Serodiagnosis of Toxoplasma gondii infection in cats by enzyme-linked immunosorbent assay using recombinant SAG1

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.

Application of Toxoplasma gondii-specific SAG1, GRA7 and BAG1 proteins in serodiagnosis of animal toxoplasmosis

Toxoplasmosis is a zoonotic disease caused by the obligate intracellular protozoan parasite T. gondii which is widely prevalent in humans and animals worldwide. The diagnosis of toxoplasmosis and distinguishing acute or chronic T. gondii infections have utmost importance for humans and animals. The TgSAG1, TgGRA7, and TgBAG1 proteins were used in the present study to develop the serological rSAG1-ELISA, rGRA7-ELISA and rBAG1-ELISA methods for the testing of T. gondii specific IgG and IgM antibodies and differentiating acute or chronic toxoplasmosis in 3733 animals, including Tibetan sheep, yaks, pigs, cows, cattle, horses, chickens, camels and donkeys from the Qinghai-Tibetan Plateau. The ELISA tests showed that the overall positivity of IgG antibody was 21.1% (786/3733), 15.3% (570/3733) and 18.2% (680/3733) for rSAG1-, rGRA7- and rBAG1-ELISA, respectively, and the positivity of IgM antibody was 11.8% (439/3733), 13.0% (486/3733) and 11.8% (442/3733) for rSAG1-, rGRA7- and rBAG1-ELISA, respectively. A total of 241 animals (6.5%) positive for all rSAG1-, rGRA7- and rBAG1-IgG were found in this study, and the 141 animals (3.8%) tested were anti-T. gondii IgM positive in all three ELISAs. Moreover, the 338, 284 and 377 animals were IgG positive in rSAG1 + rGRA7-, rBAG1 + rGRA7- and rSAG1 + rBAG1- ELISAs respectively, and the 346, 178 and 166 animals in rSAG1 + rGRA7-, rBAG1 + rGRA7- and rSAG1 + rBAG1-ELISAs were IgM positive respectively. The results confirmed that the application of SAG1, GRA7, and BAG1 recombinant antigens could successfully be used in the detection of specific IgG and IgM antibodies for distinguishing between acute or chronic T. gondii infections. It is inferred that the forms in which current animal species in the plateau area were infected with T. gondii, and the period of infection or the clinical manifestations of the current infections may be different. The present study provides substantial clinical evidence for the differential diagnosis of toxoplasmosis, and the classification of acute and chronic T. gondii infections.

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.

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.

Development and evaluation of an enzyme-linked immunosorbent assay based on recombinant TgSRS2 for serodiagnosis of Toxoplasma gondii infection in cats

An enzyme-linked immunosorbent assay (ELISA) based on recombinant SAG1-related sequence 2 of Toxoplasma gondii (rTgSRS2) was developed to detect toxoplasmosis in cats. The specificity and sensitivity of rTgSRS2 ELISA were confirmed using a series of serum samples from T. gondii-experimentally infected mice. A total of 76 field samples from cats were examined by the developed ELISA. The rTgSRS2 ELISA showed a good diagnostic performance characterized by high concordance (88.16) and kappa value (0.76) with latex agglutination test (LAT). The sensitivity and specificity of the test were 92.68% and 82.86%, respectively. These results suggest that the ELISA based on rTgSRS2 could be a useful tool for serodiagnosis of T. gondii infection in cats.

Expression of in vivo biotinylated recombinant antigens SAG1 and SAG2A from Toxoplasma gondii for improved seroepidemiological bead-based multiplex assays

BACKGROUND

Few bead-based multiplex assays have been described that detect antibodies against the protozoan parasite Toxoplasma gondii in large-scale seroepidemiological surveys. Moreover, each multiplex assay has specific variations or limitations, such as the use of truncated or fusion proteins as antigens, potentially masking important epitopes. Consequently, such an assay must be developed by interested groups as none is commercially available.

RESULTS

We report the bacterial expression and use of N-terminal fusion-free, soluble, in vivo biotinylated recombinant surface antigens SAG1 and SAG2A for the detection of anti-T. gondii IgG antibodies. The expression system relies on three compatible plasmids. An expression construct produces a fusion of maltose-binding protein with SAG1 (or SAG2A), separated by a TEV protease cleavage site, followed by a peptide sequence recognized by E. coli biotin ligase BirA (AviTag), and a terminal six histidine tag for affinity purification. TEV protease and BirA are encoded on a second plasmid, and their expression leads to proteolytic cleavage of the fusion protein and a single biotinylated lysine within the AviTag by BirA. Correct folding of the parasite proteins is dependent on proper disulfide bonding, which is facilitated by a sulfhydryl oxidase and a protein disulfide isomerase, encoded on the third plasmid. The C-terminal biotinylation allowed the oriented, reproducible coupling of the purified surface antigens to magnetic Luminex beads, requiring only minute amounts of protein per determination. We showed that an N-terminal fusion partner such as maltose-binding protein negatively influenced antibody binding, confirming that access to SAG1's N-terminal epitopes is important for antibody recognition. We validated our bead-based multiplex assay with human sera previously tested with commercial diagnostic assays and found concordance of 98-100% regarding both, sensitivity and specificity, even when only biotinylated SAG1 was used as antigen.

