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Serological speciation of human schistosome infections by ELISA with a panel of three antigens

¹ The Hospital for Tropical Diseases, Capper Street, London WC1E 6AU, UK
² School of Biological Sciences, University of Wales, Deiniol Road, Bangor, Gwynedd LL57 2UW, Wales, UK

Correspondence to:
Dr P Turner
Department of Clinical Microbiology, University College London Hospital, 3rd Floor A&E Building, Grafton Way, London WC1E 6DB; pturner{at}doctors.org.uk Aims: To find out whether serology can reliably speciate human schistosomiasis using a simple enzyme linked immunosorbent assay (ELISA) technique.

Methods: Stored sera from 66 patients with microscopically confirmed schistosomiasis were subjected to ELISA using a panel of three antigens, namely: unfractionated Schistosoma mansoni soluble egg antigen (SEA); CEF6, a cationic fraction of SEA; and crude S margrebowiei egg antigen, prepared from an animal schistosome closely related to S haematobium.

Results: The optical densities (ODs) obtained using CEF6 as antigen were significantly higher in sera from S mansoni infected patients than in sera from S haematobium infected patients (median OD, 0.810 v 0.595). Using S margrebowiei egg antigen, the optical densities were significantly higher in S haematobium sera than in S mansoni sera (median OD, 0.794 v 0.544). There was no significant difference in optical densities between S mansoni and S haematobium sera using SEA (median OD, 0.725 v 0.737). The ratio of ODs (CEF6 to S margrebowiei egg antigen) was calculated: a ratio of >1 indicated S mansoni infection (sensitivity, 88%) and a ratio of <1 indicated S haematobium infection (sensitivity, 84%). The odds ratio for S haematobium having an OD ratio of <1 was 36.8 (95% confidence interval, 7.0 to 194).

Conclusions: The identity of the infecting species of schistosome can be determined using the panel of antigens described. SEA should be used to screen serum samples, and the CEF6 : S margrebowiei egg antigen ELISA optical density ratio can be used where serological speciation is required.

Abbreviations: ELISA, enzyme linked immunosorbent assay; FAST, falcon assay screening test; HTD, Hospital for Tropical Diseases London; OD, optical density; SEA, Schistosoma mansoni soluble egg antigen

Keywords: schistosomiasis; serodiagnosis; enzyme linked immunosorbent assay