Resource competition drives natural and rebound dynamics of snails and schistosomes

资源竞争推动蜗牛的自然和反弹动态 和血吸虫 项目总结 超过2.5亿人感染了血吸虫属的扁虫 有2000万人因血吸虫病而患上严重的疾病。 人类在接触到幼虫寄生虫(尾蚴)后会被感染，这种寄生虫由 淡水栖息地受感染的蜗牛。因此，钉螺种群产生尾蚴 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项目，包括药物管理， 行为干预和灭螺。钉螺控制计划通过以下方式降低钉螺密度 使用有毒化学杀螺剂或致命的捕食者。然而，蜗牛本身并不 直接感染人类。取而代之的是，蜗牛释放出自由生活的尾虫，这种尾虫直接导致人类 皮肤接触后的感染。这种控制目标(蜗牛)和 人类感染的直接原因(尾蚴)使血吸虫控制变得复杂，因为 每只蜗牛的尾蚴产量对生态条件很敏感，例如蜗牛密度。 绝大多数模型和对照试验检验了自然动力学和 血吸虫的控制假设所有的蜗牛都具有同等的传染性，这导致了这样的假设 钉螺密度与尾蚴密度直接相关，因此对人类的潜在影响 曝光。然而，受感染的蜗牛可以产生50倍以上的尾蚴，当食物 资源丰富，竞争对手稀缺，而物质条件在其他方面都是良性的。因此，计数器 在传统观点看来，尾蚴密度和人类暴露潜力可能是最大的。 当蜗牛密度较低且不断增长时。因此，研究二者之间的动态联系 钉螺和尾虫密度对于设计最佳的钉螺控制策略至关重要，因为这些 动态决定了人类风险的时机和大小。 这项研究将结合现场和实验室实验来检验新的假设 尾蚴在自然环境中的动态，这源于我们发展到显式的理论 将蜗牛和血吸虫的能量吸收和利用纳入动态情景。 具体地说，我们将测试如下预测：(1)尾蚴密度有短暂而强烈的峰值 在季节的早期，当单个蜗牛体型较大且繁殖力强时，(2) 其他食物来源，如腐烂的植物，可以维持较长时间的尾蚴生产。 (3)减少但不是消灭水体中的蜗牛可能会适得其反，导致 通过放松对食物的竞争，尾蚴的数量几乎没有减少，甚至增加了。归根结底，这 这项工作可以改进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.