Environmental DNA for improved detection and environmental surveillance of schistosomiasis

Abstract

Schistosomiasis is a water-based, infectious disease with high morbidity and significant economic burdens affecting >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 toward 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 nonhuman part of the parasite life cycle occurs. This is a report of the successful detection of S. mansoni in freshwater samples by using aquatic eDNA. True eDNA was detected in as few as 10 cercariae per liter of 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 tool to substantially 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.

Schistosoma species detection by environmental DNA assays in African freshwaters

“…Successful detections of trematode parasites using aquatic eDNA include Ribeiroia ondatrae in North America [29], Opisthorchis viverrini in southeast Asia [30], and Fasciola hepatica and Calicophoron daubneyi in Europe [31]. Previous studies have also shown the feasibility of recovering Schistosoma mansoni DNA from both field and laboratory environments [32,33]. They have also demonstrated that Schistosoma DNA present in laboratory water decayed below levels of detection eight days after the removal of source snails [33].…”

“…Previous studies have also shown the feasibility of recovering Schistosoma mansoni DNA from both field and laboratory environments [32,33]. They have also demonstrated that Schistosoma DNA present in laboratory water decayed below levels of detection eight days after the removal of source snails [33]. Collectively, this evidence is highly supportive of the potential of eDNA methods for improved surveillance of all harmful schistosome species [34], but also indicates that improvements are needed to adapt these methods to large-scale surveillance, and to identify species other than S. mansoni.…”

Analysis of Environmental DNA and Edaphic Factors for the Detection of the Snail Intermediate Host Oncomelania hupensis quadrasi

“…The use of environmental DNA (eDNA) has been demonstrated to be useful in tracking S. japonicum in water through quantitative PCR (qPCR) [28,29]. It was also successfully applied to other schistosome species, such as S. mansoni in field samples for better surveillance [30,31]. In this study, O. hupensis quadrasi eDNA was detected from soil samples.…”

To improve ecological understanding, collect infection data

“…Further, the increasing capacity of sequencing technologies has expanded the value of non-destructive sample collection techniques and allows researchers to inexpensively archive samples in ethanol (Bi et al 2013, Yeates et al 2016. Newly developed eDNA techniques can make detection of free-living stages possible (Sengupta et al 2019). Complementarily, whole organism sampling designs that preserve parasite type specimens for taxonomic ground-truthing could provide reference libraries of reliable DNA barcodes.…”