Idaho Researchers Combat Bighorn Sheep Diseases

Tools including DNA fingerprinting and DNA probes are employed to detect how strains vary in their potential to cause disease.

Researchers at the university 's Caine Veterinary Teaching and Research Center at Caldwell focus on sorting through bacteria carried by many species of wildlife. The work is being done in cooperation with wildlife agencies in Idaho and other western states.

A better understanding of the bacteria, which can have wildly different effects on different species, will help eliminate the threat disease poses to bighorn restoration projects. Hells Canyon along the Snake River between Idaho and Oregon is the focus of a bighorn restoration project led by the Foundation for North American Wild Sheep. The group has committed more than $10 million to the project.

So far, UI microbiologist Alton C.S. Ward and his colleagues at Caine have studied thousands of samples from wild and domestic sheep, bison, pronghorn antelope, elk, moose, mountain goats and domestic goats and cattle.

The samples taken from animals from Alaska to Arizona and from the Dakotas westward to Washington are part of research into the disease potential of bacterial strains by location and the animals carrying them.

In the case of bighorn sheep, the curl-horned rams that battle to see who will be king of the mountain by butting heads, pneumonia epidemics sweep like wild fire through herds. Pasturella bacteria cause most outbreaks. In some cases, researchers report outbreaks killed 75 percent of herds.

In many cases, domestic sheep catch the blame for introducing the deadly microbes to their wild cousins. But domestic sheep are not always to blame, Ward says. He does not dispute that domestic sheep can transmit lethal diseases to wild bighorns, but believes bighorns also harbor disease-causing bacteria within their own herds or can be infected by bighorns introduced from other herds.

Ward believes bighorn transplants from other areas, a common technique employed with varied success to bolster wild herds, also can spread disease.

That means wildlife officials must take care to consider both the source of bighorns for transplants and the herds next to their new homes.

"Management is critical. Not only should bighorn sheep be kept from contact with domestic sheep which may carry some strains of Pasturella with greater disease potentials than those common to bighorns," Ward said, "but precautions must also be taken to prevent transmission of disease between bighorns from different populations."

The analysis of 3,000 Pasturella cultures from wildlife and domestic animals throughout the West shows the bacterial strains can vary extensively. Biochemical tests and DNA fingerprinting can identify which samples are identical, information that can detect transmission of strains.

DNA probes now can detect the genetic message carried by some strains of Pasturella that gives them greater potential for causing disease. Ward said, "We know that these same probes can be used to identify animals carrying organisms associated with disease and are currently optimizing test procedures."

Caine Center researchers cooperated with Colorado Wildlife Division veterinarian Dr. Mike Miller to evaluate a vaccine developed to protect sheep against disease caused by Pasturella strains.

The vaccine prompted both bighorn and domestic sheep to produce more antibodies to common and deadly serotypes of Pasturella haemolytica, according to a report scheduled for April publication in the Journal of Wildlife Diseases.

Coauthors of that publication included other UI researchers as well as Idaho Fish and Game Department and Colorado Wildlife Division personnel.

"This vaccine appears to be safe for use in bighorn sheep and stimulated moderate but transient increases in antibody levels which should provide some protection against naturally occurring disease," according to the authors.

They also cite the need to expand on the effectiveness of the experimental vaccine so it would stimulate greater resistance to the multiple strains of Pasturella. Such a vaccine, the authors said, "would be valuable for use in bighorn sheep maintained in captivity or when captured for relocation."