This infection caused by the bacteria Yersinia pestis.

Yersinia infection is uncommon, but rarely occurs in some western states, including:

• Arizona
• California
• Montana
• Nevada
• New Mexico
• Utah

Animals found to be infected with plague in Montana have included coyotes, bobcats, domestic dogs, cats, rabbits and hares, antelope, deer, elk, prairie dogs, squirrels and other rodents.