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

病原体是微小的生物体，它们会导致疾病，有时会导致“宿主”物种的死亡。由于病原体入侵新的宿主种群会对包括人类在内的宿主产生巨大影响，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），以及当一种稀有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）。本项目将首次深入研究第二种情况。它将探讨一个罕见的主机和常见的病原体如何相互作用，从最初的重新引入主机和病原体的入侵，他们的长期持久性或消亡。调查人员将研究一个濒临灭绝的岛狐种群，最近重新引入加州的一个岛屿。狐狸现在正在经历一场名为钩端螺旋体病的疾病的大爆发，这种疾病给世界各地的人类和野生动物带来了重大的健康问题。该项目将建立对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的理解。岛上的狐狸是一个罕见的成功故事，其中濒危物种法的保护使狐狸人口恢复;这项工作将指导未来的管理岛狐狸。 更一般地说，这项工作将为其他再引入计划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童在内的公众宣传保护和疾病问题的外展工作。在20世纪90年代末的一次人口崩溃后，圣罗莎上剩下的14只狐狸都被圈养起来。2004年开始的一项重新引入计划在岛上重新建立了狐狸，但在2010年发现了钩端螺旋体病的爆发。对库存血清样本的分析表明，到2009-10年，疫情已经在岛上广泛传播，病原体可能在狐狸重新引入后重新定居岛上时入侵狐狸种群。岛上的斑点臭鼬（Spilogale gracilis）也被发现受到感染，遗传分析表明与经常出现在该岛的加州海狮（Zalophus californianus）中流行的钩端螺旋体菌株密切相关。大量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一个独特的机会。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，描述整个建立过程中岛屿社区的传播动态，预测钩端螺旋体是否会在岛上持续存在，并评估钩端螺旋体对狐狸健康和保护的影响。研究人员将概括这些发现，以提取适用于其他疾病系统的经验教训和工具。

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.