Pathology of Chronic Mycoplasma ovipneumoniae Carriers in a Declining Bighorn Sheep (Ovis canadensis) Population

Authors

Jennifer L. Malmberg, United States Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services, National Wildlife Research Center, Fort Collins, ColoradoFollow
Samantha E. Allen, Wyoming Game and Fish Department, Veterinary Services
Jessica E. Jennings-Gaines, Wyoming Game and Fish Department, Veterinary Services, Wildlife Health Laboratory
Marguerite Johnson, Wyoming Game and Fish Department, Veterinary Services, Wildlife Health Laboratory
Katie L. Luukkonen, Wyoming Game and Fish Department, Veterinary Services, Wildlife Health Laboratory
Kara M. Robbins, Wyoming Game and Fish Department, Veterinary Services, Wildlife Health Laboratory
Todd E. Cornish, University of California, Davis
Rachel A. Smiley, University of Wyoming
Brittany L. Wagler, University of Wyoming
Zach Gregory, Wyoming Game and Fish Department
Daryl Lutz, Wyoming Game and Fish Department
Pat Hnlicka, United States Fish and Wildlife Service, Lander Wyoming
Kevin L. Monteith, University of Wyoming
William H. Edwards, Wyoming Game and Fish Department, Veterinary Services, Wildlife Health Laboratory

Document Type

Article

Date of this Version

2024

Citation

Journal of Wildlife Diseases (2024) 60(2): 448-460

doi: 10.7589/JWD-D-23-00132

Comments

United States government work

Abstract

Bighorn sheep (Ovis canadensis) across North America commonly experience populationlimiting epizootics of respiratory disease. Although many cases of bighorn sheep pneumonia are polymicrobial, Mycoplasma ovipneumoniae is most frequently associated with all-age mortality events followed by years of low recruitment. Chronic carriage of M. ovipneumoniae by adult females serves as a source of exposure of naïve juveniles; relatively few ewes may be responsible for maintenance of infection within a herd. Test-and-remove strategies focused on removal of adult females with evidence of persistent or intermittent shedding (hereafter chronic carriers) may reduce prevalence and mitigate mortality. Postmortem confirmation of pneumonia in chronic carriers has been inadequately reported and the pathology has not been thoroughly characterized, limiting our understanding of important processes shaping the epidemiology of pneumonia in bighorn sheep. Here we document postmortem findings and characterize the lesions of seven ewes removed from a declining bighorn sheep population in Wyoming, USA, following at least two antemortem detections of M. ovipneumoniae within a 14-mo period. We confirmed that 6/7 (85.7%) had variable degrees of chronic pneumonia. Mycoplasma ovipneumoniae was detected in the lung of 4/7 (57.1%) animals postmortem. Four (57.1%) had paranasal sinus masses, all of which were classified as inflammatory, hyperplastic lesions. Pasteurella multocida was detected in all seven (100%) animals, while Trueperella pyogenes was detected in 5/7 (71.4%). Our findings indicate that not all chronic carriers have pneumonia, nor do all have detectable M. ovipneumoniae in the lung. Further, paranasal sinus masses are a common but inconsistent finding, and whether sinus lesions predispose to persistence or result from chronic carriage remains unclear. Our findings indicate that disease is variable in chronic M. ovipneumoniae carriers, underscoring the need for further efforts to characterize pathologic processes and underlying mechanisms in this system to inform management.