Serotyping of naturally Toxoplasma gondii infected meat-producing animals

Diagnostic methods and protocols used in investigating Toxoplasma gondii in humans: A review

Toxoplasmosis, a zoonotic disease, is a parasitic infection caused by a coccidian protozoan Toxoplasma gondii. In immunocompetent people, the infection is asymptomatic, while it can produce serious signs in immunocompromised people and in developing fetuses. Accurate diagnosis is dependent, mainly, on the clinical features. However, in immunocompromised patients, the diagnosis is very difficult and may lead to misdiagnosis and improper treatment. Today, molecular diagnosis and serotyping are widely used for the diagnosis of T. gondii in many countries. The aim of the present short review is to highlight the current diagnostic methods and protocols that are used for the diagnosis of T. gondii in humans.

Biosensor Based Immunoassay: A New Approach for Serotyping of Toxoplasma gondii

Toxoplasmosis is the most reported parasitic zoonosis in Europe, with implications in human health and in the veterinary field. There is an increasing need to develop serotyping of Toxoplasma gondii (T. gondii) in view of greater sensitivity and efficiency, through the definition of new targets and new methodologies. Nanotechnology is a promising approach, with impact in the development of point-of-care devices. The aim of this work was to develop a simple but highly efficient method for Toxoplasma gondii serotyping based on gold nanoparticles. A simple colorimetric method was developed using gold nanoparticles modified with the synthetic polymorphic peptide derived from GRA6 antigen specific for type II T. gondii. The method of preparation of the gold nanoprobes and the experimental conditions for the detection were found to be critical for a sensitive discrimination between positive and negative sera. The optimized method was used to detect antibodies anti-GRA6II both in mice and human serum samples. These results clearly demonstrate that a biosensor-based immunoassay using AuNPs conjugated with polymorphic synthetic peptides can be developed and used as a serotyping device

Toxoplasma GRA Peptide-Specific Serologic Fingerprints Discriminate Among Major Strains Causing Toxoplasmosis

The severity of toxoplasmosis depends on a combination of host and parasite factors. Among them, the Toxoplasma strain causing the infection is an important determinant of the disease outcome. Type 2 strains dominate in Europe, whereas in North America type 2, followed by type 3 and 12 strains are commonly isolated from wildlife and patients. To identify the strain type a person is infected with, serological typing provides a promising alternative to the often risky and not always possible biopsy-based DNA methods of genotyping. However, despite recent advances in serotyping, improvements in the sensitivity and specificity are still needed, and it does not yet discriminate among the major Toxoplasma lineages infecting people. Moreover, since infections caused by non-1/2/3 strains have been associated with more severe disease, the ability to identify these is critical. In the present study we investigated the diagnostic potential of an ELISA-based assay using 28 immunogenic Toxoplasma peptides derived from a recent large-scale peptide array screen. Our results show that a discrete number of peptides, derived from Toxoplasma dense granule proteins (GRA3, GRA5, GRA6, and GRA7) was sufficient to discriminate among archetypal strains that infect mice and humans. The assay specifically relies on ratios that compare individual serum reactivities against GRA-specific polymorphic peptide variants in order to determine a "reactivity fingerprint" for each of the major strains. Importantly, nonarchetypal strains that possess a unique combination of alleles, different from types 1/2/3, showed either a non-reactive, or different combinatorial, mixed serum reactivity signature that was diagnostic in its own right, and that can be used to identify these strains. Of note, we identified a distinct "HG11/12" reactivity pattern using the GRA6 peptides that is able to distinguish HG11/12 from archetypal North American/European strain infections.

Application of Toxoplasma gondii GRA15 peptides in diagnosis and serotyping

Previous studies showed that three clonal strain types (I, II, and III) of Toxoplasma gondii can be distinguished using serotyping based on a series of polymorphic proteins. However, to establish a systematic serotyping method with higher resolution even being equal to that of genotyping, more specific peptide markers are needed. The objective of the present study was to determine the possibility of the polymorphic dense granule protein 15 (GRA15) for diagnosis and serotyping of T. gondii infection. Three different T. gondii GT1 strain GRA15 gene fragments encoding a 584-residue peptide, a 199-residue peptide and a 84-residue peptide were amplified, expressed and purified, respectively. Anti-T. gondii GT1 strain antibodies, anti-T. gondii RH strain antibodies and anti-T. gondii PRU strain antibodies were used for immunoblotting analysis of the three peptides. Western blotting analysis showed that the 584-residue peptide of GT1 strain GRA15 was a potential candidate for serological diagnosis of T. gondii infection. RH strain from GT1 strain could be distinguished by serotyping based on the GRA15₁₉₉ or GRA15₈₄, and T. gondii GT1 strain could be distinguished from PRU strain by using serotyping based on the GRA15₈₄. These findings reveal, for the first time, a novel potential role of GRA15-derived peptides in diagnosis and serological differentiation of T. gondii infection.

