and WWTPs. To our knowledge, this is the first investigation describing T. gondii detection in wastewater and environmental water samples collected from the territory of P.R. China using sensitive molecular tools.

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.

Direct enzyme-linked aptamer assay (DELAA) for diagnosis of toxoplasmosis by detection of SAG1 protein in mice and humans

Toxoplasma gondii is a single-celled parasite commonly found in mammals and birds. Diagnosis of toxoplasmosis largely depends on measurements of the antibody and/or antigen and Toxoplasma DNAs due to the presence of tissue dwelling duplicating tachyzoites, or quiescent cysts in latent infection of the parasite. As a major surface antigen of T.gondii tachyzoites, SAG1 is a key molecule for laboratory diagnosis. However, there are no methods available yet for SAG1 detection using aptamer-based technology. Recombinant SAG1 (r-SAG1) of Toxoplasma WH3 strain (type Chinese 1) was expressed in E.coli and subjected to the synthetic oligonucleotide library for selection of nucleic acid aptamers which target the r-SAG1 antigen, with systematic evolution of ligands by exponential enrichment (SELEX) strategy. The specific aptamers were screened out and used in direct enzyme-linked aptamer assay (DELAA) for detection of native SAG1 (n-SAG1) obtained from tachyzoite lysates, mouse sera of acute infection, and human sera that had been verified for Toxoplasma DNAs by PCR amplification. As results, the soluble r-SAG1 protein was obtained from E.coli lysates by purification and identification with immunoblotting, followed by biotinylation. The selected aptamers were amplified by PCR and DNA sequencing. The results showed that the aptamer-2, with the highest affinity to n-SAG1 in the sera of animals with minimal difference in the four aptamer candidates, has a high specificity and sensitivity when used in detection of n-SAG1 in the sera of humans when compared with the commercial kit of ELISA for T.gondii circulating antigen test. We concluded that a new direct enzyme-linked aptamer assay (DELAA) was developed for the detection of the n-SAG1 protein of T. gondii. With increased sensitivity and specificity, stability, easy and cheap preparation, the aptamer-based technology is considered an efficient method for the diagnosis of active as well as reactivated toxoplasmosis.

Toxoplasma gondii Genotypes Circulating in Serbia-Insight into the Population Structure and Diversity of the Species in Southeastern Europe, a Region of Intercontinental Strain Exchange

In Europe, Toxoplasma gondii lineage II is dominant, and ToxoDB#1 the most frequently occurring genotype. The abundance of lineage III genotypes varies geographically and lineage I are rare, yet present in several regions of the continent. Data on the T. gondii population structure in southeastern Europe (SEE) are scarce, yet necessary to appreciate the diversity of the species in Europe. To help fill this gap, we genotyped 67 strains from nine species of intermediate hosts in Serbia by MnPCR-RFLP, determined the population structure, and identified the genotypes using ToxoDB. A neighbor-joining tree was also constructed from the isolates genotyped on nine loci. While 42% of the total genotype population consisted of ToxoDB#1 and ToxoDB#2, variant genotypes of both lineages comprised 46% of the population in wildlife and 28% in domestic animals and humans. One genotype of Africa 4 lineage was detected in a human sample. Interestingly, the findings include one lineage III variant and one II/III recombinant isolate with intercontinental distribution, which appear to be moderately related to South American genotypes. Based on these findings, SEE is a region of underappreciated T. gondii genetic diversity and possible strain exchange between Europe and Africa.

Molecular detection and genetic characterization of Toxoplasma gondii in pork from Chongqing, southwest China

Raw or undercooked meat is an important source of Toxoplasma gondii infection in China, but there is little research data on these infections in Chongqing. This study determined the prevalence of T. gondii, and its genotypes, in pork. A total of 1,223 diaphragm muscle samples were collected from eight slaughterhouses and 79 markets and detected by PCR amplification of the ITS gene. All of the positive samples were used for genotype identification by PCR-RFLP with 11 genetic markers. The total positive rate of T. gondii in Chongqing pork was 8.7%, and differences in T. gondii infection rates were found between different districts (0%-23.3%), seasons (e.g., 4.3% from Spring, 7.3% from Summer, 11.4% from Autumn, 12.0% from Winter) and years (2.7%-14.3%). Six samples were successfully genotyped, of which one was identified as ToxoDB#9 and five were ToxoDB#9-like. This was the first continuous study about the prevalence of T. gondii in pork in Chongqing for several years. Slaughterhouses in different districts, pork source, farm scale, season and year were potential risk factors for T. gondii contamination by the univariate logistic regression, and using multivariate logistic regression districts, pork source and year were the independent risk factor. These data may help reducing the levels of toxoplasmosis in pigs and humans in Chongqing.

Evidence of Hearing Loss and Unrelated Toxoplasmosis in a Free-Ranging Harbour Porpoise (Phocoena phocoena)

Simple Summary

Evidence of hearing impairment was identified in a female harbour porpoise (Phocoena phocoena) on the basis of inner ear analysis. The animal live stranded on the Dutch coast at Domburg in 2016 and died a few hours later. Ultrastructural examination of the inner ear revealed evidence of sensory cell loss, which is compatible with noise exposure. In addition, histopathology also revealed multifocal necrotising protozoal encephalitis. A diagnosis of toxoplasmosis was confirmed by positive staining of tissue with anti-Toxoplasma gondii antibodies; however, T. gondii tachyzoites were not observed histologically in any of the examined tissues. This is the first case of presumptive noise-induced hearing loss and demonstration of T. gondii cysts in the brain of a free-ranging harbour porpoise from the North Sea.

Abstract

Evidence of hearing impairment was identified in a harbour porpoise (Phocoena phocoena) on the basis of scanning electron microscopy. In addition, based on histopathology and immunohistochemistry, there were signs of unrelated cerebral toxoplasmosis. The six-year old individual live stranded on the Dutch coast at Domburg in 2016 and died a few hours later. The most significant gross lesion was multifocal necrosis and haemorrhage of the cerebrum. Histopathology of the brain revealed extensive necrosis and haemorrhage in the cerebrum with multifocal accumulations of degenerated neutrophils, lymphocytes and macrophages, and perivascular lymphocytic cuffing. The diagnosis of cerebral toxoplasmosis was confirmed by positive staining of protozoa with anti-Toxoplasma gondii antibodies. Tachyzoites were not observed histologically in any of the examined tissues. Ultrastructural evaluation of the inner ear revealed evidence of scattered loss of outer hair cells in a 290 µm long segment of the apical turn of the cochlea, and in a focal region of ~ 1.5 mm from the apex of the cochlea, which was compatible with noise-induced hearing loss. This is the first case of concurrent presumptive noise-induced hearing loss and toxoplasmosis in a free-ranging harbour porpoise from the North Sea.

