Resource competition drives natural and rebound dynamics of snails and schistosomes

资源竞争驱动钉螺和血吸虫的自然和反弹动态

基本信息

批准号：
10582537
负责人：
David James Civitello
金额：
$ 34.2万
依托单位：
EMORY UNIVERSITY
依托单位国家：
美国
项目类别：
财政年份：
2020
资助国家：
美国
起止时间：
2020-03-16 至 2025-02-28
项目状态：
未结题

项目摘要

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.

资源竞争推动了蜗牛的自然和反弹动态和血块项目摘要超过2.5亿人感染了血块，属的扁虫感染血吸虫和2000万人类由于血吸虫病引起的严重发病率。人类在暴露于幼体寄生虫（Cercariae）后被感染在淡水栖息地中被感染的蜗牛。因此，由蜗牛种群生产cercariae 代表了人类暴露，感染和疾病风险的重要组成部分。血吸虫病控制结合了包括药物管理在内的许多计划，行为干预和蜗牛控制。蜗牛控制程序将蜗牛密度降低施用有毒化学软蛋白酶或致命的捕食者。但是，蜗牛本身不会直接感染人类。相反，蜗牛释放直接引起人类的免费生活cercariae 皮肤接触后的感染。控制目标（蜗牛）和人类感染的近端原因（cercariae）使血吸虫的控制复杂化，因为每蜗牛的尾car骨的产生对蜗牛密度等生态状况敏感。绝大多数模型和控制试验检查了自然动态和对血吸虫的控制假设蜗牛都同样具有感染力，导致了假设蜗牛密度与尾密度直接相关，因此可能对人类接触。但是，被感染的蜗牛在食物时会产生高度> 50倍丰富的竞争者稀缺，身体状况是良性的。因此，计数器对于传统的智慧，cercarial密度和人类暴露潜力可能是最大的当蜗牛的密度较低且增长时。因此，研究动态联系蜗牛和尾密度对于设计最佳蜗牛控制策略至关重要，因为这些动力学决定了人类风险的时机和幅度。这项研究将结合现场和实验室实验，以测试新的假设我们开发的理论产生的自然环境中cercariae的动态在动态场景中纳入蜗牛和血块的能量吸收和使用。具体而言，我们将测试预测：（1）存在短暂而强烈的圆锥密度峰在季节初，当单个蜗牛大且高度生殖时，（2）存在其他食物来源，例如腐烂的植物可以持续更长时期，（3）减少但不会消除水体的蜗牛可能适得其反，导致通过放松食物竞争，很少减少甚至增加cercariae。最终，这个工作可以改善对寄生虫的预测和控制，从而造成全球重大的健康负担。