Leptospirosis in Endangered Island Foxes and California Sea Lions: Outbreak Prediction and Prevention in a Changing World

Dr. James Lloyd-Smith | University of California, Los Angeles

RC-2635

Objective

Leptospirosis, the disease caused by pathogenic bacteria of the genus Leptospira, is a major health burden for humans and animals worldwide and a recognized risk for military personnel. The project team is conducting a long-term study of Leptospira ecology in California sea lions (CSL: Zalophus californianus) and recently discovered an outbreak of the same strain of Leptospira in island foxes (Urocyon littoralis) on Santa Rosa Island (SRI), California. This raises immediate concerns about risks to subspecies of island fox on three nearby DoD islands, one of which is endangered and another of which is currently undergoing a population decline. This project will study the ecology of Leptospira in these two wildlife species of concern, and it will build models to analyze how non-stationary conditions affect disease incidence and impact. Specific project objectives are

  1. To identify the source of the current Leptospira outbreak in the endangered Santa Rosa Island fox (U. littoralis santarosae).
  2. To understand how non-stationary drivers shape Leptospira dynamics in the CSL population to enable formulating a model capable of short-term outbreak prediction and long-term trend projection.
  3. To characterize the ecology of Leptospira in island foxes and develop a data-driven model to project impacts and assess prevention and control strategies under changing conditions.

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Technical Approach

This project consists of an integrative program of field, laboratory, and modeling research. With partners at the National Parks Service, fieldwork will be conducted to learn about the disease ecology of Leptospira in island fox populations. With partners at The Marine Mammal Center and the National Marine Fisheries Service’s National Marine Mammal Laboratory, fieldwork will be conducted to extend long-term studies of Leptospira in California sea lions and understand how demography and environmental conditions interact to drive disease exposure and impact. Laboratory analyses (primarily serology, PCR, culture, and serum chemistry) will be conducted on prospective and archived samples to detect current infections and prior exposure and to assess clinical status. Whole-genome sequences of Leptospira isolates from marine and terrestrial hosts will be analyzed to understand the number, timing, and direction of transmission events that led this pathogen to cause major outbreaks in both marine and terrestrial communities.

Throughout the project, statistical and mathematical models will be developed to integrate lines of evidence, learn about pathways of exposure, and make projections of future disease impacts under changing conditions. Many modeling approaches will be used, as appropriate, including compartmental models of disease spread, multistate mark-resight models to assess disease impact on foxes, and a semiparametric approach to disentangle the intrinsic drivers (related to demography and herd immunity) and extrinsic drivers (related to environmental variation) of disease patterns. Each of these models will be used first to learn about the determinants of past patterns and then to project how disease incidence and impact can be expected to change under future non-stationarities.

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Benefits

Research outcomes will yield fundamental and applied insights, and they will extend long-term data sets that are essential for research on climate change impacts. The findings will have direct relevance to present and future pathogen control and wildlife management strategies. For the foxes the project will clarify when control of Leptospira is warranted and how it should be structured to optimally reduce disease impact on DoD lands. Screening for Leptospira exposure in an island fox population on a DoD-owned island, which is presently in decline, also will be conducted. For the sea lions, also a protected species, research will predict risk of major outbreaks (which drive exposure of other species) and build ecological understanding to clarify when mass stranding events are due to natural causes. The findings will be communicated to end users through our existing, strong relationships with the Island Fox Working Group and Marine Mammal Stranding Network, and through direct contacts with DoD colleagues. The core modeling products will be released as a documented software package in the R environment, so that end users can explore scenarios and update results when new data become available.

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Points of Contact

Principal Investigator

Dr. James Lloyd-Smith

University of California, Los Angeles

Phone: 310-206-8207

Program Manager

Resource Conservation and Resiliency

SERDP and ESTCP

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