Differential expression of TgMIC1 in isolates of Chinese 1 Toxoplasma with different virulence

BACKGROUND

The predominant genotype of Toxoplasma in China is the Chinese 1 (ToxoDB#9) lineage. TgCtwh3 and TgCtwh6 are two representative strains of Chinese 1, exhibiting high and low virulence to mice, respectively. Little is known regarding the virulence mechanism of this non-classical genotype. Our previous RNA sequencing data revealed differential mRNA levels of TgMIC1 in TgCtwh3 and TgCtwh6. We aim to further confirm the differential expression of TgMIC1 and its significance in this atypical genotype.

METHODS

Quantitative real-time PCR was used to verify the RNA sequencing data; then, polyclonal antibodies against TgMIC1 were prepared and identified. Moreover, the invasion and proliferation of the parasite in HFF cells were observed after treatment with TgMIC1 polyclonal antibody or not.

RESULTS

The data showed that the protein level of TgMIC1 was significantly higher in high-virulence strain TgCtwh3 than in low-virulence strain TgCtwh6 and that the invasion and proliferation of TgCtwh3 were inhibited by TgMIC1 polyclonal antibody.

CONCLUSION

Differential expression of TgMIC1 in TgCtwh3 and TgCtwh6 may explain, at least partly, the virulence mechanism of this atypical genotype.

Molecular Detection of Toxoplasma gondii and Neospora caninum in Domestic Ducks in Hunan Province, China

Toxoplasma gondii and Neospora caninum are protozoan parasites that infect warm-blooded animals, and cause major economic losses in livestock industries worldwide. However, little is known about the genotypes of T. gondii and N. caninum in domestic ducks in China. Herein, brain samples from 588 domestic ducks from Hunan province in China were examined for the presence of T. gondii and N. caninum. Polymerase chain reaction (PCR) was used to detect T. gondii B1 gene and N. caninum NC-5 gene. Forty-five DNA samples (7.7%; 95% CI: 5.5–9.9) were positive for B1 gene, and two (0.3%; 95% CI: 0–0.7) were positive for NC-5 gene. The risk factors significantly associated with T. gondii infection were age and sex. The 45 samples positive for T. gondii were genotyped using multi-locus PCR-RFLP analysis and only one sample was fully genotyped as ToxoDB#9 (Chinese I). These results provide new information about the epidemiology of T. gondii and N. caninum in ducks in Hunan province in China. The data also highlight the importance of a “One Health” approach to dealing with toxoplasmosis.

The Host Autophagy During Toxoplasma Infection

Autophagy is an important homeostatic mechanism, in which lysosomes degrade and recycle cytosolic components. As a key defense mechanism against infections, autophagy is involved in the capture and elimination of intracellular parasites. However, intracellular parasites, such as Toxoplasma gondii, have developed several evasion mechanisms to manipulate the host cell autophagy for their growth and establish a chronic infection. This review provides an insight into the autophagy mechanism used by the host cells in the control of T. gondii and the host exploitation by the parasite. First, we summarize the mechanism of autophagy, xenophagy, and LC3-associated phagocytosis. Then, we illustrate the process of autophagy proteins-mediated T. gondii clearance. Furthermore, we discuss how the parasite blocks and exploits this process for its survival.

Seroprevalence of Toxoplasma gondii in household cats in Myanmar and molecular identification of parasites using feline faecal oocysts

Felids play an important role in the transmission of Toxoplasma gondii to humans and other animals since they can excrete millions of oocysts into the environment as definitive hosts. In the present study, seroprevalence and risk factors of feline Toxoplasma infection were investigated, and molecular identification was conducted for T. gondii oocysts isolated from faecal samples of seropositive cats. A total of 276 cat serum samples collected from the Yangon, Myanmar were tested for T. gondii antibodies by ELISA. The overall seroprevalence of T. gondii infection was 41.30% (114 seropositive cats). Age between 1 and 6 years (OR = 3.284; 95% CI = 1.462–7.375), age > 6 years (OR = 4.560; 95% CI = 1.588–13.100) and sex (OR = 1.725; 95% CI = 1.026–2.899) were found to be significant (P < 0.05) factors associated with T. gondii infection. DNA samples extracted from a single oocyst of seropositive cats were employed in three PCR assays amplifying parasite TOX-element and mitochondrial COI, and SAG2 locus. The obtained sequences of TOX-elements (n = 6) and COI (n = 5) were identical to those of T. gondii previously deposited in Genbank. SAG2 PCR yielded three different sequences, all of which were clustered with Type I T. gondii isolates in a phylogenetic tree. This study reported the seroprevalence and risk factors for T. gondii infection in cats and provided the molecular information on the parasite in Myanmar.

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Seroprevalence of Toxoplasma gondii in cats was investigated for the first time in Myanmar.

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The overall seroprevalence of T. gondii infection in cats was 41.30% (out of 114 seropositive individuals).

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Age, sex, and type of feed were associated with T. gondii infection.

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The obtained sequences of TOX-element and COI were identical to those of T. gondii deposited in GenBank.

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The obtained SAG2 sequences were clustered with T. gondii Type I isolates.

