Toxoplasma gondii recombinant antigens as tools for serodiagnosis of human toxoplasmosis: current status of studies. Clin Vaccine Immunol. 2013;20:1343-1351. [PMID: 23784855 DOI: 10.1128/cvi.00117-13]

Trend in serological and molecular diagnostic methods for Toxoplasma gondii infection

BACKGROUND

Toxoplasma gondii, an intracellular parasite, is a significant cause of zoonotic disease, with an estimated one-third of the world's human population believed to be infected. T. gondii is transmitted to humans through the consumption of contaminated water, soil, vegetables, fruits, shellfish or undercooked meat, and can also be passed from human to human through vertical transmission, transplants and blood transfusion. While T. gondii infection typically manifests mild symptoms such as colds among immunocompetent individuals, it can prove lethal for those with weakened immune systems.

METHODS

To summarize the diagnostic methods for Toxoplasma gondii infection, we performed a literature search on PubMed from 1948 to 2023 using the keywords "T. gondii serological diagnosis" or "T. gondii molecular diagnosis".

RESULTS

Rapid and accurate diagnosis of T. gondii infection is imperative. Although a diagnostic kit is currently commercially available, there are a number of disadvantages to the validation principles applied to each diagnostic kit. Consequently, multiple diagnostic methods are concurrently employed to offset these limitations. Serological methods for diagnosing T. gondii infection include the Dye Test (DT), Agglutination Test (AT), Modified Agglutination Test (MAT), Latex Agglutination Test (LAT), Enzyme-Linked Immunosorbent Assay (ELISA), and Western Blot. Meanwhile, molecular methods such as polymerase chain reaction (PCR), nested PCR, real-time PCR, loop-mediated isothermal amplification (LAMP), multiplex PCR, and PCR-restriction fragment length polymorphism (PCR-RFLP) are also utilized. Each of these methods possess its own set of advantages and disadvantages.

CONCLUSIONS

By summarizing the advantages and disadvantages of different diagnostic techniques, it is hoped that the epidemiology, prevention, and control of toxoplasmosis will be improved in the future through the use of appropriate technologies.

Single Cell Expression Systems for the Production of Recombinant Proteins for Immunodiagnosis and Immunoprophylaxis of Toxoplasmosis

Toxoplasmosis represents a significant public health and veterinary concern due to its widespread distribution, zoonotic transmission, and potential for severe health impacts in susceptible individuals and animal populations. The ability to design and produce recombinant proteins with precise antigenic properties is fundamental, as they serve as tools for accurate disease detection and effective immunization strategies, contributing to improved healthcare outcomes and disease control. Most commonly, a prokaryotic expression system is employed for the production of both single antigens and multi-epitope chimeric proteins; however, the cloning strategies, bacterial strain, vector, and expression conditions vary. Moreover, literature reports show the use of alternative microbial systems such as yeast or Leishmania tarentolae. This review provides an overview of the methods and strategies employed for the production of recombinant Toxoplasma gondii antigenic proteins for the serological detection of T. gondii infection and vaccine development.

Comparison of the performance of SAG2, GRA6, and GRA7 for serological diagnosis of Toxoplasma gondii infection in cats

Toxoplasmosis is an important zoonotic disease caused by Toxoplasma gondii that can infect almost all warm-blooded animals worldwide, including humans. The high prevalence of T. gondii infection and its ability to cause serious harm to humans and animals, especially immunodeficient individuals, make it a key public health issue. Accurate diagnostic tools with high sensitivity are needed for controlling T. gondii infection. In the current study, we compared the performance of recombinant SAG2, GRA6, and GRA7 in ELISA for the serological diagnosis of T. gondii infection in cats. We further investigated the antigenicity of recombinant dense granule protein 3 (rGRA3), rGRA5, rGRA8, and rSRS29A expressed in a plant-based, cell-free expression system for detecting antibodies in T. gondii-infected cats. In summary, our data suggest that GRA7 is more sensitive than the other two antigens for the serodiagnosis of T. gondii infection in cats, and GRA3 expressed in the cell-free system is also a priming antigen in serological tests for detecting T. gondii infection in cats.

Identification of novel biomarkers for anti-Toxoplasma gondii IgM detection and the potential application in rapid diagnostic fluorescent tests

Toxoplasmosis, while often asymptomatic and prevalent as a foodborne disease, poses a considerable mortality risk for immunocompromised individuals during pregnancy. Point-of-care serological tests that detect specific IgG and IgM in patient sera are critical for disease management under limited resources. Despite many efforts to replace the T. gondii total lysate antigens (TLAs) by recombinant antigens (rAgs) in commercial kits, while IgG detection provides significant specificity and sensitivity, IgM detection remains comparatively low in sensitivity. In this study, we attempted to identify novel antigens targeting IgM in early infection, thereby establishing an IgM on-site detection kit. Using two-dimensional gel electrophoresis (2DE) and mouse serum immunoblotting, three novel antigens, including EF1γ, PGKI, and GAP50, were indicated to target T. gondii IgM. However, rAg EF1γ was undetectable by IgM of mice sera in Western blotting verification experiments, and ELISA coated with PGKI did not eliminate cross-reactivity, in contrast to GAP50. Subsequently, the lateral flow reaction employing a strip coated with 0.3 mg/mL purified rAg GAP50 and exhibited remarkable sensitivity compared with the conventional ELISA based on tachyzoite TLA, which successfully identified IgM in mouse sera infected with tachyzoites, ranging from 103 to 104 at 5 dpi and 104 at 7 dpi, respectively. Furthermore, by using standard T. gondii-infected human sera from WHO, the limit of detection (LOD) for the rapid fluorescence immunochromatographic test (FICT) using GAP50 was observed at 0.65 IU (international unit). These findings underline the particular immunoreactivity of GAP50, suggesting its potential as a specific biomarker for increasing the sensitivity of the FICT in IgM detection.

The Development of Toxoplasma gondii Recombinant Trivalent Chimeric Proteins as an Alternative to Toxoplasma Lysate Antigen (TLA) in Enzyme-Linked Immunosorbent Assay (ELISA) for the Detection of Immunoglobulin G (IgG) in Small Ruminants

This study presents an evaluation of seventeen newly produced recombinant trivalent chimeric proteins (containing the same immunodominant fragment of SAG1 and SAG2 of Toxoplasma gondii antigens, and an additional immunodominant fragment of one of the parasite antigens, such as AMA1, GRA1, GRA2, GRA5, GRA6, GRA7, GRA9, LDH2, MAG1, MIC1, MIC3, P35, and ROP1) as a potential alternative to the whole-cell tachyzoite lysate (TLA) used in the detection of infection in small ruminants. These recombinant proteins, obtained by genetic engineering and molecular biology methods, were tested for their reactivity with specific anti-Toxoplasma IgG antibodies contained in serum samples of small ruminants (192 samples of sheep serum and 95 samples of goat serum) using an enzyme-linked immunosorbent assay (ELISA). The reactivity of six recombinant trivalent chimeric proteins (SAG1-SAG2-GRA5, SAG1-SAG2-GRA9, SAG1-SAG2-MIC1, SAG1-SAG2-MIC3, SAG1-SAG2-P35, and SAG1-SAG2-ROP1) with IgG antibodies generated during T. gondii invasion was comparable to the sensitivity of TLA-based IgG ELISA (100%). The obtained results show a strong correlation with the results obtained for TLA. This suggests that these protein preparations may be a potential alternative to TLA used in commercial tests and could be used to develop a cheaper test for the detection of parasite infection in small ruminants.

Newly optimized ELISA kit and LAT reveal significantly higher seroprevalence in sheep raised in agro-ecological zone as against range-ecological zone, with a significant association of meteorological parameters

BACKGROUND

Toxoplasma gondii is a zoonotic and foodborne intracellular parasite capable of inducing congenital infections, stillbirths and abortions in humans and animals, globally. The consumption of undercooked or raw mutton is "one of the vital risks" for acquiring toxoplasmosis: an asymptomatic condition in healthy persons, while life-threatening in immunodeficient individuals like "HIV/AIDS" patients.

OBJECTIVES

The current study has multiple objectives: to optimize a newly ELISA kit for Sheep, to find out the seroprevalence of ovine toxoplasmosis of two ecological zones of the Punjab, Pakistan through LAT and newly Optimized Sheep ELISA kit, to do the comparison of efficacies of various tests (LAT with newly Optimized ELISA kit and newly Optimized ELISA kit with commercial ELISA kit) and to determine the different meteorological parameters as the risk factors for T. gondii infection in sheep.

METHODS

A cross-sectional study was conducted on 400 sheep sera, 200 were collected from sheep raised on open grazing system by local farmers in the adjoining areas of Civil Veterinary Dispensaries (CVDs) of range-ecological zone i.e. tehsil Kot Chutta (Dera Ghazi khan). Similarly, the remaining 200 were collected from agro-ecological zone i.e. tehsil Sharaqpur (Sheikhupura), to evaluate the comparative efficacy of LAT with optimized ELISA kit and newly optimized ELISA kit with commercial ELISA kit.

