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Modelling how resource competition among snail hosts affects the mollusciciding frequency and intensity needed to control human schistosomes
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- Ecological interactions among intermediate hosts or vectors of human pathogens can enhance or hinder control efforts. However, we currently lack quantitative frameworks to predict how interactions among host physiology, ecology, and control effort shape human disease risk.
- We explore this approach for human schistosomiasis, a major, historically neglected tropical disease. A recent re-emphasis on snail host control using molluscicides highlights the need to re-evaluate the ecological mechanisms driving emergence of schistosome cercariae, the life stage that directly infects humans.
- We integrate physiology, resource competition, and control using individual-based models based on general metabolic theory, Dynamic Energy Budget theory, to simulate human-infectious schistosome density under molluscicide scenarios varying in frequency and intensity throughout a 150-day transmission season. Without molluscicide control, our model predicts intense resource competition among hosts and large and early parasite peaks under algae and detritus resources. Consistent monthly control, as recommended by the WHO, can work if intense, i.e. > 90% host mortality. In contrast, one-off, intense, and early mollusciciding induces large delayed rebounds in parasites by releasing the few remaining snails from resource competition.
- Our simulations confirm the WHO recommendation that frequent mollusciciding can disrupt transmission, but contradict recent suggestions for infrequent mollusciciding, e.g. annually, which can backfire because relaxed resource competition among hosts stimulates parasite production. Our results identify resource competition as a key ecological mechanism driving parasite population intensity for schistosome habitats across ecosystems.
- Our results show resource ecology models can identify peaks in parasite density. More generally, resource competition among hosts may complicate efforts to control infected snail host densities in the field and thus disease risk through culling or mortality-based interventions. Connecting individuals to community and disease dynamics with resource ecology can inform better field control strategies and help managers avoid unintended consequences for human health.
Keywords: disease, individual-based model, bioenergetics, resource competition, schistosome
Matt Malishev
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📧 matthew.malishev [at] gmail.com