A Double antibody sandwich ELISA for the diagnosis of vivax malaria: a tool for further research

Abstract

A diagnostic assay for Plasmodium vivax based on a double antibody sandwich enzyme-linked immunosorbent assay (DAS ELISA) was established to detect the merozoite surface protein 1 (PvMSP1) in wild isolates. This assay was based on the recombinant protein p19, a C-terminal processing product of PvMSP1. Of the two anti-P. vivax monoclonal antibodies (MAbs) selected, A21 was used as the capture antibody while horse radish peroxidase labelled A8 served as the probing second antibody. Optimized conditions established for p19 based DAS ELISA with the exception of a lower concentration of Tween-20 in buffers were suitable to screen lysed whole blood of malaria patients. This assay had a specificity of 100 percent for P. vivax and all the isolates of P. falciparum tested negative. Of the P. vivax-infected blood samples, only those containing both compact and schizont stages were diagnosed positive. The rest of the isolates tested negative either due to stage specificity of this assay or to the antigenic diversity of PvMSP1 in wild isolates. This test demonstrated a sensitivity of 27.58 percent and an accuracy of 63.15 percent. The positive and negative predicted values of this ELISA were 100 percent and 57.14 percent, respectively. Therefore, the P. vivax specific DAS ELISA developed and tested in the present study is not sufficiently sensitive to be used as a diagnostic tool for vivax malaria. Nevertheless, a baseline was established for development of diagnostic ELISA for future use with a more appropriate antigen.