A novel pan-Leishmania loop-mediated isothermal amplification (Loopamp) assay for diagnosis of cutaneous and visceral leishmaniasis: a systematic review and meta-analysis

Abstract

Background: There is an urgent need for accurate and robust point-of-care (PoC) assays for visceral and cutaneous leishmaniasis (VL and CL). The Loopamp™ Leishmania detection kit (Loopamp), a novel loop-mediated isothermal amplification (LAMP) assay, has shown promise for VL and CL diagnosis using Qiagen and simpler boil-and-spin (B&S) DNA extraction methods. But diagnostic performances were inconsistent across studies. This systematic review and meta-analysis aimed to evaluate the pooled sensitivity and specificity of Loopamp for CL and VL diagnosis.

Methods: A comprehensive search of PubMed, Scopus, EMBASE, and Google Scholar was conducted to identify studies that evaluated the diagnostic performance of Loopamp for VL and CL suspects. Using the Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2), the methodological qualities of the included studies were evaluated. A bivariate random-effects meta-analysis was performed using R and Stata 14.2.

Results: Ten studies comprising 18 datasets were included. Sensitivity among individual VL studies ranged from 92 to 100%, while specificity varied from 41 to 100%. For CL, sensitivity varied from 48 to 100% and specificity from 31 to 100%. Pooled sensitivity was 96% (95% CI, 94-98%) for VL and 93% (95% CI, 70-99%) for CL. Pooled specificity was 99% (95% CI, 94-100%) for VL and 87% (95% CI, 55-97%) for CL. Subgroup analysis revealed that whole-blood B&S-Loopamp for VL had similar sensitivity (96%, 95% CI: 93-98%) and specificity (99%, 95% CI: 89-100%) to Qiagen-Loopamp.

Conclusions: Loopamp demonstrated robust diagnostic performance for VL in whole blood, meeting the 95% sensitivity and 99% specificity criteria outlined in the Target Product Profile (TPP). Similar to Loopamp-Qiagen, Loopamp-B&S performed excellently for VL diagnosis and is feasible to deploy in remote endemic areas. Loopamp showed high sensitivity and good specificity for CL diagnosis but fell short of the 95% sensitivity and 90% specificity required for CL PoC tests. Data on CL are limited, and its effectiveness in New World VL patients is unclear. Future research is needed to address this gap.

Trial registration: CRD42023489463.

Keywords: Cutaneous leishmaniasis; Diagnosis; LAMP; Loop-mediated isothermal amplification; Loopamp; Meta-analysis; Systematic review; Visceral leishmaniasis.

Fig. 1

PRISMA flow diagram of study selection for systematic review and meta-analysis of Loopamp for VL and CL diagnosis. CL: Cutaneous leishmaniasis, PRISMA: Preferred Reporting Items for Systematic Reviews and Meta-Analysis, n: number of articles, and VL: visceral leishmaniasis

Fig. 2

Forest plot for pooled sensitivity and specificity of Loopamp for VL diagnosis. Value and pooled estimate (last rows per sensitivity and specificity analysis, red diamond)

Fig. 3

Forest plot for pooled sensitivity and specificity of Loopamp for CL diagnosis. Value and pooled estimate (last rows per sensitivity and specificity analysis, red diamond)

Fig. 4

SROC curve for Loopamp for VL (a) and CL (b) diagnosis. SROC: summary receiver operating characteristic. Arrows represent the single study data, and circles indicate summary estimates with 95% CI

Fig. 5

Forest plot of subgroup analysis for pooled sensitivity and specificity of Loopamp for VL diagnosis. a shows results grouped by DNA extraction method (Qiagen kit [QIA] and Boil-&-Spin [B&S]). b shows results grouped by reference test (Microscopy, Polymerase Chain Reaction [PCR], and rk39-Rapid Diagnostic Test [rk39-RDT]). The red diamond in each plot represents the pooled estimate