Bartonicek, Zikmund; (2023) Schistosomes and how to find them – advancing the molecular environmental monitoring of schistosomiasis. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Schistosomiasis is a parasitic neglected tropical disease affecting over 230 million people and claiming over 250 thousand lives annually, mainly in Sub-Saharan Africa. The parasite is transmitted to humans by freshwater snails releasing infective zooplanktonic cercariae, which infect people during water contact. However, current environmental monitoring methods are insensitive and laborious, requiring trained parasitologists to collect the intermediate snails and check them for emerging cercariae or Schistosoma DNA. This PhD advances molecular monitoring of schistosomiasis by improving our understanding of Schistosoma environmental DNA (eDNA) and developing a novel Fish Faecal Xenomonitoring (FFX) method. Monitoring using eDNA was further advanced by testing different field-friendly DNA capture and preservation methods, investigating the effects of biotic and abiotic factors on eDNA degradation, and field-testing the method against the standard monitoring approach of snail shedding. Results from the novel eDNA qPCR assay demonstrated high sensitivity for detecting Schistosoma DNA, despite it degrading rapidly in the tested environments. The FFX method was developed and tested in both laboratory and field settings, comparing it to eDNA and snail shedding. FFX was highly sensitive and capable of detecting the DNA of a single S. mansoni cercaria in the faeces of juvenile Nile tilapia (Oreochromis niloticus) in laboratory tests. When tested at Lake Albert (Uganda), which is endemic for Schistosoma mansoni, the FFX outperformed both the traditional and eDNA methods, identifying 90% of suspected transmission sites as positive. These findings show that molecular methods of schistosomiasis environmental monitoring are highly sensitive and can outperform traditional monitoring methods. The advancement of eDNA and the development of the novel FFX method presented in this PhD expand the current toolkit for schistosomiasis monitoring and directly contribute to WHO’s call for improved molecular methods of schistosomiasis environmental surveillance.

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