Use of an iron superoxide dismutase excreted by Trypanosoma cruzi in the diagnosis of Chagas disease: seroprevalence in rural zones of the state of Queretaro, Mexico.

Four iron superoxide dismutase (SODI, SODII, SODIII, and SODIV) activities with pI values of 6.9, 6.8, 5.25, and 3.8, respectively, were isolated from epimastigote forms of the Maracay strain of Trypanosoma cruzi cultivated at 28 degrees C in Grace's medium supplemented with 10% heat-inactivated fetal bovine serum. The activity of SODe (pI 3.8), which coincides with that of SODIV, was detected in Grace's medium without serum in which T. cruzi epimastigotes were cultivated for 24 hours at 28 degrees C. SODe, which was excreted into the medium by the parasite, was immunogenic and antibodies to SODe were detected in serum to a dilution of 1:2,500 by Western blot. The role of SODe is related to the establishment of the parasite within the host, and its high immunogenicity and specificity make it a useful molecular marker in diagnosing infection with this parasite. To validate a Western blot result using SODe as a antigen fraction, 1,029 sera of individuals from 11 municipalities in the state of Queretaro, Mexico were analyzed. Sampling was done randomly and results were compared with those for the same sera with three conventional serologic methods: an enzyme-linked immunosorbent assay (ELISA), indirect hemagglutination (IHA), and an indirect immunofluorescence assay (IFA) to detect antibodies to T. cruzi SODe. Samples that were positive by these three techniques were also positive by the Western blot method. The seroprevalence values for SODe (8.16% by ELISA and Western blot) in Queretaro were considerably higher than those reported in regions of Mexico considered to be endemic for Chagas disease. These results support the use of SODe in the serodiagnosis of Chagas disease.