Molecular detection and identification of Trichobilharzia: development of a LAMP, qPCR, and multiplex PCR toolkit.

Background: Cercarial dermatitis (CD), or swimmer's itch, is a water-borne allergic skin reaction caused by the penetration of the larval stages of bird schistosomes (cercariae) into the skin. Members of the genus Trichobilharzia are the primary causative agents of CD worldwide. Due to the increasing number of cases, CD is regarded as a (re)emerging disease. Outbreaks in recreational waters can significantly impact public health and local economies. Environmental monitoring of Trichobilharzia is crucial for outbreak prediction and public health management. However, conventional methods, such as cercarial shedding and snail dissections, are labour-intensive and lack sensitivity. To overcome these limitations, we present a molecular toolkit that combines loop-mediated isothermal amplification (LAMP), quantitative polymerase chain reaction (qPCR), and multiplex PCR for rapid, sensitive, and accurate detection and identification of Trichobilharzia spp. from various biological samples.

Methods: Tricho-LAMP and Tricho-qPCR were designed and optimised for Trichobilharzia DNA detection. A multiplex PCR assay was also developed and optimised to identify the three main species causing CD in Europe (Trichobilharzia franki, T. szidati, and T. regenti).

Results: Tricho-LAMP specifically detected T. regenti and T. franki at 10^-3 ng, and T. szidati at 10^-2 ng per reaction with genomic DNA. Using gBlocks synthetic DNA, Tricho-LAMP achieved 100% amplification at 10,000 copies and 85% amplification at 1000 copies, with decreasing success at lower concentrations. Tricho-qPCR showed the highest sensitivity, detecting all species down to 10^-4 ng per reaction and showing a limit of detection at 10 copies of synthetic DNA in the reaction. Multiplex PCR allowed reliable species differentiation via gel electrophoresis of the PCR products, but the assay had the lowest sensitivity.

Conclusions: We provide a molecular toolkit consisting of LAMP, qPCR, and multiplex PCR. By exhibiting high sensitivity, Tricho-LAMP and Tricho-qPCR assays are potentially suitable for environmental DNA (eDNA)-based environmental monitoring of bird schistosomes, by both researchers and public health authorities. Multiplex PCR can be used for species determination without the need for further sequencing.