Validation of a β-ME ELISA for detection of anti Leishmania donovani antibodies in Eastern Sudan.

Background: A β-mercaptoethnol (β-ME)-treated promastigote antigen of L. donovani was successfully employed in direct agglutination test (DAT) for the diagnosis of visceral leishmaniasis (VL).

Objective: The β-ME-treated antigen was further incorporated into an enzyme-linked immunosorbent assay set-up (β-ME ELISA) and evaluated for VL diagnosis against outcome of reference freeze-dried DAT (FD-DAT) and rK39 strip test (RKT) commercial kits.

Methods: Two-hundred and ninety-two sera from patients with high VL suspicion of whom 105 had confirmed L. donovani infection were tested.

Results: Relatively higher sensitivities of 93.3% (95% CI: 88.4-98.2) and 92.4% (95% CI: 87.3-97.5) were determined for β-ME ELISA and FD-DAT as compared to 83.8% (95% CI: 76.7-90.8) for RKT. Of 73 VL sera that scored maximum absorbance values (>0.81) in β-ME ELISA, 66 (90.4%) tested at the highest agglutination titres (>1:51200) in FD-DAT as did 56 (76.7%) also at comparable reaction intensities (3 + colour intensity) in RKT. Compared with FD-DAT (94.7%, 95% CI: 91.5-97.9) or RKT (93.0%, 95% CI: 89.3-96.6), lower specificity was estimated for β-ME ELISA (90.4%, 95% CI: 86.1-94.6). Based both on positive and negative microscopy for L. donovani in organ aspirates of all VL suspects enrolled (292), significantly higher correlation (p<0.01, 0.919) was established between β-ME ELISA and FD-DAT than between β-ME ELISA and RKT (p<0.01, 0.824). Taking into calculation the combined estimates of sensitivity, specificity, positive and negative predictive values, higher agreement (94.8%) was determined between total performance of β-ME ELISA and FD-DAT than between that of β-ME ELISA and RKT (90.7%).

Conclusion: Based on results and merits discussed, we recommend application of this β-ME ELISA both for diagnosis of VL at laboratory level and confirmation of results obtained with DAT or RKT in the field.