Reatividade de anticorpos a frações antigênicas de Strongyloides venezuelensis no diagnóstico diferencial da estrongiloidíase humana

Abstract

Strongyloides stercoralis, a human intestinal nematode, causes one of the most common worldwide parasitic infections. Early detection prevines the development of disseminated and hyperinfection syndromes. In search for immune response markers for strongyloidiasis, antigenic properties of glycosylated components from Strongyloides and IgG avidity performance were tested in immunoassays. Considering sugar-binding capacity of lectins, as concanavalin-A (Con-A) and immunodiagnosis importance we tested total saline extract of Strongyloides venezuelensis filariform larvae (SE) and its fractions obtained in Con-A column: Con-A unbound (Con-A UF) and Con-A bound (Con-A BF) in immunoglobulin detection (IgG and IgA). IgG avidity determination was investigated to detect patients with strongyloidiasis and characterize sources of disagreement between serology and coproparasitology. Sensitivity (Se), specificity (Sp), area under curve (AUC), likelihood ratio (LR), and correlation coefficients were calculated, statistical analyzes were performed by Mann Whitney and Fisher exact test. Con-A UF showed the highest diagnostic parameters for IgG detection (Se 95.0%, Sp 92.5%, AUC 0.99, LR 12.7) and high correlation (r = 0.700) with SE. Con-A fractions did not clearly demonstrate usefulness for IgA detection. Avidity index (AI) was calculated to each serum considering: (a) screening AI (serum 1:160) and (b) mean of AI at different dilutions. To differentiate groups at screening and mean AI a value of 75% was established (p < 0.001). Avidity immunoblot was auxiliary for ELISA data analysis of discrepant cases and served as a complementary tool for identifying antigens responsible for affinity maturation. In conclusion, the results obtained demonstrate that Con-A UF is an important source of specific peptides efficient to detect IgG in strongyloidiasis immunodiagnosis and IgG avidity assay may distinguish active infection with Strongyloides stercoralis larvae output from suspect or false positive cases.