Causes of Pneumonia Epizootics among Bighorn Sheep, Western United States, 2008–2010

Thomas E Besser,E Frances Cassirer,Kristin Mansfield,Neil J Anderson,Margaret Highland,Peregrine Wolff,Jonathan A Jenks,Darren L Bruning,Joshua B Smith,Katherine Baker,Jennifer M Ramsey

doi:10.3201/eid1803.111554

Abstract

Epizootic pneumonia of bighorn sheep is a devastating disease of uncertain etiology. To help clarify the etiology, we used culture and culture-independent methods to compare the prevalence of the bacterial respiratory pathogens Mannheimia haemolytica, Bibersteinia trehalosi, Pasteurella multocida, and Mycoplasma ovipneumoniae in lung tissue from 44 bighorn sheep from herds affected by 8 outbreaks in the western United States. M. ovipneumoniae, the only agent detected at significantly higher prevalence in animals from outbreaks (95%) than in animals from unaffected healthy populations (0%), was the most consistently detected agent and the only agent that exhibited single strain types within each outbreak. The other respiratory pathogens were frequently but inconsistently detected, as were several obligate anaerobic bacterial species, all of which might represent secondary or opportunistic infections that could contribute to disease severity. These data provide evidence that M. ovipneumoniae plays a primary role in the etiology of epizootic pneumonia of bighorn sheep.

Highlights

Epizootic pneumonia of bighorn sheep is a devastating disease of uncertain etiology
M. ovipneumoniae was detected in the pneumonic lungs of >95% of study animals involved in the 8 discrete pneumonia epizootics, significantly more frequently than any of the other respiratory agents sought except the bighorn sheep commensal bacterium B. trehalosi [34,35]
We identified identical ribosomal intergenic spacer (IGS) strains of M. ovipneumoniae within the affected animals in each outbreak, consistent with epizootic spread [24]; M. ovipneumoniae was not detected in the healthy populations sampled

Summary

Introduction

Epizootic pneumonia of bighorn sheep is a devastating disease of uncertain etiology. To help clarify the etiology, we used culture and culture-independent methods to compare the prevalence of the bacterial respiratory pathogens Mannheimia haemolytica, Bibersteinia trehalosi, Pasteurella multocida, and Mycoplasma ovipneumoniae in lung tissue from 44 bighorn sheep from herds affected by 8 outbreaks in the western United States. The other respiratory pathogens were frequently but inconsistently detected, as were several obligate anaerobic bacterial species, all of which might represent secondary or opportunistic infections that could contribute to disease severity These data provide evidence that M. ovipneumoniae plays a primary role in the etiology of epizootic pneumonia of bighorn sheep. Other Pasteurellaceae, Bibersteinia trehalosi and Pasteurella multocida, have been more frequently isolated from pneumonia-affected animals during natural outbreaks than has M. haemolytica [11,12,15] Another candidate pathogen, Mycoplasma ovipneumoniae, has recently been isolated from pneumonia-affected bighorn sheep during 2 epizootics [11,16,17]; antibodies against this agent were detected in bighorn sheep from 9 populations undergoing. To clarify the etiology of epizootic pneumonia, we applied these criteria to the bacterial respiratory pathogens detected in multiple bighorn sheep epizootics

Methods

Results

Conclusion