A framework for reconciling competing effects of competitors on disease transmission

生物多样性正在以惊人的速度消失，与此同时，传染病越来越多地从野生动物蔓延到人类。因此，迫切需要了解物种多样性如何影响野生动物的传染病。在某些生态系统中，竞争物种多样性的增加降低了疾病风险，这被称为“稀释”效应，因为多样性稀释了感染。然而，在其他系统中，更多样化的社区增加了疾病风险，称为“放大”效应。何时期望稀释或放大是疾病生态学家争论的话题。本项目旨在利用鹿鼠体内的辛诺布雷汉坦病毒（SNV）作为模型，调和生物多样性的竞争效应。该系统同时显示了稀释和放大的两个方面。本项目提出了一个框架，用于检查稀释和放大的潜在机制，以及它们如何相互作用以潜在地协同或拮抗。这将有助于超越长期以来关于哪种模式（稀释或放大）更普遍的争论，澄清不同的机制何时可能占主导地位，并有助于解释在各种研究中看到的不同模式。它还将通过推进汉坦病毒肺综合征（HPS）的预防工作而造福社会。这种由SNV引起的人类疾病自1993年发现以来，已影响到700多人（造成250多人死亡）。这项研究的其他更广泛的影响包括推广和与印第安人合作，特别关注K-12的推广。三种机制决定了竞争对手多样性的增加是否会导致直接传播病原体的稀释或扩增。如果物种多样性增加导致1)宿主密度降低，2)接触率降低，或3)接触后传播概率降低（传播率），就会发生稀释。相反，如果增加的多样性起到相反的作用，则可能发生放大。该项目开发了一个框架，以一个数学模型为中心，将SIR（易感-感染-恢复）动力学与Lotka-Volterra竞争系数相结合，来解开这些成分的稀释和放大效应。目的1是通过对纵向数据进行贝叶斯种群分析，确定增加的小型哺乳动物多样性/组成如何影响小鼠种群人口统计和随后的SNV患病率。目的2是通过对自然种群的长期生理监测和野外实验操作相结合，确定增加的小型哺乳动物多样性如何通过传播性（通过压力、共感染、免疫和病毒脱落）和/或鹿鼠之间接触率的变化影响传播率。目标3是将目标1和目标2的发现综合成一个一般模型，说明竞争对手如何以不同的方式影响传播的所有三个组成部分，并扩大规模，以确定系统内和系统间疾病流行中观察到的模式的多样性。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Biodiversity is disappearing at an alarming rate, and at the same time, infectious diseases increasingly spill over from wildlife to humans. Therefore, it is urgent to understand how species diversity affects infectious diseases in wildlife. In some ecosystems, increasing diversity of competitor species decreases disease risk, termed the 'dilution' effect because diversity dilutes out infection. However, in other systems, a more diverse community increases disease risk, termed the ‘amplification’ effect. When to expect dilution or amplification is a topic of debate among disease ecologists. This project aims to reconcile the competing effects of biodiversity using Sin Nombre hantavirus (SNV) in deer mice as a model. This system displays aspects of both dilution and amplification at the same time. This project lays out a framework for examining potential mechanisms of dilution and amplification and how they can interact to potentially be synergistic or antagonistic. This will facilitate moving beyond the long-standing debate of which pattern (dilution or amplification) is more prevalent, clarifying when different mechanisms may be dominant and help explain the different patterns seen in various studies. It will also benefit society by advancing prevention efforts for hantavirus pulmonary syndrome (HPS). This human illness caused by SNV, has affected more than 700 people (killing more than 250) since its discovery in 1993. Other broader Impacts of this research include outreach and work with Native Americans, with particular focus on K-12 outreach. Three mechanisms determine if increasing competitor diversity will lead to dilution or amplification of a directly transmitted pathogen. Dilution will occur if increased species diversity leads to 1) decreased host density, 2) decreased contact rates, or 3) decreased probability of transmission given contact (transmissibility). Conversely, amplification could occur if increased diversity does the opposite. This project develops a framework to disentangle these component dilution and amplification effects, centered around a mathematical model that combines SIR (Susceptible-Infected-Recovered) dynamics with a Lotka-Volterra competition coefficient. Aim 1 is to determine how increased small mammal diversity / composition affects mouse population demography and subsequent SNV prevalence, by performing Bayesian population analyses on longitudinal data. Aim 2 is to determine how increased small mammal diversity affects the transmission rate, through changes in transmissibility (via stress, co-infections, immunity, and viral shedding) and/or contact rates between deer mice, using a combination of long-term monitoring of physiology in natural populations, and experimental manipulation in the field. Aim 3 is to synthesize the findings from Aims 1 and 2 into a general model of how competitors can differentially affect all three components of transmission and scale up to determine the variety of observed patterns in disease prevalence within and across systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.