Evaluation of the direct agglutination test based on freeze‐dried Leishmania donovani promastigotes for the serodiagnosis of visceral leishmaniasis in Sudanese patients

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Abstract
Summary: The direct agglutination test (DAT) based on freeze‐dried (FD) Leishmania donovani antigen was evaluated for the serodiagnosis of kala‐azar in a rural setting in eastern Sudan. The performance of the FD‐DAT was compared with standard liquid antigen (LQ) by testing serum samples and blood samples collected on filter paper of microscopically and PCR‐confirmed VL patients, apparently healthy endemic controls and patients with other relevant infectious diseases for the region. In the present study, the FD‐DAT had a sensitivity of 96.8% and a specificity of 96.2%. The LQ‐DAT had a sensitivity of 91.0% and a specificity of 96.6%. A high degree of agreement (97.3%; r‐value 0.94) was observed between the FD‐DAT and the LQ‐DAT, as well as between the FD‐DAT performed on serum samples and corresponding blood samples collected on filter paper (agreement 97.8%; r‐value 0.79). The FD‐DAT is very suitable as diagnostic test for kala‐azar in remote rural conditions as it is sensitive, specific and stable. The antigen is affordable, reproducible and available, which contributes to the sustainability of the DAT as a diagnostic test for VL.