Toxoplasma gondii ROP16I Deletion: The Exacerbated Impact on Adverse Pregnant Outcomes in Mice

Imbalance of Th1 and Th2 response at the maternal-fetal interface is considered as a radical event in the pathogenesis of immunity-related pregnant diseases. It has been demonstrated that the ROP16_I, a rhoptry protein of Toxoplasma gondii, and the viable parasite with ROP16_I may induce M2 macrophage polarization in host innate immunity and may be involved in the adverse pregnant outcomes. However, the mechanisms by which T. gondii-derived effectors subvert the immune tolerance in the pathology of pregnancy remain unclear. Here, we constructed the RH strain with ROP16_I deletion (RHΔrop16) to explore the pathogenesis of abnormal pregnancy. We found that C57BL/6 mice infected with RHΔrop16 exhibited the increased resorption of fetuses and more severe adverse pathology of placentae at the early phase of gestation, as compared to the mice infected with RH wild type (RH WT) parasite. Additionally, RHΔrop16 strain infection significantly promoted M1 macrophage phenotypes of CD80 and CD86, and decreased CD206 expression of M2 macrophages, with upregulation of the iNOS and downregulation of the Arg-1 expression in placental homogenates. Simultaneously, the pro-inflammatory cytokines of IL-12 and TNF-α were elevated whereas the anti-inflammatory cytokine of TGF-β1 was dampened. Moreover, the p38α mitogen-activated protein kinase (p38α MAPK) was notably phosphorylated in placental macrophages infected with both RHΔrop16 and RH WT strains compared with the control. Taken together, our findings indicated that ROP16_I deletion of type I RH strain may cause exacerbated adverse pregnant outcomes, which is attributable to subversion of the maternal immune tolerance due to the increased pro-inflammatory cytokines in the pregnant animals. The results also suggest that ROP16_I might be a protective factor and other T. gondii-derived molecules might be involved in the M1-Th1 biased pathological process in aberrant pregnancy at the early phase of gestation.

First molecular detection of Toxoplasma gondii in vegetable samples in China using qualitative, quantitative real-time PCR and multilocus genotyping

Toxoplasma gondii infection is becoming increasing problem in China but there is no data concerning contamination of vegetables intended for consumption with this parasite. The aim of the present study was to investigate fresh vegetables originated from open markets located in the Xining City, the Qinghai-Tibet Plateau (QTP), P.R. China for their contamination with T. gondii. A total of 279 fresh vegetable samples were collected and analysed using real-time PCR assay targeting B1 gene and multilocus genotyping. T. gondii DNA was found in 10 (3.6%) samples tested; eight of them represented T. gondii type I and remaining two T. gondii type II. The approximate level of contamination of positive vegetables samples, estimated based on quantitative real-time PCR (qPCR), ranged between less than one and 27000 T. gondii oocysts per sample, with majority not exceeding several oocysts per sample. The results of the study confirmed that T. gondii is present in vegetables offered in open markets in the Qinghai province, P.R. China; eating them unwashed and raw may therefore pose a threat to consumers. This is the first investigation describing T. gondii detection in fresh vegetables intended for consumption collected from the territory of P.R. China using sensitive molecular tools.

Label-Free Quantitative Acetylome Analysis Reveals Toxoplasma gondii Genotype-Specific Acetylomic Signatures

Distinct genotypic and pathogenic differences exist between Toxoplasma gondii genotypes. For example, genotype I is highly virulent, whereas genotype II and genotype III are less virulent. Moreover, Chinese 1 genotype (ToxoDB#9) is also virulent. Here, we compare the acetylomes of genotype 1 (RH strain) and Chinese 1 genotype (ToxoDB#9, PYS strain) of T. gondii. Using mass spectrometry enriched for acetylated peptides, we found a relationship between the levels of protein acetylation and parasite genotype-specific virulence. Notably, lysine acetylation was the largest (458 acetylated proteins) in RH strain, followed by PYS strain (188 acetylated proteins), whereas only 115 acetylated proteins were detected in PRU strain. Our analysis revealed four, three, and four motifs in RH strain, PRU strain and PYS strain, respectively. Three conserved sequences around acetylation sites, namely, xxxxxK^AcHxxxx, xxxxxK^AcFxxxx, and xxxxGK^AcSxxxx, were detected in the acetylome of the three strains. However, xxxxxK^AcNxxxx (asparagine) was found in RH and PYS strains but was absent in PRU strain. Our analysis also identified 15, 3, and 26 differentially expressed acetylated proteins in RH strain vs. PRU strain, PRU strain vs. PYS strain and PYS strain vs. RH strain, respectively. KEGG pathway analysis showed that a large proportion of the acetylated proteins are involved in metabolic processes. Pathways for the biosynthesis of secondary metabolites, biosynthesis of antibiotics and microbial metabolism in diverse environments were featured in the top five enriched pathways in all three strains. However, acetylated proteins from the virulent strains (RH and PYS) were more enriched in the pyruvate metabolism pathway compared to acetylated proteins from PRU strain. Increased levels of histone-acetyl-transferase and glycyl-tRNA synthase were detected in RH strain compared to PRU strain and PYS strain. Both enzymes play roles in stress tolerance and proliferation, key features in the parasite virulence. These findings reveal novel insight into the acetylomic profiles of major T. gondii genotypes and provide a new important resource for further investigations of the roles of the acetylated parasite proteins in the modulation of the host cell response to the infection of T. gondii.

Prevalence and Genotyping of Toxoplasma gondii Infection in Raccoon Dogs (Nyctereutes procyonoides) in Northern China

Toxoplasma gondii is one of protozoan parasites resulting in zoonosis, which can infect nearly all of warm-blooded hosts, including humans and raccoon dogs (Nyctereutes procyonoides). However, related reports on prevalence and genetic characterization of T. gondii strains in raccoon dogs were few in China. The aim of this study was to survey the prevalence and genetic characterization of T. gondii strains in domestic raccoon dogs from Jilin, Liaoning, and Hebei provinces, northern China. During April 2016 to November 2017, a total of 337 tissue samples collected from domestic raccoon dogs were detected with B1 gene using a nested PCR. And the positive samples were genotyped at 11 genetic markers (SAG1, 5'-and 3'-SAG2, alternative SAG2, SAG3, BTUB, GRA6, L358, PK1, c22-8, c29-2, and Apico) using multilocus PCR-restriction fragment length polymorphism technology. Sixteen out of 337 sika deer (4.75%) were positive with B1 gene by nest PCR. Furthermore, four positive DNA samples were completely typed through further being genotyped, in which three samples were identified as ToxoDB Genotype #9, and one sample was confirmed as ToxoDB Genotype #10. The results of molecular detection not only revealed the existence of T. gondii in domestic raccoon dogs in Jilin, Liaoning, and Hebei for the first time, but also provided the information of genetic diversity. This study also indicated that ToxoDB Genotype #9 as a kind of potential reservoir for T. gondii transmission, may be main genotype in domestic raccoon dogs in China, posing a risk of infection in human health.

