Pathogen invasion and persistence in an establishing host population: Leptospirosis in the endangered island fox

病原体是在“宿主”物种中引起疾病，有时甚至死亡的微小生物体。由于病原体侵入新的宿主种群会对宿主（包括人类）产生巨大影响，生态学家长期以来一直在研究病原体入侵的原因和后果。以前的工作集中在病原体入侵稳定和已经建立的宿主种群的情况下。这项工作并不能帮助我们理解另外两种重要情况下的传染病：当一种新的宿主物种在景观中传播时（疾病可能有助于减缓其传播），以及当一种罕见的宿主物种作为保护计划的一部分被故意重新引入时（疾病对保护目标构成威胁）。本课题将首先深入研究第二种情况。它将探讨一个罕见的宿主和常见的病原体如何相互作用，从最初的重新引入宿主和病原体的入侵到它们的长期持续或灭绝。调查人员将研究一种濒危的岛屿狐狸种群，它们最近被重新引入加利福尼亚的一个岛屿。这些狐狸现在正在经历一种叫做钩端螺旋体病的疾病的大爆发，这种疾病会给世界各地的人类和野生动物带来严重的健康问题。该项目将有助于了解钩端螺旋体病如何在野生动物中传播，并最终感染人类和牲畜。岛屿狐狸是一个罕见的成功案例，濒危物种法案的保护使狐狸数量得以恢复；这项工作将指导海岛狐的未来管理。更广泛地说，这项工作将为其他放归项目的风险评估和疾病控制提供信息。该项目包括向包括南加州学龄儿童在内的公众宣传保护和疾病问题。研究对象是加州圣罗莎岛上的岛狐（Urocyon littoralis）。在20世纪90年代末数量锐减后，圣罗莎岛上剩下的14只狐狸全部被圈养起来。从2004年开始的重新引入计划在岛上重新安置了狐狸，但2010年发现了钩端螺旋体（钩端螺旋体病的病原体）的爆发。对储存的血清样本的分析表明，到2009-10年，疫情已经在岛上广泛爆发，并且在狐狸重新引入该岛后，病原体可能侵入了狐狸种群。岛上的斑点臭鼬（Spilogale gracilis）也被发现感染，基因分析表明，它与经常出现在岛上的加利福尼亚海狮（Zalophus californianus）中流传的钩端螺旋体菌株有密切联系。广泛的样本库和种群监测数据为重建这种病原体入侵的历史提供了独特的机会。该项目将整合现场、实验室、基因组和建模方法。其目标是确定圣罗莎疫情中钩端螺旋体的来源，描述该岛社区在整个建立过程中的传播动态，预测钩端螺旋体是否会在该岛持续存在，并评估钩端螺旋体对狐狸健康和保护的影响。研究人员将对这些发现进行概括，以提取教训和工具，应用于其他疾病系统。

Pathogens are tiny organisms that cause disease and sometimes death in a "host" species. Because invasion of pathogens into new host populations can have dramatic effects on hosts, including humans, ecologists have long studied the causes and consequences of pathogen invasion. Previous work has focused on situations in which pathogens invade host populations that are stable and already established. That work does not help us understand infectious disease in two other situations that are important: when a new host species is spreading across a landscape (where disease might help slow its spread) and when a rare host species is deliberately reintroduced as part of a conservation program (where disease is a threat to conservation goals). This project will be the first in-depth study of the second situation. It will explore how a rare host and common pathogen interact from the initial reintroduction of the host and invasion of the pathogen to their long-term persistence or die-out. The investigators will study an endangered Island Fox population, recently reintroduced to a California island. The foxes are now experiencing a major outbreak of a disease called leptospirosis, which causes major health problems for humans and wildlife around the world. This project will build understanding of how leptospirosis spreads in wildlife and eventually can infect humans and livestock. Island foxes are a rare success story in which Endangered Species Act protections have enabled the fox population to recover; this work will guide future management of Island Foxes. More generally, this work will inform risk assessment and disease control in other reintroduction programs. The project includes outreach efforts to inform the public, including southern California school-children, about conservation and disease issues.The study system is the Island Fox (Urocyon littoralis) on Santa Rosa Island, California. After a population crash in the late 1990s, all 14 remaining foxes on Santa Rosa were taken into captivity. A reintroduction program, beginning in 2004, reestablished foxes on the island, but an outbreak of Leptospira interrogans (the agent of leptospirosis) was discovered in 2010. Analysis of banked serum samples showed that the outbreak was already widespread on the island by 2009-10, and the pathogen likely invaded the fox population as it re-colonized the island after fox reintroduction. The island spotted skunk (Spilogale gracilis) was also found to be infected, and genetic analyses indicate a close link to a Leptospira strain circulating in California sea lions (Zalophus californianus) that frequent the island. Extensive sample banks and population monitoring data provide a unique opportunity to reconstruct the history of this pathogen invasion. This project will integrate field, laboratory, genomic and modeling approaches. Its goals are to determine the source of Leptospira in the Santa Rosa outbreak, characterize transmission dynamics in the island community throughout the establishment process, predict whether Leptospira will persist on the island, and assess the impact of Leptospira on fox health and conservation. The investigators will generalize the findings to extract lessons and tools to be applied to other disease systems.