Four monoclonal antibodies (MAb) to Echinococcus granulosus Antigen 5 (Ag5) and Antigen B (AgB) were assessed in an enzyme-linked immunosorbent assay (ELISA) for detection of circulating antigens (CAg) in sera of human patients with E. granulosus infection. Around 5·5–8% of 200 sera from 42 surgically proven hydatid patients contained detectable CAg by individual MAb. The combined detection rate for CAg, using four MAb, was 19% (38/200). Although hydatid CAg was detected by MAb in at least one serum sample from 21 of 42 patients, some patients remained negative in the assay regardless of the time when serum samples were taken (pre- or post-operatively), or of the continuing presence of hydatid cysts, their location or fertility. In addition, it was observed that the binding capacity of MAb for sheep hydatid cyst fluid antigen (SHCF) was somewhat reduced in the presence of normal human serum. The CAg detection assay would only be useful for assessment of hydatid infection status in patients with detectable CAg in serum samples.

An antibody competition enzyme-linked immunosorbent assay (ELISA) using 4 different monoclonal antibodies (MAb) raised against major antigens (Antigen 5 and Antigen B) of Echinococcus granulosus was evaluated for the diagnosis of human hydatidosis. The competition assay, using anti-Ag5 MAb 24.14, detected specific antibodies in 70% (131/188) of sera from patients with surgically confirmed E. granulosus infection and 38·5% (10/26) of sera from patients with E. multilocularis infection. None of the sera from patients with Taenia solium cysticercosis (10), T. saginata (2), filariasis (22), strongyloidiasis (19), fascioliasis (4), bilharziasis (4) and amoebiasis (2) tested were positive using a cut-off point established through reaction between MAb 24.14 and normal human sera. The combined use of the MAb 24.14-based competition ELISA with the conventional antibody-binding assay provides a highly sensitive (92·8%) and specific screening system for human hydatid disease diagnosis.

Murine monoclonal and polyclonal antisera, raised against the 38 kDa subunit of Echinococcus granulosus antigen 5, were used to investigate the tissue distribution of the antigen in hydatid cysts. Immunoreactivity was visualized by indirect immunofluorescence on whole protoscoleces, and ultrastructural immunocytochemistry utilizing colloidal gold-based labelling procedures on unsectioned and cryosectioned brood capsules and protoscoleces. In protoscoleces, the 38 kDa subunit of antigen 5 was localized at the interface of parenchymal cells and associated extracellular matrices, as well as along the interface of the tegumentary syncytium in the somal region and its basal matrix. Cytoplasmic labelling of parenchymal cells was rare; when observed, it was associated with vesicles and membranes in cytoplasmic extensions of parenchymal cells. In brood capsules, the antigen was associated with the external face of the plasma of degenerating parenchymal cells. The 38 kDa subunit occurs along the extracellular face of cell membranes, suggesting that antigen 5 is either a component of the membranes or associated extracellular matrices.