A systematic review of Toxoplasma gondii genotypes and feline: Geographical distribution trends

Toxoplasma gondii (T. gondii) is well known for its ability to virtually infect all warm-blooded vertebrates. Although felines as the definitive hosts have an important role in the epidemiology of toxoplasmosis, there are few descriptions of genetic diversity in the world. The present review study aimed to describe the population structure of T. gondii in these animal species. For the purpose of the study, five English language databases reporting data on T. gondii genotyping in cats were searched within March-June 2019. This study is registered on the site of CAMARADES-NC3Rs (15-Jan-2018). The searching process resulted in the inclusion of 50 reports published from 1992 to June 2019. The data revealed that 47,390 samples were genotyped into 662 T. gondii DNA/isolates. Globally, atypical genotypes were predominant (47.7%, n = 316); in addition, Type II clonal strains were the second most common genotype (37%, n = 244). These results suggested an epidemic population structure in America and Asia, and a clonal population structure in Europe and Africa. Genotype #3 was found to be dominant in Africa, Europe and Oceania continents. Furthermore, genotypes #9 and #5 were prevalent in Asia and America, respectively. Additionally, genotypes #2, #3, #5 and #20 were common genotypes in domestic and sylvatic cycles from family Felidae. Collectively, this systematic review indicated a large degree of genetic diversity and circulation of mouse-virulent T. gondii strains in this family. However, further studies are necessary to better understand the population structure of T. gondii in these animal species and determine the significance of their features.

Genetic Characterization of Toxoplasma gondii DNA Samples Isolated From Humans Living in North America: An Unexpected High Prevalence of Atypical Genotypes

Background

Whereas in Europe most of Toxoplasma gondii genotypes belong to the type II lineage, in Latin America, type II is rare and atypical strains predominate. In North America, data on T. gondii genotypes in humans are scarce.

Methods

In this study, T. gondii DNA samples from 67 patients with diagnosed toxoplasmosis in the United States were available for genotyping. Discriminant analysis of principal components was used to infer each atypical genotype to a geographic area where patients were probably infected. Associations between genotype, disease severity, immune status, and geographic region were also estimated.

Results

Of 67 DNA samples, 41 were successfully genotyped: 18 (43.9%) and 5 (12.2%) were characterized as types II and III, respectively. The remaining 18 genotypes (43.9%) were atypical and were assigned to a geographic area. Ten genotypes originated from Latin America, 7 from North America, and 1 from Asia (China). In North America, unlike in Europe, T. gondii atypical genotypes are common in humans and, unlike in Latin America, type II strains are still present with significant frequency.

Conclusions

Clinicians should be aware that atypical genotypes are common in North America and have been associated with severe ocular and systemic disease and unusual presentations of toxoplasmosis in immunocompetent patients.

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.

Strategies Developed by Toxoplasma gondii to Survive in the Host

One of the most successful intracellular parasites, Toxoplasma gondii has developed several strategies to avoid destruction by the host. These include approaches such as rapid and efficient cell invasion to avoid phagocytic engulfment, negative regulation of the canonical CD40-CD40L-mediated autophagy pathway, impairment of the noncanonical IFN-γ-dependent autophagy pathway, and modulation of host cell survival and death to obtain lifelong parasite survival. Different virulent strains have even evolved different ways to cope with and evade destruction by the host. This review aims to illustrate every aspect of the game between the host and Toxoplasma during the process of infection. A better understanding of all aspects of the battle between Toxoplasma and its hosts will be useful for the development of better strategies and drugs to control the parasite.

Virulence in Mice of a Toxoplasma gondii Type II Isolate Does Not Correlate With the Outcome of Experimental Infection in Pregnant Sheep

Toxoplasma gondii is an apicomplexan parasite that infects almost all warm-blooded animals. Little is known about how the parasite virulence in mice extrapolates to other relevant hosts. In the current study, in vitro phenotype and in vivo behavior in mice and sheep of a type II T. gondii isolate (TgShSp1) were compared with the reference type II T. gondii isolate (TgME49). The results of in vitro assays and the intraperitoneal inoculation of tachyzoites in mice indicated an enhanced virulence for the laboratory isolate, TgME49, compared to the recently obtained TgShSp1 isolate. TgShSp1 proliferated at a slower rate and had delayed lysis plaque formation compared to TgME49, but it formed more cyst-like structures in vitro. No mortality was observed in adult mice after infection with 1–10⁵ tachyzoites intraperitoneally or with 25–2,000 oocysts orally of TgShSp1. In sheep orally challenged with oocysts, TgME49 infection resulted in sporadically higher rectal temperatures and higher parasite load in cotyledons from ewes that gave birth and brain tissues of the respective lambs, but no differences between these two isolates were found on fetal/lamb mortality or lesions and number of T. gondii-positive lambs. The congenital infection after challenge at mid-pregnancy with TgShSp1, measured as offspring mortality and vertical transmission, was different depending on the challenged host. In mice, mortality in 50% of the pups was observed when a dam was challenged with a high oocyst dose (500 TgShSp1 oocysts), whereas in sheep infected with the same dose of oocysts, mortality occurred in all fetuses. Likewise, mortality of 9 and 27% of the pups was observed in mice after infection with 100 and 25 TgShSp1 oocysts, respectively, while in sheep, infection with 50 and 10 TgShSp1 oocysts triggered mortality in 68 and 66% of the fetuses/lambs. Differences in vertical transmission in the surviving offspring were only found with the lower oocyst doses (100% after infection with 10 TgShSp1 oocysts in sheep and only 37% in mice after infection with 25 TgShSp1 oocysts). In conclusion, virulence in mice of T. gondii type II isolates may not be a good indicator to predict the outcome of infection in pregnant sheep.

Genetic Characterization of Toxoplasma gondii from Wild Rodents in Sichuan Province, Southwestern China

BACKGROUND

Wild rodents are the intermediate hosts of Toxoplasma gondii. The distribution of genetic diversity of T. gondii in wild rodents is of importance to understand the transmission of this parasite. This study aimed to genetically characterize T. gondii isolates from wild rodents in Sichuan province, southwestern China in 2013.

METHODS

Genomic DNA was extracted from 10 g wild rodents' brain samples. Semi-nested PCR and multilocous PCR-RFLP technology were performed to examine genetic diversity of T. gondii isolates as described previously.

