In the Spotlight- Recent Disease Investigation from USGS National Wildlife Health Center

From the Latest USGS National Wildlife Health Center Quarterly Wildlife Mortality Report - Jan 2010 to Mar 2010

Pneumonia outbreaks in bighorn sheep across western states (Montana, Washington, Utah, Nevada)

Multiple herds of bighorn sheep in several states experienced mortality from pneumonia outbreaks during winter 2009-2010. Montana was the first to observe mortality in mid-November and at least four herds were affected from three different counties. Washington was next to report sick sheep in the Yakima River Canyon, primarily on the west side of the river. Sick sheep were observed coughing and had difficulty moving. Nevada also experienced mortality in two distinct herds, reported in mid-December. Utah had an outbreak in February where they eliminated a small herd to prevent transmission to a larger group nearby.

Image courtesy of Arizona Game and Fish Dept

Management activities this year included culling sick sheep to control outbreaks and prevent transmission to nearby herds and treatment with antibiotics. Pneumonia in bighorn sheep is often fatal and affects all age groups. Preliminary disease mortality estimates range from 50-80% of individuals within affected herds. The potential exists for surviving bighorn sheep to serve as carriers, and populations that experience outbreaks subsequently have low recruitment of lambs, as reported by South Dakota’s Custer State Park.

 A variety of bacterial pathogens have previously been identified in the pneumonia-complex, including Mycoplasma spp., Pasturella multocida, Pasturella trehalosi, and Mannheimia haemolytica, in addition to respiratory viruses and lungworm infections. Pneumonia is a challenging issue for bighorn sheep managers because of the difficulty associated with identifying the disease agent, remote locations, and limited management options. This year was unique because of the large number of outbreaks and few indications of a potential source or cause. Further investigations are in progress.

Further information is provided by the Western Association of Fish and Wildlife Agencies Wild Sheep Working Group Summary: Winter 2009-2010 Bighorn Sheep Die-offs (3/16/10) or Western Association of Fish and Wildlife Agencies - Wild Sheep Working Group website.

Source: USGS National Wildlife Health Center, Quarterly Wildlife Mortality Report -
January 2010 to March 2010

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