Enzyme-linked immunosorbent assay for diagnosis of human strongyloidiasis

Crude antigen (CA) was prepared from Strongyloides stercoralis filariform larvae obtained from in vitro culture of the human feces containing rhabditiform larvae. The lyophilized filariform larvae were ground and ultrasonicated in distilled water then the soluble antigenic preparation was delipidized. The protein content of the crude soluble antigen was 20% of the original dried larvae. The CA was passed through a gel filtration chromatography column and yielded three different protein fractions namely F1, F2 and F3. CA and its fractions were used in the indirect enzyme-linked immunosorbent assay (ELISA) for detecting antibodies to S. stercoralis in serum samples of 5 groups of individuals. These were patients with parasitologically confirmed strongyloidiasis (group 1), patients with mixed S. stercoralis and other parasitic infections (group 2), non-strongyloidiasis patients with other worm infestation(s) (group 3), normal parasite-free Thais (group 4) and normal parasite-free Swedes (group 5). It was found that F2 was the best antigen in the ELISA. The sensitivity, specificity and positive and negative predictive values of the test using F2 as the antigen were 95.0%, 96.4%, 95.0% and 96.4%, respectively.