A rapid and sensitive extraction-free HiFi-LAMP assay for detecting Mycobacterium leprae.

Background: Timely and accurate detection of Mycobacterium leprae (M. leprae) is crucial for efficient treatment and early intervention of leprosy, which requires a simple and rapid extraction-free assay.

Methods: A HiFi-loop-mediated isothermal amplification (LAMP) assay was developed for detection of M. leprae. The performance of the assay was assessed by comparing with qPCR and nested PCR assays using clinical samples. The extraction-free HiFi-LAMP assay was assessed by saliva from individuals with leprosy.

Results: The M. leprae HiFi-LAMP assay has high specificity and sensitivity with a limit of detection (LOD) of 43 copies/25 µL reaction. Both sensitivity and specificity of the HiFi-LAMP assay were 100% for 130 purified DNA from nasal and oral samples, and the sensitivity was slightly higher than 50%-88.9% by the qPCR assay. A higher detection rate of M. leprae was observed in nasal swabs than oral swabs. The extraction-free assay directly using 6 µL saliva has a LOD of 11,833 M. leprae RLEP copies/mL saliva, can be completed within 30 mins, and showed 66.7% sensitivity for three saliva samples when compared with the assay using purified DNA.

Conclusion: The standard and/or extraction-free HiFi-LAMP assays can be used for detecting and monitoring M. leprae in endemic areas in resource-limited settings.