Serological diagnosis of visceral leishmaniasis by a dot-enzyme immunoassay for the detection of a Leishmania donovani-related circulating antigen

Field medicine in tropical areas needs laboratory assays which are inexpensive and easy to perform. To meet this need a semi-quantitative dot-enzyme immunoassay (EIA) was developed for the detection of an L. donovani-related circulating antigen and tested for clinical relevance in the diagnosis of visceral leishmaniasis (VL). The dot-EIA probes serum spotted on nitrocellulose for the presence of the antigen using a monoclonal antibody raised against L. donovani promastigotes, a peroxidase-conjugated rabbit anti-mouse immunoglobulin antiserum and chloronaphthol as peroxidase substrate. The intensity of dot staining by chloronaphthol is read by eye and scored. The dot-EIA was used to test the following groups: 69 patients with VL from Brazil, Kenya, China and France, nine patients with cutaneous leishmaniasis, 38 patients with tropical diseases other than VL, five patients with rheumatoid arthritis and 40 health blood donors. The specificity of the assay was 96.7% (3/92 false positive) and the sensitivity 98.5% (1/69 false negative). A quantitative EIA for the detection of serum antibodies which makes use of a crude, soluble L. infantum promastigote extract as capture antigen and which was used as the reference method, proved to be more specific (98.9%) but similarly sensitive (98.5%). It should be possible to produce a kit, suitable for large scale application at low cost in order to facilitate routine use of the dot-EIA in the diagnosis of VL.