LAMP-coupled CRISPR-Cas12a assays: A promising new tool for molecular diagnosis of leishmaniasis

Tegumentary leishmaniasis is a parasitic disease endemic in the Americas. Its clinical management and control rely on early and accurate diagnosis and adequate treatment. PCR-based molecular diagnostics offer high sensitivity and specificity over microscopy or culture but are less accessible in low-resource settings. New molecular tools for detecting Leishmania infections are needed in rural endemic regions. A promising tool harnessing CRISPR-Cas technology enables highly specific and sensitive detection of nucleic acid targets, offering an exciting potential for portable molecular diagnostics. Previously, we developed CRISPR-Cas12a-based assays coupled to PCR preamplification for Leishmania detection. Here, we adapted our assays, which target the multicopy 18S rDNA and kinetoplast DNA (kDNA) minicircles, by replacing PCR with loop-mediated isothermal amplification (LAMP).

LAMP-coupled CRISPR assays were optimized for fluorescence-based and lateral flow readouts. The assays could detect as low as 0.2 genome equivalents per reaction using L. braziliensis M2904 strain genomic DNA. The kDNA assay reliably detected all tested species of the L. (Viannia) subgenus, while the 18S assay showed pan-Leishmania detection capability. There was no cross-reactivity with other protozoan (Trypanosoma cruzi and Plasmodium falciparum) and bacterial (Mycobacterium tuberculosis) pathogen DNA, nor with human DNA. When applied to 90 clinical samples (skin lesions) from the Cusco region of Peru and compared to kDNA real-time PCR, LAMP-CRISPR assays with a fluorescence readout achieved a sensitivity of 90.9% (95% CI: 80.1-97.0%) for kDNA and 72.7% (95% CI: 59.0-83.9%) for 18S rDNA, both with 100% (95% CI: 90-100%) specificity. Overall, lateral flow strip results agreed with fluorescence-based detection in 18 tested samples, with one discrepancy observed in the 18S assay associated with low parasite load.

These new proof-of-concept LAMP-CRISPR assays, combining high sensitivity, multiple Leishmania species detection capability, and a portable lateral flow readout, hold promise as next-generation molecular tools to improve leishmaniasis diagnosis and surveillance, supporting One Health strategies for disease control.