Serotyping of Toxoplasma gondii Infection Using Peptide Membrane Arrays

The intracellular parasite Toxoplasma gondii can cause chronic infections in most warm-blooded animals, including humans. In the USA, strains belonging to four different Toxoplasma clonal lineages (types 1, 2, 3, and 12) are commonly isolated, whereas strains not belonging to these lineages are predominant in other continents such as South America. Strain type plays a pivotal role in determining the severity of Toxoplasma infection. Therefore, it is epidemiologically relevant to develop a non-invasive and inexpensive method for determining the strain type in Toxoplasma infections and to correlate the genotype with disease outcome. Serological typing is based on the fact that many host antibodies are raised against immunodominant parasite proteins that are highly polymorphic between strains. However, current serological assays can only reliably distinguish type 2 from non-type 2 infections. To improve these assays, mouse, rabbit, and human infection serum were reacted against 950 peptides from 62 different polymorphic Toxoplasma proteins by using cellulose membrane peptide arrays. This allowed us to identify the most antigenic peptides and to pinpoint the most relevant polymorphisms that determine strain specificity. Our results confirm the utility of previously described peptides and identify novel peptides that improve and increase the specificity of the assay. In addition, a large number of novel proteins showed potential to be used for Toxoplasma diagnosis. Among these, peptides derived from several rhoptry, dense granule, and surface proteins represented promising candidates that may be used in future experiments to improve Toxoplasma serotyping. Moreover, a redesigned version of the published GRA7 typing peptide performed better and specifically distinguished type 3 from non-type 3 infections in sera from mice, rabbits, and humans.

Behavioral evaluation of BALB/c (Mus musculus) mice infected with genetically distinct strains of Toxoplasma gondii

In relation to behavioral changes in rodents infected with Toxoplasma gondii (T. gondii), it is believed that the genotype of the infecting strain can have some influence. In this sense, the present work has sought to evaluate the effect of chronic infection by genetically distinct cystogenic strains of T. gondii on the behavior of mice. For this, experimental models of infection with ME-49 (type II) and VEG (type III) strains were developed in isogenic BALB/c mice. ELISA test was performed to evaluate the humoral immune response and real-time PCR test to quantify parasites in the CNS. Behavioral tests such as passive avoidance, open-field and Y-maze tests were also used for, respectively, evaluation of learning and memory, locomotor activity and aversion to feline odor. The results showed that mice infected with VEG strain had higher total IgG level of anti-toxoplasma, higher tissue burden of T. gondii in the CNS, reduction in the long-term memory, lower activity (mobility) and lower aversion to cat urine and l-felinine than mice infected with ME-49 strain. The results suggest that different T. gondii genotypes have a differential impact on behavioral changes in infected mice.

Toxoplasma gondii infection and biosecurity levels in fattening pigs and sows: serological and molecular epidemiology in the intensive pig industry (Lombardy, Northern Italy)

Toxoplasma gondii is a widespread protozoan affecting animals and humans. One of the major routes of human infection is through the consumption of raw or under-cooked meat, particularly of certain animal species, including pigs. Although T. gondii represents an important public health issue, its control at slaughter is not mandatory. Consequently, available information on T. gondii infection in domestic animals destined for human consumption is scarce. Thus, an epidemiologic survey was designed to update information on T. gondii infection in pigs from intensive production. Fattening pigs and sows from conventional farms were sampled. Sera were tested with a commercial ELISA for anti-T. gondii antibodies, whereas molecular analysis by 529 bp repetitive element PCR and B1 real-time PCR with subsequent genotyping was performed on heart samples. Statistical analysis was carried out to detect farm management features and sanitary procedures enhancing the risk of infection. At the farm level, 63.6% (7/11) of farms housing sows and 6.7% (1/15) housing fattening pigs scored positive, with individual prevalences of 8.6% (13/151) in sows and 0.5% (1/219) in fattening pigs. T. gondii DNA was detected in eight sows and one fattening pig, and sequencing revealed the presence of all three genotypes (types I, II, and III). Furthermore, the decrease in the biosecurity level enhanced the risk of infection within a farm. The present survey outcomes confirm the spread of T. gondii infection in pig farms in an area of intensive swine production. The application of stricter sanitary procedures may contribute to a further reduction of infection.

