Natural history of a bighorn sheep pneumonia epizootic: Source of infection, course of disease, and pathogen clearance.

A respiratory disease epizootic at the National Bison Range (NBR) in Montana in 2016-2017 caused an 85% decline in the bighorn sheep population, documented by observations of its unmarked but individually identifiable members, the subjects of an ongoing long-term study. The index case was likely one of a small group of young bighorn sheep on a short-term exploratory foray in early summer of 2016. Disease subsequently spread through the population, with peak mortality in September and October and continuing signs of respiratory disease and sporadic mortality of all age classes through early July 2017. Body condition scores and clinical signs suggested that the disease affected ewe groups before rams, although by the end of the epizootic, ram mortality (90% of 71) exceeded ewe mortality (79% of 84). Microbiological sampling 10 years to 3 months prior to the epizootic had documented no evidence of infection or exposure to

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© 2021 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.

Déclaration de conflit d'intérêts

This study was supported by funding sources cited in the Acknowledgments. Additional research funding for the authors’ bighorn sheep pneumonia‐related research has been received from the US Department of Agriculture (including the Animal Plant Health Inspection Service and the US Forest Service), the US Geologic Survey, the Federal Aid to Wildlife Restoration program, numerous chapters and affiliates of the Wild Sheep Foundation, and the WSU Fowler Emerging Infectious Diseases Endowment, all listed here because they may represent perceived conflicts of interest.