Valor diagnostico de la inmunofluorescencia indirecta con anti-IgM para Enfermedad de Chagas, en adultos y recién nacidos

Abstract

Myriam Lorca y Erica ThiermannDiagnostic value of the IgM Immunofluorescence test for chagas' disease in infants andadults.The IFAT-IgM with Trypanosoma cruzi antigen was applied in a double blind study of 242 serum samplespreviously examined by the IFAT-IgG for Chagas' disease. The sensitivity of the test was enhanced by prolongedincubation at 4°C. The specificity of the IgM reaction in normal sera, was checked repeting the test in alliquots,absorbed with IgG. The results were tabulated according to the origin of the samples and the presence, orabsence, of IgG antibodies for Chagas' disease. 84 of die samples belonged to infants and 158 to adults,131 hadIgG antibodies against T. cruzi and the remaining 111 served as negative controls in both groups.In was demonstrated that a high proportion of positive IgM-results obtained in normal sera, of infants (15,5%)and adults (28,5%), were due to otfier factors: Elimination of nonspecific IgM antibodies, by absorbtion, reducedthe reactions of IgM, at liters of 1/10 and 1/20, to three samples in the infant's group. However, in the sera of adults,positive IgM results remained after absorbtion, at titers up to 1/20, in the infected individuals as well as incontrols. Only one serum gaveatiterof 1/40, suggesting specificity.The three samples of the infant's group, in which IgM antibodies to T. cruzi were demonstrated, belonged to achild with Chagas' disease demonstrated by xeno-diagnosis. The specimen oi the adult in which a positiveIFAT-IgM-Chagas was obtained at a titer of 1/40, corresponded to a women with recently acquired infection, asjugdedbyaseroconversion(from(-)to( + ) 1/40) in the IFAT-IgG for Chagas' disease.The results indicate that the test yields specific results, if it is applied in sera previously absorbed with IgG andconfirm that low titers are of diagnostic value in sera of infants. However, in sera of adults, only titers from 1/40onward are considered to be specific for Chagas's disease.