No abstract

IgG avidity assays have been developed for several parasitic diseases although there are no researches focused in strongyloidiasis diagnosis. Definitive diagnosis of strongyloidiasis is based on the presence of Strongyloides larvae in stool, but majority of cases involve low and irregular larval output. While limitations of serological assays for strongyloidiasis are well known, characteristics of persons who are misdiagnosed based on negative coproparasitological tests have been little explored. The aim of the present study was to evaluate the use of IgG avidity to detect patients with active strongyloidiasis and to characterize sources of disagreement between serology and coproparasitology. A total of 80 serum samples was analyzed, 40 from patients with Strongyloides larvae in stool (G1) and 40 from individuals with negative coproparasitology, but positive serology (G2). Serum samples were analyzed in an indirect IgG avidity ELISA using urea 6M in serial double dilutions from 1:80 to 1:2560. Avidity index (AI) was calculated to each serum dilution and analyzed as screening AI (serum dilution of 1:160) or mean AI of different serum dilutions that had a positive result. Statistical analyzes were performed by Mann-Whitney's (U) and Fisher's exact tests. At screening dilution, median of AI was 68% in G1 and 88% in G2 (P<0.0001), whereas median of mean AI in G1 was 72% and in G2 94% (P<0.0001), but there was no significant differences between both AI in each patient group. A cut off value established at AI of 75% demonstrated a significant difference between groups, with G1 sera showing AI<75% and G2 sera with AI>75% (P<0.0001). In conclusion, IgG avidity assays may distinguish active infection with Strongyloides stercoralis from suspect or serologically false positive cases.

The aim of this study was to detect levels of IgG and IgA by enzyme-linked immunosorbent assay (ELISA) using alkaline extracts of larvae, adult female worms, and eggs of Strongyloides venezuelensis as antigen. One hundred twenty serum samples divided into 3 groups were analysed: group I (40 strongyloidiasis patients), group II (40 patients with other parasitic infections), and group III (40 healthy subjects). Statistical variations were analyzed using analysis of variance. There was a significant statistical difference (P < 0.001) in the detection of antibodies in group I between larvae and female antigens and between larvae and egg antigens, with higher positivity using larvae antigen. The larvae antigen showed the highest values for sensitivity, specificity, and diagnostic efficiency in ELISA. This study is the first that examines the use of adult female worm and egg antigens to detect antibodies for human strongyloidiasis diagnosis compared with the larval extract. By comparing all 3 extracts, larval antigens demonstrated better diagnostic parameters.

Glycosylated components from Strongyloides have an important role in parasite establishment and host recognition of these substances. Considering the sugar-binding capacity of lectins, such as concanavalin-A (Con-A), IgG and IgA detection in serum samples from strongyloidiasis patients was tested using different antigenic preparations. The total saline extract (SE) of Strongyloides venezuelensis filariform larvae was fractionated in Con-A column to obtain Con-A unbound (Con-A UF) and Con-A bound (Con-A BF) fractions. Sensitivity (Se), specificity (Sp), area under the ROC curve (AUC), likelihood ratio (LR), and correlation coefficients were calculated. 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 any usefulness for IgA detection. In conclusion, the results obtained demonstrate that Con-A UF is an important source of specific peptides efficient to detect IgG in strongyloidiasis immunodiagnosis.

BackgroundStrongyloidiasis, a human intestinal infection caused by the nematode Strongyloides stercoralis, is frequently underdiagnosed and although its high prevalence is still a neglected parasitic disease because conventional diagnostic tests based on parasitological examination (presence of Strongyloides larvae in stool) are not sufficiently sensitive due to the low parasitic load and to the irregular larval output. There is an urgent need to improve diagnostic assays, especially for immunocompromised patients with high parasitic load as consequence of self-infection cycle, which can disseminate throughout the body, resulting in a potentially fatal hyperinfection syndrome often accompanied by sepsis or meningitis.Methods/Principal FindingsWe have performed Phage Display technology to select peptides that mimic S. stercoralis antigens, capable of detecting a humoral response in patients with strongyloidiasis. The peptides reactivity was investigated by Phage-ELISA through different panels of serum samples. We have successfully selected five peptides with significant immunoreactivity to circulating IgG from patients' sera with strongyloidiasis. The phage displayed peptides C9 and C10 presented the highest diagnostic potential (AUC>0.87) with excellent sensitivity (>85%) and good specificity (>77.5%), suggesting that some S. stercoralis antigens trigger systemic immune response.Conclusions/SignificanceThese novel antigens are interesting serum biomarkers for routine strongyloidiasis screenings due to the easy production and simple assay using Phage-ELISA. Such markers may also present a promising application for therapeutic monitoring.