Comparison of coproprevalence and seroprevalence to guide decision-making in national soil-transmitted helminthiasis control programs: Ethiopia as a case study

Technical evaluation of the InBios Strongy Detect IgG ELISA assay for the diagnosis of Strongyloides stercoralis infection

BACKGROUND

Strongyloidiasis is a neglected tropical disease (NTD) caused by the soil-transmitted helminth Strongyloides stercoralis, recently included in the 2030 targets of the World Health Organization for the control of STHs. Assessment of infection prevalence is fundamental for decision-making about the implementation of control programs, but diagnostic assays to be applied in such context require evaluation. Seroassays based on recombinant antigens, which could be produced in a standardized and scalable manner, are particularly appealing for use in control programs. In this study, we performed a technical evaluation of the InBios Strongy Detect IgG ELISA, based on recombinant antigens NIE and SsIR, which has shown promising for field use.

METHODS

A total of 46 plasma samples from Ethiopian children were used for this technical evaluation. Repeatability was evaluated on duplicate samples per plate, on four plates per day for 3 days using Bland-Altman plots, analysis of residuals, and variance components analysis. Three samples were selected for evaluation of the uniformity of test results within a single plate (border effect) by two-sided t-test. Correlation between samples and internal ELISA positive controls was analyzed using Spearman's rank correlation coefficient applied on the results of 777 samples analyzed with the assay in a previous field-based study.

RESULTS

Within and between plate residuals ranged from -0.05 to + 0.05 and -0.1 to + 0.1, respectively. Total variance was estimated at 0.327; 99.6% of variation could be attributed to the samples. There was no systematic border effect and a negligible correlation between positive internal control and samples results (R2 = 0.213; p < 0.001).

CONCLUSION

The results obtained in this study, in highly controlled conditions, point toward the InBios Strongy Detect IgG ELISA assay being reproducible, with no systematic border effect. These results encourage further assay's development and evaluation for use in practice, including determination of preset cutoff values for positivity, which is currently not provided.

Serological diagnosis of soil-transmitted helminth (Ascaris, Trichuris and hookworm) infections: A scoping review

BACKGROUND

The World Health Organization emphasizes the importance of integrated monitoring and evaluation in neglected tropical disease (NTD) control programs. Serological assays offer a potential solution for integrated diagnosis of NTDs, particularly for those requiring mass drug administration (MDA) as primary control and elimination strategy. This scoping review aims (i) to provide an overview of assays using serum or plasma to detect infections with soil-transmitted helminths (STHs) in both humans and animals, (ii) to examine the methodologies used in this research field and (iii) to discuss advancements in serological diagnosis of STHs to guide prevention and control programs in veterinary and human medicine.

METHODOLOGY

We conducted a systematic search in the Ovid MEDLINE, Embase and Cochrane Library databases, supplemented by a Google search using predefined keywords to identify commercially available serological assays. Additionally, we performed a patent search through Espacenet.

PRINCIPAL FINDINGS

We identified 85 relevant literature records spanning over 50 years, with a notable increased interest in serological assay development in recent years. Most of the research efforts concentrated on diagnosing Ascaris infections in both humans and pigs, primarily using ELISA and western blot technologies. Almost all records targeted antibodies as analytes, employing proteins and peptides as analyte detection agents. Approximately 60% of sample sets described pertained to human samples. No commercially available tests for Trichuris or hookworms were identified, while for Ascaris, there are at least seven different ELISAs on the market.

CONCLUSIONS

While a substantial number of assays are employed in epidemiological research, the current state of serological diagnosis for guiding STH prevention and control programs is limited. Only two assays designed for pigs are used to inform efficient deworming practices in pig populations. Regarding human diagnosis, none of the existing assays has undergone extensive large-scale validation or integration into routine diagnostics for MDA programs.