Use of dried blood spots to define antibody response to the Strongyloides stercoralis recombinant antigen NIE

Abstract

An approach to improve the diagnosis of Strongyloides stercoralis infection is the use of serologic assays utilising the NIE antigen from S. stercoralis, with good diagnostic sensitivity and excellent specificity reported. Detection of antibody eluted from dried blood spots (DBS) has shown utility in large-scale seroepidemiological studies for a range of conditions and is appealing for use with children where sample collection is difficult. We adapted an existing NIE-enzyme linked immunosorbent assay (ELISA) for the testing of strongyloides antibody response on DBS, and evaluated it in a population screening and mass drug administration programme (MDA) for strongyloidiasis conducted in an Australian indigenous community. Study participants were treated with 200 μg/kg ivermectin (>15 kg) or 3× 400 mg albendazole (<15kg). The sensitivity of the NIE DBS-ELISA was determined by receiver operator characteristic (ROC) analysis to be 85.7%. A total of 214 DBS were collected from 184 participants across two screening and MDA encounters. A total of 27 of 164 participants (16.5%) tested positive for S. stercoralis NIE-DBS prior to MDA treatment, and 6 of 50 participants (12.0%) tested positive after treatment. These prevalence values are similar to those documented by standard serology in the same community. For 30 participants where a DBS was collected at both MDA 1 and 2, a significant decline in ELISA values was evident post treatment (0.12-0.02, p=0.0012). These results are in agreement with previous studies documenting the high seroprevalence of S. stercoralis in remote Australian Indigenous communities, and suggest that collection of dried blood spots may be a useful approach for field diagnosis of S. stercoralis seroprevalence.

Keywords: Helminth infection; Indigenous health; Serological diagnosis; Strongyloides stercoralis.

Fig. 1

Determination of optimal dried blood spot (DBS) dilutions (A) and storage conditions (B) for NIE DBS-ELISA. (A) Spiked pooled positive and negative control blood spots were prepared and eluted in PBS-T, and different dilutions tested in NIE antigen ELISA. (B) Control blood spots were stored under different conditions for 1, 3 and 7 days. At the conclusion of the storage period all dried blood spots were stored at 4 °C, with elutions and ELISAs of all spots performed in a single assay. Each experiment/storage condition/dilution was repeated twice, and ELISAs were done in triplicate. RT = room temperature. For reference the 0.21 cut-off line is indicated.

Fig. 2

ROC curve for S. stercoralis NIE-DBS ELISA. The cut-off, sensitivity and specificity indicated were determined using ROC analysis using positive (n = 13) and negative controls (n = 18). AUC = area under curve, ± standard error.

Fig. 3

Change in ELISA values in participants (n = 30) where a dried blood spot was collected at both MDA 1 & 2. p = 0.0012 (Wilcoxon matched pairs signed rank test).