Antigen Discovery for Serological Diagnosis of Visceral Leishmaniasis

Visceral leishmaniasis (VL) is the most severe form of leishmaniasis and results from parasitic infection by certain species of the protozoan genus Leishmania. Because VL is often fatal unless treated, rapid and accurate diagnosis of the disease is indispensable for case control. Currently, the gold standard diagnosis of VL is detection of parasites in a spleen or bone marrow aspirate. Because this method is invasive, time-consuming, and not sufficiently sensitive, rendering it inefficient, alternative methods including serological diagnosis have been developed. The 'first generation' serological tests that detect antibodies to Leishmania parasites in peripheral blood, serum or plasma, have utilized crude antigen, e.g., whole parasites or parasite lysate, that often have cross-reactivity / low specificity issues. As a result, efforts have been focused on characterizing antigens for 'second generation' diagnostic tests. The best example of such defined antigens is the recombinant K39 protein, or rK39, which contains a 39-amino acid repeat, and diagnostic tests based on this antigen are now commercially available and used world-wide. This review discusses advances in and the current status on antigen discovery for antibody detection-type diagnostic tests of visceral leishmaniasis.