Nutritional effects of invasive macrophyte detritus on Schistosoma mansoni infections in snail intermediate hosts

Schistosomes are parasitic flatworms that cycle between humans and freshwater snails, infecting more than 200 million humans. Many schistosome-endemic sites are invaded by non-native plants that snails cannot consume. Inedible plants could suppress snail growth, reproduction, and schistosome production by outcompeting edible resources. Alternatively, their decomposition could create edible detritus that fuels snail growth, reproduction, or schistosome production. We evaluated the nutritional effects of detritus from four widespread invasive plants on human schistosomes, Schistosoma mansoni, and snail intermediate hosts, Biomphalaria glabrata. We predicted that water hyacinth, which is fibrous and waxy, would cause poor growth, reproduction, and parasite production. In contrast, we predicted water lettuce, water fern, and duckweed would enable rapid growth, reproduction, and parasite production via better nutrient content and digestibility. Infected snails consuming water fern and water lettuce grew ~100% larger and produced ~9-fold more cercariae than those consuming water hyacinth or duckweed. We then tested whether extended decomposition of water hyacinth could improve snail and schistosome performance but found negligible effects. Managers should prioritize removal of plants that produce nutritious detritus, because in situ destruction could increase schistosome transmission. Characterizing interactions among plant invasions, management, and parasites could facilitate solutions that improve human and environmental health.