Evaluation of Toxoplasma gondii soluble, whole and excretory/secretary antigens for diagnosis of toxoplasmosis by ELISA test

Detection of Toxoplasma gondii Infections using Virus-Like Particles Displaying T. gondii ROP4 Antigen

Toxoplasma gondii ME49 infections are typically diagnosed by serological tests. However, serological diagnosis of RH strain-induced toxoplasmosis remains unknown. In order to develop seradiagnosis of above 2 kinds of infections, we generated recombinant virus-like particles (VLPs) displaying the T. gondii rhoptry protein 4 (ROP4) and evaluated their potential in T. gondii ME49 or RH strain infection diagnostics. Mice were orally infected with either the tachyzoites of T. gondii (RH) or cysts of T. gondii (ME49) at various dosages, and sera were collected at regular intervals. ELISA-based serological tests were performed to assess IgG, IgM, and IgA antibody responses against ROP4 VLP antigen and tissue lysate antigen (TLA). Compared to TLA, IgG, IgM, and IgA levels to ROP4 VLP antigen were significantly higher in the sera of T. gondii RH-infected mice 1 and 2 week post-infection (PI). T. gondii-specific IgG antibody was detected at 1, 2, 4, and 8 week PI in the T. gondii ME49-infected mice with infection dose-dependent manner. These results indicated that the ROP4 VLP antigen was highly sensitive antigens detecting T. gondii RH and ME49 antibodies at an early stage.

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.

Toxoplasma gondii ADSL Knockout Provides Excellent Immune Protection against a Variety of Strains

Toxoplasma gondii is a protozoan parasite, occurring worldwide, endangers human health and causes enormous economic losses to the Ministry of Agriculture. A safe and effective vaccination is needed to handle these problems. In addition, ideal vaccine production is a challenge in the future. In this study, we knocked out the adenylosuccinate lyase (ADSL) gene and found that the gene reduces the growth rate of T. gondii tachyzoites in vitro under standard growth conditions by plaque or replication experiments. Furthermore, mice that were immunized with tachyzoites of the ME49ΔADSL strain induced 100% protection efficacy against challenge with the type 1 strain RH, type 2 strain ME49 and type 3 strain VEG. All mice that were immunized with ME49ΔADSL had a survival rate of 100% when they were reinfected with wild-type strains, either 30 days or 70 days after immunization, and immunization was also protective against homologous infection with 50 T. gondii ME49 tissue cysts. In addition, the level of Toxoplasma-specific IgG was significantly elevated at 30 and 70 days after immunization. ME49ΔADSL induced high levels of Th1 cytokines (interferon gamma (IFN-γ), interleukin (IL)-12) at 4 weeks after immunization and spleen cell cultures from mice vaccinated for 150 days were able to produce robust INF-γ and IL-12 levels in the supernatant. The results of the present study showed that ΔADSL vaccination induced a T. gondii-specific cellular immune response against further infections. These results suggest that the ADSL-deficient vaccine can induce anti-Toxoplasma gondii humoral and cellular immune responses and has 100% immune protection against post-challenge by the type 1 strain RH, type 2 strain ME49 and type 3 strain VEG. It will be used as an excellent candidate for live vaccines and may contribute in a positive meaning to control human toxoplasmosis.

Evaluation of Toxoplasma gondii propagated in specific pathogen free embryonated chicken egg, for diagnosis of toxoplasmosis in equids and human

