New vaccine may protect wild sheep

New vaccine may protect wild sheep
New vaccine may protect wild sheep

A new vaccine for wild bighorn sheep shows early signs of promise but still faces several obstacles, a researcher at Washington State University says.

WSU professor Sri Srikumaran began testing a vaccine for pneumonia in bighorn sheep earlier this year at his research facility in Pullman.

In February, Srikumaran inoculated four bighorn sheep with an inactive form of the leading pneumonia-causing pathogen in the sheep. All four survived the exposure, but sheep that did not receive the vaccine died within two days, Srikumaran said.

The inactive vaccine, delivered by a shot, would also only work for about six months, so the bighorn sheep would need to be vaccinated twice a year. 

“Shots are impractical because you’d have to capture (the sheep) and it takes a lot of money,” he said, “and you can’t capture them all.”

Now, Srikumaran is working to develop an oral vaccine to put in food.

Last year, Srikumaran and his team of researchers conducted several necropsies on bighorn sheep that died from pneumonia. Their work showed that the bacterial pathogen can move from domestic sheep to wild bighorn sheep when they commingle. 

With a population size once estimated near two million at the dawn of the 1800s, the Rocky Mountain bighorn sheep now number fewer than 70,000. The spread of pneumonia has contributed to the diminished population, devastating some herds in the Northwest.

“When they start dying, 75 to 90 percent of the herd can die in two weeks,” he said.

To protect the bighorn sheep, the Payette National Forest in western Idaho announced last year it would close nearly 70 percent of its sheep grazing allotments over the next three years, angering some Idaho ranchers.

Ron Shirts, 44, a rancher near Hells Canyon, recently sold off his domestic sheep and switched to cattle.

“We tried to figure out any way to not sell the sheep but we couldn’t get anywhere,” he said. “They cut us back so far, we just couldn’t operate without our high mountain country.”

But some environmental leaders, including John Robison, public lands director of the Idaho Conservation League, said the three-year plan to phase out sheep ranching is moving too slow. 

“It seems like bighorn sheep, if they are going to recover, need their own space,” Robison said. “One thing that is striking to our members is that few things represent the west better than a bighorn sheep perched on a crag overlooking a river. They add immeasurably to the quality of life for local visitors and the citizens of Idaho.”

Srikumaran, a microbiologist born in Sri Lanka, finds himself caught in the middle. He said the oral vaccine might be the best method to distribute it to the wild sheep.

Each winter, wild bighorn sheep run out of food at high elevations where snow overtakes their habitat. Traversing to lower lands, they get food from wildlife biologists who set out long metal troughs of pellets. Srikumaran observed this in the mountains near Yakima.

“I have seen about a hundred animals coming single file to eat the food and go,” he said. “This happens all the time.”

Srikumaran does not expect every wild bighorn to find its way to a trough to ingest the vaccine, but he thinks it could be the best alternative to protect the population. Replicating itself inside the sheep, the active vaccine would require wildlife biologists to administer less frequent doses, rendering it a less expensive option.

“Live vaccines last at least one year,” he said, but some can last two or three times longer. “If it works, then we’ll try to incorporate it into the pellets. That will take an additional several months or maybe more than a year to figure out.”

Srikumaran hopes the vaccine can prevent the end of sheep ranching in parts of Idaho.

“The domestic sheep industry is a viable economic industry,” Srikumaran said. “A lot of people’s livelihoods depend on it, so, we are trying to develop some strategies to make these two species compatible.”

The Murrow News Service provides local, regional and statewide stories reported and written by journalism students at the Edward R. Murrow College of Communication at Washington State University.