Performance Assessment of ELISA Using the Trypanosoma cruzi-Specific Antigen Tc323 for the Diagnosis of Chronic Chagas Disease.

In the chronic phase of Chagas disease (CCD), diagnosis relies on detecting specific IgG antibodies due to the low or absent presence of the parasiteTrypanosoma cruzi in human blood. However, the performance of current serological tests is highly variable, lacking a "gold standard" assay with 100% sensitivity and specificity, which challenges the exploration of new biomarkers. In the present study, we evaluated the diagnostic accuracy of an optimized ELISA using the predicted immunogenic domains (called TcD3 and TcD6) of Tc323, a protein highly conserved among T. cruzi strains but absent in other clinically significant parasites such as Leishmania spp. This study was conducted using plasma or serum samples from CCD individuals with different clinical manifestations and living in endemic regions in Latin America, subjects with unrelated infectious diseases, and noninfected donors. The sensitivity and specificity of recombinant TcD3 were 90.8% and 92.6%, respectively, while rTcD6 displayed values of 93.1% and 93.6% for the same parameters. Area under curve (AUC) values were 0.949 for rTcD3 and 0.954 for rTcD6. The receiver operative characteristic (ROC) curve showed a highly significant difference between CCD individuals and noninfected donors. Cross-reactivity was 10.2% for rTcD3 and 8.2% for rTcD6 in subjects infected with leishmaniasis or with toxoplasmosis. In addition, the reactivity against rTcD3 differed among some geographical areas while no significant difference was found using both domains for the detection of T. cruzi-infected individuals with or without cardiac symptoms. Our findings show that the recombinant antigens rTcD3 and rTcD6 could be used as highly potential biomarkers for the serological diagnosis of CCD.