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

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.

Serological Investigation of Bovine Toxoplasmosis Using Commercial and Indigenous ELISA Kits While Validating Cattle Toxo IgG ELISA Kit

Simple Summary

Toxoplasmosis is a zoonotic disease caused by T. gondii infection. The main aims of this study were to assess the seropositivity to toxoplasmosis of an exotic breed of cattle (n = 400) from different farms using the Latex Agglutination Test, validate the Cattle Toxo IgG ELISA kit with the help of the commercially available ELISA kit and compare the efficacy of the LAT and Cattle Toxo IgG ELISA kit for assessing seropositivity of cattle to toxoplasmosis. Four hundred cattle sera were collected from an exotic breed of cattle in Pakistan. These sera were evaluated through an LAT and Cattle Toxo IgG ELISA kit. Of 400 samples, 90 were elected and screened through a commercially available ELISA kit. The sensitivity and specificity of the Cattle Toxo IgG ELISA kit came out to be 100% and 96.15%, and in LAT, it was found as 26.31% and 61.53%, respectively. The Cattle Toxo IgG ELISA kit revealed 29.75% (119/400) seropositivity, 6% less than that found through LAT. The results of this study show that Cattle Toxo IgG ELISA kit is a highly accurate and reliable serodiagnostic tool to diagnose bovine toxoplasmosis.

Abstract

Toxoplasma gondii is a protozoan parasite that causes toxoplasmosis in warm-blooded vertebrates, globally. The main aims of this study were to assess the seropositivity to toxoplasmosis of an exotic breed of cattle (n = 400) from different farms using the Latex Agglutination Test and validate Cattle Toxo IgG ELISA kit. Of a total of 400 cattle sera that were evaluated by LAT, 143 (35.75%) were found positive. Based on these data, 90 samples (n = 60 seronegative by LAT; n = 30 seropositive by LAT) were elected for screening through a commercially available ELISA kit. The same 90 samples were screened through a Cattle Toxo IgG ELISA kit for validation purposes. Of 90 samples, 40 were seropositive in the Cattle Toxo IgG ELISA kit (100% sensitivity), and 38 were seropositive in a commercially available ELISA kit. All 50 samples in the Cattle Toxo IgG ELISA kit (96.15% specificity) were also seronegative in the commercially available ELISA kit. Hence, the sensitivity and specificity of the Cattle Toxo IgG ELISA kit came out to be 100% and 96.15%, and in LAT, it was found as 26.31% and 61.53%, respectively. Therefore, the Cattle Toxo IgG ELISA kit is a highly reliable serodiagnostic tool to diagnose bovine toxoplasmosis.

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.

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.

Descriptive Comparison of ELISAs for the Detection of Toxoplasma gondii Antibodies in Animals: A Systematic Review

Toxoplasma gondii is the zoonotic parasite responsible for toxoplasmosis in warm-blooded vertebrates. This systematic review compares and evaluates the available knowledge on enzyme-linked immunosorbent assays (ELISAs), their components, and performance in detecting T. gondii antibodies in animals. Four databases were searched for published scientific studies on T. gondii and ELISA, and 57 articles were included. Overall, indirect (95%) and in-house (67%) ELISAs were the most used types of test among the studies examined, but the 'ID Screen® Toxoplasmosis Indirect Multi-species' was common among commercially available tests. Varying diagnostic performance (sensitivity and specificity) and Kappa agreements were observed depending on the type of sample (serum, meat juice, milk), antigen (native, recombinant, chimeric) and antibody-binding reagents used. Combinations of recombinant and chimeric antigens resulted in better performance than native or single recombinant antigens. Protein A/G appeared to be useful in detecting IgG antibodies in a wide range of animal species due to its non-species-specific binding. One study reported cross-reactivity, with Hammondia hammondi and Eimeria spp. This is the first systematic review to descriptively compare ELISAs for the detection of T. gondii antibodies across different animal species.

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.

