Pneumonia in bighorn sheep: Risk and resilience

Abstract

Infectious disease contributed to historical declines and extirpations of bighorn sheep (Ovis canadensis) in North America and continues to impede population restoration and management. Reports of pneumonia outbreaks in freeranging bighorn sheep following contact with domestic sheep have been validated by the results of 13 captive commingling experiments. However, ecological and etiological complexities still hinder our understanding and control of respiratory disease in wild sheep. In this paper, we review the literature and summarize recent data to present an overview of the biology and management of pneumonia in bighorn sheep. Many factors contribute to this population-limiting disease, but a bacterium (Mycoplasma ovipneumoniae) host-specific to Caprinae and commonly carried by healthy domestic sheep and goats, appears to be a primary agent necessary for initiating epizootics. All-age epizootics are usually associated with significant population declines, but mortality rates vary widely and factors influencing disease severity are not well understood. Once introduced, M. ovipneumoniae can persist in bighorn sheep populations for decades. Carrier females may transmit the pathogen to their susceptible lambs, triggering fatal pneumonia outbreaks in nursery groups, which limit recruitment and slow or prevent population recovery. The demographic costs of disease persistence can be equal to or greater than the impacts of the initial epizootic. Strain typing suggests that spillover of M. ovipneumoniae into bighorn sheep populations from domestic small ruminants is ongoing and that consequences of spillover are amplified by movements of infected bighorn sheep across populations. Therefore, current disease management strategies focus on reducing risk of spillover from reservoir populations of domestic sheep and goats and on limiting transmission among bighorn sheep.

Age‐specific infectious period shapes dynamics of pneumonia in bighorn sheep

“…Introduction of M. ovipneumoniae into naïve bighorn sheep populations can result in severe mortality ranging from 10 to 100% (Cassirer et al . , ). Animals that survive acute infection and associated disease can clear infection or can remain subclinically infected in the upper respiratory tract.…”

Special section: Controversies in mountain sheep management

“…Transporting diseases is another burden associated with translocation of mountain sheep (Boyce et al ). Because one of the most serious diseases of mountain sheep is pneumonia, we invited a comprehensive review by Cassirer et al (). Seldom can wild sheep persist when there is contact with domestic sheep or goats because diseases are latent in domesticated animals.…”

Horn size and nutrition in mountain sheep: Can ewe handle the truth?

“…The occurrence of epizootic pneumonia in bighorn sheep populations muddles the already complicated processes underlying population dynamics, and respiratory disease often is the cause of massive population crashes (Monello et al , Cassaigne et al , Cassirer et al ). Respiratory disease has afflicted populations of bighorn sheep for the past century (Grinnell ) and, despite substantial research on the topic (Miller et al ), pneumonia continues to be one of the most poorly understood diseases that afflict wildlife in North America (Plowright et al ).…”