RESULTS

Overall, 181 brain tissues of different wild rodents, including Eothenomys miletus (n=88), Crocidura attenuate (n=9), Rattus rattus sladeni (n=46), Mus musculus Linnaeus (n=6) and R. niviventer (n=32) were tested for T. gondii DNA, respectively. Six of them were positive for the T. gondii B1 gene by semi-nested PCR amplification, 4 showed complete genotyping results for all 11 polymorphic loci (SAG1, SAG2, alt. SAG2, SAG3, BTUB, GRA6, L358, PK1, C22-8, C29-2 and Apico) by PCR-RFLP, determined to represent a potential new genotype (http://toxodb.org/toxo/).

CONCLUSION

These results documented genetic characterization of T. gondii in wild rodents from Sichuan province, and enriched the genetic diversity of T. gondii in China.

Human toxoplasmosis: a systematic review for genetic diversity of Toxoplasma gondii in clinical samples

Toxoplasma gondii (T. gondii) as an obligate intracellular protozoan with a worldwide distribution can infect virtually all warm-blooded animals and humans. This study aims to provide a summary of the available data on genotypes of T. gondii in human. Five databases including MEDLINE in PubMed, Scopus, Science Direct, Web of Science and Google Scholar were searched for the T. gondii genotyping in human during 1995-August 2017. Next, we screened all the articles based on the inclusion and exclusion criteria. Overall, 26 studies were eligible regarding genotyping T. gondii in human samples. In clonal genotyping, 167 out of 286 cases (58%) were infected with type II. Genetic characterisation of T. gondii isolates displayed that type II was the most predominant genotype in human with the prevalence of 64.3%, 62.1% and 41.7% in patients with AIDS, congenital and ocular toxoplasmosis, respectively. In ToxoDB genotyping, most individuals were infected with genotypes #9 and #65 (21.2%). Based on these results, genotype profile of T. gondii isolates is different throughout the world. The strains in Asian and African countries are characterised by low genetic diversity, while in North and South America a wide diversity of this parasite is found. In countries without any data (e.g. Australia, Western and Southern Africa and Western Asia), identification of T. gondii genotypes might discover higher genetic diversity.

Genotyping and virulence analysis of Toxoplasma gondii isolates from a dead human fetus and dead pigs in Jiangsu province, Eastern China

Toxoplasma gondii is an obligate intracellular parasite with worldwide distribution. Virulence of T. gondii is a multigenic trait. Genetic and virulence data for T. gondii isolates from humans and animals in China have been reported. However, almost all biological materials used for genotyping of T. gondii from humans and pigs were DNA samples prepared from tissues, and T. gondii strains used for virulence analysis were isolated mainly from cats. In this study, one isolate from a dead human fetus was identified as type I (ToxoDB #10) while the two isolates from dead pigs were type Chinese I (ToxoDB #9) with PCR-restriction fragment length polymorphism using 10 markers (SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1 and Apico). Three isolates were comfirmed as virulent strains in mice. By cloning and sequences analysis, all isolates contained a Pvu II restriction site (572-577 bp) in the KHB fragment and five tandem repeats in the 5' UTR region of SAG1, which were associated with T. gondii virulence. The type Chinese I isolates contained two deletions of 15 and 3 bp at positions 635 to 649 and 658 to 660 in the GRA6, which were correlated with genotype, but not with virulence. To our knowledge, this is the first report on the systematic analysis of murine virulence of type Chinese I strain from pigs, and the associations of sequences of the KHB fragment and SAG1 with virulence of type Chinese I strain. The Chinese I genotype was more closely related to type II strains.

Prevalence of toxoplasmosis and genetic characterization of Toxoplasma gondii strains isolated in wild birds of prey and their relation with previously isolated strains from Turkey

Toxoplasma gondii is a protozoon parasite that causes congenital toxoplasmosis, as well as other serious clinical presentations, in immune compromised humans. Analyses of the prevalence and genotyping of strains from the definitive host and intermediate hosts will help to understanding the circulation of the different strains and elucidating the role of the genotype(s) in human toxoplasmosis. Turkey has a specific geographic location bridging Africa, Europe, and Asia. We hypothesized that T. gondii strains may have been transferred to Turkey from these continents via migratory birds or vice versa. The present study aimed to assess the prevalence of toxoplasmosis in wild birds of prey of İzmir and Manisa provinces as well as genetically characterize T. gondii strains from these wild birds to show the relation between bird strains and neighboring stray cats as well as human strains previously isolated in Turkey. Tissues obtained from 48 wild birds were investigated for the presence of T. gondii DNA and then bioassayed in mouse. Isolated strains were genotyped using 15 microsatellite markers. The prevalence of T. gondii DNA was found to be 89.6% (n: 43/48) in wild birds. Out of 43 positive samples, a total of 14 strains were genotyped by 15 microsatellite markers. Among them, eight were type II, three were type III and three were mixture of genotypes (two type II/II and one was II/III). These are the first data that showed the presence of T. gondii and types II and III genotypes in wild birds of Turkey. Moreover, Africa 1 was not detected. In addition, cluster analysis showed that T. gondii strains within type II and III lineage have close relation with strains previously isolated from stray cats in İzmir. Further studies are required to isolate more strains from human cases, other intermediate hosts, and water sources to reveal this relation.

The association between Toxoplasma gondii infection and hypertensive disorders in T2DM patients: a case-control study in the Han Chinese population

Type 2 diabetes mellitus (T2DM) is a major global health problem. The rate of infection with Toxoplasma gondii (T. gondii) is more than one-third of the total world population. The effects of T. gondii infection on the risk of diabetic complications and comorbidities are unclear. This study aims to determine the relationship between T. gondii infection and complications of T2DM in the Han Chinese population. We collected 1580 blood samples from T2DM patients and measured the levels of specific IgG antibodies against T. gondii in the sera of these patients using an ELISA assay. A logistic regression analysis was performed to estimate the effect of T. gondii infection on the complications of T2DM, while adjusting for age, gender, and triglyceride level (TG). We applied the multifactor dimensionality reduction (MDR) method to detect the interactions between T. gondii infections, demographic indexes and biochemical indicators among the different complications. Gender (the odds ratio (OR) = 0.63, 95%CI =0.45-0.89, P = 0.008) and TG level (OR = 0.64, 95%CI =0.45-0.89, P = 0.009) were influencing factors in T. gondii infections. T2DM patients who were infected with T. gondii had a 2.34 times risk of developing hypertension than those patients without T. gondii infection (OR = 2.34, 95%CI = 1.12-4.88, P = 0.024). The multiplicative interaction analysis and the additive interaction analysis did not reveal any evidence of interactive effects on diabetic complications and comorbidities. T. gondii might be a factor associated with hypertension in T2DM patients.

