Environmental DNA-based xenomonitoring for determining Schistosoma presence in tropical freshwaters

Abstract

Background: Schistosomiasis is a neglected tropical disease that infects over 200 million people worldwide. Control measures can benefit from improved surveillance methods in freshwaters, with environmental DNA (eDNA) surveys having the potential to offer effective and rapid detection of schistosomes. However, sampling eDNA directly from natural water bodies can lead to inaccurate estimation of infection risk if schistosome eDNA is rare in the environment. Here we report a xenomonitoring method that allows schistosome infections of host snail species to be determined from eDNA in water used to house those snails. Methods: Host snail species were collected and placed in containers of water and allowed to shed cercariae, and then water samples were filtered and tested using qPCR assays specific to the African species Schistosoma mansoni and Schistosoma haematobium. We evaluated this "eDNA-based xenomonitoring" approach by experimentally comparing the results to those obtained from direct qPCR screening of tissue sourced from the snails in the experiment. Results: We found that our method accurately diagnosed the presence of S. mansoni-infected snails in all tests, and S. haematobium-infected snails in 92% of tests. Moreover, we found that the abundance of Schistosoma eDNA in experiments was directly dependent on the number and biomass of infected snails. Conclusions: These results provide a strong indication that this surveillance method combining the utility of eDNAbased monitoring with the reliability of traditional xenomonitoring approaches could be used to accurately assay the presence of Schistosoma species in natural habitats. This approach may be well-suited for epidemiological studies and monitoring in endemic areas, where it can assist schistosomiasis control by indicating infection risk from freshwaters and guiding necessary interventions to eliminate the disease.

Simultaneous genotyping of snails and infecting trematode parasites using high‐throughput amplicon sequencing

“…Nevertheless, the substantial cost and time required to implement HTAS limit its use for routine diagnostics or monitoring. For this, shedding experiments, xenomonitoring PCR, qPCR or environmental DNA tools that detect cell‐free DNA of larval parasite stages (Alzaylaee et al, 2020) or the intermediate snail host (Mulero et al, 2020) in water samples are much more appropriate. Also, in the broader perspective of transmission ecology, it is known that not all infected snails contribute equally to transmission to further hosts.…”

Simplifying Schistosome Surveillance: Using Molecular Cercariometry to Detect and Quantify Cercariae in Water

“…Cercariometry as a technique for monitoring schistosomes has experienced many methodological advancements. These include filtration (used in both manual and molecular cercariometry) [ 8 , 17 , 19 , 22 , 24 , 25 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 36 , 37 ], positive phototropism [ 38 ], overlay technique [ 39 ], centrifugation [ 40 , 41 , 42 ], and finally qPCR [ 15 , 17 , 19 , 24 , 25 , 37 , 43 , 44 , 45 , 46 ]. In the early years of using cercariometry, most of the focus was on human schistosomes, and many studies highlighted the need for fast, sensitive, and specific tests for use on a larger scale [ 7 , 19 , 33 , 44 , 47 , 48 , 49 , 50 ].…”

“…The overlay technique developed by Sandt [ 39 ] used the positive phototropism phenomenon explored by Klock [ 38 ], while also attempting to combat the effect of water turbidity on the recovery of cercariae—a common problem with environmental samples [ 30 , 39 , 45 , 48 , 49 ]. This method involved an overlay chamber with turbid water on the bottom and clear water above.…”

Intestinal Schistosomiasis and Giardiasis Co-Infection in Sub-Saharan Africa: Can a One Health Approach Improve Control of Each Waterborne Parasite Simultaneously?

“…Dependence of both parasites on freshwater provides an ideal target for sample collection and assessment using PCR/qPCR, LAMP or RPA assays [83,100,101]. In addition, collection of water samples to detect eDNA derived from Schistosoma freshwater snail hosts to identify and monitor the presence of snail species capable of transmitting infection within a given waterbody has also been assessed [102,103].…”