Serological studies on rK39 negative Visceral Leishmaniasis in an endemic focus of Leishmania donovani induced Cutaneous Leishmaniasis.

• Previous ELISA studies showed a high sero-positivity in Leishmania donovani induced cutaneous leishmaniasis (CL). • Visceral Leishmaniasis (VL) is very rare in Sri Lanka and unresponsive to established rK39 dipstick test. • The described assay was highly sensitive and specific for detection of local VL. Sri Lanka reports a focus of L. donovani i nduced cutaneous leishmaniasis (CL). Our more recent parasite and clinical studies and historical evidence point towards long term existence of Leishmania in the country, indicating a possible evolution leading to antigenic heterogenicity as well. In-house enzyme-linked immunosorbent assay (ELISA) that was developed during phase 1 study indicated >80% sero-positivity in local CL, while visceral leishmaniasis (VL) remained very rare with majority being negative when tested with rK39 assay. A novel serological tool was developed and sero-positivity of VL was assessed for the first time. The assay showed 100.0% sensitivity and 98.3% specificity for detection of VL. Samples were showed less positivity with established direct agglutination test (DAT) and rK39 strip test. The assay was less expensive than that of established rapid diagnostic tests (RDTs), culture and PCR assays. This assay may be useful in diagnosing clinical VL infections, detection of light microscopy (LM) negative patients, tracking post treatment stages, field screening of asymptomatic cases and in further serological studies. [ABSTRACT FROM AUTHOR]