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.

Sixty Years (1957-2017) of Research on Toxoplasmosis in China-An Overview

Toxoplasma gondii is a ubiquitous zoonotic pathogen belonging to apicomplexan parasites. Infection in humans and animals may cause abortion and other severe symptoms under certain circumstances, leading to great economical losses and public health problems. T. gondii was first discovered in China in 1955 and the corresponding work was published in 1957. Since then, a lot of work has been done on this parasite and the diseases it causes. This review summarizes the major progress made by Chinese scientists over the last 60 years, and gives our perspectives on what should be done in the near future. A wide variety of diagnostic approaches were designed, including the ones to detect T. gondii specific antibodies in host sera, and T. gondii specific antigens or DNA in tissue and environmental samples. Further work will be needed to translate some of the laboratory assays into reliable products for clinic uses. Epidemiological studies were extensively done in China and the sero-prevalence in humans increased over the years, but is still below the world average, likely due to the unique eating and cooking habits. Infection rates were shown to be fairly high in meat producing animals such as, pigs, sheep, and chickens, as well as in the definitive host cats. Numerous subunit vaccines in the form of recombinant proteins or DNA vaccines were developed, but none of them is satisfactory in the current form. Live attenuated parasites using genetically modified strains may be a better option for vaccine design. The strains isolated from China are dominated by the ToxoDB #9 genotype, but it likely contains multiple subtypes since different ToxoDB #9 strains exhibited phenotypic differences. Further studies are needed to understand the general biology, as well as the unique features of strains prevalent in China.

Antibody Detection, Isolation, Genotyping, and Virulence of Toxoplasma gondii in Captive Felids from China

The felids are the only definitive hosts of Toxoplasma gondii, which could excrete oocysts into the environment and provide an infection source for toxoplasmosis in various warm-blooded animal species, particularly the captive felids that live close to human communities. The infection rate of the captive felids is a perfect standard in detecting the presence of Toxoplasma gondii oocysts in the environment. In this study, sera or tissue samples from zoo (1 young tiger, 2 adult tigers, 6 young lions), farm (10 masked palm civets), and pet hospital (28 cats) from Henan Province (China) were collected. The sera (n = 47) were tested for immunoglobulin G (IgG) antibodies against T. gondii by using modified agglutination test (MAT), whereas the hearts tissue (n = 40) were bioassayed in mice to isolate T. gondii strains. The genotype was distinguished by using PCR-RFLP of 10 loci (SAG1, SAG2, SAG3, GRA6, BTUB, L358, c22-8, PK1, c29-2, and Apico). The detection rate for the T. gondii antibody in captive felids was 21.3% (10/47). One viable T. gondii strain (TgCatCHn4) was obtained from a cat heart tissue, and its genotype was ToxoDB#9. The oocysts of ToxoDB#9 were collected from a T. gondii-free cat. The virulence of TgCatCHn4 was low and no cysts were detected in the brain of mice at 60 days post-inoculation. The finding of the present study suggested a widespread exposure of T. gondii for felids in Henan Province of central China, particularly those from the zoological gardens and homes. ToxoDB#9 was the predominant strain in China. Preventive measures against T. gondii oocyst contamination of various components of the environment should thus be implemented, including providing pre-frozen meat, well-cooked cat food, cleaned fruits and vegetables, monitoring birds and rodents, inactive T. gondii oocysts in felids feces, and proper hygiene.

Diagnosis of Swine Toxoplasmosis by PCR and Genotyping of Toxoplasma gondii from pigs in Henan, Central China

Background

Toxoplasma gondii, a widely prevalent protozoan parasite, causes serious toxoplasmosis infections in humans and other animals. Among livestock, pigs are susceptible to T. gondii infection. Despite Henan being one of the biggest pig-raising provinces in China, little information exists on the epidemiology of toxoplasmosis in this location. Therefore, we molecularly characterized DNA samples from pigs in Henan. A total of 1647 samples, including 952 from dead piglets, 478 from seriously sick fattening pigs and 217 from abortion sows, were collected from different animal hospitals or pig farms from 10 different cities in Henan (2006–2008). Each pig corresponded to a separate pig farm. DNA was extracted from 3 to 5 g of the most severely affected pig tissue (liver, spleen, lung, hilar lymph nodes and amniotic fluid) after postmortem examination. The presence of the T. gondii B1 gene was detected using nested polymerase chain reactions (PCR). Genotyping was performed directly on DNA from the PCR-positive tissue samples using 11 PCR restriction fragment length polymorphism markers (SAG1, 5′- and 3′-SAG2, alternative SAG2, SAG3, BTUB, GRA6, L358, PK1, c22–8, c29–2, and Apico).

Results

Of all samples, thirty-four were positive for the T. gondii B1 gene (2.06%, 95% CI: 1.86%–2.26%) from four cities, including 31 from NanYang city, one (PgXY 1) from Xinyang City, one (PgZZ 1) from Zhengzhou City and one (PgZK1) from Zhoukou City. The prevalence was found to be highest in piglets than in fattening pigs and sows. And the difference was statistically significant (P<0.01). The following 32 samples were genotyped with complete data: 13 hilar lymph node tissue samples, seven liver tissue samples, seven lung tissue samples, four spleen tissue samples, and one amniotic fluid sample. Only one genotype, belonging to ToxoDB Genotype #9, was identified.

Conclusions

This is the first large-scale survey molecularly characterizing T. gondii from pigs in Henan. The results of the present study revealed that T. gondii infection is present in swine in Henan and is a potential source of foodborne toxoplasmosis in the investigated areas. Implementation of effective control measures for T. gondii to reduce the chance of zoonotic toxoplasmosis spreading from pig farms may be warranted. The results show that the ToxoDB #9 genotype may be the dominant T. gondii lineage in mainland China. These findings strengthen the limited Chinese T. gondii epidemiology database.

Toxoplasma gondii Type I, predominant genotype isolated from sheep in South of Iran

Aim:

This study was performed to determine the genetic diversity of Toxoplasma gondii in sheep using nested-polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in Southern Iran.

