Comparative serology techniques for the diagnosis of Trypanosoma cruzi infection in a rural population from the state of Querétaro, Mexico

Abstract

Immunological diagnostic methods for Trypanosoma cruzi depend specifically on the presence of antibodies and parasitological methods lack sensitivity during the chronic and “indeterminate” stages of the disease. This study performed a serological survey of 1,033 subjects from 52 rural communities in 12 of the 18 municipalities in the state of Querétaro, Mexico. We detected anti-T. cruzi antibodies using the following tests: indirect haemagglutination assay (IHA), indirect immunofluorescence assay (IFA), ELISA and recombinant ELISA (rELISA). We also performed Western blot (WB) analysis using iron superoxide dismutase (FeSOD), a detoxifying enzyme excreted by the parasite, as the antigen. Positive test results were distributed as follows: ELISA 8%, rELISA 6.2%, IFA and IHA 5.4% in both cases and FeSOD 8%. A comparative study of the five tests was undertaken. Sensitivity levels, specificity, positive and negative predictive values, concordance percentage and kappa index were considered. Living with animals, trips to other communities, gender, age, type of housing and symptomatology at the time of the survey were statistically analysed using SPSS software v.11.5. Detection of the FeSOD enzyme that was secreted by the parasite and used as an antigenic fraction in WBs showed a 100% correlation with traditional ELISA tests.

How effective are rapid diagnostic tests for Chagas disease?

“…Given the ample genetic and antigenic diversity of T. cruzi, the predominant strains that circulate in the distinct regions will surely have an impact in the performance of RDTs, and of diagnostics in general. For instance, this would be the explanation to the poor performance of several serological diagnostics in Mexico [25][26][27]. Similarly, results reported by Verani and co-workers on the distinct performance of Chagas Stat Pak and Chagas Detect Plus in Bolivia and Peru could also be due to differences in the antigenic profiles of prevalent strains in each studied site [24].…”

Concordancia entre una prueba in-house de inmunofluorescencia indirecta y un test comercial de hemoaglutinación indirecta para la detección de anticuerpos anti-Trypanosoma cruzi

“…El diagnóstico de la enfermedad de Chagas, en la mayoría de los casos, es realizado en fase crónica de la patología. Las pruebas serológicas que se basan en la detección de anticuerpos anti-T. cruzi son los métodos de elección y el empleo de dos o más pruebas inmunoserológicas que utilicen antígenos diferentes para el diagnóstico en esta etapa de la enfermedad es frecuente (14,15) . La OMS y la OPS recomiendan emplear la combinación de dos técnicas serológicas, y una tercera en caso de resultados discordantes para dar un diagnóstico de la enfermedad (10) .…”