Use of a newly developed beta-mercaptoethanol enzyme-linked immunosorbent assay to diagnose visceral leishmaniasis in patients in eastern Sudan.

Corroboration of serology results is essential for restricting the risk of inappropriate antileishmanial prescription. A direct agglutination test (DAT) and a recently developed beta-mercaptoethanol-modified enzyme-linked immunosorbent assay (beta-ME ELISA) based on the use of antigen prepared as described for the DAT were applied to 416 sera from two Sudanese populations with and without clinical evidence of visceral leishmaniasis (VL). Of 285 sera with the lowest antileishmanial DAT titers (</=1:100 to 1:1,600), 270 (94.7%) scored comparable minimum beta-ME ELISA absorbance values (</=0.1 to 0.26). In 117 sera that demonstrated the highest DAT titers (1:12,800 to >/=1:25,600), 86 (73.5%) scored maximum (0.81 to >/=1.35) and 30 (25.6%) medium (0.27 to 0.80) beta-ME ELISA absorbance values. VL diagnosis was established for 142 (44.1%) patients in the VL-symptomatic group (n = 322), based on positive microscopy for Leishmania donovani in lymph node aspirates or positive DAT (titer, >/=1:3,200). Of the 125 sera from the symptomatic patients for whom microscopy was positive for VL, 111 (88.8%) had comparable positive DAT and beta-ME ELISA readings. In all 17 sera from the symptomatic DAT-positive patients for whom leishmaniasis was not established by microscopy but who responded favorably to antileishmanial therapy, absorbance values (>/=0.27) indicative of VL were obtained by beta-ME ELISA. Of 197 symptomatic patients for whom microscopy was negative for VL, 172 (87.3%) tested negative in beta-ME ELISA and 180 (91.4%) in DAT. Based on the high reliability demonstrated here for VL detection, beta-ME ELISA fulfills the requirement of confirming DAT results in patients manifesting suspected VL.