Materials and Methods:

The tissue samples of diaphragm and heart from 125 sheep were collected from the main slaughterhouses of Jahrom district in South of Fars province, Iran, between Aprils and June 2013. The DNA were extracted and analyzed by nested-PCR using specific primers for SAG2 and GRA6 loci. RFLP was used to classify strains into one of the three major lineages of T. gondii.

Results:

T. gondii Type I was predominant in this area. The data obtained from both loci demonstrated that the frequency of each genotype was 72% Type I, 2.4% Type III, 7.2% mixed Type I and II, 16.8% mixed Type I and III, 0.8% mixed Type II and III, and 0.8% mixed Type I, II and III.

Conclusions:

Although the previously published data indicated that Type II is the predominant T. gondii genotype in sheep in the other parts of the world, this study showed that genotype I is the dominant genotype of T. gondii in the southern Iran; however, other genotypes were detected. High diversity of T. gondii genotypes including mix genotypes in lambs is of importance for the public health. These studies depict a new mapping of T. gondii genotypes pattern which could be very helpful in toxoplasmosis control and prevention.

Isolation and characterization of Toxoplasma gondii from small ruminants (sheep and goats) in Chennai City, South India

The present study aimed for the isolation and genotyping of Toxoplasma gondii from small ruminants (sheep and goats). 14 out of 193 tissue samples (either brain and heart) tested positive by MDAT for anti-T. gondii antibodies, were selected and bioassayed, which resulted 4 samples positive for T. gondii after 40 days of post inoculation. Four samples consisting of 3 numbers of sheep and 1 number of goat tissues out of 14 samples detected by B1 PCR, were genotyped at SAG3 locus by nested polymerase chain reaction-restriction fragment length polymorphism technique (nPCR-RFLP). The results of the present study revealed that the four isolates designated as TgShIn19, TgShIn76, TgShIn77 and TgGtIn27 were circulating in small ruminants, were belonged to genotypes of type II (TgShIn19) and type III (TgShIn76, TgShIn77 and TgGtIn27) which are in concordance with the previously reported genotypes from other animal species and further this presumptive results indicating that the genotype II and III could be the predominant in different animal species including birds and humans in India.

Seroprevalence, Isolation, Genotyping, and Pathogenicity of Toxoplasma gondii Strains from Sheep in China

Toxoplasma gondii is an important cause of reproductive failure in small ruminants that also poses a risk to consumers who consume undercooked meat. However, little is known about sheep toxoplasmosis in China for the world. Therefore, this study was conducted to assess the prevalence of T. gondii infection in sheep from China, to isolate T. gondii via bioassay in mice and to evaluate the virulence of the isolated T. gondii based on vero cell invasion and mice. A total of 840 samples (304 unfrozen hearts and 536 sera) from sheep in China were collected from 2014 to 2016. Heart samples (n = 36) of T. gondii seropositive sheep (MAT, ≥25) were bioassayed in mice individually. DNA derived from cell cultured tachyzoites of the isolated T. gondii was characterized by PCR-RFLP of 10 loci (SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, and Apico). The virulence of the T. gondii was evaluated based on the mortality and encystation in mice, as well as their growth characteristics in cell culture. Antibodies to T. gondii were found in 174 of 840 (20.71%, 304 hearts juice and 536 sera) sheep by the modified agglutination test (cut-off 1:25). Viable T. gondii was isolated from the hearts of two of 36 seropositive sheep hearts. Both genotypes of the sheep heart isolates were ToxoDB#9. The virulence of the two ToxoDB#9 isolations varied significantly. To the best of our knowledge, this is the first report of isolation of ToxoDB#9 strain of T. gondii from sheep in China.

Identification of a TNF-α inducer MIC3 originating from the microneme of non-cystogenic, virulent Toxoplasma gondii

Toxoplasma gondii is an opportunistic parasite with avirulent cystogenic and highly virulent non-cystogenic isolates. Although non-cystogenic strains are considered the most virulent, there are also marked genetic and virulence differences among these strains. Excretory-secretory antigens (ESAs) of T. gondii are critical for the invasion process and the immune response of the host. To better understand the differences in virulence between non-cystogenic T. gondii isolates, we studied ESAs of the RH strain (Type I), and the very prevalent in China, but less virulent TgCtwh3 strain (Chinese 1). ESAs of RH and TgCtwh3 triggered different levels of TNF-α production and macrophage M1 polarization. Using iTRAQ analysis, 27 differentially expressed proteins originating from secretory organelles and surface were quantified. Of these proteins, 11 microneme-associated proteins (MICs), 6 rhoptry proteins, 2 dense granule proteins and 5 surface proteins were more abundant in RH than in TgCtwh3. The protein-protein correlation network was employed to identify the important functional node protein MIC3, which was upregulated 5-fold in RH compared with TgCtwh3. MIC3 was experimentally confirmed to evoke a TNF-α secretory response, and it also induced macrophage M1 polarization. This result suggests that MIC3 is a potentially useful immunomodulator that induces TNF-α secretion and macrophage M1 polarization.

Transcriptomic analysis of mouse liver reveals a potential hepato-enteric pathogenic mechanism in acute Toxoplasma gondii infection

Background

Toxoplasma gondii is a worldwide spread pathogen which can infect all tissues of its host. The transcriptomic responses of infected brain and spleen have been reported. However, our knowledge of the global transcriptomic change in infected liver is limited. Additionally, T. gondii infection represents a highly dynamic process involving complex biological responses of the host at many levels. Herein, we describe such processes at a global level by discovering gene expression changes in mouse livers after acute infection with T. gondii ToxoDB#9 strain.

Results

Global transcriptomic analysis identified 2,758 differentially expressed transcripts in infected liver, of which 1,356 were significantly downregulated and 1,402 upregulated. GO and KEGG database analyses showed that host immune responses were upregulated, while the metabolic-related processes/pathways were downregulated, especially xenobiotic metabolism, fatty acid metabolism, energy metabolism, and bile biosynthesis and secretion. The metabolism of more than 800 chemical compounds including anti-Toxoplasma prescribed medicines were predicted to be modulated during acute T. gondii infection due to the downregulation of enzymes involved in xenobiotic metabolism.

