Montana livestock officials said Tuesday that a Park County cattle herd has been quarantined after six of the animals tested positive for the disease brucellosis.
Additional testing on the animals was under way to confirm the disease, said state veterinarian Marty Zaluski. If confirmed, it would be the region's 15th infection in livestock since 2004.
Introduced by early European settlers and once widespread, brucellosis has since been largely eradicated from cattle nationwide after a decades-long government effort. It persists in parts of Texas and in wildlife in and around Yellowstone National Park.
Brucellosis can cause pregnant animals to miscarry and has been blamed for weight loss and other problems in cattle. It is not considered a significant threat to human health.
Errol Rice with the Montana Stockgrowers Association said the suspected infection in the 150-head herd demonstrated that more needs to be done to eliminate the disease.
"The more cases we continue to identify, it makes you wonder have we really made that much progress on mitigating the problem," Rice said. "The fact remains we still have a large reservoir of the disease in a particular area of Montana that continues to affect our industry."
Thousands of Yellowstone bison have been captured and sent to slaughter over the last decade to prevent transmissions to cattle when the bison migrate to lower elevations in Montana. That has not stopped transmissions from the tens of thousands of elk that roam freely across the Yellowstone region.
Tests on elk over the last year revealed a new area of wildlife infections in parts of Montana west of Yellowstone. Montana, Idaho and Wyoming in recent years started requiring more stringent testing and vaccinations against the disease. That prompted the federal government to stop automatically imposing trade restrictions on states that have multiple infections.
The government also no longer requires that infected herds be slaughtered.
State officials did not disclose the name of the ranch where the disease was found. The Park County infections, if confirmed, would mark Montana's fourth case in recent years, including one in November on a bison ranch owned by media mogul and philanthropist Ted Turner.
Turner's bison remain under quarantine, although testing is under way to lift restrictions on the animals, state officials said.
Wyoming had two outbreaks last year and one in February. Idaho's last outbreak was in 2009.
Park County and the Park County Stockgrowers Association each have lawsuits pending over the management of Yellowstone's bison by the state and federal governments. A hearing in those cases was scheduled next month in Lewistown.