FINDINGS

The newly ELISA kit optimized against a commercial ELISA kit was found to have 100% sensitivity, 97.6% specificity with 98% Positive Predictive Value, 100% Negative Predictive Value, Cut off value = 0.505, 28.28 LR+, 0.0104 LR-, and 2719.23 DOR. Seroprevalence of toxoplasmosis was detected significantly (P < 0.01; χ2) higher in Sharaqpur (44.5% by LAT; 35.5% by ELISA) as compared to that in Kot Chutta (39.5% by LAT; 31% by ELISA). The highest seroprevalence was seen in the sheep of the 1-2 years age group (P < 0.01; χ2), whereas the lowest in the oldest animals (≥ 4 years). Investigation of meteorological data of both the regions reveals that the zone with higher seroprevalence has relatively higher rainfall, higher humidity, lower environmental temperatures, and higher altitude as the critical factors, potentially behind the significant difference seen in seroprevalence level. The partial correlation of both tests (newly optimized ELISA kit and LAT) was 0.991 at maximum temperature in Sharaqpur while it was 0.981 in Kot Chutta.

INTERPRETATION

A novel significant correlation was found between the meteorological parameters (relative humidity, minimum, maximum, and average temperatures) divided into yearly units of both the ecological zones, and year-wise seroprevalence (birth years of age-wise groups) of the corresponding regions. We hypothesize that such environmental conditions increase the risk of toxoplasmosis in grazing sheep, owing to a more favorable environment for coccidian oocyst survival. The ELISA kit optimized in this study will be helpful for the detection of seroprevalence of ovine toxoplasmosis in other ecological zones of Pakistan as well as of any other country in the world. More studies are recommended involving regions from other ecological zones of Pakistan to further explore the seroprevalence of ovine toxoplasmosis and to ratify the novel correlation of meteorological parameters with seroprevalence.

Epitope Mapping of BmpA and BBK32 Borrelia burgdorferi Sensu Stricto Antigens for the Design of Chimeric Proteins with Potential Diagnostic Value

Lyme disease is a tick-borne zoonosis caused by Gram-negative bacteria belonging to the Borrelia burgdorferi sensu lato (s.l.) group. In this study, IgM- and IgG-specific linear epitopes of two B. burgdorferi sensu stricto (s.s.) antigens BmpA and BBK32 were mapped using a polypeptide array. Subsequently, two chimeric proteins BmpA-BBK32-M and BmpA-BBK32-G were designed to validate the construction of chimeras using the identified epitopes for the detection of IgM and IgG, respectively, by ELISA. IgG-ELISA based on the BmpA-BBK32-G antigen showed 71% sensitivity and 95% specificity, whereas a slightly lower diagnostic utility was obtained for IgM-ELISA based on BmpA-BBK32-M, where the sensitivity was also 71% but the specificity decreased to 89%. The reactivity of chimeric proteins with nondedicated antibodies was much lower. These results suggest that the identified epitopes may be useful in the design of new forms of antigens to increase the effectiveness of Lyme disease serodiagnosis. It has also been proven that appropriate selection of epitopes enables the construction of chimeric proteins exhibiting reactivity with a specific antibody isotype.

Establishment and application of an iELISA detection method for measuring apical membrane antigen 1 (AMA1) antibodies of Toxoplasma gondii in cats

BACKGROUND

Diseases caused by Toxoplasma gondii (T. gondii) have introduced serious threats to public health. There is an urgent need to develop a rapid detection method for T. gondii infection in cats, which are definitive hosts. Recombinant apical membrane antigen 1 (rAMA1) was produced in a prokaryotic expression system and used as the detection antigen. The aim of this study was to evaluate and optimize a reliable indirect enzyme-linked immunosorbent assay (iELISA) method based on rAMA1 for the detection of antibodies against T. gondii in cats.

RESULTS

The rAMA1-iELISA method was developed and optimized by the chessboard titration method. There were no cross-reactions between T. gondii-positive cat serum and positive serum for other pathogens, indicating that rAMA1-iELISA could only detect T. gondii in most cases. The lowest detection limit of rAMA1-iELISA was 1:3200 (dilution of positive serum), and the CV of repeated tests within batches and between batches were confirmed to be less than 10%. The results of 247 cat serum samples detected by rAMA1-iELISA (kappa value = 0.622, p < 0.001) were in substantial agreement with commercial ELISA. The ROC curve analysis revealed the higher overall check accuracy of rAMA1-iELISA (sensitivity = 91.7%, specificity = 93.6%, AUC = 0.956, 95% CI 0.905 to 1.000) than GRA7-based iELISA (sensitivity = 91.7%, specificity = 85.5%, AUC = 0.936, 95% CI 0.892 to 0.980). Moreover, the positive rate of rAMA1-iELISA (6.5%, 16/247) was higher than that of GRA7-based iELISA (3.6%, 9/247) and that of commercial ELISA kit (4.9%, 12/247).

CONCLUSION

The iELISA method with good specificity, sensitivity, and reproducibility was established and can be used for large-scale detection of T. gondii infection in clinical cat samples.

Past and present seroprevalence and disease burden estimates of Toxoplasma gondii infections in Germany: An appreciation of the role of serodiagnostics

Toxoplasmosis is one of the major foodborne parasitic diseases in Germany, with 49% of its population chronically infected with its causative agent, Toxoplasma gondii. Although the acute disease is usually benign in immunocompetent individuals, it is a threat for immunocompromised patients as well as for fetuses of seronegative mothers. As a result of infection, congenital and ocular toxoplasmosis can have serious lifelong consequences. Here I will highlight the epidemiologic situation, from its past in the two separate parts of Germany, to its unification 30 years ago and up to the present day. The main identified risk factor for infection in Germany is thought to be the consumption of undercooked or raw meat or sausages. However, the relative impact of this risky eating habit as well as that of other risk factors are changing and are discussed and compared to the situation in the Netherlands. Finally, the importance of robust and efficient high-throughput serological assays for obtaining reliable epidemiological data, on which public health decisions can be made, is highlighted. The potential of bead-based multiplex assays, which allow the incorporation of multiple antigens with different analytical properties and thus yield additional information, are described in this context. It illustrates the interdependence of new analytic assay developments and sound epidemiology, a foundation that decades-old data from Germany did not have.

Detection of Toxoplasma gondii Infection in Small Ruminants: Old Problems, and Current Solutions

Toxoplasmosis is a parasitic zoonosis of veterinary importance, with implications for public health. Toxoplasma gondii infection causes abortion or congenital disease in small ruminants. Moreover, the consumption of infected meat, cured meat products, or unpasteurized milk and dairy products can facilitate zoonotic transmission. Serological studies conducted in various European countries have shown the high seroprevalence of specific anti-T. gondii antibodies in sheep and goats related to the presence of oocysts in the environment, as well as climatic conditions. This article presents the current status of the detection possibilities for T. gondii infection in small ruminants and their milk. Serological testing is considered the most practical method for diagnosing toxoplasmosis; therefore, many studies have shown that recombinant antigens as single proteins, mixtures of various antigens, or chimeric proteins can be successfully used as an alternative to Toxoplasma lysate antigens (TLA). Several assays based on DNA amplification have been developed as alternative diagnostic methods, which are especially useful when serodiagnosis is not possible, e.g., the detection of intrauterine T. gondii infection when the fetus is not immunocompetent. These techniques employ multicopy sequences highly conserved among different strains of T. gondii in conventional, nested, competitive, and quantitative reverse transcriptase-PCR.

Toxoplasma gondii microneme protein MIC3 induces macrophage TNF-α production and Ly6C expression via TLR11/MyD88 pathway

Toxoplasma gondii is the most successful parasite worldwide. It is of great interest to understand how T. gondii induce different immune responses in different hosts. In this study, we found that a peptide of T. gondii microneme protein MIC3 induced TNF-α production, NF-κB phosphorylation, iNOS transcription and Ly6C expression in mouse macrophage RAW264.7 cells. MyD88 inhibition, small interfering RNA against Tlr11 and CRISPR/Cas9-mediated knock-out of Tlr11 all reduced MIC3-induced TNF-α production, NF-κB phosphorylation, iNOS transcription and Ly6C expression. Additionally, we determined the location of MIC3 peptide in mouse macrophages using immunofluorescence. MIC3 could both adhere to the cell membrane of mouse macrophages and enter the cells. These results suggest that MIC3 triggered the immune responses in mouse macrophages via TLR11/MyD88/NF-κB pathway. It is known that human macrophages lacking TLR11. We predicted that the immune responses induced by MIC3 in human macrophages were significantly different from those in mouse macrophages. As expected, MIC3 peptide failed to induce TNF-α expression, iNOS expression and NF-κB phosphorylation in human THP-1 derived macrophages. MIC3 induced macrophage immune responses via TLR11. Intriguingly, the amino acid sequence of MIC3 is completely different from the well-known TLR11 ligand profilin, which generates a potent IL-12p40, TNF-α and IL-6 response. In marked contrast to profilin, MIC3 could not induce IL-12p40 expression in both mouse RAW264.7 cells and human THP-1 derived macrophages. Furthermore, the simulated tertiary structure of MIC3 peptide shows poor similarity with the crystal structure of profilin, suggesting that MIC3 might be a different ligand from profilin. These findings about MIC3 and TLR11 will provide us with important insights into the pathogenesis of toxoplasmosis and coevolution during host-parasite interaction.