Protective immunity against toxoplasmosis in mice induced by single-dose immunization with rSAG1/2 protein released from poly(lactide-co-glycolide) microparticles

Triphasic sustained release of tachyzoite chimeric protein, rSAG1/2, from poly(lactide-co-glycolide) (PLG)-encapsulated rSAG1/2 (PLG-rSAG1/2) microparticles (MPs) is a promising characteristic for developing a single-dose vaccine against Toxoplasma gondii in domestic animals. In the present study, we aimed to evaluate whether single immunization with PLG-rSAG1/2 MPs in BALB/c mice would achieve effective immunity and protection against T. gondii. Peritoneal immunization of mice with a single dose of PLG-rSAG1/2 MPs enhanced serum IgG titers and lymphocyte proliferation in a triphasic model over a long 12-week period. In addition, 12 weeks after immunization, significant production of IFN-γ was also monitored in mice vaccinated with one dose of PLG-rSAG1/2 MPs. More importantly, the immunity induced by one dose of PLG-rSAG1/2 MPs protected 70% of mice (14/20) against a lethal subcutaneous challenge of 1 × 10⁴ live tachyzoites of T. gondii (RH strain). In conclusion, a single dose of PLG-rSAG1/2 MPs capable of sustaining triphasic release of rSAG1/2 protein induces long-lasting triphasic immunity against T. gondii in mice. Our data indicate the feasibility of PLG-rSAG1/2 MPs to be developed as a single-dose vaccine against T. gondii for potential use in domestic animals.

Diagnosis of toxoplasmosis and typing of Toxoplasma gondii

Toxoplasmosis, caused by the obligate intracellular protozoan Toxoplasma gondii, is an important zoonosis with medical and veterinary importance worldwide. The disease is mainly contracted by ingesting undercooked or raw meat containing viable tissue cysts, or by ingesting food or water contaminated with oocysts. The diagnosis and genetic characterization of T. gondii infection is crucial for the surveillance, prevention and control of toxoplasmosis. Traditional approaches for the diagnosis of toxoplasmosis include etiological, immunological and imaging techniques. Diagnosis of toxoplasmosis has been improved by the emergence of molecular technologies to amplify parasite nucleic acids. Among these, polymerase chain reaction (PCR)-based molecular techniques have been useful for the genetic characterization of T. gondii. Serotyping methods based on polymorphic polypeptides have the potential to become the choice for typing T. gondii in humans and animals. In this review, we summarize conventional non-DNA-based diagnostic methods, and the DNA-based molecular techniques for the diagnosis and genetic characterization of T. gondii. These techniques have provided foundations for further development of more effective and accurate detection of T. gondii infection. These advances will contribute to an improved understanding of the epidemiology, prevention and control of toxoplasmosis.

Strain hypothesis of Toxoplasma gondii infection on the outcome of human diseases

The intracellular protozoan Toxoplasma gondii is an exceptionally successful food and waterborne parasite that infects approximately 1 billion people worldwide. Genotyping of T. gondii isolates from all continents revealed a complex population structure. Recent research supports the notion that T. gondii genotype may be associated with disease severity. Here, we (1) discuss molecular and serological approaches for designation of T. gondii strain type, (2) overview the literatures on the association of T. gondii strain type and the outcome of human disease and (3) explore possible mechanisms underlying these strain-specific pathology and severity of human toxoplasmosis. Although no final conclusions can be drawn, it is clear that virulent strains (e.g. strains containing type I or atypical alleles) are significantly more often associated with increased frequency and severity of human toxoplasmosis. The significance of highly virulent strains can cause severe diseases in immunocompetent patients and might implicated in brain disorders such as schizophrenia should led to reconsideration of toxoplasmosis. Further studies that combine parasite strain typing and human factor analysis (e.g. immune status and genetic background) are required for better understanding of human susceptibility or resistance to toxoplasmosis.

Genetic characterization of Toxoplasma gondii isolates from Portugal, Austria and Israel reveals higher genetic variability within the type II lineage

This study compared genetic diversity of Toxoplasma gondii isolates from Portugal, Austria and Israel. For this, we genotyped 90 T. gondii isolates (16 from Portugal, 67 from Austria and 7 from Israel) using 10 nested PCR-restriction length polymorphism (RFLP) genetic markers and 15 microsatellite (MS) markers. By PCR-RFLP typing, 7 isolates from Portugal chickens were identified as type II (ToxoDB #1 or #3), 4 were type III (ToxoDB #2) and the remaining 4 isolates have unique genotype pattern were designated as ToxoDB #254. One mouse virulent isolate from a bovine fetus (Bos taurus) in Portugal was type I (ToxoDB #10) at all loci and designated as TgCowPr1. All 67 isolates from Austria and 7 from Israel were type II (ToxoDB #1 or #3). By MS typing, many additional genetic variations were revealed among the type II and type III isolates. Phylogenetic analysis showed that isolates from the same geographical locations tend to cluster together, and there is little overlapping of genotypes among different locations. This study demonstrated that the MS markers can provide higher discriminatory power to reveal association of genotypes with geographical locations. Future studies of the type II strains in Europe by these MS markers will be useful to reveal transmission patterns of the parasite.