CONCLUSIONS

Our recombinant in vivo-biotinylated T. gondii antigens offer distinct advantages compared to previously described proteins used in multiplex serological assays for T. gondii. They offer a cheap, specific and sensitive alternative to either parasite lysates or eukaryotic-cell expressed SAG1/SAG2A for BBMA and other formats. The described general expression strategy can also be used for other antigens where oriented immobilization is key for sensitive recognition by antibodies and ligands.

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.

Hydroxylamine and Carboxymethoxylamine Can Inhibit Toxoplasma gondii Growth through an Aspartate Aminotransferase-Independent Pathway

Toxoplasma gondii is an obligate intracellular protozoan parasite and a successful parasitic pathogen in diverse organisms and host cell types. Hydroxylamine (HYD) and carboxymethoxylamine (CAR) have been reported as inhibitors of aspartate aminotransferases (AATs) and interfere with the proliferation in Plasmodium falciparum Therefore, AATs are suggested as drug targets against Plasmodium The T. gondii genome encodes only one predicted AAT in both T. gondii type I strain RH and type II strain PLK. However, the effects of HYD and CAR, as well as their relationship with AAT, on T. gondii remain unclear. In this study, we found that HYD and CAR impaired the lytic cycle of T. gondii in vitro, including the inhibition of invasion or reinvasion, intracellular replication, and egress. Importantly, HYD and CAR could control acute toxoplasmosis in vivo Further studies showed that HYD and CAR could inhibit the transamination activity of rTgAAT in vitro However, our results confirmed that deficiency of AAT in both RH and PLK did not reduce the virulence in mice, although the growth ability of the parasites was affected in vitro HYD and CAR could still inhibit the growth of AAT-deficient parasites. These findings indicated that HYD and CAR inhibition of T. gondii growth and control of toxoplasmosis can occur in an AAT-independent pathway. Overall, further studies focusing on the elucidation of the mechanism of inhibition are warranted. Our study hints at new substrates of HYD and CAR as potential drug targets to inhibit T. gondii growth.

Characterization of strain-specific phenotypes associated with knockout of dense granule protein 9 in Toxoplasma gondii

Toxoplasma gondii is an obligate intracellular parasite that can invade any nucleated cell of mammals and cause toxoplasmosis. Dense granule proteins play major structural functions within the parasitophorous vacuole (PV) and the cyst wall of T. gondii. Moreover, their particular location within the PV allows them to be involved in various interactions between parasites and the host cells. Dense granule protein 9 (GRA9) gene has been identified in T. gondii, although its role in the lytic cycle remains unclear. In the current study, the function of GRA9 in type I and type II Toxoplasma parasites was characterized. T. gondii GRA9 sequence and its expression were analyzed and derivatives of T. gondii RH and PLK strains with a null mutation in GRA9 were generated using CRISPR/Cas9 system. The phenotypes of GRA9 in wild types, knockout and complemented strains were analyzed in vitro and in vivo using Vero cells and BALB/c mice, respectively. Alignment of the amino acid sequence indicated that RH strain GRA9 contained one amino acid substitution when compared with PLK strain. Western blot analysis revealed that PLK strain had a higher expression level of GRA9 than RH strain. The phenotype analysis revealed that knockout of GRA9 in PLK parasites inhibited the plaque formation and egress from PV. Both the plaque formation and egress ability of PLKΔGRA9 strain were restored by complementation with a synonymous allele of PLK strain GRA9. Mouse experiments demonstrated that loss of GRA9 in PLK strain significantly reduced the pathogenicity of T. gondii. However, there was no phenotypic diferences between RH and RHΔGRA9 strains except the defect in host cell invasion. Overall, T. gondii GRA9 knockout only influenced the growth and virulence of PLK strain. These results indicate that GRA9 may be involved in parasite egress and virulence in mice in a strain-specific manner.

