PULLMAN, Wash. -- A wildlife disease researcher at Washington State University successfully used an experimental vaccine to inoculate a small number of bighorn sheep against a deadly form of pneumonia.
The achievement is considered a promising development in the effort to protect wild bighorn sheep from a disease carried by domestic sheep, but far from a final solution in the ongoing saga that pits native wildlife against the sheep ranching industry.
Earlier this year, Subramaniam Srikumaran, a professor at WSU, developed and gave a shot of the vaccine 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.
Srikumaran said it is the first time a vaccine has proven 100 percent effective. He acknowledged the sample size of inoculated bighorns was small and said years of research are needed to fully develop the vaccine.
"But 100 percent is something convincing to me," he said.
Wildlife managers and biologists across the West have documented numerous cases of bighorn sheep suffering die-offs after coming in contact with domestic sheep. Many in the ranching industry have disputed claims by wildlife managers that domestics are making their wild cousins sick. With lots of anecdotal evidence that comingling results in disease transmission, wildlife managers have called for keeping the two species separate.
Srikumaran previously conducted an experiment that documented the transmission of the disease from domestic sheep to captive wild sheep. Armed with that evidence and other science, public land managers are increasingly enacting regulations to separate the animals and even going so far as to end sheep grazing on some public lands. For example, last year the Payette National Forest approved a plan that will reduce domestic sheep grazing by nearly 70 percent.
As the debate raged over the extent to which domestic grazing on public land should be curtailed to protect bighorns, many looked to science and a vaccine as a potential silver bullet.
Srikumaran and others who are working either to solve the disease or to manage populations of wild sheep said relying on a vaccine given to wild sheep can be problematic. It would require capturing all the wild animals that live in steep and remote terrain and by their nature are elusive.
"How do you know who has got it, how do you control the dosage? This is lots of difficulty with that," said Keith Lawrence, director of the Nez Perce Tribes wildlife program. "That is why until we get all this stuff figured out separation is the key."
Srikumaran hopes to develop an oral version of the vaccine that can be delivered to wild sheep through feed. He noted some herds are fed by state wildlife agencies in the winter when they move from high elevations to valleys. But many other herds, such as the ones in Hells Canyon or those along the Salmon River in Idaho, are not fed and remain in remote country throughout the year.
Srikumaran is also working on a method that would treat the domestic sheep instead of the bighorns. Domestic sheep are rounded up and kept in pastures during the winter and typically allowed to graze during the spring and summer where they can come in contact with bighorns.
"We are trying to eliminate the disease-causing bacteria from the throats of domestic sheep."
Frances Cassirer, a wildlife research biologist for the Idaho Department of Fish and Game at Lewiston said even if Srikumaran's experimental vaccine can't be delivered to wild sheep it may prove a valuable tool in the fight to learn more about the disease. She said scientists are still not certain what causes wild sheep to contract pneumonia from domestics or if there is more than one cause.
She said the vaccine may help narrow the search. Srikumaran exposed the sheep to a pathogen known to be deadly, but some researchers believe there is a bacteria that doesn't cause the disease but makes sheep more susceptible to getting it.
Barker may be contacted at ebarkerlmtribune.com or at (208) 848-2273.
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(c) 2011, The Lewiston Morning Tribune, Idaho
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