HELENA — Montana livestock officials announced this morning that the brucellosis that infected a Paradise Valley cow this spring likely came from elk, not bison.

Marty Zaluski, the Montana state veterinarian, said recently completed genetic tests of the bacteria, along with other studies of the case, suggest the cow did not get the disease from bison in and around Yellowstone National Park, nor did the disease come from domestic stock.

“We’ve now had two cases of the disease in two years, and no contact with bison in either case,” Zaluski said. “It supports our conclusion that elk were the source in both cases.”

Brucellosis is a serious disease in livestock and wildlife that causes cows to abort their calves. The disease has been eradicated in the United States, except for bison and elk in and around Yellowstone Park, where the animals contracted the disease for domestic stock almost 100 years ago.

Montana has recently experienced two incidents of the disease in cattle, which means the state will lose its official “brucellosis-free” status. The change means Montana ranchers will have to conduct more tests of their stock before shipping them to the out-of-state markets where almost all Montana’s cattle crop ends up.

Zaluski said the latest results mean managers must begin dealing with brucellosis in elk. Thus far, state and federal officials have only looked at bison as a potential source of the disease and are managing the bison to prevent the spread of brucellosis.

The Montana Board of Livestock on Tuesday instructed Zaluski and others to begin looking at ways to control the spread of the disease from elk to domestic stock.