A bacterial illness has spread through Baker County’s biggest herd of bighorn sheep, but a state wildlife biologist said it won’t be clear until later this year how severe the death toll is likely to be.

Oregon Department of Fish and Wildlife (ODFW) employees continue to monitor sheep in the Lookout Mountain unit in eastern Baker County, said Brian Ratliff, district wildlife biologist at the agency’s Baker City office.

Ratliff said he and other biologists have seen bighorns coughing — something the sheep rarely do unless they’re suffering from pneumonia — throughout the range of the Lookout Mountain herd.

With close to 400 sheep, it’s the largest herd of Rocky Mountain bighorns in Oregon.

The state also is home to California bighorns, mostly in the central and southeast parts of the state. Baker County has a herd of California bighorns in the Burnt River Canyon between Durkee and Bridgeport.

Until this winter the Lookout Mountain herd had apparently been healthy.

But on Feb. 13 ODFW received a report of a dead bighorn ram lying on the Snake River Road near Connor Creek, about 18 miles north of Huntington.

Ratliff said samples from the sheep were tested, and a lab confirmed the animal had been infected with a strain of Mycoplasma ovipneumoniae bacteria that had not been found before in bighorns in Oregon.

There are more than 50 strains of that bacteria, and they have varying levels of lethality.

The test results prompted ODFW to cancel the two bighorn hunts scheduled this summer and fall in the Lookout Mountain unit.

Those hunts included three tags — two for Oregon hunters and one for a nonresident.

Ratliff said ODFW has confirmed 10 to 12 bighorns have died, the most recent being found on April 5. Of the carcasses that were fresh enough to be tested — two had decomposed too much — all were infected with the same strain of bacteria.

Biologists don’t know — indeed, they might never confirm — how the herd was infected, Ratliff said.

Two people who have domestic sheep in the Lookout Mountain unit volunteered to have some of their animals tested, but results are pending.

Even if the domestic sheep are carrying the bacteria, that wouldn’t be conclusive proof that the bighorns were infected by contact with domestic sheep, Ratliff said.

He said ODFW will pay to test domestic sheep, and he encourages owners to call the agency at 541-523-5832.

Ratliff said ODFW also tested one llama, which did not have the bacteria.

ODFW will continue to monitor the Lookout Mountain herd through the summer.

The agency’s strategy will depend on how many sheep die, Ratliff said.

One option that has proved successful in other bighorn herds infected with virulent diseases is the “test/cull” strategy.

The goal is to test as many bighorns as possible and fit them with identifying collars.

Sheep that are infected would be euthanized to prevent them from sickening other bighorns.

Collaring the sheep would allow biologists to capture those animals later and test them again. That’s important, Ratliff said, because some sheep are likely to be “intermittent shedders,” meaning they carry the bacteria but shed it only some of the time.

Those sheep might test negative but then later begin shedding and possibly infecting other bighorns, he said.

Intermittent shedders might also need to be euthanized to protect the herd.

The Lookout Mountain herd was established in the early 1990s when a few dozen bighorns were captured elsewhere and released along Fox Creek. The animals have thrived in the steep canyons on the breaks of the Snake River.

“It’s been the healthiest herd in Oregon,” Ratliff said.

The only previous concern among Lookout Mountain bighorns was a minor rash of pneumonia that lasted a couple of months in 2012, he said. Those illnesses were caused by a virus rather than a bacteria, but it was a mild type that killed few bighorns, Ratliff said.

Although the Lookout Mountain bighorns aren’t known to mingle with the Burnt River Canyon herd — the two generally are more than a dozen miles apart — ODFW is monitoring the Burnt River bighorns for coughing or other signs of pneumonia.

So far the biologists haven’t seen any such evidence, Ratliff said.

Like the Rocky Mountain subspecies, the California bighorns are vulnerable to a variety of bacterial and viral infections that can lead to fatal pneumonia, Ratliff said.

“Bighorn sheep are susceptible to a lot of things,” he said. “They’re not the strongest species out there.”

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