Wildlife biologists believe they now may know the cause of bighorn sheep die-off above Dubois

Wildlife biologist Greg Anderson and John Robinet of Dubois discuss findings from January's Bighorn Sheep herd sampling. (photo by Monie Finley)

By June Bonasera, County10.com

(Dubois) – Wildlife biologists believe they may have finally identified bacterial pathogens that may be responsible for killing bighorn sheep in the Dubois area, reducing the herd by 50 percent over the past several decades. The pathogens may contribute to the spread of a pneumonia-like disease that has been fatal to infected sheep.This preliminary conclusion was reported Monday night by Greg Anderson, wildlife biologist with the Wyoming Game and Fish Department, at the annual meeting of the National Bighorn Sheep Interpretive Center in Dubois. Anderson said his report is the preliminary finding from a recent disease testing project of the Northern Wind River Range Bighorn Sheep herd.

Anderson began his presentation with an overview of the population, lamb recruitment, and disease history of the herd, which winters in the  Dubois area and is a familiar site on Whiskey Mountain, just above town.  Charts were presented which depicted the height of the sheep populations in 1990 and the steady decline in populations since a catastrophic all-age pneumonic die-off occurred, which has reduced the population by close to half.

Blood sample being taken from a bighorn ram during the January trapping event (Wyoming G&F photo)

In January this year, in an effort to collect data to determine the cause of the pneumonic die-off, a combination of Wyoming Game and Fish biologists and volunteers, including local Game and Fish Commissioner Richard Klouda of Lander, gathered to trap and sample the sheep herd for the first time in approximately 20 years. Blood was drawn for sampling, along with nose and throat swabs of the captured sheep.

Pathogen testing results of the January trapping, where a total of 47 bighorn sheep were captured, included the following data:

Mycoplasma ovapneumonia positive: 14 of 47 (30%)
Lambs in the trapping found to be Mycoplasma positive: 3 of 6 (50%)

Pasteurella Bacteria:
Bibersteina triholosi: 46 of 47 (98%)
Pasteurella mottocida: 2 of 47 (4%)
Mannheimia aemolytica: 1 of 47 (2%) LKT+
Mannheimia glucosidal: 1 of 47 (2%) LKT+

Of the results, the Mannheimia aemolytica, leukotoxic positive sheep was the most concerning to Anderson, as that is believed to be the combination responsible for the pneumonic die-off. The Mannheimia glucosidal, leukotoxic infected sheep was also of concern, as that bacterial pathogen has unknown implications for the health of the herd.

In closing, Anderson said he was hopeful that within the next 10-15 years, an innoculation might be developed to protect the sheep against what is now believed to be the cause of the herd decline; which has been preliminarily determined to be the combination of the bacterial pathogen Mannhiemia aemolytica in conjunction with the sheep being leukotoxic posivie.

National Bighorn Sheep Interpretive Center Board president Mark Hinschberger began Monday night's presentation. (photo by Monie Finley)

A video of the trapping effort and introduction to the herd and project background was presented to the group of 21 attendees at the annual meeting. The video may be viewed at the following link: