Study: Yellowstone bison not to blame for brucellosis

Elk deemed mostly responsible for spreading disease to livestock

Elk feeding a big factor in spread of brucellosis. @bberwyn photo.

Staff Report

The most rapidly spreading strains of brucellosis, a disease with implications for livestock and wildlife management, appear to be centered around areas where humans feed elk to keep populations artificially high for hunters.

Those findings come from scientists with the U.S. Geological Survey and partners, who studied how the disease is transmitted back and forth between cattle, bison and elk in the greater Yellowstone area. Notably, the researchers found that a fifth, genetically distinct strain, originated, and was mainly found in bison of Yellowstone National Park. This strain appeared to be spreading less rapidly.

Brucellosis, which often causes a termination of pregnancy in animals. The disease was unintentionally introduced to elk and bison in the greater Yellowstone area on at least five separate occasions over the past century, but, more recently, is transmitting from elk to cattle and undermining livestock control efforts.

“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,” said Pauline Kamath, USGS ecologist and lead author of the study.

The genomic study included data spanning 30 years from cattle, bison and elk. Four out of the five strains are now primarily associated with elk and originated from the Wyoming feeding grounds, where state and federal land managers provide feed for elk in the winter.

Two of these elk-associated strains have spread at about 4 to 8 kilometers per-year. Scientists conclude that elk are the most likely source of current brucellosis outbreaks in livestock.

Previously, it was not known whether elk could sustain the disease in the absence of bison or supplemental feeding grounds. This study shows that elk, in some areas distant from the feeding grounds, have strains that are unrelated to bison, suggesting that management of bison and feeding grounds may not affect brucellosis dynamics in these other elk populations, where the disease has been spreading.

“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. Focus on bison alone, as was suggested in the past, will not meet the disease eradication objective and conserve wildlife,” said the National Park Service’s Rick Wallen, lead wildlife biologist for the bison program in Yellowstone National Park and co-author on the study.

In North America, the greater Yellowstone area is the last remaining reservoir of Brucella abortus. Over 20 cattle and farmed bison herds have been infected in Wyoming, Idaho and Montana since 2002, and the presence of the disease within livestock results in additional testing requirements and trade restrictions.

The article “Genomics Reveals Historic and Contemporary Transmission Dynamics of a Bacterial Disease among Wildlife and Livestock” is published in Nature Communications. Partners on the study included the USGS, Northern Arizona University, University of Montana, U.S. Department of Agriculture, U.S. Fish and Wildlife Services, Idaho Department of Fish and Game, Wyoming Game and Fish Department, Montana Fish Wildlife and Parks, the National Park Service and the University of New Hampshire.



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