Epidemiological review of Toxoplasma gondii infection in humans and animals in Portugal

Toxoplasmosis is a worldwide zoonosis. However, data from Portugal are limited and a considerable part of the literature is in Portuguese. Currently, the rate of congenital infection in Portugal is unknown, and almost nothing is known of sequelae of congenital toxoplasmosis. There is no recent general population-based serological survey of Toxoplasma gondii in humans in Portugal. In addition, there is little information on genetic characteristics of T. gondii in animals and humans. In the present paper, we review prevalence, clinical spectrum and epidemiology of T. gondii in humans and animals in Portugal. This knowledge should be useful to biologists, public health workers, physicians and veterinarians.

Serotyping of Toxoplasma gondii in cats (Felis domesticus) reveals predominance of type II infections in Germany

Background

Cats are definitive hosts of Toxoplasma gondii and play an essential role in the epidemiology of this parasite. The study aims at clarifying whether cats are able to develop specific antibodies against different clonal types of T. gondii and to determine by serotyping the T. gondii clonal types prevailing in cats as intermediate hosts in Germany.

Methodology

To establish a peptide-microarray serotyping test, we identified 24 suitable peptides using serological T. gondii positive (n=21) and negative cat sera (n=52). To determine the clonal type-specific antibody response of cats in Germany, 86 field sera from T. gondii seropositive naturally infected cats were tested. In addition, we analyzed the antibody response in cats experimentally infected with non-canonical T. gondii types (n=7).

Findings

Positive cat reference sera reacted predominantly with peptides harbouring amino acid sequences specific for the clonal T. gondii type the cats were infected with. When the array was applied to field sera from Germany, 98.8% (85/86) of naturally-infected cats recognized similar peptide patterns as T. gondii type II reference sera and showed the strongest reaction intensities with clonal type II-specific peptides. In addition, naturally infected cats recognized type II-specific peptides significantly more frequently than peptides of other type-specificities. Cats infected with non-canonical types showed the strongest reactivity with peptides presenting amino-acid sequences specific for both, type I and type III.

Conclusions

Cats are able to mount a clonal type-specific antibody response against T. gondii. Serotyping revealed for most seropositive field sera patterns resembling those observed after clonal type II-T. gondii infection. This finding is in accord with our previous results on the occurrence of T. gondii clonal types in oocysts shed by cats in Germany.

Analysis of clonal type-specific antibody reactions in Toxoplasma gondii seropositive humans from Germany by peptide-microarray

Background

Different clonal types of Toxoplasma gondii are thought to be associated with distinct clinical manifestations of infections. Serotyping is a novel technique which may allow to determine the clonal type of T. gondii humans are infected with and to extend typing studies to larger populations which include infected but non-diseased individuals.

Methodology

A peptide-microarray test for T. gondii serotyping was established with 54 previously published synthetic peptides, which mimic clonal type-specific epitopes. The test was applied to human sera (n = 174) collected from individuals with an acute T. gondii infection (n = 21), a latent T. gondii infection (n = 53) and from T. gondii-seropositive forest workers (n = 100).

Findings

The majority (n = 124; 71%) of all T. gondii seropositive human sera showed reactions against synthetic peptides with sequences specific for clonal type II (type II peptides). Type I and type III peptides were recognized by 42% (n = 73) or 16% (n = 28) of the human sera, respectively, while type II–III, type I–III or type I–II peptides were recognized by 49% (n = 85), 36% (n = 62) or 14% (n = 25) of the sera, respectively. Highest reaction intensities were observed with synthetic peptides mimicking type II-specific epitopes. A proportion of the sera (n = 22; 13%) showed no reaction with type-specific peptides. Individuals with acute toxoplasmosis reacted with a statistically significantly higher number of peptides as compared to individuals with latent T. gondii infection or seropositive forest workers.

Conclusions

Type II-specific reactions were overrepresented and higher in intensity in the study population, which was in accord with genotyping studies on T. gondii oocysts previously conducted in the same area. There were also individuals with type I- or type III-specific reactions. Well-characterized reference sera and further specific peptide markers are needed to establish and to perform future serotyping approaches with higher resolution.