Disease Takes A Heavy Toll On Wild Sheep Bacterial Pneumonia Sweeps Through Snake River Bighorns

At the state’s Wildlife Research Clinic, Dr. David Hunter watches from a unique vantage point a virulent outbreak of a bacterial pneumonia epidemic slash into one of the West’s most promising herds of Rocky Mountain bighorn sheep.

The outbreak stands as the best documented. “We’re learning things that it would have taken us 20 or 40 years to learn from watching die-offs on the hill,” Hunter says.

Of the 72 bighorns plucked from the Snake River’s breaks in December, 61 have died despite an ambitious treatment program with the best available antibiotics.

A veterinarian for the Idaho Fish and Game Department, Hunter helped with the early December effort that pulled the bighorns from southeastern Washington.

The epidemic began to sweep through the Asotin County herd shortly before Thanksgiving. The Washington Fish and Wildlife Department mobilized the operation with the help of Idaho and Oregon wildlife agencies.

The states and Foundation for North American Wild Sheep joined forces in hope of preventing the outbreak from spreading into Hells Canyon to the south.

The goal was to strip the area of its sheep herd so the epidemic couldn’t spread and treat the sick sheep so they could possibly be released.

After watching bacterial pneumonia rip through the captive herd in the holding pens, Hunter said there was little chance of returning any survivors to Asotin County.

There’s too much of a risk that just a few bacteria of the deadly strain could be hiding in a tonsil and reemerge to devastate the herds in Hells Canyon to the south.

If the Fish and Game Department’s Wildlife Research Clinic can’t stop the bacterial pneumonia with all the antibiotics available, some argue there’s next to no hope of stopping it in the wild.

For nearly three weeks after the rescue began Dec. 2, it appeared a miracle was in progress. None of the sheep plucked from the wild died despite expert opinions that up to 40 percent could die during the rescue.

But in mid-December, bighorns started dropping at the Caldwell clinic. And the disease continued to spread in the wild.

The epidemic that began in mid-November killed at least three dozen sheep in the field. The Ten Mile area south of Asotin appeared to be the outbreak’s epicenter, killing 11 bighorns from a herd of 16.

A dead domestic goat gone wild was taken from the same area and so far has provided one of the few clues to the outbreak.

Hunter said the goat and two of the bighorns taken from the area shared a common strain of bacteria. The bighorns could have given the bacteria to the goat or vice versa. Still, the goat-to-bighorn path is far likelier, Hunter said.

He believes domestic livestock, sheep in particular, get unfairly targeted as the only cause of the bighorn’s disease problems.

Domestic sheep carry bacteria that can kill bighorns under the right circumstances, Hunter said. But so do other animals.

The evidence argues that bighorns just aren’t that hardy. Their immune systems can’t overcome pneumonia bacteria in particular.

There are other diseases that kill the sheep, too. Some of the wild sheep carry bacteria that cause pneumonia and flare up periodically. Deer and elk can transmit diseases to the sheep, too, Hunter said.

“Even if we took all the grazing allotments out of the West, we’d still have die-offs,” he said.

Despite the effort to capture all of the sick sheep, the epidemic began to spread again in January. It crossed the Grande Ronde River into southeastern Washington and then spread to Oregon.

A few weekends ago, Oregon and Washington wildlife biologists, with help from the U.S. Forest Service, tried a new strategy.

Capturing the bighorns from the air with netguns, the biologists planned to inject them with antibiotics and equip about half with radio collars to track their progress.