Bighorn Sheep and Pneumonia

WDFW Fact Sheet
March 2013

  • Wild bighorn sheep are susceptible to pneumonia, a respiratory disease.
  • Preventing pneumonia outbreaks is one of the main concerns for sustaining Washington’s estimated 1,650 bighorn sheep in 17 herds.
  • In bighorn sheep, pneumonia is most often caused by an array of bacteria, mostly within the family Pasteurella. Most biologists now believe that bighorns are predisposed to morbidity or mortality from these bacteria after first being infected by the Mycoplasma ovipneumoniae.
  • Various species of Pasteurella are common in many wild and domestic mammals. However, Mycoplasma ovipneumoniae is not a native pathogen of wild sheep and goats in North America. When wild bighorns contract this pathogen, it is invariably because of close contact with domestic sheep or domestic goats.
  • Domestic sheep and goats often carry Pasteurella and Mycoplasma but are not clinically affected.
  • There is presently no effective treatment or preventive vaccination for bighorn sheep with pneumonia.
  • Pneumonia is not transmitted from wild bighorn sheep to humans, nor to domestic livestock.
  • If a bighorn sheep ewe survives a pneumonia outbreak, she generally produces a very weak lamb that is vulnerable to early mortality (if producing a lamb at all). Thus recruitment of new bighorns is very low. This situation can continue for many years (although, in some cases, it lasts only a year or two).
  • Pneumonia outbreaks occur periodically in wild bighorn sheep herds throughout the western United States.
  • In 1995-96, a pneumonia outbreak nearly decimated three wild bighorn herds in southeast Washington’s Blue Mountains and others in the Hell’s Canyon area of Idaho and Oregon along the Snake River. The Wenaha, Cottonwood Creek, and Black Butte or Joseph Creek herds are still suffering from the lingering effects of that outbreak. In 2012, the Asotin herd was also affected by pneumonia, and we expect to see it decline over the next few years.
  • In late 2009 and early 2010, a pneumonia outbreak was detected in the Umtanum herd in the Yakima River Valley. Many bighorns died, and others were culled by a combined state-federal project, in an attempt to stem the epidemic. This herd suffered poor recruitment in spring 2010, but returned to normal recruitment in 2011 and 2012. In cooperation with the Idaho Department of Fish and Game and Washington State University, WDFW is currently monitoring the recovery of this population. It appears that, in contrast to the affected populations in the Blue Mountains, the bighorns in the Yakima canyon are no longer infected with Mycoplasma ovipneumoniae.
  • Washington Department of Fish and Wildlife (WDFW) biologists are also monitoring the nearby Quilomene and Cleman Mountain herds.
  • Because pneumonia outbreaks have been associated with interactions among wild sheep and domestic sheep or goats, WDFW biologists are working with both public and private land managers to avoid such interactions.
WDFW’s Game Management Plan addresses disease in bighorn sheep through monitoring of herds, reducing interactions between bighorns and domestic sheep, and conducting joint research with Washington State University, the Idaho Department of Fish and Game and the Oregon Department of Fish and Wildlife.