Serological studies on rK39 negative visceral leishmaniasis in an endemic focus of Leishmania donovani induced cutaneous leishmaniasis

Leishmaniasis, a vector-borne disease found in parts of the tropics, subtropics and southern Europe, has recently been categorized into the group of neglected tropical diseases (NTD) by world health organization (WHO). Leishmaniasis results in a considerable health burden in many low-income populations in developing regions of Africa, Asia and America [1].

Clinical outcome of leishmaniasis; cutaneous, mucosal and visceral leishmaniasis (CL, ML, VL) are mainly species dependent [1]. Untreated VL is usually fatal [2, 3]. VL accounts for 20,000 to 40,000 deaths annually [4, 5]. South Asia harbours >70.0% of the global burden of VL [5]. A regional drive for elimination of VL is on-going [6, 7].

Posing a threat to these efforts, Sri Lanka reports a large focus of human leishmaniasis [8, 9, 10, 11]. Interestingly, local infection is caused by a genetic variant of L. donovani and mainly results in CL [12]. CL in Sri Lanka presents a complex picture [13, 14, 15]. Few cases of VL and ML have also been reported [16,17].

Field screening and point of care diagnosis are considered as priorities in leishmaniasis [18, 19]. Due to lack of obvious sites of infection in early infections in leishmaniasis and the need for invasive, complex and risky internal organ aspirations in VL, serological assays are routinely used for field screening of leishmaniasis and laboratory confirmation of VL [18], [19], [20].

The rK39 dipstick test (InBios International, Inc. Seattle, WA98104) is recommended for detection of VL and used for field screening as well. However, in Sri Lanka, only a few local cases of laboratory confirmed VL responded well with this assay. Antigenic variations in local parasites is a possibility [16]. Our more recent clinical and parasite studies and historical evidence suggest long term local existence of leishmaniasis, [13, 14, 15, 21, 22,23,24]. Possible parasite evolution and antigenic heretogeneity was suggested [25,26]. Further confirming this, local CL is associated with a high sero-conversion rate in Sri Lanka [27], [28], [29], [30].

Due to lack of evidence on the suitability of CL antigen-based ELISA for detection of VL, a novel serological assay based on Leishmania local VL antigens was developed and demonstrated high specificity and sensitivity.

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