Immunodiagnosis of dracunculiasis by dot-ELISA

Development of a Multiplex Bead Assay for the Detection of IgG Antibody Responses to Guinea Worm

The success of the Guinea Worm (GW) Eradication Program over the past three decades has been tempered by the persistence of GW disease in a few African nations and the potential for a future resurgence in cases. Domestic dogs are now a major concern as a disease reservoir as large numbers of cases of canine GW disease are now reported each year, mainly along the Chari River in Chad. As a first step toward the development of a serologic assay for dogs, archived human plasma samples from dracunculiasis-positive donors from Togo were used to select adult female GW antigens for peptide sequencing and cloning. Eight protein sequences of interest were expressed as recombinant glutathione-S-transferase (GST) fusion proteins, and the most promising proteins were coupled to carboxylated microspheres for use in multiplex assays. A thioredoxin-like protein (TRXL1) and a domain of unknown function (DUF148) were assessed for total IgG and IgG4 reactivities using a panel of specimens from GW cases, uninfected donors, and individuals infected with various nematode worms, including Onchocerca volvulus. Both the DUF148-GST and the TRXL1-GST assays cross-reacted with O. volvulus sera, but the latter assay was always the more specific. The IgG4 and total IgG TRXL1-GST assays both had sensitivities > 87% and specificities > 90%. Maximum specificity (> 96%) was obtained with the total IgG assay when reactivity to both antigens was used to define a positive case. Given the good performance of the human assay, we are now working to modify the assay for dog assessments.

Studies on immunodiagnosis of dracunculiasis. I. Detection of specific serum antibodies

To explore the possibility for development of an immunodiagnostic test for Dracunculus medinensis infections, the antibody responses (IgG1, IgG2, IgG3, IgG4 and IgE) to antigen preparations made from adult female worms (ADGW) and first stage larvae (LVGW) of D. medinensis were analysed. By sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE)/Western blotting, sera from individuals with patent D. medinensis infection reacted extensively and similarly with ADGW and LVGW over a broad molecular weight range (5-200 kDa). Sera from individuals infected with Onchocerca volvulus (the major cross-reacting infection) had a more pronounced reaction with ADGW than LVGW, and only with antigens of molecular weights above 23 kDa. These findings were used to design an enzyme-linked immunosorbent assay (ELISA) with high sensitivity and specificity for D. medinensis infection. The most promising results were obtained when detecting for specific IgG4. Thus, when using LVGW, the assay had a sensitivity of 83% and a specificity of 97%. Refining the antigen into a low molecular weight filtrate improved the sensitivity to 92%, and the sensitivity was further improved (to 96%) when combining the results from two or more antibody types measured simultaneously, without affecting the specificity. The results were encouraging for the prospects for developing an applicable immunodiagnostic test for patent D. medinensis infections based on detection of specific serum antibodies.