Native SAG1 in Toxoplasma gondii lysates is superior to recombinant SAG1 for serodiagnosis of T. gondii infections in chickens

Toxoplasma gondii can infect almost all mammals and birds, including chickens. The aim of this study was to identify an appropriate immunogenic antigen for serodiagnosis of T. gondii infections in chickens. We examined serum samples from chickens that were intravenously or intraperitoneally infected with 10⁶-10⁸ tachyzoites of T. gondii strains PLK, RH, CTG, ME49 or TgCatJpGi1/TaJ using enzyme-linked immunosorbent assays (ELISAs), latex agglutination tests (LATs) and western blotting. Regardless of parasite strain or infection dose and route, the commercial LAT was positive for almost all sera collected 1 week post-infection. However, at 2 weeks post-infection, LATs were negative in the same birds. ELISAs using the Escherichia coli-produced recombinant T. gondii antigens SAG1 and GRA7 showed strong signals at 1-2 weeks post infection, but thereafter diminished for the majority of serum samples. In contrast, western blotting against crude tachyzoite antigens showed a persistent band up to 4 weeks post-infection. Sera from these chickens reacted much more strongly with SAG1 from crude tachyzoite antigens than with recombinant SAG1. Even in experimentally-infected birds whose parasite burdens in tissue were undetectable, sera still reacted with native SAG1. We tested sera from free-range chickens on a small farm in Ghana, Africa, using western blotting and found that the serum of one bird reacted with a single band of approximately 27 kDa, the putative molecular weight of SAG1. Thus we conclude that native SAG1, but not E. coli-produced recombinant SAG1, is suitable for serodiagnosis of T. gondii infections in chickens.

Prevalence of Toxoplasma gondii and other intestinal parasites in cats in Tokachi sub-prefecture, Japan

The present study investigated the prevalence of Toxoplasma gondii and other intestinal parasites in cats in the Tokachi subprefecture in Japan. A total of 365 household cats were included in the study, and 353 serum and 351 fecal samples were collected and analyzed. T. gondii IgG antibodies were detected in the sera of 16.14% of cats based on Latex agglutination test and ELISA. For ELISA, T. gondii RH strain tachyzoites lysate and T. gondii SAG2 recombinant protein were used as antigens. Low seropositivity was detected in cats younger than one year and older than 11 years; outdoor and hunter cats showed significantly high seropositivities. Neutering either in male or female cats, but not gender, had a considerable effect on seroprevalence. Toxoplasma gondii oocysts were detected in one fecal sample. The overall parasitic infestation in cats was 12.5%. Other detected parasites included Toxocara species, which showed the highest prevalence of 7.7%, followed by Isospora spp. (2%), Taenia spp. (1.7%), and Ancylostoma spp. (0.9%). Spirometra spp. was detected in only one sample. Outdoor cats comprised 50% of all 44 parasite-infested cats. Although T. gondii oocysts were detected in only one sample, the relatively high seroprevalence of T. gondii indicated that it can pose significant risks to the environment. Our findings highlighted the potential of outdoor cats as a source of T. gondii and other parasites.

Toxoplasma gondii: history and diagnostic test development

Toxoplasma gondiiis a protozoa that causes toxoplasmosis in people and other animals. It is considered one of the most common parasitic infections in the world due to its impressive range of hosts, widespread environmental contamination and the diverse means by which animals can be infected. Despite its ubiquity and numerous ongoing research efforts into both its basic biology and clinical management, many aspects of diagnosis and management of this disease are poorly understood. The range of diagnostic options that is available for veterinary diagnostic investigators are notably more limited than those available to medical diagnosticians, making accurate interpretation of each test result critical. The current review joins other reviews on the parasite with a particular emphasis on the history and continued development of diagnostic tests that are useful for veterinary diagnostic investigations. An understanding of the strengths and shortcomings of current diagnostic techniques will assist veterinary and public health officials in formulating effective treatment and control strategies in diverse animal populations.

Seroprevalence of Toxoplasma gondii infection in domestic dogs in an area from northwest of Iran: a cross-sectional study using immunodominant surface antigen 1 (SAG1)

Toxoplasma gondii is an obligate intracellular protozoan parasite that infects humans and animals. T. gondii surface antigen 1 (SAG1) is an appropriate antigen with high specificity and sensitivity for the detection of T. gondii infection in humans and animal hosts. The aim of this study was to determine the seroprevalence of T. gondii infection using SAG1 antigen (P30) in ownership dogs in Meshkin-Shahr district in the northwestern Iran. The sera samples were collected from 171 domestic dogs and tested using indirect ELISA (SAG1 antigen). The data were analyzed using SPSS software version 13. From a total of 171 dogs, 82 (48 %) of them were sero-positive. No statistical significant difference was seen between T. gondii infection and gender (P = 0.995). The highest sero-prevalence of rate was observed in >5 years animals; but no statistical significant difference was seen between T. gondii infection and age (P = 0.589). Our findings indicate that Toxoplasma seropositivity rate is high in ownership dogs in northwest of Iran. This is probably due to high exposure to contaminated food, soil, or water sources with sporulated Toxoplasma oocysts.

