Loop-Mediated Isothermal Amplification Allows Rapid, Simple and Accurate Molecular Diagnosis of Human Cutaneous and Visceral Leishmaniasis Caused by Leishmania infantum When Compared to PCR.

Loop-mediated isothermal amplification allows the rapid, sensitive and specific amplification of DNA without complex and expensive equipment. We compared the diagnostic performance of Loopamp™ Leishmania Detection Kit (Eiken Chemical Co., Ltd., Tokyo, Japan) with conventional and real-time polymerase chain reaction (PCR) for human cutaneous and visceral leishmaniasis caused by L. infantum. A total of 230 DNA samples from cutaneous (CL) and visceral (VL) leishmaniasis cases and controls from Spain, characterized by Leishmania nested PCR (LnPCR) were tested by: (i) the Loopamp™ Leishmania Detection Kit (Loopamp), run on Genie III real-time fluorimeter (OptiGene, UK); and (ii) real-time quantitative PCR (qPCR). The Loopamp test returned 98.8% (95% confidence interval-CI: 96.0-100.00) sensitivity and specificity of 97.7% (95% CI: 92.2-100) on VL samples, and 100% (95% CI: 99.1-100) sensitivity and 100.0% (95% CI: 98.8-100.0) specificity on CL samples. The Loopamp time-to-positivity (Tp) obtained by real-time fluorimetry showed excellent concordance (C = 97.91%) and strong correlation (r = 0.799) with qPCR's cycle threshold (Ct). The performance of Loopamp is comparable to that of LnPCR and qPCR in the diagnosis of cutaneous and visceral leishmaniasis due to L. infantum. The excellent correlation between the Tp and Ct should be further investigated to determine the accuracy of Loopamp to quantify parasite load in tissues.