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Low-coverage vaccination strategies for the conservation of endangered species

Abstract

The conventional objective of vaccination programmes is to eliminate infection by reducing the reproduction number of an infectious agent to less than one1, which generally requires vaccination of the majority of individuals. In populations of endangered wildlife, the intervention required to deliver such coverage can be undesirable and impractical2; however, endangered populations are increasingly threatened by outbreaks of infectious disease for which effective vaccines exist3,4. As an alternative, wildlife epidemiologists could adopt a vaccination strategy that protects a population from the consequences of only the largest outbreaks of disease. Here we provide a successful example of this strategy in the Ethiopian wolf, the world's rarest canid5, which persists in small subpopulations threatened by repeated outbreaks of rabies introduced by domestic dogs6. On the basis of data from past outbreaks, we propose an approach that controls the spread of disease through habitat corridors between subpopulations and that requires only low vaccination coverage. This approach reduces the extent of rabies outbreaks and should significantly enhance the long-term persistence of the population. Our study shows that vaccination used to enhance metapopulation persistence through elimination of the largest outbreaks of disease requires lower coverage than the conventional objective of reducing the reproduction number of an infectious agent to less than one1.

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Figure 1: Known distribution of Ethiopian wolf packs in three subpopulations in the Bale Mountains.
Figure 2: R 0 map of the Web Valley and Morebawa subpopulations.
Figure 3: Model projections.

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Acknowledgements

We thank Ethiopia's Wildlife Conservation Department, the Oromiya Rural Land and Natural Resources Administration Authority, and the Bale Mountains National Park for permission to undertake this work. We thank the staff of the EWCP for field work; the WCD veterinarians F. Shiferaw and K. Argaw; C. Rupprecht and staff at CDC; T. Fooks and staff at the VLA; R. K. Wayne for the work in his genetics laboratory, supported in part by his grant from the NSF; and the IUCN/SSC Canid and Veterinary Specialist Groups for advice. D.T.H. acknowledges the award of a MacLagan Travel Grant from the Royal Society of Edinburgh in support of this research. Funding was provided by the Born Free Foundation, Frankfurt Zoological Society, the Wellcome Trust, Wildlife Conservation Network, Morris Animal Foundation, Conservation International and Siren UK. Author Contributions D.T.H. undertook much of the model formulation and analysis, and coordinated the synthesis of ideas and information. D.A.R. generated and compiled much of the empirical and all of the genetic data. L.M. assisted with formulation and interpretation of the analyses. D.L.K. managed the implementation of the vaccination programme. L.A.T. provided data and analysis for spatial distribution of the wolf population. M.B.G. assisted with early formulation of the modelling work and interpretation of later model output. S.D.W. coordinated fieldwork for much of the period over which this study applies. J.P.P. was instrumental in overseeing the genetic analyses. S.C. assisted in formulation of the vaccination strategy and in writing the manuscript. M.E.J.W. suggested analyses and assisted in writing the manuscript. C.S.-Z. was responsible for funding and coordinating Ethiopian wolf research and conservation work, and provided data on the 1992 outbreak. J.M. provided essential data on wolf demography for use in the PVA model. D.W.M. conceived and supervised several doctoral studies that have underpinned the project since its inception. M.K.L. was responsible for designing and implementing the disease control strategy.

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This file contains Supplementary Methods, Supplementary Results Supplementary Tables 1–4 and Supplementary Figures 1–3. (PDF 508 kb)

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Haydon, D., Randall, D., Matthews, L. et al. Low-coverage vaccination strategies for the conservation of endangered species. Nature 443, 692–695 (2006). https://doi.org/10.1038/nature05177

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