Recombinant AMA1 Virus-like Particle Antigen for Serodiagnosis of Toxoplasma gondii Infection

Toxoplasmosis diagnosis predominantly relies on serology testing via enzyme-linked immunosorbent assay (ELISA), but these results are highly variable. Consequently, various antigens are being evaluated to improve the sensitivity and specificity of toxoplasmosis serological diagnosis. Here, we generated Toxoplasma gondii virus-like particles displaying AMA1 of T. gondii and evaluated their diagnostic potential. We found that AMA1 VLPs were highly sensitive and reacted with the sera acquired from mice infected with either T. gondii ME49 or RH strains. The overall IgG and IgM antibody responses elicited by AMA1 VLPs were substantially higher than those induced by the conventionally used T. gondii lysate antigen (TLA). Importantly, AMA1 VLPs were capable of detecting parasitic infection with T. gondii RH and ME49 as early as 1 week post-infection, even when mice were exposed to low infectious doses (5 × 10³ and 10 cysts, respectively). AMA1 VLPs also did not cross-react with the immune sera acquired from Plasmodium berghei-infected mice. Compared to TLA, stronger antibody responses were induced by AMA1 VLPs when tested using T. gondii-infected human sera. The sensitivities and specificities of the two antigens were substantially different, with AMA1 VLPs demonstrating over 90% sensitivity and specificity, whereas these values were in the 70% range for the TLA. These results indicated that AMA1 VLPs can detect infections of both T. gondii ME49 and RH at an early stage of infection caused by very low infection doses in mice, and these could be used for serological diagnosis of human toxoplasmosis.

IgG Avidity Test as a Tool for Discrimination between Recent and Distant Toxoplasma gondii Infection—Current Status of Studies

Toxoplasma gondii, an obligate intracellular protozoan parasite, is the causative agent of one of the most prevalent zoonoses worldwide. T. gondii infection is extremely important from a medical point of view, especially for pregnant women, newborns with congenital infections, and immunocompromised individuals. Thus, an accurate and proper diagnosis of this infection is essential. Among the available diagnostic tests, serology is commonly used. However, traditional serological techniques have certain limitations in evaluating the duration of T. gondii infection, which is problematic, especially for pregnant women. Avidity of T. gondii-specific IgG antibodies seems to be a significant tool for discrimination between recent and distant infections. This article describes the problem of diagnosis of T. gondii infection, with regard to IgG avidity tests. The IgG avidity test is a useful serological indicator of toxoplasmosis, which in many cases can confirm or exclude the active form of the disease. IgG antibodies produced in the recent primary T. gondii infection are of low avidity while IgG antibodies with high avidity are detected in the chronic phase of infection. Furthermore, this paper presents important topics of current research that concern the usage of parasite recombinant antigens that may improve the performance of IgG avidity tests.

Development of an Immunochromatographic Test Based on Rhoptry Protein 14 for Serological Detection of Toxoplasma gondii Infection in Swine

Toxoplasma gondii, a worldwide distributed apicomplexan protozoan, can infect almost all warm-blooded animals and may cause toxoplasmosis. In order to provide a point-of-care detection method for T. gondii infection, an immunochromatographic test (ICT) was established. The proposed test uses recombinant T. gondii rhoptry protein 14 (ROP14) conjugated with 20 nm gold particles, recombinant protein A as the detection line and monoclonal antibody TgROP14-5D5 as the control line. The specificity, sensitivity, positive predictive value, negative predictive value and stability of this new ICT were evaluated. rTgROP14 was specifically recognized by positive serum of T. gondii but not negative serum. mAb TgROP14-5D5 showed higher specific recognition of T. gondii antigens and was therefore selected for subsequent colloidal gold strip construction. The new ICT based on TgROP14 exhibited good diagnostic performance with high specificity (86.9%) and sensitivity (90.9%) using IHA as a “reference standard”. Among 436 field porcine sera, ICT and IHA detected 134 (30.7%) and 99 (22.7%) positive samples, respectively. The relative agreement was 87.8%. These data indicate that this new ICT based on TgROP14 is a suitable candidate for routine testing of T. gondii in the field.

Diagnostic value of recombinant nanoluciferase fused Toxoplasma gondii antigens in Luciferase-linked Antibody Capture Assay (LACA) for Toxoplasma infection in pigs

Toxoplasmosis is a widespread protozoan zoonosis. Since ingesting undercooked meat harboring Toxoplasma gondii cyst is considered one of the major transmission routes to humans, the screening of T. gondii in meat-producing animals can reduce the risk of food-borne toxoplasmosis in humans. Among serological diagnostic methods, Luciferase-linked Antibody Capture Assay (LACA) has been found to be a promising platform with high sensitivity and specificity. In this study, we aimed to evaluate recombinant nanoluciferase fused-T. gondii antigens (rNluc-GRA6, rNluc-GRA7, rNluc-GRA8 and rNluc-BAG1) for their potential use in LACA for pigs. As a result, the sensitivity of GRA6-, GRA7-, GRA8- and BAG1-LACA were 70.0%, 80.0%, 80.0% and 30.0% with specificity 87.0%, 81.5%, 74.1% and 50.0%, respectively. The cocktail LACA using a mixture of rNluc-GRA6, rNluc-GRA7 and rNluc-GRA8 indicated higher sensitivity (90.0%) and a similar specificity (96.3%) in comparison with the commercial ELISA kit. Compared to the Dye-Test as a reference test, cocktail LACA showed strong agreement (kappa value=0.811) when we assessed pig sera collected at the slaughterhouse. In addition, we also successfully established the rapid LACA format for the detection of Toxoplasma infection in pigs (called Rapid-LACA) in which the test could be performed within 30 min. In Rapid-LACA, the protein A pre-coated/blocked plates could be preserved at −30°C, 4°C or room temperature conditions for at least two months without compromising on the quality of assay.

Development and evaluation of indirect enzyme-linked immunosorbent assay using recombinant dense granule antigen 7 protein for the detection of Toxoplasma gondii infection in cats in Thailand

Background and Aim:

Toxoplasma gondii is recognized as a zoonosis causing toxoplasmosis in animals globally. Cat is a definitive host of T. gondii and sheds oocyst through feces, which can infect human beings and animals through contaminated food ingestion. A precise diagnostic test is essential to prevent T. gondii infection in both humans and animals. This study aimed to develop and evaluate the pETite-dense granule antigen 7(GRA7)-based indirect enzyme-linked immunosorbent assay (ELISA) to detect T. gondii infection in cats.

Materials and Methods:

T. gondii-GRA7 was cloned and expressed in the Expresso^®small ubiquitin-related modifier (SUMO) T7 Cloning and Expression System. The recombinant pETite-GRA7 was purified using HisTrap affinity chromatography and confirmed using Western blot analysis. The recombinant protein was used to develop and evaluate the indirect ELISA for T. gondii infection detection. In total, 200 cat sera were tested using pETite-GRA7-based indirect ELISA and indirect fluorescent antibody test (IFAT). The statistical analysis based on Kappa value, sensitivity, specificity, positive predictive value, negative predictive value, χ² test, and receiver operating characteristic (ROC) curve was used to evaluate the performance of the test.

Results:

A 606 bp GRA7 polymerase chain reaction (PCR) product was obtained from T. gondii RH strain genomic DNA. The gene was cloned into the pETite™ vector and transformed to HI-Control Escherichia coli BL21 (DE3) for protein expression. Approximately 35 kDa of recombinant pETite-GRA7 was observed and Western blot analysis showed positive bands against anti-6-His antibody and positive-T. gondii cat serum. A sample of 0.5 μg/mL of pETite-GRA7 was subjected to indirect ELISA to detect T. gondii infection in the cat sera. The results showed sensitivity and specificity of pETite-GRA7-based indirect ELISA at 72% and 96%, respectively. An acceptable diagnostic performance was characterized by high concordant results (94%) and substantial agreement (Kappa value=0.65) with IFAT. The seroprevalence levels of ELISA and IFAT were 10% and 9%, respectively, and were not significantly (p>0.05) different. The expected performance of ELISA at different cutoff points using the ROC curve analysis revealed 89% sensitivity and 92% specificity at the cutoff value of 0.146, with a high overall assay accuracy (area under the curve=0.94).

Conclusion:

In this study, the pETite™ vector, N-terminal 6xHis SUMO fusion tag, was used to improve the solubility and expression level of GRA7. The recombinant pETite-GRA7 showed enhanced protein solubility and purification without special condition requirements. This pETite-GRA7-based indirect ELISA showed high concordant results and substantial agreement with IFAT. ELISA revealed an acceptable sensitivity and specificity. These initial data obtained from cats’ sera demonstrated that pETite-GRA7-based indirect ELISA could be a useful method for local serological diagnosis of T. gondii infection in cats in Thailand.

