Researchers on trail of bighorn sheep killer

Pasturella bacteria have been known to cause most pneumonia epidemics that sweep through bighorn sheep herds

Bighorn sheep restoration projects are threatened by a tiny but deadly killer.

Scientists from the University of Idaho are working with wildlife agencies around the West to identify this killer -- a deadly strain of bacteria that affects many different animal species but can wipe out the already endangered sheep populations.

The researchers are using tools such as DNA fingerprinting and DNA probes to study different strains of bacteria in livestock and wildlife to detect how they vary in their potential to cause disease. According to the scientists, a better understanding of the bacteria, which can have wildly different effects on different species, will help eliminate the disease threat to bighorn restoration projects.

UI microbiologist Alton C.S. Ward and his colleagues at Caine Veterinary Teaching and Research Center at Caldwell, Idaho, are sorting through more than 3,000 Pasturella cultures carried by many species of wildlife. They 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 around the West will help researchers identify which animals are carrying the deadly strains and pinpoint their location.

The bacterial strains can vary extensively. However, biochemical tests and DNA fingerprinting can help scientists identify the transmission of certain strains.

DNA probes detect the genetic message carried by some strains of Pasturella that gives them greater potential for causing disease.

Pasturella bacteria have been known to cause most pneumonia epidemics in bighorn sheep herds. Scientists often blame domestic sheep for passing the disease to bighorn populations, however, according to Ward, domestic sheep are not always to blame.

Ward 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.

Wildlife officials must take this into consideration before transplanting herds for restoration projects, Ward says.

"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."

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."

The University of Idaho researchers are using what they have learned to help develop a vaccine for the disease caused by Pasturella strains. Caine Center researchers cooperated with Colorado Wildlife Division veterinarian Dr. Mike Miller to evaluate an experimental vaccine.

"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 their report in the April edition of the Journal of Wildlife Diseases.

The scientists 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 scientists said, "would be valuable for use in bighorn sheep maintained in captivity or when captured for relocation."

For more information, contact Alton Ward, University of Idaho, (208)454-8657, email: award@uidaho.edu.

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