Leishmania Antigen Rapid Diagnostic Test Proof-of-Concept and Validation Study

Visceral leishmaniasis (VL) or kala azar is a neglected tropical disease(NTD) caused by protozoan parasites of the Leishmania donovani complex that are transmitted by phlebotomine sand flies. An estimated 50,000 - 90,000 new cases occur worldwide annually. It is characterized by fever, weight loss, enlargement of the spleen and liver, and anaemia, and it can be fatal in more than 95% of cases without treatment. The Horn of Africa accounts for the largest number of VL cases worldwide, and communities living in remote, resource-limited settings are at greatest risk of infection. Therefore, early and accurate diagnosis of VL in health facilities is essential. VL is fatal if it is not adequately treated. The drugs currently used to treat VL can have severe side effects and the clinical presentation of VL is not sufficiently specific to guide treatment. Highly accurate (both sensitive and specific), cheap and simple rapid diagnostic tests (RDTs) are therefore crucial for case-management of VL. Early case detection followed by adequate treatment is also central to control of VL. In Kenya, Visceral leishmaniasis is diagnosed by the rK39 RDT based on detection of host antibody to a 39-aminoacid-repeat recombinant leishmanial antigen in clinically suspected cases. Because this test has a suboptimal sensitivity of around 85%, other additional diagnostic tests are often necessary. These include the direct agglutination test (DAT) based on agglutination of whole parasite antigen by parasite specific host antibodies and microscopy detection of amastigotes in stained smears from lymph node punctures, bone marrow or spleen aspirates currently the gold standard for confirmatory diagnosis. While the use of rK39 RDT and DAT has been on the increase, the tests cannot distinguish active from past infections as they are based on detection of antileishmania antibodies which are present in both active and past infections. Furthermore, DAT requires some laboratory skills and overnight in