Comparative Performance of Recombinant GRA6, GRA7, and GRA14 for the Serodetection of T. gondii Infection and Analysis of IgG Subclasses in Human Sera from the Philippines

Highly specific and sensitive diagnostic methods are vital for the effective control and treatment of toxoplasmosis. Routine diagnosis is primarily serological because T. gondii infections stimulate persistently high IgG antibody responses. The sensitivity and specificity of methods are crucial factors for the proper diagnosis of toxoplasmosis, primarily dependent on the antigens used in different assays. In the present study, we compared the serodiagnostic performances of three recombinant dense granule antigens, namely, the GRA6, GRA7, and GRA14, to detect IgG antibodies against T. gondii in human sera from the Philippines. Moreover, we evaluated the IgG1, IgG2, IgG3, and IgG4 responses against the different recombinant antigens, which has not been performed previously. Our results revealed that the TgGRA7 has consistently displayed superior diagnostic capability, while TgGRA6 can be a satisfactory alternative antigen among the GRA proteins. Furthermore, IgG1 is the predominant subclass stimulated by the different recombinant antigens. This study's results provide options to researchers and manufacturers to choose recombinant antigens suitable for their purpose.

Utility of blood as the clinical specimen for the diagnosis of ocular toxoplasmosis using uracil DNA glycosylase-supplemented loop-mediated isothermal amplification and real-time polymerase chain reaction assays based on REP-529 sequence and B1 gene

BACKGROUND

Ocular infection with Toxoplasma gondii is a major preventable cause of blindness, especially in young people. The aim of the present study was to assess detection rate of T. gondii DNA in blood samples of clinically diagnosed of ocular toxoplasmosis using uracil DNA glycosylase-supplemented loop-mediated isothermal amplification (UDG-LAMP) and real-time quantitative PCR (qPCR) based on REP-529 and B1.

METHODS

One hundred and seventeen patients with clinically diagnosed ocular toxoplasmosis (OT) were participated in the study as well as 200 control patients. Peripheral blood samples were assessed using UDG-LAMP and qPCR techniques targeting REP-529 and B1.

RESULTS

Detection limits of qPCR using REP-529 and B1 were estimated as 0.1 and 1 fg of T. gondii genomic DNA, respectively. The limits of detection for UDG-LAMP using REP-529 and B1 were 1 and 100 fg, respectively. In this study, 18 and 16 patients were positive in qPCR using REP-529 and B1, respectively. Based on the results of UDG-LAMP, 15 and 14 patients were positive using REP-529 and B1, respectively. Results of the study on patients with active ocular lesion showed that sensitivity of REP-529 and BI targets included 64 and 63%, respectively using qPCR. Sensitivity of 62 and 61%, were concluded from UDG-LAMP using REP-529 and B1 in the blood cases of active ocular lesion. qPCR was more sensitive than UDG-LAMP for the detection of Toxoplasma gondii DNA in peripheral blood samples of patients with clinically diagnosed toxoplasmic chorioretinitis. Furthermore, the REP-529 included a better detection rate for the diagnosis of ocular toxoplasmosis in blood samples, compared to that the B1 gene did. Moreover, the qPCR and UDG-LAMP specificity assessments have demonstrated no amplifications of DNAs extracted from other microorganisms based on REP-529 and B1.

CONCLUSIONS

Data from the current study suggest that qPCR and UDG-LAMP based on the REP-529 are promising diagnostic methods for the diagnosis of ocular toxoplasmosis in blood samples of patients with active chorioretinal lesions.

Identification of Oocyst-Driven Toxoplasma gondii Infections in Humans and Animals through Stage-Specific Serology-Current Status and Future Perspectives

The apicomplexan zoonotic parasite Toxoplasma gondii has three infective stages: sporozoites in sporulated oocysts, which are shed in unsporulated form into the environment by infected felids; tissue cysts containing bradyzoites, and fast replicating tachyzoites that are responsible for acute toxoplasmosis. The contribution of oocysts to infections in both humans and animals is understudied despite being highly relevant. Only a few diagnostic antigens have been described to be capable of discriminating which parasite stage has caused an infection. Here we provide an extensive overview of the antigens and serological assays used to detect oocyst-driven infections in humans and animals according to the literature. In addition, we critically discuss the possibility to exploit the increasing knowledge of the T. gondii genome and the various 'omics datasets available, by applying predictive algorithms, for the identification of new oocyst-specific proteins for diagnostic purposes. Finally, we propose a workflow for how such antigens and assays based on them should be evaluated to ensure reproducible and robust results.

Development of Human Toxo IgG ELISA Kit, and False-Positivity of Latex Agglutination Test for the Diagnosis of Toxoplasmosis

Toxoplasma gondii is an intracellular zoonotic parasite that causes infection in a wide range of warm-blooded animals and humans. The main aim of this study was to assess the diagnostic value of the recombinant SAG1 antigen (rSAG1) for T. gondii-IgG screening through the Human Toxo IgG ELISA Kit (K). The rSAG1 was expressed in E. coli (DE3), and it was purified through metal-affinity chromatography. The rSAG1 was confirmed by immunoblotting, and it had a band on 35 kDa. Total of 400 human sera were tested by LAT and K. One hundred and twenty-two (30.5%) sera were found positive by LAT and eighty-nine (22.25%) sera were found positive by K. Out of 400 samples, 80 were selected to evaluate the performance of K through commercial Toxoplasma gondii IgG ELISA Kit (C). Out of 80 human sera, 55 (68.75%) were found positive, 25 (31.25%) were found negative by K and C, respectively. The cut-off value for K was 0.398 and it was calculated through the receiver operator characteristic curve. The ELISA plates were coated at optimized concentration of rSAG1 = 0.125 µg/mL, and the test was performed by diluting the sera at 1:50. The sensitivity and specificity of K were observed to be 98.5% and 100%, respectively. The six sera (K⁻L⁺) were found positive through LAT and these human sera were later evaluated by Western blot analysis. These sera did not produce a band equivalent to 35 kDa on WB analysis thus, LAT produced false-positive results.

Characterization and evaluation of a recombinant multiepitope peptide antigen MAG in the serological diagnosis of Toxoplasma gondii infection in pigs

Background

Toxoplasmosis caused by Toxoplasma gondii is a serious disease threatening human and animal health. People can be infected with T. gondii by ingesting raw pork contaminated with cysts or oocysts. Serological test is a sensitive and specific method usually used for large-scale diagnosis of T. gondii infection in humans and animals (such as pigs). Commercial pig Toxoplasma antibody ELISA diagnostic kits are expensive, which limits their use; moreover, the wide antigen composition used in these diagnostic kits is still unclear and difficult to standardize. The multiepitope peptide antigen is a novel diagnostic marker, and it has potential to be developed into more accurate and inexpensive diagnostic kits.

Methods

The synthetic multiepitope antigen (MAG) cDNA encoding a protein with epitopes from five T. gondii-dominant antigens (SAG1, GRA1, ROP2, GRA4, and MIC3) was designed, synthesized, and expressed in Escherichia coli BL21 (DE3) strain. The recombinant protein was detected through western blot with pig anti-T. gondii-positive and -negative serum, and then IgG enzyme-linked immunosorbent assay (ELISA) named MAG-ELISA was designed. The MAG-ELISA was evaluated in terms of specificity, sensitivity, and stability. The MAG-ELISA was also compared with a commercial PrioCHECK^®Toxoplasma Ab porcine ELISA (PrioCHECK ELISA). Finally, the trend of pig anti-T. gondii IgG levels after artificial infection with RH tachyzoites was evaluated using MAG-ELISA and two other ELISA methods (rMIC3-ELISA and PrioCHECK ELISA).

Results

MAG antigen could be specifically recognized by pig anti-T. gondii-positive but not -negative serum. MAG-ELISA showed high diagnostic performance in terms of specificity (88.6%) and sensitivity (79.1%). MAG-ELISA could be used for detecting anti-T. gondii IgG in the early stage of T. gondii infection in pigs (at least 7 days after artificial infection).

Conclusions

Our results suggest that MAG antigen can be applied to specifically recognize anti-T. gondii IgG in pig, and MAG-ELISA has the potential for large-scale screening tests of T. gondii infection in pig farms and intensive industries.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04917-w.

Assessment of an In-House Enzyme-Linked Immunosorbent Assay and IgG Avidity Test Based on SAG1 and GRA7 Proteins for Discriminating between Acute and Chronic Toxoplasmosis in Humans

To improve serodiagnostic methods for diagnosis of acute from chronic toxoplasmosis, an economical in-house enzyme-linked immunosorbent assay (ELISA) for measuring Toxoplasma-specific IgG, IgM, and IgG avidity has been developed and assessed based on use of various Toxoplasma gondii antigens, including SAG1, GRA7, and a combination of SAG1 and GRA7 (SAG1+GRA7), as well as Toxoplasma lysate antigens (TLAs). Performances of in-house IgM, IgG, and IgG avidity assays were compared to those of ELISA commercial kits and VIDAS Toxo IgG avidity. A set of 138 sera from patients with acquired T. gondii infection and seronegative people were assessed. Receiver operating characteristic (ROC) analysis revealed an area under curve (AUC) of 0.98, 0.97, 0.99, and 0.99 for IgM-TLAs, IgM-SAG1, IgM-GRA7, and IgM-SAG1+GRA7, respectively. Furthermore, AUC was calculated as 0.99, 0.99, 0.98, and 0.99 for IgG-TLAs, IgG-SAG1, IgG-GRA7, and IgG-SAG1+GRA7, respectively. The current study showed that GRA7 included 100% sensitivity for the detection of Toxo IgM, while SAG1 included 89.7% sensitivity. Furthermore, the highest specificity (97.2%) to detect Toxo IgM was achieved using SAG1+GRA7 antigen. For the detection of Toxo IgG, the highest sensitivity (100%) was recorded for SAG1+GRA7, followed by TLAs (97.9%). The SAG1+GRA7 showed the greatest potential for assessing avidity of IgG antibodies, with 97.1% sensitivity and 96.6% specificity compared to those of VIDAS Toxo IgG avidity. The preliminary results have promised better discriminations between acute and chronic infections using a combination of SAG1 and GRA7 recombinant antigens compared to those using TLAs.

