Strongy Detect: Preliminary Validation of a Prototype Recombinant Ss-NIE/Ss-IR Based ELISA to Detect Strongyloides stercoralis Infection

Abstract

Background Strongyloides stercoralis (Ss) is the etiological agent of strongyloidiasis, a neglected tropical disease of global concern. Laboratory diagnosis of strongyloidiasis is most often based on detection of antibodies against antigens in an enzyme linked immunosorbent assay (ELISA). Herein, we report a preliminary validation study of newly developed IgG4- and/or IgG- based ELISAs to detect strongyloidiasis (Strongy Detect, InBios) incorporating a cocktail of 2 previously described recombinant antigens, Ss-NIE and Ss-IR. Methods The sensitivity and specificity were determined by using the assay in 150 cryopreserved serum samples from humans known to be Ss infected (n = 74), helminth uninfected (n = 47), or infected with a helminth other than Ss [n = 29). The treatment associated dynamics of antibody detection were then assessed using 35 paired samples obtained before and after definitive therapy. Results The IgG and IgG4 assays were 99% and 96% sensitive, respectively, and 99% and 100% specific, respectively. Neither the IgG or IgG4 assay showed cross reactions with sera from those infected with other helminths. Although ELISA values did decline post-treatment few returned to levels below the cutoff for infection. Conclusion Strongy Detect is the most sensitive and specific commercialized immunoassay for detection of strongyloidiasis. The assay remains positive for greater than a year post-treatment. Author summary Strongyloides stercoralis is a worm that infects people and some animals. It can live in its host for decades because it can continually produce more larvae that develop inside the body of its host. The initial infection usually occurs by larvae burrowing through the skin of a person. The growing larvae travel to the lungs where they are coughed up and swallowed. Then, in the intestine, they mature to adults capable of producing eggs. The eggs hatch before they can be passed out of the body in the stool. The newly hatched larvae burrow through the gut wall and repeat this internal cycle. To diagnose this infection, one strategy is detecting antibodies against these worms. Herein, we discuss a prototype ELISA assay using recombinant Strongyloides stercoralis proteins. The test, called Strongy Detect, did well at detecting antibodies in patients known to have the infection and at calling samples negative when the patients were uninfected. The antibodies were detectable more than a year after patients were treated for the disease. If further validation studies confirm the utility of this assay, it will be an important addition to the armamentarium of tests to diagnose Strongyloides stercoralis infection.