Evaluation of recombinant SAG1, SAG2, and SAG3 antigens for serodiagnosis of toxoplasmosis

Serologic tests are widely accepted for diagnosing Toxoplasma gondii but purification and standardization of antigen needs to be improved. Recently, surface tachyzoite and bradyzoite antigens have become more attractive for this purpose. In this study, diagnostic usefulness of 3 recombinant antigens (SAG1, SAG2, and SAG3) were evaluated, and their efficacy was compared with the available commercial ELISA. The recombinant plasmids were transformed to JM109 strain of Escherichia coli, and the recombinants were expressed and purified. Recombinant SAG1, SAG2, and SAG3 antigens were evaluated using different groups of sera in an ELISA system, and the results were compared to those of a commercial IgG and IgM ELISA kit. The sensitivity and specificity of recombinant surface antigens for detection of anti-Toxoplasma IgG in comparison with commercially available ELISA were as follows: SAG1 (93.6% and 92.9%), SAG2 (100.0% and 89.4%), and SAG3 (95.4% and 91.2%), respectively. A high degree of agreement (96.9%) was observed between recombinant SAG2 and commercial ELISA in terms of detecting IgG anti-Toxoplasma antibodies. P22 had the best performance in detecting anti-Toxoplasma IgM in comparison with the other 2 recombinant antigens. Recombinant SAG1, SAG2, and SAG3 could all be used for diagnosis of IgG-specific antibodies against T. gondii.

Seroprevalences of Toxoplasma gondii and Neospora caninum in pet rabbits in Japan

The potential contamination of Toxoplasma gondii and Neospora caninum oocysts in the human environment is a concern from the public health viewpoint. However, estimation of their seroprevalences in humans cannot be performed in a manner that distinguishes between oocysts and tissue cysts as a source of infection. Rabbits are considered popular pet animals in Japan that can acquire natural infections by the aforementioned parasites only through the ingestion of oocysts. Therefore, this study was conducted to estimate the seroprevalences of T. gondii and N. caninum in pet rabbits in Japan as an indicator of the possible oocyst contamination in the environment surrounding human beings. Serum samples of 337 rabbits were examined by different serological methods. Enzyme-linked immunosorbent assays were performed to measure the titer of IgG and IgM antibodies. Samples revealed to be seropositive by ELISA were further analyzed by a latex agglutination test, Western blotting and an indirect immunofluorescence assay. The rates of seropositivity for T. gondii were 0.89% (3/337) and 0.29% (1/337) in IgG and IgM ELISA, respectively. SAG1 and SAG2 were detected as major antigens by the positive rabbit sera in Western blotting associated with strong staining observed by IFA in T. gondii tachyzoites. Regarding N. caninum, none of the serum samples showed a specific reaction in both Western blotting and the IFA. The results of this study indicate low seroprevalences of toxoplasmosis and neosporosis in pet rabbits in Japan, suggesting low oocyst contamination in the human environment.

Prevalence of Toxoplasma gondii infection in rabbits of Korea by serological tests and nested polymerase chain reaction

>This study surveyed the Toxoplasma (T.) gondii infection prevalence in the Korean rabbit population. Rabbits (n=142) were obtained from two breeding farms in the Gongju area, Chungnam Province, and in the Kochang area, Junbuk Province, Korea. Of 142 sera samples analyzed by enzyme-linked immunosorbent assay (ELISA), 15 (10.6%) exhibited T. gondii-specific IgG antibodies, and 1 (0.7%) rabbit harbored T. gondii-specific IgM. Female rabbits (9/84; 10.7%) had a similar T. gondii prevalence to males (6/58; 10.3%). When stratified by age, rabbits aged >1 year had a similar prevalence of T. gondii infection (7/66; 10.6%) to rabbits aged <1 year (8/76; 10.5%). Immunoblotting detected 6 major antigenic bands corresponding to T. gondii-positive sera at 20, 28, 30, 35, 63 and 77 kDa. Nested polymerase chain reaction (PCR) of whole-blood samples detected the T. gondii B1 gene in 23 rabbits (16.2%). All PCR-positive samples corresponded to partial T. gondii B1 gene sequences with 99% homology to a T. gondii sequence deposited in GenBank (accession number EU340874). Female rabbits (13/84; 15.5%) harbored a similar prevalence of T. gondii DNA to males (10/58; 17.2%). Rabbits aged >1 year had a similar prevalence (12/66; 18.2%) of T. gondii infection to rabbits aged <1 year (11/76; 14.5%). No statistically significant differences were observed regarding the prevalences of infection according to sex or age using molecular or serological tests. This study is the first survey using serological tests and nested PCR to analyze the T. gondii prevalence in rabbits in Korea.

