Resource competition drives natural and rebound dynamics of snails and schistosomes

资源竞争驱动蜗牛的自然繁殖和反弹 和血吸虫 项目摘要 超过2.5亿人感染了扁虫，扁虫属 2000万人因血吸虫病而严重发病。 人类在接触到由寄生虫产生的幼虫寄生虫（尾蚴）后受到感染， 淡水栖息地的感染蜗牛。因此，由蜗牛种群产生的尾蚴 是人类暴露、感染和疾病风险的重要组成部分。 血吸虫病控制包括许多方案，包括药物管理， 行为干预和灭螺。蜗牛控制计划通过以下方式降低蜗牛密度： 使用有毒的化学杀软体动物剂或致命的捕食者。然而，蜗牛本身并不 直接感染人类。相反，蜗牛释放自由生活的尾蚴， 皮肤接触后感染。这种控制目标（蜗牛）和 人类感染的近因（尾蚴）使棘手的控制复杂化，因为 每只蜗牛的尾蚴产量对生态条件如蜗牛密度很敏感。 绝大多数的模型和控制试验检查自然动态和 对蜗牛的控制假设所有蜗牛都具有相同的传染性，导致假设 蜗牛密度与尾蚴密度直接相关，因此可能对人类 exposure.然而，受感染的蜗牛可以产生超过50倍的尾蚴时，食物是 资源丰富，竞争者稀少，自然条件也很好。因此， 根据传统观念，尾蚴密度和人类暴露的可能性可能是最大的， 当蜗牛的密度较低并在增长时。因此，研究 蜗牛和尾蚴密度对设计最佳蜗牛控制策略至关重要，因为这些 动态决定了人类风险的时间和程度。 这项研究将结合联合收割机现场和实验室实验，以测试新的假设， 尾蚴在自然环境中的动力学，这是我们发展的理论， 在动态情景中纳入蜗牛和拟钉螺的能量吸收和使用。 具体来说，我们将测试预测：（1）有短暂的，强烈的峰值尾蚴密度 在季节的早期，当个体蜗牛很大并且高度繁殖时，（2）存在 其他食物来源，如腐烂的植物，可以维持尾蚴生产更长的时间， （3）减少但不消除水体中的蜗牛可能适得其反， 通过放松对食物的竞争，尾蚴的数量几乎没有减少，甚至有所增加。最终这 这项工作可以改善对造成重大全球健康负担的寄生虫的预测和控制。

RESOURCE COMPETITION DRIVES NATURAL AND REBOUND DYNAMICS OF SNAILS AND SCHISTOSOMES Project summary More than 250 million people are infected with schistosomes, flatworms in the genus Schistosoma, and 20 million humans suffer from severe morbidity due to schistosomiasis. Humans become infected after exposure to larval parasites (cercariae) that are produced by infected snails in freshwater habitats. Therefore, the production of cercariae by snail populations represents an important component of the human risk of exposure, infection, and disease. Schistosomiasis control incorporates many programs, including drug administration, behavioral intervention and snail control. Snail control programs reduce snail density by applying toxic chemical molluscicides or lethal predators. However, snails themselves do not directly infect humans. Instead, snails release free living cercariae that directly cause human infections following skin contact. This mismatch between the target of control (snails) and the proximate cause of human infections (cercariae) complicates schistosome control because the production of cercariae per snail is sensitive to ecological conditions, such as snail density. The vast majority of models and control trials examining the natural dynamics and control of schistosomes assume that snails are all equally infectious, leading to the assumption that snail density directly correlates with cercariae density, and therefore potential for human exposure. However, infected snails can produce >50-fold more cercariae when food is abundant, competitors are scarce, and physical conditions are otherwise benign. Thus, counter to conventional wisdom, cercarial densities, and human exposure potential, could be greatest when the density of snails is lower and growing. Therefore, studying the dynamic link between snail and cercarial density is critical to designing optimal snail control strategies, because these dynamics determine the timing and magnitude of human risk. This research will combine field and laboratory experiments to test novel hypotheses for the dynamics of cercariae in natural settings that arise from theory we developed to explicitly incorporate energy uptake and use by snails and schistosomes in dynamic scenarios. Specifically, we will test predictions that: (1) there are brief, intense peaks of cercarial density early in the season, when individual snails are large and highly reproductive, (2) the presence of other food sources, such as decaying plants can sustain cercarial production over longer periods, and (3) reducing, but not eliminating, snails from water bodies could backfire, causing little reduction or even an increase in cercariae, by relaxing competition for food. Ultimately, this work can improve the prediction and control of a parasite causing major global health burden.