Measuring the sero-prevalence of Leishmania donovani induced cutaneous leishmaniasis: A method comparison study

An in-house enzyme-linked immunosorbent assay (ELISA) based on crude antigen of Leishmania reported a high sero-prevalence (82.0%) in Leishmania donovani induced cutaneous leishmaniasis (CL) in Sri Lanka. ELISA was further compared with established serological tools to identify a suitable point of care diagnostic tool. Sero-prevalence of 100 CL samples were analyzed using in-house ELISA, Indian dipstick test and rK39 strip test. Results obtained were further compared with direct agglutination test (DAT) for 40 CL. Test performance was evaluated using Kappa index value. Clinico-epidemiological characteristics of patients were analyzed using SPSSv25.0. Cost analysis of tests was carried out. ELISA showed a high sero-positivity of 81.0% (n = 81/100) while DAT (57.5%,n = 23/40), Indian dipstick test (22.0%,n = 22/100) and rK39 test (15.0%,n = 15/100) showed a comparatively less sero-positivity. According to Kappa index values, there were no perfect agreement between tests. Among ELISA positive patients (n = 81/100), DAT, Indian dipstick test and rK39 demonstrated sero-positivity rates of 61.3% (n = 19/31), 25.9% (n = 21/81) and 16.0% (n = 13/81) respectively. Among ELISA negative patients (n = 19/100), three assays demonstrated sero-positivity rates of 44.4% (n = 4/9), 5.3% (n = 1/9) and 10.5% (n = 2/19) respectively. DAT can be used as an alternative test when ELISA is not available or negative. Clinico-epidemiological profiles of patients that showed sero-positivity by each assay were different. Cost per patient was approximately 5.5 USD for DAT and 3.0 USD for each other tests. Established serological tests demonstrated different and relatively lower detection rates. Species, strain and antigen heterogeneity, inconsistency in amount of used antigens, sera, antibody expression patterns and testing methodologies could be responsible. This study highlighted the importance of designing an in-house serological assay based on local parasite.