Identification and characterization of Eimeria tenella apical membrane antigen-1 (AMA1)

Apical membrane antigen-1 (AMA1) is a micronemal protein of apicomplexan parasites that appears to be essential during the invasion of host cells. In this study, a full-length cDNA of AMA1 was identified from Eimeria tenella (Et) using expressed sequence tag and the rapid amplification of cDNA ends technique. EtAMA1 had an open reading frame of 1608 bp encoding a protein of 535 amino acids. Quantitative real-time PCR analysis revealed that EtAMA1 was expressed at higher levels in sporozoites than in the other developmental stages (unsporulated oocysts, sporulated oocysts and second-generation merozoites). The ectodomain sequence was expressed as recombinant EtAMA1 (rEtAMA1) and rabbit polyclonal antibodies raised against the rEtAMA1 recognized a 58-kDa native parasite protein by Western Blotting and had a potent inhibitory effect on parasite invasion, decreasing it by approximately 70%. Immunofluorescence analysis and immunohistochemistry analysis showed EtAMA1 might play an important role in sporozoite invasion and development.

Development of latex agglutination test with recombinant NcSAG1 for the rapid detection of antibodies to Neospora caninum in cattle

Neospora caninum, an apicomplexan protozoan parasite, is recognized as a major cause of abortion in cattle. Surface antigen 1 of N. caninum (NcSAG1) is an important immunodominant candidate for the development of a diagnostic reagent for neosporosis. The present study describes the development and evaluation of a latex agglutination test (LAT) with recombinant NcSAG1 (rNcSAG1) for the detection of antibodies to N. caninum in cattle. The rNcSAG1 gene was cloned in pET-28a and protein was expressed in Escherichia coli BL21 (DE3). Carboxylated latex particles were coated with rNcSAG1 and the degree of agreement between LAT and a commercial enzyme-linked immunosorbent assay (iscomELISA) was evaluated by using of 164 serum samples. Twenty-two (13.4%) and 23 (14.0%) of samples were positive for antibodies to N. caninum by LAT and ELISA respectively. Eighteen of 23 ELISA-positive samples were positive according to the LAT and a substantial agreement (κ=0.77) was found between the results of LAT and ELISA. The results indicated that the LAT with rNcSAG1 would be a rapid, simple, relatively inexpensive and suitable diagnostic test for detection of specific antibodies in N. caninum infection under field conditions. Improvement in purification of rNcSAG1 can reduce probable false positive reactions and so increase the degree of agreement between the LAT and ELISA.

Comparing the effect of IL-12 genetic adjuvant and alum non-genetic adjuvant on the efficiency of the cocktail DNA vaccine containing plasmids encoding SAG-1 and ROP-2 of Toxoplasma gondii

Various methods are available for enhancing the potency of DNA vaccines, including employment of different forms of adjuvant. The current study was carried out to evaluate and compare the effects of genetic and non-genetic adjuvants on the immune response stimulated by DNA vaccine. Thus, two adjuvants, IL-12 (genetic adjuvant) and aluminum hydroxide (alum, non-genetic adjuvant), were used with cocktail DNA vaccine containing plasmids encoding complete rhoptry antigen 2 (ROP-2) and surface major antigen 1 (SAG-1) of Toxoplasma gondii. The efficacy of pcROP2+pcSAG1 in stimulation of the immune response against toxoplasmosis with and without adjuvant was evaluated in female BALB/c mice by measuring the level of total IgG antibody and cytokines. The results obtained indicated that after challenging the mice with the fatal RH strain of T. gondii, the survival rates of mice immunized with pcROP2+pcSAG1 (DNA cocktail), pcSAG1+pcROP2+alum, and pcSAG1+pcROP2+IL-12 were significantly greater than that of the control groups (p<0.05). Moreover, measurement of total IgG antibody indicated the significant difference between the control and experimental groups (p<0.05). Finally, the results obtained by measurement of cytokines (IFN-γ and IL-4) showed high levels of IFN-γ and low levels of IL-4 in groups vaccinated with pcROP2+pcSAG1 (DNA cocktail), pcSAG1+pcROP2+alum, and pcSAG1+pcROP2+IL-12 as the experiment groups, in comparison with the controls groups (PBS, pc-DNA3, alum+PBS, and pCAGGS-IL-12+pcDNA3). The results of the study showed that use of adjuvants (IL-12 and alum) coincident with DNA cocktail leads to significant change in the survival rates of the experiment groups in comparison with control groups. Also, there is no significant difference between adjuvants to induce immune responses.

Sequential recognition of antigenic markers of Toxoplasma gondii tachyzoite by pooled sera of mice with experimental toxoplasmosis

Accurate diagnosis of maternal toxoplasmosis can enhance the success of medical treatment and prevent congenital transmission. The current diagnostic methods have many limits, and they poorly differentiate between recent and latent infections. The present work was conducted to record the sequential recognition of antigenic markers of both Toxoplasma tachyzoites whole extract and glycosylinositolphospholipids (GIPLs)-enriched fraction by specific IgG and IgM, respectively, by immunoblotting analysis of the antigens against daily pooled serum samples from mice with experimentally induced recent and latent toxoplasmosis. IgG avidity immunoblotting was tested by using a wash with 6 M urea solution as antigen-antibody disrupting agent. Band of 10 kDa reacted exclusively with low-avidity IgG in pooled sera of mice with recent infection. Band of 39 kDa was a good marker for the infection; reacting with both low-avidity IgG in recent infection and with high-avidity IgG in latent one. Bands of 15, 23, 30, 60, 66, and 97 kDa reacted with variable avidity in both phases of infection. Two antigenic bands were detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the GIPLs-enriched fraction of tachyzoite, the 14- and 30-kDa band. The 14-kDa band was recognized by IgM in pooled serum samples of recently infected mice only, while the 30-kDa band was recognized by serum samples of both recent and latent phases of infections. The study highlights the value of avidity immunoblotting assay to discriminate between recent and latent experimental toxoplasmosis. Further study must be carried on human to evaluate the values of the used technique.

