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Invasive species cause environmental degradation, decrease biodiversity, and alter ecosystem function. Invasions can also drive changes in vector‐borne and zoonotic diseases by altering important traits of wildlife hosts or disease vectors. Managing invasive species can restore biodiversity and ecosystem function, but it may have cascading effects on hosts, parasites, and human risk of infection. Water hyacinth, Eichhornia crassipes, is an extremely detrimental invader in many sites of human schistosome transmission, especially in Lake Victoria, where hyacinth is correlated with high snail abundance and hotspots of human schistosome infection. Hyacinth is often managed via removal or in situ destruction, but the effects of these strategies on snail intermediate hosts and schistosomes are not known. We evaluated the effects of water hyacinth invasion and these management strategies on the dynamics of human schistosomes, Schistosoma mansoni, and snails, Biomphalaria glabrata, in experimental mesocosms over 17 weeks. We hypothesized that hyacinth, which is inedible to snails, would affect snail growth, reproduction, and cercariae production through the balance of its competitive effects on edible algae and its production of edible detritus. We predicted that destruction would create a pulse of edible detrital resources, thereby increasing snail growth, reproduction, and parasite production. Conversely, we predicted that removal would have small or negligible effects on snails and schistosomes, because it would alleviate competition on edible algae without generating a resource pulse. We found that hyacinth invasion suppressed algae, changed the timing of peak snail abundance, and increased total production of human‐infectious cercariae ~6‐fold relative to uninvaded controls. Hyacinth management had complex effects on algae, snails, and schistosomes. Removal increased algal growth and snail abundance (but not biomass), and slightly reduced schistosome production. In contrast, destruction increased snail biomass (but not abundance), indicating increases in body size. Destruction caused the greatest schistosome production (10‐fold more than the control), consistent with evidence that larger snails with greater access to food are most infectious. Our results highlight the dynamic effects of invasion and management on a globally impactful human parasite and its intermediate host. Ultimately, preventing or removing hyacinth invasions would simultaneously benefit human and environmental health outcomes. [ABSTRACT FROM AUTHOR]

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 ~ ninefold 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. [ABSTRACT FROM AUTHOR]