Evaluation of three immunodiagnostic procedures for porcine strongyloidiasis

An indirect fluorescent antibody test (IFAT), an indirect radioimmune antibody test (IRAT), and an enzyme-linked immunosorbent antibody assay (ELISA) were compared for their efficacies in detecting antibody to Strongyloides ransomi in pigs. The greatest sensitivity was exhibited by the ELISA, using a soluble, whole larval extract. The 2 indirect antibody assays, IFAT and IRAT, using intact 3rd-stage larvae (L3) were comparable in sensitivities. The use of live L3 in the IFAT and IRAT presented technical problems, because the larvae shed antibody complexes at ambient room temperature. This could be inhibited by the addition of 20 mM of sodium azide to all working solutions or by doing the tests at 4 C. Fixation of the L3 by either formalin or heat also eliminated the shedding problem. The specificities of the ELISA and IFAT were supported by the negative results obtained with serum from pigs infected with Ascaris suum, Stephanurus dentatus, and Trichinella spiralis.