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WSU study tests new vaccine for bighorn sheep

Bighorn sheep are suffering from pathogens rendering them susceptible to pneumonia while having no effect on domestic sheep. Montana has killed 200 bighorns to thwart an outbreak.  (File Associated Press)
Bighorn sheep are suffering from pathogens rendering them susceptible to pneumonia while having no effect on domestic sheep. Montana has killed 200 bighorns to thwart an outbreak. (File Associated Press)

WILDLIFE RESEARCH -- Reseachers may finally be on track of a tool to deal with the diseases wreaking havoc with bighorn sheep herds in the West.

 A Washington State University wildlife disease researcher has produced an experimental vaccine that appears to have protected four bighorn sheep against deadly pneumonia.

Subramaniam Srikumaran, the WSU professor in Pullman, says his findings are a promising but concedes years of work remain to help safeguard wild bighorn herds from periodic die-offs that have plagued the species in Idaho.

Read on for more details from an Associated Press report:

His research comes at a time when domestic sheep that roam the same habitat as bighorns are blamed for spreading disease to their more vulnerable wild cousins. That’s led federal managers to close sheep grazing allotments in Idaho’s Payette National Forest to protect the wild sheep. That move has angered the region’s ranchers, who see the federal government as protecting wildlife over their livelihoods.

Srikumaran told the Lewiston Tribune this week that he developed the vaccine in his laboratory, then gave it to four bighorn sheep. They all survived after being exposed to a pathogen that causes pneumonia. Sheep not given the vaccine died within days of exposure. He acknowledged the sample size of inoculated bighorns was small, but "100 percent is something convincing to me."

Idaho bighorn numbers have dwindled by half since 1990, to about 3,500. Die-offs such as ones where 300 sheep died in 1995 and 1996 in Hell’s Canyon have contributed to the declines. And most scientists believe contact between the wild sheep and domestic sheep during the spring and summer has contributed to transmission of deadly pneumonia.

Last year the Payette National Forest approved a plan that will reduce domestic sheep grazing by nearly 70 percent.

Some see a vaccine along the lines of what Srikumaran is working on as a solution to allowing historic ranching activities and wild sheep to coexist in the high country — not just in Idaho but in other states including Washington and California, where similar efforts to separate the animals are under consideration.

Wildlife biologists following the debate say a solution remains elusive, despite the positive rumblings from Srikumaran’s lab. For instance, relying on a vaccine given to wild sheep can be problematic, because it probably would require capturing all the wild animals that live in steep and remote terrain.

Once they’re captured, the questions continue, said Keith Lawrence, director of the Nez Perce Tribes wildlife program.

"How do you know who has got it? How do you control the dosage? (There) is lots of difficulty with that," Lawrence said. "That is why until we get all this stuff figured out, separation is the key."

That’s one reason why Srikumaran is also working on a method that would treat the domestic sheep that are rounded up annually instead of the bighorns.

"We are trying to eliminate the disease-causing bacteria from the throats of domestic sheep," he said.

Frances Cassirer, a wildlife research biologist for the Idaho Department of Fish and Game in Lewiston, said Srikumaran’s experimental vaccine may prove a valuable tool in the fight to learn more about what causes wild sheep to contract pneumonia from domestics or if there is more than one cause.

For instance, Srikumaran exposed the sheep to a pathogen known to be deadly, but some researchers believe there is another bacteria that weakens the bighorns’ immune system and makes them more susceptible to deadly bacteria.

“If you could inoculate bighorn with the vaccine and expose them to domestic sheep and they survived, at least you would know that is the organism; it suggests that is the organism we have to get rid of in domestic sheep,” Cassirer said.




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Rich Landers
Rich Landers writes and photographs stories for a wide range of outdoors coverage, including a Sunday feature section and a Thursday column. He also writes the Outdoors Blog.

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