Toxoplasma gondii (T. gondii) is a worldwide distribution infects a wide variety of mammals, including humans. The present study aimed to detect the efficacy of soluble and whole T. gondii antigens propagated in specific pathogen-free of embryonated chicken egg (SPF-ECE) used to improve the potency of serological assays for diagnosis of toxoplasmosis in equids and human. Total of 220 serum samples from 170 equids (90 donkeys and 55 horses and 25 mules) and 50 humans were collected from different governorates in Egypt during the period from October 2017 to March 2018. Crude T. gondii tachyzoites antigens from low or high passages propagated in mice or SPF-ECE was used for modifying some serological tests. The experiment showed that the mortality rate of T. gondii for 10³ and 10⁴ low passages were 6/8 (75%) and 7/8 (88%) dead embryos but, lower mortality rate in high passage T. gondii were 4/8 (50%) and 5/8 (63%) dead embryos, respectively. No mortality or inflammatory signs were observed in control of negative groups. In equids sera were examined by S-ELISA using soluble T. gondii antigen propagated in SPF-ECE showed the highest positive results 26 (28.8%), followed by LAT 37 (22%) and MAGPT 36 (21.17%). While, W-ELISA and IFAT used whole T. gondii antigen prepared in SPF-ECE were 35 (20.58%) and 28 (19.41%) showed highly positive results than the same test used the whole antigen prepared in mice. The highest seroprevalence of T. gondii in human and donkeys were 19/50 (38%). and 26/90 (28.88%), more than mules were 6/25 (24%) and horses were 9/55 (16.3%) examined by S-ELISA respectively. SPF-ECE is considered an appropriate experimental model for isolation and propagation of T. gondii tachyzoites, and their soluble antigens used in serological tests (S-ELISA, LAT, and MAGPT) have sensitivity and specificity more than the whole antigen and provided reliable diagnostic tools for detection of toxoplasmosis in human and equids.

New prevalence surveillance of Toxoplasma gondii among rodents and stray cats by ELISA avidity and nested PCR methods, Northeast of Iran

Rodents and stray cats are the sources of many parasitic infections including T. gondii, for other animals and human. Toxoplasmosis has a wide range of laboratory factors in its intermediate and definite hosts. Regarding the importance of rodents and stray cats as the hosts that spread the Toxoplasma gondii, it is necessary to obtain comprehensive information about these animals in the life cycle of T. gondii. The objective was to investigate the new prevalence of toxoplasmosis among target animals in Iran, using GRA6 gene in combinacion with ELISA avidity. In this study, 286 rodents and 210 stray cats were collected and their heart tissues extracted to obtain DNA, blood samples and IgG Ab of T.gondii parasite. We detected the positive tissue samples in our study by the nested-PCR method. Then, we examined T. gondii IgG ELISA avidity for assessment of toxoplasmosis among rodents and stray cats. This study, was conducted in January to March 2017, based on the prevalence study. The findings revealed that 246/286 (86.01%) of rodents and 180/210 (85.71%) of stray cats were positive by IgG ELISA avidity methods. moreover, 68 rodents samples and 38 stray cats samples were positive concerning the GRA6 Toxoplasma gene; and these positive samples were at intermediate levels for IgG avidity. We concluded that the new prevalence of toxoplasmosis among rodents and stray cats was at high levels, using the serologic method in Northeast of Iran and the results of quantitative ELISA avidity were as the same as those of the nested-PCR for detecting recent toxoplasmosis in these hosts.

Validity of a new immunochromatographic test in detection of Toxoplasma gondii in cancer patients

Screening of toxoplasmosis in cancer patients is mandatory especially before starting treatment to guard against life-threatening disseminated disease. Diagnosis of toxoplasmosis rely mainly on serology. The most widely used method for detection of anti-Toxoplasma gondii (T. gondii) antibodies is the enzyme linked immunosorbent assay (ELISA), being available and reliable. Immunochromatographic tests (ICT) attracted a lot of attention recently being one of the high quality, rapid and easy to perform tests. Available data comparing the performance of ICT versus ELISA techniques have yielded inconsistent results and none compared their performance among the immunocompromised cancer patients. Therefore, we designed this study to compare the performance of a new ICT (the OnSite Toxo IgG/IgM Combo Rapid test) and ELISA techniques for the detection of anti-T. gondii antibody as a tool for screening for toxoplasmosis among cancer patients in Cairo-Egypt. Among 180 cancer patients, a total of 110 patients (61.1%) were positive for anti-T. gondii antibodies by one or both methods. Agreement between both methods was found in 78.8% of the samples. By using ELISA technique as a gold standard test for the detection of anti-T. gondii antibodies, our results showed 87.5% specificity and 74% sensitivity of ICT technique. Moreover, our results proved that ICT is more sensitive in detecting lower level of antibodies than ELISA, that makes it preferable as a screening test for the immunocompromised patients.