Construction of Neospora caninum stably expressing TgSAG1 and evaluation of its protective effects against Toxoplasma gondii infection in mice

Toxoplasma gondii and Neospora caninum are closely related apicomplexan parasites. The surface antigen 1 of T. gondii (TgSAG1) is a major immunodominant antigen and, therefore, is considered to be a good candidate for the development of an effective recombinant vaccine against toxoplasmosis. In this study, N. caninum stably expressing the TgSAG1 gene (Nc/TgSAG1) was constructed using pyrimethamine-resistant DHFR-TS and GFP genes as double-selection markers. The expression level, molecular weight, and antigenic property of recombinant TgSAG1 expressed by the Nc/TgSAG1 were similar to those of the native TgSAG1. The mice immunized with Nc/TgSAG1 induced TgSAG1-specific Th1-dominant immune responses and protected the mice from a lethal challenge infection with T. gondii. These results indicate that N. caninum may provide a new tool for the production of a live recombinant vector vaccine against toxoplasmosis in animals. To our knowledge, this is the first report to evaluate the usefulness of N. caninum-based live vaccine.

Waterborne toxoplasmosis--recent developments

Humans become infected with Toxoplasma gondii mainly by ingesting uncooked meat containing viable tissue cysts or by ingesting food or water contaminated with oocysts from the feces of infected cats. Circumstantial evidence suggests that oocyst-induced infections in humans are clinically more severe than tissue cyst-acquired infections. Until recently, waterborne transmission of T. gondii was considered uncommon, but a large human outbreak linked to contamination of a municipal water reservoir in Canada by wild felids and the widespread infection of marine mammals in the USA provided reasons to question this view. The present paper examines the possible importance of T. gondii transmission by water.

Evaluation of a recombinant MIC3 based latex agglutination test for the rapid serodiagnosis of Toxoplasma gondii infection in swines

The entire gene encoding microneme protein 3 (MIC3) from Toxoplasma gondii was cloned into the plasmid pGEX-KG and subsequently expressed in Escherichia coli as a glutathione-S-transferase (GST) fusion protein. The recombinant MIC3 (rMIC3) was purified and evaluated in a latex agglutination test (LAT) as the diagnostic antigen for the detection of antibodies to T. gondii in pig sera. The specificity, stability, and reproducibility of the test were examined. No agglutination was found when the sensitized latex beads were mixed with phosphate-buffered saline (PBS), borate-buffered saline (BBS), normal saline, and negative serum samples. There was no cross-reactivity with the standard positive sera of other pathogens. But intense agglutination occurred with T. gondii antibody positive serum samples. In our study, the coincidence rate of tested positive-sera of the LAT with rMIC3-sensitized latex particles and the ELISA with rSAG1 was up to 92.8%, T. gondii specific antibodies were detected by the LAT in all piglets that were experimentally infected with T. gondii tachyzoites from 8 to 42 days after infection. Our results indicated that the rMIC3 based latex agglutination test appears to be suitable for the detection of T. gondii antibodies at the early stage of infection.

IGM and IGG response to 29-35-kDa Toxoplasma gondii protein fractions in experimentally infected goats

The evolution of the humoral responses of IgG and IgM against 29-35-kDa Toxoplasma gondii fractions from experimentally infected goats were studied and compared by ELISA with the use of whole T. gondii soluble extracts and 29-35-kDa electroeluted proteins as antigens. The IgM response to electroeluted proteins was detected from wk 1 to wk 3 postinfection, showing a similar evolution to that observed when T. gondii crude extracts were used as antigens. These results suggest that this group of proteins could be used for a more specific detection of anti-T. gondii IgM. In the same way, the IgG response was equivalent in both cases, although when 29-35-kDa T. gondii fractions were used as antigens, the level of specific IgGs reached a peak 2 wk before than when T. gondii crude extract was used. The detection by ELISA of anti-T. gondii IgM in goats does not seem to be affected by the presence of specific IgG in serum samples when 29-35-kDa protein fractions were used as antigens.

