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For years, bison took the rap for the spread of brucellosis, leading to massive hunting, butchering and quarantining of thousands of the animals in an effort to keep the outbreaks away from domestic cattle bordering Yellowstone National Park. Yet a new study published this month shows that bison may not be behind the disease after all. What is? Montana elk.

 “Of all the cases we had, we found no direct links from bison to livestock,” says Pauline Kamath, U.S. Geological Survey ecologist and lead author of the study. “That’s suggesting there’s little transmission from bison to animals in other areas in the Greater Yellowstone.”

There is, however, a link between elk and livestock, especially within the elk herds that use Wyoming state winter feeding grounds. The study traced 30 years of Brucella abortus’ genomic history in cattle, bison and elk tissue samples and identified five specific strains of the bacteria. Four of these strains are found in these winter feeding grounds, according to the Billings Gazette. 

“This study provides the most definitive evidence to date that brucellosis is now self-sustaining in Montana elk and has spread at an increased rate in elk populations outside of the feeding grounds,” says Kamath.

Continued below.

Previous research has shown a slow progression of the disease with relation to bison, but with regard to elk, the disease seems to be persevering and spreading at a rate of two to four miles per year. This means that solely focusing on bison isn’t going to stop brucellosis in the Greater Yellowstone Area, which is one of the last brucellosis breeding grounds in North America. According to the Billings Gazette, Montana, Idaho and Wyoming have collectively experienced about 20 outbreaks of the disease in either private herds of cattle or bison since 2002.

“Any attempt to control the rate of spread in wildlife must be evaluated at the ecosystem scale and include an effective strategy to address infection in elk across the greater Yellowstone area,” says co-author Rick Wallen, lead wildlife biologist for the bison program in Yellowstone National Park. “Focus on bison alone, as was suggested in the past, will not meet the disease eradication objective and conserve wildlife.”

While the study is helpful in identifying where the disease is originating, changing how elk are managed within the area will be difficult, especially since they roam freely across the state. Additionally, once state officials decide on a protocol to manage the elk, it could impact current big game hunting regulations, including those on private land. Regardless, controlling the reach of the disease will be tricky since researchers also confirmed that not only do the elk act as carriers of brucellosis, but elk and bison pass the disease between one another, which will greatly affect how officials will eliminate the fatal disease.