Diseases

North American mountain sheep provide suitable habitat for a wide range of other, smaller organisms that can live in harmony with or upon them. Disease is generally an outlier condition. The effects of most diseases are limited to impairing individual or local (i.e., herd-level) productivity, survival, or resilience. Nonetheless, a few can have more widespread or lasting effects, limiting population growth, persistence, or management options. Diseases in their broadest context, particularly those involving non-native (i.e., introduced) agents, have had cumulative, range-wide consequences for mountain sheep (bighorn [ Ovis canadensis ], thinhorn [ Ovis dalli ]). Some continue to undermine conservation of bighorn subspecies and threaten similar harm to native thinhorn subspecies. We provide an overview of an array of diseases that can affect mountain sheep in North America, emphasizing those of significance to mountain sheep or their populations. We provide brief summaries of the apparent cause(s) and effects, including conservation and management implications where relevant. We intend to provide those interested in the history, ecology, management, and conservation of North American mountain sheep with an accessible primer on native and introduced diseases that can affect these species.