Dot enzyme-linked immunosorbent assay (Dot-ELISA): a micro technique for the rapid diagnosis of visceral leishmaniasis.

A micro enzyme-linked immunosorbent assay utilizing antigen dotted onto nitrocellulose filter discs (Dot-ELISA) was developed for the rapid diagnosis of visceral leishmaniasis. Leishmania donovani promastigotes applied to filter discs in volumes of 1 microliter were placed in 96-well microtiter plates, blocked with bovine serum albumin, then incubated with 4-fold dilutions of patient sera. After incubation with peroxidase-conjugated anti-human antibody, washing and addition of precipitable substrate, positive reactions appeared as blue dots on a white background which were easily read by eye. The procedure is performed at room temperature, takes about 2 h and is economical. At a reciprocal diagnostic titer of greater than or equal to 32, 41 of 42 (98%) leishmaniasis patients were positive, and positive titers ranged from 512 to 524,288. Control sera from healthy individuals showed 1 of 50 (2%) false positive reactions. Sera from patients with African trypanosomiasis, Chagas' disease, and lupus erythematosus were cross-reactive in the Dot-ELISA. No cross-reactivity was noted with sera from patients with amebiasis, coccidioidomycosis, cutaneous leishmaniasis, viral hepatitis, hydatidosis, malaria, schistosomiasis, syphilis, toxoplasmosis or trichinosis. In replicate experiments, 90% of 167 sera tested did not vary in titer. This rapid and inexpensive test should prove to be an important field diagnostic technique for visceral leishmaniasis.