Comparison of prototype ELISAs for serodiagnosis of visceral leishmaniasis

Abstract text

Introduction

Leishmaniasis is a (sub-)tropical disease that is caused by Leishmania protozoa and transmitted by infected sandflies. Diagnosis of visceral leishmaniasis (VL) requires demonstration of Leishmania sp. in biopsy material using microscopy, culture, or PCR, which are specific but lack sensitivity in cases with low parasite density. As a non-invasive alternative, serological assays enable examination of the immune response to Leishmania.

Objective

Comparing the performance of three prototype ELISAs for the detection of Leishmania-specific antibodies.

Materials & methods

The prototype ELISAs were based on three substrates: i) Leishmania donovani lysate, ii) Leishmania donovani excretory/secretory (E/S) proteins from cell culture supernatant, iii) recombinant K39. Assay performance was compared between these prototypes as well as with established anti-Leishmania ELISAs (Bordier, Virion\Serion, Vircell) using serum samples from 52 VL patients and 75 healthy controls (25 blood donors, 25 pregnant women, 25 children). Additionally, a cross-reactivity panel was tested, comprising 33 serologically pre-characterized samples from patients with other parasitic infections (15 anti-Trypanosoma cruzi IgG positive, 8 anti-Schistosoma mansoni IgG positive, 10 anti-Plasmodium IgG positive).

Results

Among the prototype ELISAs, the best discrimination between VL patients and healthy controls was observed with the E/S-based ELISA, yielding a sensitivity of 90% (IgG) to 96% (IgG/IgM) at a specificity of 100%, with cross-reactivity rates between 0% for samples positive for Schistosoma or Plasmodium and 100% for Trypanosoma-positive samples. The K39-based ELISA performed with a sensitivity of only 58% (IgG, IgG/IgM), while specificity and cross-reactivity amounted to 100% and 0%, respectively. In contrast, the established ELISAs showed sensitivities between 86% (Bordier, IgG) and 94% (Vircell, IgG/IgM) [specificity data not available], with cross-reactivity ranging from 0% (Schistosoma, Plasmodium) to 100% (Trypanosoma).

Conclusion

The use of Leishmania donovani E/S antigen provides highest ELISA sensitivity and specificity for the detection of VL-associated antibodies but implies substantial cross-reactivity with Trypanosoma. The K39 antigen, however, results in a highly specific ELISA that is devoid of cross-reactivity. Future studies will aim at optimizing the antigenic substrates to enhance the serodiagnostic performance for VL.