Borrelia burgdorferi BmpA-BBK32 and BmpA-BBA64: New Recombinant Chimeric Proteins with Potential Diagnostic Value

Currently, the diagnosis of Lyme disease is based mostly on two-tiered serologic testing. In the new generation of immunoenzymatic assays, antigens comprise whole-cell lysates of members of the Borrelia burgdorferi sensu lato (s.l.) species complex, with the addition of selected recombinant proteins. Due to the high diversity of members of the B. burgdorferi s.l. genospecies and the low degree of conservation among the amino acid sequences of their proteins, serodiagnostic methods currently in use are not sufficient for the correct diagnosis of borreliosis. Two divalent chimeric proteins (BmpA-BBK32 and BmpA-BBA64) were expressed in Escherichia coli. Following purification by one-step metal-affinity chromatography, preparations were obtained containing milligram levels of chimeric protein exhibiting electrophoretic purity in excess of 98%. Reactivity of the new chimeric proteins with specific human IgG antibodies was preliminarily determined by Western blot. For this purpose, 20 negative sera and 20 positive sera was used. The new chimeric proteins were highly reactive with IgG antibodies contained in the serum of patients suffering from borreliosis. Moreover, no immunoreactivity of chimeric proteins was observed with antibodies in the sera of healthy people. These promising results suggest that new chimeric proteins have the potential to discriminate between positive and negative sera.

Development and evaluation of recombinant GRA8 protein for the serodiagnosis of Toxoplasma gondii infection in goats

BACKGROUND

The development of sensitive and specific methods for detecting Toxoplasma gondii infection is critical for preventing and controlling toxoplasmosis in humans and other animals. Recently, various recombinant proteins have been used in serological tests for diagnosing toxoplasmosis. The production of these antigens is associated with live tachyzoites obtained from cell cultures or laboratory animals for genomic extraction to amplify target genes. Synthetic genes have gained a key role in recombinant protein production. For the first time, we demonstrated the production of the recombinant protein of the T. gondii dense granular antigen 8 (TgGRA8) gene based on commercial gene synthesis. Recombinant TgGRA8 plasmids were successfully expressed in an Escherichia coli system. The recombinant protein was affinity-purified and characterized via sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting. Furthermore, the diagnostic potential of the recombinant protein was assessed using 306 field serum samples from goats via indirect enzyme-linked immunosorbent assay (iELISA) and the latex agglutination test (LAT).

RESULTS

Western blotting using known positive serum samples from goats identified a single antigen at the expected molecular weight of TgGRA8 (27 kDa). iELISA illustrated that 15.40% of goat samples were positive for T. gondii-specific IgG antibodies. In addition, TgGRA8 provided high sensitivity and specificity, with significant concordance (91.83) and kappa values (0.69) compared with the results obtained using LAT.

CONCLUSION

Our findings highlight the production of a recombinant protein from a synthetic TgGRA8 gene and the ability to detect T. gondii infection in field samples. The sensitivity and specificity of TgGRA8 demonstrated that this protein could be a good serological marker for detecting specific IgG in goat sera.

Toxoplasma gondii induces robust humoral immune response against cyst wall antigens in chronically infected animals and humans

Toxoplasma gondii differentiation from proliferating tachyzoites into latent bradyzoites is central to pathogenesis and transmission. Strong humoral immune response has been reported against tachyzoite antigens, however, antibody-mediated response towards bradyzoite antigens is poorly characterized. This work aimed to study the humoral immune response towards bradyzoite and associated cyst wall antigens particularly CST1. The immunoreactivity of 404 goats, 88 sheep and 92 human sera to recombinant (CST1 and SRS9) and native proteins of encysted bradyzoite along with well-established tachyzoite antigens (SAG1 and GRA7) was determined using ELISA, Western blot and immunofluorescence analysis (IFA). ELISA results revealed nearly 50% of sera contain T. gondii specific antibodies. Results were further validated using Western blot and IFA. T. gondii positive sera predominantly recognized the cyst wall besides the known tachyzoite surface antigens. The presence of CST1 antibodies in seropositive samples were in line with the staining patterns which were consistent with CST localization. Notably, T. gondii IgM- IgG+ sera recognize the cyst wall whereas IgM + IgG-sera recognize tachyzoite antigens indicating acute infection consistent with presence of parasite DNA. The study demonstrates a strong humoral response against bradyzoite associated cyst wall antigens across naturally infected animals and humans. CST1 emerged as a key immunomodulatory antigen which may have direct implications for clinical immunodiagnostics.

Fluorescent bead-based serological detection of Toxoplasma gondii infection in chickens

BACKGROUND

Free-ranging chickens are often infected with Toxoplasma gondii and seroconvert upon infection. This indicates environmental contamination with T. gondii.

METHODS

Here, we established a bead-based multiplex assay (BBMA) using the Luminex technology for the detection of T. gondii infections in chickens. Recombinant biotinylated T. gondii surface antigen 1 (TgSAG1bio) bound to streptavidin-conjugated magnetic Luminex beads served as antigen. Serum antibodies were detected by a fluorophore-coupled secondary antibody. Beads of differing color codes were conjugated with anti-chicken IgY or chicken serum albumin and served for each sample as an internal positive or negative control, respectively. The assay was validated with sera from experimentally and naturally infected chickens. The results were compared to those from reference methods, including other serological tests, PCRs and bioassay in mice.

RESULTS

In experimentally infected chickens, the vast majority (98.5%, n = 65/66) of birds tested seropositive in the BBMA. This included all chickens positive by magnetic-capture PCR (100%, n = 45/45). Most, but not all inoculated and TgSAG1bio-BBMA-positive chickens were also positive in two previously established TgSAG1-ELISAs (TgSAG1-ELISASL, n = 61/65; or TgSAG1-ELISASH, n = 60/65), or positive in an immunofluorescence assay (IFAT, n = 64/65) and in a modified agglutination test (MAT, n = 61/65). All non-inoculated control animals (n = 28/28, 100%) tested negative. In naturally exposed chickens, the TgSAG1bio-BBMA showed a high sensitivity (98.5%; 95% confidence interval, CI: 90.7-99.9%) and specificity (100%; 95% CI: 85.0-100%) relative to a reference standard established using ELISA, IFAT and MAT. Almost all naturally exposed chickens that were positive in bioassay or by PCR tested positive in the TgSAG1bio-BBMA (93.5%; 95% CI: 77.1-98.9%), while all bioassay- or PCR-negative chickens remained negative (100%; 95% CI: 85.0-100%).

CONCLUSIONS

The TgSAG1bio-BBMA represents a suitable method for the detection of T. gondii infections in chickens with high sensitivity and specificity, which is comparable or even superior to other tests. Since assays based on this methodology allow for the simultaneous analysis of a single biological sample with respect to multiple analytes, the described assay may represent a component in future multiplex assays for broad serological monitoring of poultry and other farm animals for various pathogens.

Toxoplasma gondii Recombinant Antigens in the Serodiagnosis of Toxoplasmosis in Domestic and Farm Animals

Simple Summary

The very common parasite infections in animals are caused by members of Apicomplexa, including Toxoplasma gondii, Neospora sp., and Sarcocystis sp. These parasites pose serious veterinary problems. For example, the development of unambiguous diagnostic algorithms and determining the correct diagnosis are hindered by the similar antigenic structure of these parasites, as well as the multitude of similar disease symptoms presented in an infected animal. The intracellular parasite, T. gondii, infects a wide range of warm-blooded animals, including humans. This parasite is widespread among different animal populations, contributes to the loss of reproductive and malformations in young individuals, and can become a serious economic concern for farmers. Additionally, the consumption of undercooked or raw meat and the consumption of improperly processed milk product derived from farm animals are the main parasite transmission routes in humans. This work reviews potential improvements to diagnostic techniques that use recombinant antigens for serodiagnosis of toxoplasmosis in various species of animals.