Conclusions

To the best of our knowledge, this is the first global transcriptomic analysis of mouse liver infected by T. gondii. The present data indicate that during the early stage of liver infection, T. gondii can induce changes in liver xenobiotic metabolism, upregulating inflammatory response and downregulating hepatocellular PPAR signaling pathway, altering host bile biosynthesis and secretion pathway; these changes could enhance host intestinal dysbacteriosis and thus contribute to the pathological changes of both liver and intestine of infected mice. These findings describe the biological changes in infected liver, providing a potential mechanistic pathway that links hepatic and intestinal pathologies to T. gondii infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1716-x) contains supplementary material, which is available to authorized users.

Analysis of the virulence determination mechanisms in a local Toxoplasma strain (T.gHB1) isolated from central China

Several rhoptry proteins (ROPs) have been confirmed to be critical virulence factors of Toxoplasma gondii strains from North America and Europe. The two active kinases ROP17 and ROP18, and pseudokinase ROP5 were thought to be the key determinants of parasites' virulence in laboratory mice. Given the genetic diversity of Toxoplasma strains from different geographical regions, the virulence determinants in other strains, particularly the ones that are phylogenetically distant to the North American and European strains, are yet to be elucidated. In this study, we sought to examine the contribution of three known virulence factors to the virulence of a type I strain (T.gHB1) isolated from Central China. We deleted ROP17 and ROP18 individually, as well as in combination with GRA7 by the CRISPR-Cas9 system in this local isolate. Subsequent virulence tests in mice indicated that deletion of GRA7, ROP17, or ROP18 in T.gHB1showed similar attenuation in mice as the type I RH strain lacking the corresponding proteins. However, in contrast to the reported double knockouts in RH, double deletions of GRA7 plus ROP17 or GRA7 plus ROP18 in T.gHB1 did not show significant further virulence attenuation compared to the ROP17 or ROP18 single knockouts. These results indicated that GRA7, ROP18 and ROP17 may play different roles in virulence determination in genetically diverse strains of Toxoplasma.

Seroprevalence and genotypes of Toxoplasma gondii isolated from pigs intended for human consumption in Liaoning province, northeastern China

Background

Genetic information for Toxoplasma gondii isolates from pigs in eastern, south, and southwestern regions of China has been reported previously. However, there are no data from pigs in the northeastern area of the country. To better understand the epidemiology of T. gondii, we determined the seroprevalence and genotypes of T. gondii from pigs slaughtered for human consumption in Liaoning province, northeastern China.

Findings

Out of 2063 pigs examined, 233 (11.26 %) were seropositive for T. gondii by the modified agglutination test (MAT), and viable parasites were isolated by bioassay in mice from 23 (9.87 %) of the 233 seropositive pigs. Fifteen out of 23 isolates were genotyped using 10 PCR-restriction fragment length polymorphism (RFLP) genetic markers including SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1 and Apico. One isolate was identified as ToxoDB genotype #3 (type II-variant), and one was genotype #1 or #3. The other 13 isolates were ToxoDB #9 (type Chinese 1).

Conclusions

To our knowledge, this is the first report of T. gondii isolation and genotyping from pigs in northeastern China. This study indicates that pigs are a potential source for transmission of T. gondii to humans, therefore poses a potential public health concern. The genotyping results revealed the presence of genotype Chinese 1 in northeastern China, enriching the scope of T. gondii genotypes distribution in eastern Asia.

Genetic characterization of Toxoplasma gondii from autopsy proven cases of AIDS associated cerebral toxoplasmosis in South India

Toxoplasma gondii (T.gondii) infection can be devastating in the immunodeficient causing high morbidity and mortality. Due to limited availability of both diagnostic facilities and Highly Active Antiretroviral Therapy (HAART), toxoplasmosis continues to be a significant problem amongst Acquired Immuno Deficiency Syndrome (AIDS) patients in India. While scanty literature is available on T. gondii isolates in animals in India, little is known about the genetic diversity of the parasite in humans. Therefore, the present study investigated the genetic diversity of T. gondii in 25 confirmed cases of cerebral toxoplasmosis developing on the background of human immunodeficiency virus (HIV) infection/AIDS. PCR DNA sequencing was performed at four important genetic loci of T. gondii: BTUB, GRA6, alternative SAG2 (alt SAG2) and SAG3 on DNA from tissues obtained at postmortem. The amplified products from all the cases were successfully sequenced except at one locus for one case. Results of the present study suggest that majority of the patients (22/25; 88%) in South India are infected with strains that are recombinants of type II/III and/or strains representing T. gondii different from the archetypal lineages I, II, and III. In addition, clonal types III, MAS, and MAS variant genotypes were encountered. No clonal type I or II was seen in the present study. In addition, variants were observed at alt SAG2 and SAG3 but BTUB and GRA6 were highly conserved. Single nucleotide polymorphisms were observed mainly at two loci which are coding for surface antigens at alt SAG2 and SAG3. In conclusion, the present study reveals genetic diversity in India amongst strains of T. gondii from clinical cases of toxoplasmosis which is in accordance with other recent studies showing a high rate of genetic diversity in this parasite across the globe. There is a need to genotype T. gondii from different forms of toxoplasmosis in humans in India.

Genetic Characterization of Toxoplasma gondii Isolates from Pigs in Jilin Province, Northeastern China

Toxoplasma gondii is prevalent in humans and animals worldwide. The present study aimed to determine the genetic diversity of T. gondii isolates from pigs in Jilin province, northeastern China. A total of 100 DNA samples were extracted from the hilar lymph nodes of slaughtered pigs, and 9 (9.0%, 95% confidence interval: 3.4-14.6%) were detected positive for T. gondii B1 gene by a nested polymerase chain reaction (PCR). The positive DNA samples were typed at 11 genetic markers, including 10 nuclear loci (SAG1, 5'-SAG2, and 3'-SAG2, alternative SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, and PK1) and an apicoplast locus (Apico) using the multilocus PCR-restriction fragment length polymorphism technology. Only three isolates were completely typed at all loci, showing that they all belonged to the clonal type I. One isolate was typed at five loci, including 5' +3'-SAG2, SAG2, SAG3, GRA6, and L358, revealing the possible clonal type I. This is the first report of the genetic characterization of T. gondii isolates in pigs in Jilin province, northeastern China, which has implications for better understanding the population structure of T. gondii infection in China.

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.