ELISA-based coproantigen in human strongyloidiaisis: a diagnostic method correlating with worm burden.

In order to overcome the false negative diagnosis of strongyloidiasis in the absence of rhabditiform larvae in stools, an ELISA-based Strongyloides stercoralis-specific coproantigen detection assay in stools of infected patients was evaluated. In a sandwich ELISA, a rabbit hyperimmune serum against S. stercoralis ES (excretory/secretory) adult antigen succeeded in capturing S. stercoralis coproantigen from infected patients and did not react with coproantigens prepared from the stool samples of patients infected with Schistosoma mansoni, Fasciola gigantica and Capillaria philippenensis. Coproantigen was able to detect anti-S. stercoralis IgG antibodies in sera of infected patients at the same OD level as produced with S. stercoralis E/S worm antigen using an indirect ELISA did not cross-react with sera from patients with S. mansoni, F. gigantica and C. philippenensis. S. stercoralis coproantigen detection proved a sensitive, simple, reliable and inexpensive ELISA-based, and an alternative to coproscopical methods in copropositive (with larvae in stool) and copronegative (without larvae in stool) stool samples. Fecal ELISA showed a positive relationship between copro-Ag and worm burdens, and considered a starting point for the development of species-specific copro-immunological diagnostic assays using monoclonal antibodies and dipstick technology.