Abstract

Toxoplasmosis is caused by an intracellular protozoan, Toxoplasma gondii, and is a parasitic disease that occurs in all warm-blooded animals, including humans. Toxoplasmosis is one of the most common parasitic diseases of animals and results in reproductive losses. Toxoplasmosis in humans is usually caused by eating raw or undercooked meat or consuming dairy products containing the parasite. Diagnosis of toxoplasmosis is currently based on serological assays using native antigens to detect specific anti-T. gondii antibodies. Due to the high price, the available commercial agglutination assays are not suited to test a large number of animal serum samples. The recent development of proteomics elucidated the antigenic structure of T. gondii and enabled the development of various recombinant antigens that can be used in new, cheaper, and more effective diagnostic tools. Continuous development of scientific disciplines, such as molecular biology and genetic engineering, allows for the production of new recombinant antigens and provides the basis for new diagnostic tests for the detection of anti-T. gondii antibodies in animal serum samples.

Toxoplasmosis in Germany

BACKGROUND

With approximately 30% of the world population infected, Toxoplasma gondii is one of the most widespread pathogenic parasites in both humans and animals and a major problem for health economics in many countries.

METHODS

This review is based on the findings of individual studies, meta-analyses, and Cochrane Reviews retrieved by a selective literature survey of the Medline and Google Scholar databases.

RESULTS

Current data indicate a high rate of Toxoplasma gondii infection in Germany, ranging from 20% to 77% depending on age (95% confidence interval for 18- to 29-year-olds [17.0; 23.1]; for 70- to 79-year-olds [72.7; 80.5]). Male sex, caring for a cat, and a body mass index of 30 or more are independent risk factors for seroconversion. Postnatally acquired (food-related) infec- tion is predominant, but maternal-to-fetal transmission still plays an important role. While most infections are asymptomatic, congenital toxoplasmosis and reactivated Toxoplasma encephalitis in immunosuppressed persons (transplant recipients and others) are sources of considerable morbidity. Toxoplasma gondii infection of the retina is the most common cause of infectious uveitis in Germany. The diagnosis and treatment of this type of parasitic infection are particular to the specific organs involved in the individual patient.

CONCLUSION

Desirable steps for the near future include development of an effective treatment for the cystic stage and identifica- tion of biomarkers to assess the risk of reactivation and predict the disease course.

Review on the Current Trends of Toxoplasmosis Serodiagnosis in Humans

Toxoplasmosis is a widely distributed zoonotic infection caused by the obligate intracellular apicomplexan parasite Toxoplasma gondii. It is mainly transmitted through the ingestion of oocysts shed by an infected cat acting as its definitive host. The key to effective control and treatment of toxoplasmosis is prompt and accurate detection of T. gondii infection. Several laboratory diagnostic methods have been established, including the most commonly used serological assays such as the dye test (DT), direct or modified agglutination test (DAT/MAT), indirect hemagglutination test (IHA), latex agglutination test (LAT), indirect immunofluorescent test (IFAT), enzyme-linked immunosorbent assays (ELISA), immunochromatographic tests (ICT), and the western blot. Nonetheless, creating specific and reliable approaches for serodiagnosis of T. gondii infection, and differentiating between acute and chronic phases of infection remains a challenge. This review provides information on the current trends in the serodiagnosis of human toxoplasmosis. It highlights the advantages of the use of recombinant proteins for serological testing and provides insight into the possible future direction of these methods.

Toxoplasma gondii-specific IgG avidity testing in pregnant women

BACKGROUND

The parasite Toxoplasma gondii can cause congenital toxoplasmosis following primary infection in a pregnant woman. It is therefore important to distinguish between recent and past infection when both T. gondii-specific IgM and IgG are detected in a single serum in pregnant women. Toxoplasma gondii-specific IgG avidity testing is an essential tool to help to date the infection. However, interpretation of its results can be complex.

OBJECTIVES

To review the benefits and limitations of T. gondii-specific avidity testing in pregnant women, to help practitioners to interpret the results and adapt the patient management.

SOURCES

PubMed search with the keywords avidity, toxoplasmosis and Toxoplasma gondii for articles published from 1989 to 2019.

CONTENT

Toxoplasma gondii-specific IgG avidity testing remains a key tool for dating a T. gondii infection in immunocompetent pregnant women. Several commercial assays are available and display comparable performances. A high avidity result obtained on a first-trimester serum sample is indicative of a past infection, which occurred before pregnancy. To date, a low avidity result must still be considered as non-informative to date the infection, although some authors suggest that very low avidity results are highly suggestive of recent infections depending on the assay. Interpretation of low or grey zone avidity results on a first-trimester serum sample, as well as any avidity result on a second-trimester or third-trimester serum sample, is more complex and requires recourse to expert toxoplasmosis laboratories.

IMPLICATIONS

Although used for about 30 years, T. gondii-specific avidity testing has scarcely evolved. The same difficulties in interpretation have persisted over the years. Some authors have proposed additional thresholds to exclude an infection of <9 months, or in contrast to confirm a recent infection. Such thresholds would be of great interest to adapt management of pregnant women and avoid unnecessary treatment; however, they need confirmation and further studies.

Toxoplasma gondii Recombinant antigen AMA1: Diagnostic Utility of Protein Fragments for the Detection of IgG and IgM Antibodies

Toxoplasma gondii is an important zoonotic protozoan that infects a wide variety of vertebrates as intermediate hosts. For this reason, the diagnosis of this disease is very important and requires continuous improvement. One possibility is to use recombinant antigens in serological tests. Apical membrane antigen 1 (AMA1), a protein located in specific secretory organelles (micronemes) of T. gondii, is very interesting in regard to its potential diagnostic utility. In the present study, we attempted to identify a fragment of the AMA1 protein with a high sensitivity and specificity for the serological diagnosis of human toxoplasmosis. The full-length AMA1 and two different fragments (AMA1N and AMA1C) were produced using an Escherichia coli expression system. After purification by metal affinity chromatography, recombinant proteins were tested for their utility as antigens in enzyme-linked immunosorbent assays (ELISAs) for the detection of IgG and IgM anti-T. gondii antibodies in human and mouse immune sera. Our data demonstrate that the full-length AMA1 recombinant antigen (corresponding to amino acid residues 67–569 of the native protein) has a better diagnostic potential than its N- or C-terminal fragments. This recombinant protein strongly interacts with specific anti-T. gondii IgG (99.4%) and IgM (80.0%) antibodies, and may be used for developing new tools for diagnostics of toxoplasmosis.

Toxoplasma gondii Tetravalent Chimeric Proteins as Novel Antigens for Detection of Specific Immunoglobulin G in Sera of Small Ruminants

Simple Summary

Toxoplasma gondii infection leads to large economic losses in the sheep and goat industry worldwide and is considered to be one of the main causes of infectious ovine and caprine abortion. Moreover, in countries where sheep and goat meat are frequently consumed, T. gondii infection in small ruminants may also pose a public health risk. Due to its medical and veterinary importance, it is essential to study the seroprevalence of T. gondii infection among farm animals and humans. This requires the development of new, low-cost diagnostic methods such as enzyme immunoassays based on recombination antigens. Thus, the study aimed to evaluate the reactivity of four different tetravalent chimeric proteins containing immunodominant regions from the AMA1 (apical membrane antigen 1), SAG2 (surface antigen 2), GRA1 (dense granule antigen 1), GRA2 (dense granule antigen 2), and ROP1 (rhoptry antigen 1) T. gondii antigens with specific IgG from the sera of small ruminants. The results demonstrate that an IgG ELISA (enzyme-linked immunosorbent assay) based on one of these chimeric proteins (AMA1-SAG2-GRA1-ROP1) may be a useful test for the determination of T. gondii infection in small ruminants.

Abstract

The detection of Toxoplasma gondii infection in small ruminants has important significance for public health and veterinary medicine. This study, for the first time, describes the reactivity of four tetravalent chimeric proteins (AMA1_N-SAG2-GRA1-ROP1, AMA1_C-SAG2-GRA1-ROP1, AMA1-SAG2-GRA1-ROP1, and SAG2-GRA1-ROP1-GRA2) containing immunodominant regions from the AMA1 (apical membrane antigen 1), SAG2 (surface antigen 2), GRA1 (dense granule antigen 1), GRA2 (dense granule antigen 2), and ROP1 (rhoptry antigen 1) with specific IgG antibodies from the sera of small ruminants with the use of an indirect enzyme-linked immunosorbent assay (ELISA). The reactivity of individual chimeric antigens was analyzed in relation to the results obtained in IgG ELISA based on a Toxoplasma lysate antigen (TLA). All chimeric proteins were characterized by high specificity (between 96.39% to 100%), whereas the sensitivity of the IgG ELISAs was variable (between 78.49% and 96.77%). The highest sensitivity was observed in the IgG ELISA test based on the AMA1-SAG2-GRA1-ROP1. These data demonstrate that this chimeric protein can be a promising serodiagnostic tool for T. gondii infection in small ruminants.

