Using environmental DNA for the detection of Schistosoma mansoni: toward improved environmental surveillance of schistosomiasis

Schistosomiasis is a waterborne, infectious disease with high morbidity and significant economic burdens affecting more than 250 million people globally. Disease control has, with notable success, for decades focused on drug treatment of infected human populations, but a recent paradigm shift now entails moving from control to elimination. To achieve this ambitious goal more sensitive diagnostic tools are needed to monitor progress towards transmission interruption in the environment, especially in low-intensity infection areas. We report on the development of an environmental DNA (eDNA) based tool to efficiently detect DNA traces of the parasite Schistosoma mansoni directly in the aquatic environment, where the non-human part of the parasite life cycle occurs. To our knowledge, this is the first report of the successful detection of S. mansoni in freshwater samples using aquatic eDNA. True eDNA was detected in as few as 10 cercariae/L water in laboratory experiments. The field applicability of the method was tested at known transmission sites in Kenya, where comparison of schistosome detection by conventional snail surveys (snail collection and cercariae shedding) with eDNA (water samples) showed 71% agreement between the methods. The eDNA method furthermore detected schistosome presence at two additional sites where snail shedding failed, demonstrating a higher sensitivity of eDNA sampling. We conclude that eDNA provides a promising new tool to significantly improve the environmental surveillance of S. mansoni. Given the proper method and guideline development, eDNA could become an essential future component of the schistosomiasis control tool box needed to achieve the goal of elimination.