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有机体。由于病原体入侵新的宿主种群可能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。这项工作无助于我们在另外两种重要的情况下理解传染病：一种是新的寄主物种在一片土地上传播(疾病可能有助于减缓其传播)，另一种是当一种稀有的寄主物种被故意作为保护计划的一部分重新引入时(在这种情况下，疾病是对保护目标的威胁)。这个项目将是第一次深入研究第二种情况。它将探索一种罕见的寄主和常见病原体如何从最初重新引入寄主和入侵病原体到它们长期存在或灭绝。调查人员将研究濒临灭绝的岛狐种群，它们最近重新引入加州的一个岛屿。狐狸现在正在经历一种名为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。《濒危物种法》的保护使狐狸数量得以恢复，这是一个罕见的成功案例；这项工作将指导未来对岛屿狐狸的管理。更广泛地说，这项工作将为其他重新引入计划中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。研究系统是加利福尼亚州圣罗莎岛的岛狐(Urocyon Littoraris)。在20世纪90年代末的一次种群崩溃之后，圣罗莎上剩下的14只狐狸都被圈养了。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年发现了问号钩端螺旋体(钩端螺旋体病的病原体)的暴发。对银行血清样本的分析表明，到2009-10年，疫情已经在岛上广泛传播，这种病原体很可能在狐狸重新引入后重新定居该岛时入侵了狐狸种群。岛上的斑点臭鼬(Spilogale Gracilis)也被发现受到感染，遗传分析表明，它与加州海狮中流行的一种钩端螺旋体菌株有密切联系，这些海狮经常出现在该岛。广泛的样本库和人口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。该项目将结合现场、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上社区的传播动态，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。研究人员将对这些发现进行概括，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.