A time-resolved fluorescence immunoassay for the detection of anti-Neospora caninum antibodies in sheep

Neospora caninum is a protozoan parasite (Phylum Apicomplexa) that has been recently suggested as a relevant cause of reproductive disorders in small ruminants. The aim of the present study is to develop and validate a new serological test based on time resolved fluorescency using N. caninum GRA7 recombinant antigen (GRA7-TRFIA) for the detection of N. caninum antibodies in sheep. A total of 346 serum samples (208 from experimentally infected sheep, 117 from a dairy farm with a previous history of Neospora-associated abortion, and 21 negative sera) were used. The validation of the new assay was performed by the evaluation of assay precision, analytical sensitivity (Se), accuracy and cross reactivity. In the experimentally infected sheep, antibody kinetics was compared between GRA7-TRFIA and an in house N. caninum tachyzoite soluble extract-based ELISA (NcSALUVET ELISA) by Wilcoxon matched-pairs signed rank test. The cut-off and diagnostic Se and specificity (Sp) of GRA7-TRFIA was estimated by ROC analysis with field samples. In addition, concordance and correlation between GRA7-TRFIA and a commercial ELISA and NcSALUVET ELISA were assessed by kappa value and Spearman correlation coefficient, respectively. Overall, GRA7-TRFIA showed an adequate precision, analytical Se and accuracy to detect anti-N. caninum antibodies in ovine serum, and no cross reactivity with the closely related protozoan Toxoplasma gondii. In naturally infected sheep, 100% Se and 95.35% Sp were obtained for a cut-off point of 62.68 Units of Fluorometry for N. caninum (UFN). Moreover, GRA7-TRFIA allowed earlier detection of N. caninum infection than NcSALUVET ELISA in experimentally infected sheep.

Prevalence of Toxoplasma gondii parasite in captive Mexican jaguars determined by recombinant surface antigens (SAG1) and dense granular antigens (GRA1 and GRA7) in ELISA-based serodiagnosis

Toxoplasma gondii is an obligate intracellular protozoan parasite that infects almost all warm-blooded animals, including humans, causing serious public health problems. In this study, the seroprevalence of T. gondii in captive jaguars in 10 Mexican zoos was determined using single and mixtures of recombinant surface antigens (SAG1) and dense granular antigens (GRA1 and GRA7) in immunoglobulin G (IgG) enzyme-linked immunosorbent assays (ELISAs). Their efficacy was compared with the tachyzoite lysate antigen. All recombinant antigens were characterised by high sensitivity (92.5-97.5%); the specificity of the IgG ELISAs was variable (83.3-91.6%). Mixtures of the two recombinant proteins were generally more reactive than single antigens. GRA7 + SAG1 showed the highest sensitivity (97.5%) and specificity (91.6%), almost perfect agreement (96.2%), and a kappa value of 0.89. An area under the curve value of 0.998 represented a highly accurate test with a cutoff value of 0.8. The seroprevalence of anti-T. gondii IgG antibodies in the single and mixed recombinant antigen ELISAs was 75.0-76.9%. This study shows that GRA7 + SAG1 can be successfully used to diagnose T. gondii infection in jaguars for effective monitoring of prevalence and for devising control methods and prevention strategies against toxoplasmosis.

Development, optimization, and validation of an in-house Dot-ELISA rapid test based on SAG1 and GRA7 proteins for serological detection of Toxoplasma gondii infections

Background

The aim of the present study was to develop a simple, portable, and rapid assay for serodiagnosis of toxoplasmosis based on recombinant Toxoplasma gondii (T. gondii) SAG1 (rSAG1) and GRA7 (rGRA7) proteins.

Methods

The rSAG1 and rGRA7 proteins were expressed in Escherichia coli (E. coli) and purified in a single step by immobilized metal ion affinity chromatography. The immunoreactivity of the recombinant antigens was tested in an in-house IgG and IgM Dot enzyme-linked immunosorbent assay (Dot-ELISA) for potential use in serodiagnosis of T. gondii infection.

Results

Results from the comparison of in-house rSAG1-Dot-ELISA with ELISA for the detection of anti-Toxoplasma IgG and IgM include sensitivity of 83.7% and 81.2%, specificity of 90.2% and 89.3%, positive predictive values of 85.9% and 68.4%, and negative predictive values of 88.6% and 94.3%, respectively. Sensitivity of 66.2%, specificity of 81.2%, positive predictive values of 71.6%, and negative predictive values of 77.1% were concluded from in-house IgG rGRA7-Dot-ELISA. The sensitivity and specificity of IgM rGRA7-Dot-ELISA included 87.5% and 83.9%, respectively. Sensitivity and specificity of in-house Dot-ELISA for a combination of rSAG1 and rGRA7 included 87.5% and 91.1% for IgG and IgM, respectively. Sensitivity and specificity of a combination of rSAG1 and rGRA7 for the detection of IgM in suspected sera to acute toxoplasmosis were higher than those for the detection of IgG in sera with chronic infections (90.6% and 92% instead of 86.2% and 91.6%, respectively).

Conclusion

The highlighted parameters of combined recombinant proteins were more significant than those of single recombinant proteins in in-house Dot-ELISA. These data suggest that the in-house Dot-ELISA based on rSAG1 and rGRA7 combination is a promising diagnostic tool with a similar sensitivity to the native antigens of T. gondii, which can be used for the serodiagnosis of toxoplasmosis in fields as well as less equipped laboratories.

Serological and molecular rapid diagnostic tests for Toxoplasma infection in humans and animals

Infection by Toxoplasma gondii is prevalent worldwide. The parasite can infect a broad spectrum of vertebrate hosts, but infection of fetuses and immunocompromised patients is of particular concern. Easy-to-perform, robust, and highly sensitive and specific methods to detect Toxoplasma infection are important for the treatment and management of patients. Rapid diagnostic methods that do not sacrifice the accuracy of the assay and give reproducible results in a short time are highly desirable. In this context, rapid diagnostic tests (RDTs), especially with point-of-care (POC) features, are promising diagnostic methods in clinical microbiology laboratories, especially in areas with minimal laboratory facilities. More advanced methods using microfluidics and sensor technology will be the future trend. In this review, we discuss serological and molecular-based rapid diagnostic tests for detecting Toxoplasma infection in humans as well as animals.

The first study on the usefulness of recombinant tetravalent chimeric proteins containing fragments of SAG2, GRA1, ROP1 and AMA1 antigens in the detection of specific anti-Toxoplasma gondii antibodies in mouse and human sera

This study presents an evaluation of four tetravalent recombinant chimeric proteins containing fragments of the Toxoplasma gondii antigens, SAG2, GRA1, ROP1 and AMA1, as potential replacements of a the soluble, whole-cell tachyzoite lysate (TLA) used in serological assays. Recombinant chimeric proteins (SAG2-GRA1-ROP1-AMA1N, AMA1N-SAG2-GRA1-ROP1, AMA1C-SAG2-GRA1-ROP1, and AMA1-SAG2-GRA1-ROP1) obtained by genetic engineering were tested for their reactivity with specific IgM and IgG antibodies from sera of experimentally infected mice and humans with T. gondii infection using an enzyme-linked immunosorbent assay (ELISA). In total 192 serum samples from patients with acquired T. gondii infection and 137 sera from seronegative individuals were examined. The reactivity of chimeric antigens with antibodies generated during T. gondii invasion was measured and compared to the results obtained in assays based on whole-cell Toxoplasma antigen. Chimeric proteins proved effective in differentiation between T. gondii-infected and uninfected individuals (100% sensitivity and specificity in the IgG ELISAs) which shows their potential usefulness as a replacements for TLA in standardized commercial tests for the serodiagnosis of toxoplasmosis. In addition, the chimeric proteins were tested for use in avidity determination. Obtained results were comparable to those of the corresponding commercial assays, suggesting the utility of these proteins for avidity assessment. Furthermore, this study demonstrated that the AMA1-SAG2-GRA1-ROP1 chimeric protein has the potential to distinguish specific antibodies from serum samples of individuals with the early and chronic phase of T. gondii infection.

Rapid diagnosis of parasitic diseases: current scenario and future needs

BACKGROUND

Parasitic diseases are one of the world's most devastating and prevalent infections, causing millions of morbidities and mortalities annually. In the past, many of these infections have been linked predominantly to tropical or subtropical areas. Nowadays, however, climatic and vector ecology changes, a significant increase in international travel, armed conflicts, and migration of humans and animals have influenced the transmission of some parasitic diseases from 'book pages' to reality in developed countries. It has also been noted that many patients who have never travelled to endemic areas suffer from blood-borne infections caused by protozoa. In the light of existing knowledge, this new trend can be explained by the fact that in the process of migration a large number of asymptomatic carriers become a part of the blood bank donor and transplant donor populations. Accurate and rapid diagnosis represents the crucial weapon in the fight against parasitic infections.

AIMS

To review old and new approaches for rapid diagnosis of parasitic infections.

SOURCES

Data for this review were obtained through searches of PubMed using combinations of the following terms: parasitological diagnostics, microscopy, lateral flow assays, immunochromatographic assays, multiplex-PCR, and transplantation.

CONTENT

In this review, we provide a brief account of the advantages and limitations of rapid methods for diagnosis of parasitic diseases and focus our attention on current and future research in this area. The approximate costs associated with the use of different techniques and their applicability in endemic and non-endemic areas are also discussed.

IMPLICATIONS

Microscopy remains the cornerstone of parasitological diagnostics, especially in the field and low-resource settings, and provides epidemiological assessment of parasite burden. However, increased use and availability of point-of-care tests and molecular assays in modern era allow more rapid and accurate diagnoses and increased sensitivity in the identification of parasitic infections.