Evaluation of toxoplasmosis in pregnant women using dot-immunogold-silver staining with recombinant Toxoplasma gondii peroxiredoxin protein

BACKGROUND

Toxoplasma gondii infection endangers human health and affects animal husbandry. Serological detection is the main method used for epidemiological investigations and diagnosis of toxoplasmosis. The key to effective diagnosis of toxoplasmosis is the use of a standardized antigen and a specific and sensitive detection method. Peroxiredoxin is an antigenic protein and vaccine candidate antigen of T. gondii that has not yet been exploited for diagnostic application.

METHODS

In this study, recombinant T. gondii peroxiredoxin protein (rTgPrx) was prepared and used in dot-immunogold-silver staining (Dot-IGSS) to detect IgG antibodies in serum from mice and pregnant women. The rTgPrx-Dot-IGSS method was established and optimized using mouse serum. Furthermore, serum samples from pregnant women were analyzed by rTgPrx-Dot-IGSS.

RESULTS

Forty serum samples from mice infected with T. gondii and twenty negative serum samples were analyzed. The sensitivity and specificity of rTgPrx-Dot-IGSS were 97.5 and 100%, respectively, equivalent to those of a commercial ELISA kit for anti-Toxoplasma IgG antibody. Furthermore, 540 serum samples from pregnant women were screened with a commercial ELISA kit. Eighty-three positive and 60 negative serum samples were analyzed by rTgPrx-Dot-IGSS. The positive rate was 95.18%, comparable to that obtained with the commercial ELISA kit.

CONCLUSIONS

The Dot-IGSS method with rTgPrx as an antigen might be useful for diagnosing T. gondii infection in individuals.

The global seroprevalence of Toxoplasma gondii in deer from 1978 to 2019: A systematic review and meta-analysis

Toxoplasma gondii infecting virtually all warm-blooded animals, including humans, is an intracellular protozoan parasite. The immunocompromised patients or pregnant women infected by Toxoplasma usually can cause encephalitis or abortion. Deer are also the important intermediate host of the parasite and people can be infected by ingesting the undercooked venison. Therefore, to raise the attention of the researchers and T. gondii infection on people in deer, we conducted the meta-analysis. All potential publications on the T. gondii infection in deer were retrieved by searching the PubMed, ScienceDirect, Springer- Link, China National Knowledge Infrastructure (CNKI), WanFang, and VIP Chinese Journal Databases. Finally, a total of 48 publications were included. The pooled seroprevalence of T. gondii infection in deer was 22.92% (95% CI 17.89-28.38) calculated by the random effect model. The seroprevalence of T. gondii infection in deer was the lowest in Asia (12.72%, 95% CI 6.29-20.89), and the highest in North America (32.21%, 95% CI 20.32-45.39). The highest point estimate of deer T. gondii in detection method subgroup was using MAT (31.28%, 95% CI 20.15-43.61). The estimated pooled seroprevalence of T. gondii infection in elk (63.50%, 95% CI 50.01-76.01) was higher than other types of deer. Our meta-regression analysis found that the subgroups including region, sampling year, age, climate, and deer species may be the main heterogeneous source in our meta-analysis. It is necessary to monitor the seroprevalence of T. gondii infection in deer at all times. Furthermore, people should be taken to precautions when ingesting the venison by cooking it well before serving to prevent the T. gondii infection via eating venison.

All about toxoplasmosis in cats: the last decade

Toxoplasma gondii infections are common in humans and animals worldwide. Toxoplasmosis continues to be of public health concern. Cats (domestic and wild felids) are the most important host in the epidemiology of toxoplasmosis because they are the only species that can excrete the environmentally resistant oocysts in feces. Cats can excrete millions of oocysts and a single cat can spread infection to many hosts. The present paper summarizes information on prevalence, persistence of infection, clinical signs, and diagnosis of T. gondii infections in domestic and wild cats for the past decade. Special emphasis is paid to genetic diversity of T. gondii isolates from cats. Review of literature indicates that a unique genotype (ToxoDB genotype #9 or Chinese 1) is widely prevalent in cats in China and it has been epidemiologically linked to outbreaks of clinical toxoplasmosis in pigs and deaths in humans in China; this genotype has rarely been detected in other countries. This review will be of interest to biologists, parasitologists, veterinarians, and public health workers.