Optimization of a Loop-Mediated Isothermal Amplification (LAMP) Assay for Schistosoma Mansoni (Trematoda: Digenea) Detection in Biomphalaria spp. from Endemic Areas for Schistosomiasis in Brazil

Abstract Background: Schistosomiasis mansoni is a neglected tropical disease endemic in Brazil caused by Schistosoma mansoni, which is transmitted by Biomphalaria snails. Among all measures to control and eliminate the disease, accurate mapping and monitoring of snail breeding sites for susceptible and/or infected hosts in endemic areas are recommended. Parasitological methods are frequently used to identify infected snails, although they have many limitations, often providing false-negative results. Loop-mediated isothermal amplification (LAMP) is a promising alternative method for a more sensitive, rapid, and cost-effective diagnosis. However, standardization of LAMP assays is challenging due to the variety of parasites that are co-endemic with S. mansoni, and their varying prevalence rates in different areas. In this work, we aimed to optimize a LAMP assay for the detection of S. mansoni in Biomphalaria snails from endemic areas in the state of Minas Gerais, Brazil. Methods: A total of 1,001 snails were collected in five municipalities of the Mucuri and Jequitinhonha Valleys. Snails were pooled and squeezed according to the collection site to detect the presence of the larval forms of S. mansoni and other trematodes. Pooled snails were submitted to pepsin digestion and DNA extraction. Then molecular assays were performed for the species-specific identification and characterization of the samples. A LAMP assay was optimized and validated using laboratory and field samples. Results: Using the parasitological method, S. mansoni cercariae were detected in snails from two collection sites. Biomphalaria glabrata, the main snail host of S. mansoni in Brazil, was detected in 72.2% of the collection sites by PCR-RFLP. Multiplex PCR, LS-PCR, and conventional PCR allowed the detection of positive snails in four additional sites. The optimized LAMP assay was effective in detecting the presence of S. mansoni infection with 100% sensitivity, 91.66% specificity, and a Kappa index of 0.88, when compared to LS-PCR and conventional PCR. Conclusions: Our findings suggest that LAMP is a good alternative for the detection and monitoring of transmission foci of S. mansoni, as it enabled the detection of infection three times more than the parasitological examination and is more applicable directly in the field when compared to other molecular approaches.