Advances in serological, imaging techniques and molecular diagnosis of Toxoplasma gondii infection

BACKGROUND

Toxoplasmosis is worldwide distributed zoonotic infection disease with medical importance in immunocompromised patients, pregnant women and congenitally infected newborns. Having basic information on the traditional and new developed methods is essential for general physicians and infectious disease specialists for choosing a suitable diagnostic approach for rapid and accurate diagnosis of the disease and, consequently, timely and effective treatment.

METHODS

We conducted English literature searches in PubMed from 1989 to 2016 using relevant keywords and summarized the recent advances in diagnosis of toxoplasmosis.

RESULTS

Enzyme-linked immunosorbent assay (ELISA) was most used method in past century. Recently advanced ELISA-based methods including chemiluminescence assays (CLIA), enzyme-linked fluorescence assay (ELFA), immunochromatographic test (ICT), serum IgG avidity test and immunosorbent agglutination assays (ISAGA) have shown high sensitivity and specificity. Recent studies using recombinant or chimeric antigens and multiepitope peptides method demonstrated very promising results to development of new strategies capable of discriminating recently acquired infections from chronic infection. Real-time PCR and loop-mediated isothermal amplification (LAMP) are two recently developed PCR-based methods with high sensitivity and specificity and could be useful to early diagnosis of infection. Computed tomography, magnetic resonance imaging, nuclear imaging and ultrasonography could be useful, although their results might be not specific alone.

CONCLUSION

This review provides a summary of recent developed methods and also attempts to improve their sensitivity for diagnosis of toxoplasmosis. Serology, molecular and imaging technologies each has their own advantages and limitations which can certainly achieve definitive diagnosis of toxoplasmosis by combining these diagnostic techniques.

AN EVALUATION STUDY OF ENZYME-LINKED IMMUNOSORBENT ASSAY (ELISA) USING RECOMBINANT PROTEIN GRA1 FOR DETECTION OF IgG ANTIBODIES AGAINTS TOXOPLASMA GONDII INFECTIONS

Toxoplasmosis is an infectious disease caused by Toxoplasma gondii, an intracellular protozoan parasite that live inside the cells of the reticulo endothelial and parenchymal cells of human and animals (mammals and birds). Some cases of toxoplasmosis usually have no symptoms, but in any cases caused severe symptoms, such as hydrocephalus, microcephalus, intracranial calcification, retinal damage, brain abscess, mental retardation, lymphadenopathy, and others. Its severe symptoms usually showed a long time after first exposure, except symptoms showed by congenital transmission caused by infected mother. Early diagnosis is important to prevent the illness but methods for toxoplasmosis screening are still too expensive for developing country. Enzyme-linked immunosorbent assay (ELISA) allow the testing of a large number samples within short time frame and based on antibody or antigen detection. This study aimed to know the sensitivity and specificity of recombinat protein GRA1 as antigen using ELISA methods. We tested the sensitivity and spesificity of GRA1 protein as antigen in ELISA methods to diagnose toxoplasmosis and compared with ELISA Kit Commercial. Reliable laboratory testing is important to detect Toxoplasma gondii infection, and focused to improving the low cost and easy-to-use diagnostic instrument. Seventy sera collected and tested using both indirect ELISA, commercial ELISA kit and GRA1 protein coated as antigen. Fourty eight and fifty one samples showed positive IgG antibody result of ELISA-GRA1 and ELISA kit. Negative sample tested by ELISA-GRA1 was 22 samples and 19 sample tested by ELISA Kit. The sensitivity and specificity of GRA1-based on ELISA were 100% and 86.36%, positive prediction value (ppv) was 94.11%. These data indicate that the recombinant protein GRA1 is a highly immunogenic protein in human toxoplasmosis and become a promising marker for the screening of toxoplasmosis.

Toxoplasma gondii-positive human sera recognise intracellular tachyzoites and bradyzoites with diverse patterns of immunoreactivity

Antibody detection assays have long been the first line test to confirm infection with the zoonotic parasite Toxoplasma gondii. However, challenges exist with serological diagnosis, especially distinguishing between acute, latent and reactivation disease states. The sensitivity and specificity of serological tests might be improved by testing for antibodies against parasite antigens other than those typically found on the parasite surface during the acute stage. To this end, we analysed the reactivity profile of human sera, identified as positive for anti-Toxoplasma gondii IgG in traditional assays, by indirect immunofluorescence reactivity to acute stage intracellular tachyzoites and in vitro-induced latent stage bradyzoites. The majority of anti-Toxoplasma gondii IgG positive sera recognised both intracellularly replicating tachyzoites and in vitro-induced bradyzoites with varying patterns of immune-reactivity. Furthermore, anti-bradyzoite antibodies were not detected in sera that were IgM-positive/IgG-negative. These results demonstrate that anti-Toxoplasma gondii-positive sera may contain antibodies to a variety of antigens in addition to those traditionally used in serological tests, and suggest the need for further investigations into the utility of anti-bradyzoite-specific antibodies to aid in diagnosis of Toxoplasma gondii infection.

Preliminary multiplex microarray IgG immunoassay for the diagnosis of toxoplasmosis and rubella

BACKGROUND

During pregnancy, toxoplasmosis and rubella can cause serious damage to the mother and the foetus through vertical transmission. Early diagnosis enables implementation of health measures aimed at preventing vertical transmission and minimising damage caused by these diseases.

OBJECTIVE

Here, we report the development of a multiplex assay for simultaneous detection of IgG antibodies produced during toxoplasmosis and rubella infection.

METHODS

This assay is based on xMap technology. Initially, by singleplex assays, we evaluated the following antigens: one Toxoplasma gondii lysate; two antigenic extracts of T. gondii (TOX8131 and TOX8122); fragments of T. gondii antigens [SAG-1 (amino acids 45-198), GRA-7 (24-100), GRA-1 (57-149), ROP-4, and MIC-3 (234-306)]; two chimeric antigens composed of fragments of SAG-1, GRA-7, and P35 (CTOX and CTOXH); and fragments of Rubella virus antigens [E-1 (157-176, 213-239, 374-390), E-2 (31-105), and C (1-123)].

FINDINGS

A multiplex assay to simultaneously diagnose toxoplasmosis and rubella was designed with the best-performing antigens in singleplex and multiplex assays, which included CTOXH, T. gondii lysate, TOX8131, E-1, and E-2. The multiplex assay showed 100% sensitivity and specificity for anti-T. gondii IgG detection and 95.6% sensitivity and 100% specificity for anti-R. virus IgG detection.

MAIN CONCLUSIONS

We found that, despite the difficulties related to developing multiplex systems, different types of antigens (extracts and recombinant proteins) can be used to develop high-performance diagnostic tests. The assay developed is suitable to screen for prior T. gondii and R. virus infections, because it is a rapid, high-throughput, low-cost alternative to the current standard diagnostic tools, which require multiple individual tests.

The standardization of 5 immunoassays for anti-Toxoplasma immunoglobulin G(IgG)

BACKGROUND

Quantitative immunoassays to detect IgG antibodies are the most commonly used tests for diagnosing toxoplasmosis. We investigated the current state of standardization of quantitative immunoassays used to measure anti-Toxoplasma IgG levels.

METHODS

Four fully automated immunoassays (Architect i4000ISR, Immulite 2000 Xpi, Siemens; Liaison, DiaSorin; Cobas e601, Roche) and one manual immunoassay (ELISA classic Toxo IgG, Virion Serion) were performed on the following: individual patient serum samples, the WHO international standards, control samples, and calibrators provided by 5 immunoassay manufacturers. Statistical analysis was used to illustrate the results.

RESULTS

No perfect correlation (slope=1.0) was found between any 2 assays. Large differences in anti-Toxoplasma IgG titers were observed among the 5 immunoassays using serum samples from individual patients. Using IS 01/600 as a calibrator minimized the inter-assay variability of anti-Toxoplasma IgG values CONCLUSIONS: There is still significant effort needed towards standardization of anti-Toxoplasma IgG quantitative immunoassays.

Influenza M1 Virus-Like Particles Consisting of Toxoplasma gondii Rhoptry Protein 4

Toxoplasma gondii infections occur throughout the world, and efforts are needed to develop various vaccine candidates expressing recombinant protein antigens. In this study, influenza matrix protein (M1) virus-like particles (VLPs) consisting of T. gondii rhoptry antigen 4 (ROP4 protein) were generated using baculovirus (rBV) expression system. Recombinant ROP4 protein with influenza M1 were cloned and expressed in rBV. SF9 insect cells were coinfected with recombinant rBVs expressing T. gondii ROP4 and influenza M1. As the results, influenza M1 VLPs showed spherical shapes, and T. gondii ROP4 protein exhibited as spikes on VLP surface under transmission electron microscopy (TEM). The M1 VLPs resemble virions in morphology and size. We found that M1 VLPs reacted with antibody from T. gondii-infected mice by western blot and ELISA. This study demonstrated that T. gondii ROP4 protein can be expressed on the surface of influenza M1 VLPs and the M1 VLPs containing T. gondii ROP4 reacted with T. gondii-infected sera, indicating the possibility that M1 VLPs could be used as a coating antigen for diagnostic and/or vaccine candidate against T. gondii infection.