Identification of ribosomal phosphoprotein P0 of Neospora caninum as a potential common vaccine candidate for the control of both neosporosis and toxoplasmosis☆

The characterization of the cross-reactive antigens of two closely related apicomplexan parasites, Neospora caninum and Toxoplasma gondii, is important to elucidate the common mechanisms of parasite-host interactions. In this context, a gene encoding N. caninum ribosomal phosphoprotein P0 (NcP0) was identified by immunoscreening of a N. caninum tachyzoite cDNA expression library with antisera from mice immunized with T. gondii tachyzoites. The NcP0 was encoded by a gene with open reading frame of 936 bp, which encoded a protein of 311 amino acids. The NcP0 gene existed as a single copy in the genome and was interrupted by a 432 bp intron. The NcP0 showed 94.5% amino acid identity to T. gondii P0 (TgP0). Anti-recombinant NcP0 (rNcP0) sera recognized a native parasite protein with a molecular mass of 34 kDa in Western blot analysis. Immunofluorescence analysis showed that the NcP0 was localized to the surface of N. caninum tachyzoites. A purified anti-rNcP0 IgG antibody inhibited the growth of N. caninum and T. gondii in vitro in a concentration-dependent manner. These results indicate that P0 is a cross-reactive antigen between N. caninum and T. gondii and a potential common vaccine candidate to control both parasites.

Identification and heterologous expression of a Sarcoptes scabiei cDNA encoding a structural antigen with immunodiagnostic potential

The mite Sarcoptes scabiei causes sarcoptic mange (or scabies), a disease of considerable human and veterinary significance. An S. scabiei cDNA clone of about 2 kb was isolated from a S. scabiei var. hominis expression library by immunological screening using blood serum from a naturally infected chamois (Rupicapra rupicapra). The nucleotide sequence of the identified cDNA contains an open reading frame of 1930 bp that encodes a 642 amino acid polypeptide. This polypeptide shows tandem repeats of a glycine-serine rich 20 residue sequence followed by a unique C-terminal glutamate rich 54 residue sequence. The cDNA or the deduced polypeptide did not show significant similarities to any of the sequences in the databases. A carboxyl-terminal fragment of this polypeptide (residues 380 to 642) was efficiently expressed in Escherichia coli as a fusion with Glutathione S-transferase and then was used to produce a specific antiserum. The antigen encoded by the cDNA was located at the integument of the mite's epidermis and the cavities surrounding its vital organs. Western blot analysis of mite extracts using the specific antiserum against the recombinant protein identified antigens larger that 60 kDa indicating that the isolated cDNA did not contain the full ORF. Moreover, we designed a diagnostic assay based on the carboxyl-terminal fragment of the antigen for the identification of infected animals.

Identification of a necessary element for Toxoplasma gondii SAG1 gene expression

SAG1 codes for the stage-specific major surface antigen P30 of Toxoplasma gondii (T. gondii) tachyzoites. Six tandemly repeated, conserved 27 bp cassettes in the region from -231 to -70 bp were previously confirmed to be essential for high-level expression of SAG1 and serve as a positioning element directing the initiation of transcription. We demonstrate here that an element located between +19 and +28 bp is necessary for SAG1 gene expression by using deletion mutagenesis analysis and electrophoresis mobility shift assay (EMSA). This will provide an insight into the regulatory mechanisms of SAG1 gene expression.

Apical membrane antigen 1 is a cross-reactive antigen between Neospora caninum and Toxoplasma gondii, and the anti-NcAMA1 antibody inhibits host cell invasion by both parasites

The cross-reactive antigens of Neospora caninum and Toxoplasma gondii are important in the exploration to determine the common mechanisms of parasite-host interaction. In this study, a gene encoding N. caninum apical membrane antigen 1 (NcAMA1) was identified by immunoscreening of a N. caninum tachyzoite cDNA expression library with antisera from mice immunized with recombinant T. gondii apical membrane antigen 1 (TgAMA1). NcAMA1 was encoded by an open reading frame of 1695 bp, which encoded a protein of 564 amino acids. The single-copy NcAMA1 gene was interrupted by seven introns. NcAMA1 showed 73.6% amino acid identity to TgAMA1. Mouse polyclonal antibodies raised against the recombinant NcAMA1 (rNcAMA1) recognized a 69-kDa native parasite protein by Western blotting. Immunofluorescence analysis showed that NcAMA1 was localized to the apical end of tachyzoites. Two-dimensional electrophoresis and Western blotting indicated that an approximately 57-kDa cleavage product was released into the excretory/secretory products of N. caninum. Preincubation of free tachyzoites with anti-rNcAMA1 IgG antibodies inhibited the invasion into host cells by N. caninum and T. gondii. These results indicated that AMA1 is a cross-reactive antigen between N. caninum and T. gondii and a potential common vaccine candidate to control two parasites.

