Monitoring schistosomiasis and sanitation interventions—The potential of environmental DNA

Abstract

Transmission of schistosomiasis, a human parasitic disease, is intrinsically linked to inadequate water, sanitation, and hygiene (WASH) facilities and/or their use. The mainstay of control is population-based chemotherapy. Globally, each year, 240 million people are estimated to require this preventative treatment. However, for longterm, sustainable control of this disease, supplementary WASH improvements are required to prevent (re)infection of humans (provision of safe water) and transmission from humans to the environment (improved sanitation). While there is established methodology for monitoring transmission in human populations, presently methods for monitoring the impact of WASH interventions, in particular sanitation, on environmental transmission are lacking. Development of such becomes paramount as integrated control programs combine drug treatments with enhanced WASH facilities and behavior change interventions, with uptake likely correlated to a reduction in fecal matter, and schistosome eggs, in the environment but any impact on infection levels in humans taking longer to become apparent. This article reports and critiques the methods currently used to monitor schistosomiasis in freshwater and soil environments and explores how environmental DNA could be used to better understand and monitor environmental contamination in relation to sanitation. Stronger evidence is required to understand how different sanitation interventions serve to limit the environmental transmission of the parasite and their relative effectiveness in preventing disease.

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

“…This group of trematodes is related to human schistosomes, which cause the devastating disease schistosomiasis, affecting 229 million people across Asia, Africa, and South America [ 4 , 5 ]. Control efforts for both human [ 6 , 7 , 8 , 9 , 10 , 11 , 12 ] and avian [ 1 , 13 , 14 , 15 , 16 , 17 ] schistosomes have been undertaken with varying degrees of success. These include the application of molluscicides [ 6 , 15 ], chemotherapy with Praziquantel (humans [ 8 , 12 ] and birds [ 14 , 16 ]), water treatment [ 10 ], and definitive host relocation [ 17 ].…”

Detecting and identifying Schistosoma infections in snails and aquatic habitats: A systematic review

“…Regarding the molecular targets that have been used for schistosome detection (see [ 28 ] for one list), they are quite understandably typically based on sequences expected to be represented many times in a single schistosome cell, thereby increasing the ability to sensitively detect a signal. They include mitochondrial markers (such as 16S rRNA, Cox1 , Cox3 , Nad5 ( ND5 ) [ 29 ]), or nuclear sequences including portions of the rRNA complex (18SrRNA, intergenic 28S-18S spacers) and repetitive sequences such as Sm1-7 and DraI [ 12 ].…”