The infectious bacterial disease brucellosis has been found in a beef cow in eastern Idaho, and state agriculture officials are scrambling to see if the infection is isolated or if it has spread to other herds.

Idaho Department of Agriculture state veterinarian Bill Barton sent a memo Monday saying that a beef cow from a newly assembled 600-head herd tested positive for the disease, which is rarely transmitted to humans but can cause spontaneous abortions, infertility, decreased milk production and weight loss in cattle, elk, bison and other mammals.

No calves or bred females have been sold from the herd, according to Barton's memo.

The herd has been quarantined and is being tested, and epidemiologists are trying to determine the source of the infection, Barton told The Associated Press on Tuesday.

"We've got just a few more head to do, and we'll be finishing that testing and have the results back in a few more days," he said.

Barton said the herd's owner, who lives in the Rigby area, was cooperating. None of his cattle had been sold, other than directly to slaughter, Barton said.

The infected animal and other cattle in the herd had been vaccinated for brucellosis, Barton said.

"The vaccine is fairly efficacious in preventing disease, but it's not 100 percent," he said.

The animals came from a variety of sources, including private sales and livestock markets, Barton said. Officials had not yet determined where the man purchased the infected animal.

Barton declined to detail what prompted the state to begin testing the animals, simply saying "there was an indication that this herd needed a whole-herd test."

A spokeswoman for the federal agency that oversees livestock diseases said an investigation has been launched into whether the infection has spread to other herds. How long that investigation could take was uncertain, said Lindsay Cole with the Agriculture Department's Animal and Plant Health Inspection Service.

The infection comes as government officials are considering softening restrictions that apply to states with brucellosis infections.

Because the disease has been eliminated nationwide except for Yellowstone National Park and surrounding counties in Idaho, Montana and Wyoming, the government has proposed turning that area into a brucellosis "hot zone." That would shield cattle producers outside the area from costly testing requirements for animals they ship out of state.

A public comment period on that proposal ends Friday. No timeline has been set for putting it into place.

Idaho was granted brucellosis-free status in 2007 after losing the status in 2006, when the disease was found in a cattle herd in Swan Valley near the Wyoming border. Wyoming lost its brucellosis-free status in 2003 when the disease was found in a herd of cattle near Pinedale but was granted it again in 2006. Montana gained brucellosis-free status in September after losing the designation in 2008.