Primary structure of mature SAG1 gene of an Indonesian Toxoplasma gondii and comparison with other strains

Toxoplasma gondii is a persistent protozoan parasite capable of infecting almost any warm-blooded vertebrates. SAG1 (p30) is the prototypic member of a superfamily of surface antigens called SRS (SAG1-related sequence). It constitutes the most abundant and predominant antigen. In this paper the primary structure of mature SAG1 gene of an Indonesian T. gondii isolate is described and sequence comparison is made with published sequence data of 7 other strains or isolates. Sequence comparison indicated that SAG1 is highly conserved through evolution and despite parasite spreading world-wide. Sequences may be divided into two major families, independent of the strain/isolate geographic origin. Variations were mainly localized at the C-terminal half or domain 2 and some clustered in restricted areas. Sequence comparison allowed us to define the Indonesian isolate as genuine virulent RH strain. A phylogenetic tree of Toxoplasma strains/isolates was constructed based on SAG1.

Enzyme-linked immunosorbent assays for detection of equine antibodies specific to Sarcocystis neurona surface antigens

Sarcocystis neurona is the primary causative agent of equine protozoal myeloencephalitis (EPM), a common neurologic disease of horses in the Americas. We have developed a set of enzyme-linked immunosorbent assays (ELISAs) based on the four major surface antigens of S. neurona (SnSAGs) to analyze the equine antibody response to S. neurona. The SnSAG ELISAs were optimized and standardized with a sample set of 36 equine sera that had been characterized by Western blotting against total S. neurona parasite antigen, the current gold standard for S. neurona serology. The recombinant SnSAG2 (rSnSAG2) ELISA showed the highest sensitivity and specificity at 95.5% and 92.9%, respectively. In contrast, only 68.2% sensitivity and 71.4% specificity were achieved with the rSnSAG1 ELISA, indicating that this antigen may not be a reliable serological marker for analyzing antibodies against S. neurona in horses. Importantly, the ELISA antigens did not show cross-reactivity with antisera to Sarcocystis fayeri or Neospora hughesi, two other equine parasites. The accuracy and reliability exhibited by the SnSAG ELISAs suggest that these assays will be valuable tools for examining the equine immune response against S. neurona infection, which may help in understanding the pathobiology of this accidental parasite-host interaction. Moreover, with modification and further investigation, the SnSAG ELISAs have potential for use as immunodiagnostic tests to aid in the identification of horses affected by EPM.

Performance of a Western immunoblot assay to detect specific anti-Toxoplasma gondii IgG antibodies in human saliva

Toxoplasma gondii represents the most prominent infectious parasitic organism found in humans. While normally asymptomatic in healthy individuals, toxoplasmosis can cause abortion in patients during pregnancy, or can be fatal in immunosupressed individuals such as persons suffering from acquired immunodeficiency syndrom (AIDS). Toxoplasma gondii infection in humans is routinely assesssed by serological means. Here, we show that detection of anti-T. gondii IgG is also possible using a non-invasive methodology employing saliva. Sera and saliva of 201 healthy volunteers were investigated for the presence of anti-T. gondii-IgG antibodies by immunoblotting. The sera of 59 (29.4%) individuals showed IgG antibodies against T. gondii by ELISA, Vidas, and immunoblotting; 58 (98.3%) of these were also positive for anti-T. gondii IgG in the saliva immunoblot, with diagnostic relevant bands of Mr of 32-35 kDa and 40-45 kDa. The saliva immunoblot test exhibits a specificity of 100% and a sensitivity of 98.5%. Thus, saliva could be used as an alternative, non-invasive means for the detection of specific anti-T. gondii IgG in humans.

Antigenic evaluation of a recombinant baculovirus-expressed Sarcocystis neurona SAG1 antigen

Sarcocystis neurona is the primary parasite associated with equine protozoal myeloencephalitis (EPM). This is a commonly diagnosed neurological disorder in the Americas that infects the central nervous system of horses. Current serologic assays utilize culture-derived parasites as antigen. This method requires large numbers of parasites to be grown in culture, which is labor intensive and time consuming. Also, a culture-derived whole-parasite preparation contains conserved antigens that could cross-react with antibodies against other Sarcocystis species and members of Sarcocystidae such as Neospora spp., Hammondia spp., and Toxoplasma gondii. Therefore, there is a need to develop an improved method for the detection of S. neurona-specific antibodies. The sera of infected horses react strongly to surface antigen 1 (SnSAG1), an approximately 29-kDa protein, in immunoblot analysis, suggesting that it is an immunodominant antigen. The SnSAG1 gene of S. neurona was cloned, and recombinant S. neurona SAG1 protein (rSnSAG1-Bac) was expressed with the use of a baculovirus system. By immunoblot analysis, the rSnSAG1-Bac antigen detected antibodies to S. neurona from naturally infected and experimentally inoculated equids, cats, rabbit, mice, and skunk. This is the first report of a baculovirus-expressed recombinant S. neurona antigen being used to detect anti-S. neurona antibodies in a variety of host species.