Four bighorn herds in western Montana have been plagued by a deadly pneumonia outbreak this winter, with impact of the latest herd being discovered earlier this month, reports the Wildlife Management Institute. There is no vaccine or effective treatment for pneumonia in wild sheep and Montana's Fish, Wildlife and Parks (FWP) Department has culled almost 200 animals in an effort to limit spread of the disease. Pneumonia is fatal to 70 to 90 percent of wild sheep that get contract it.

"We're wondering if there's some perfect storm?some ideal set of environmental circumstances favoring the pathogens," FWP's regional wildlife manager Mike Thompson said. "These organisms are in the environment and in the sheep all the time. But with [four] different herds like this [having pneumonia outbreaks], are there circumstances that increase the probability?"

According to the FWP's Bighorn Sheep Conservation Strategy, approved just last month, Montana's bighorns outside of Yellowstone and Glacier national parks were estimated at 5,700 in 45 distinct populations. Thirty-six of those populations sustain limited hunting opportunities. Since 1984, there have been significant die-offs in 14 bighorn populations in Montana prior to this winter's outbreak.

The first outbreak was discovered in November 2009, in the East Fork of the Bitterroot, south of Darby. Seventy-seven animals were culled from the population. Arecent flyover of the East Fork range found at least 71 healthy looking sheep and none that appeared sick. A second herd in the Bonner area has resulted in 88 diseased sheep being culled.

The most recent outbreak has affected two separate herds in the Rock Creek area. The disease will be allowed to run its course in the Lower Rock Creek area because of the treacherous terrain. However, FWP will remove sick sheep from the Upper Rock Creek herd to try and prevent further disease spread; the Upper Rock Creek herd had about 340 sheep in May.

"Upper Rock Creek looks like a place where we can begin as we did in the East Fork," said FWP biologist Ray Vinkey. "We are gearing up to cull sick sheep from this population. Once we get started, we'll be in a better position to judge whether we can hope to remove all the sick animals or whether the disease is too far advanced to get ahead of it."

Of the animals culled in the Upper Rock Creek area, at least 10 to 20 diseased sheep will be collected to identify the disease organism and evaluate if there is a link between the pneumonia outbreaks. (jas)