Pilot study evaluating a newly developed nanoparticle-based lateral flow assay for the diagnosis of cutaneous leishmaniasis in Sri Lanka

BACKGROUND: With the launch of Sri Lanka's National Strategic Plan for leishmaniasis control, case diagnosis has been identified as a key strategic intervention. However, the routine slit-skin smear (SSS) demonstrates variable sensitivity (33-78%), underscoring the need for rapid and sensitive diagnostic tools. This study evaluated the diagnostic performance of a newly developed nanoparticle-based anti-rKRP42 (recombinant kinesin-related protein antigen-42) IgG immunochromatographic test (rKRP42-ICT) for detecting cutaneous leishmaniasis caused by Leishmania donovani. METHODS: A cross-sectional pilot study was conducted among 58 adults with clinical CL at Base Hospital Tangalle. CL was confirmed by SSS (reference test). Serum from CL patients and Japanese negative controls was tested using rKRP42-ICT, rKRP42 IgG ELISA, and rK39-ICT. Diagnostic performance of the ICT (sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV)) was calculated against SSS. Clinical associations were analysed by Chi-square, and ELISA OD means were compared using non-parametric tests (with 95% confidence interval). RESULTS: The majority of the CL cohort (62%) were male. The mean duration at presentation was 5.1 months. Most had single, small (< 2 cm) lesions, with ulcers being the commonest type (41%). rKRP42-ICT demonstrated a positive rate of 43.1% among the clinical CL cohort while SSS and rK39-ICT positivity was 55.2% and 5.2%, respectively. The rKRP42-ICT showed 43.8% sensitivity, 57.7% specificity, and 56% PPV and 45.5% NPV against the reference test. The rKRP42-ICT could detect positive samples across a wide range of ELISA OD values, from 0.017 to 2.535. rKRP42-ICT positivity correlated with higher ELISA OD values (p < 0.05), but SSS positivity did not. The rKRP42-ICT and SSS agreement was slight (Kappa = 0.014). Negative controls (n = 43) were negative by both ICTs. Male gender, ulcerated, large (> 2 cm), and multiple lesions were associated with higher rKRP42-ICT positivity (p < 0.05) and higher mean ELISA OD values. Defining confirmed cases as clinical CL with either SSS or rKRP42-ICT positivity increased case detection from 55.2 to 74.1% (20%). CONCLUSIONS: The rKRP42 IgG-based ICT showed promise as a supplementary diagnostic tool for CL, potentially improving overall case detection beyond routine microscopy and providing rapid results for clinical decision-making. With further optimization and validation, it may support national diagnostic and surveillance efforts.