Study Shows Pathways of Disease Transmission Between Elk, Bison and Cattle in the Greater Yellowstone Area

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The U.S. Geological Survey and its partners have shown how brucellosis has impacted cattle, bison and elk in the greater Yellowstone area.

BOZEMAN, Mont. – Scientists with the U.S. Geological Survey and its partners have shown how brucellosis, a disease which has significant economic implications for the cattle industry and wildlife health, has been transmitted back and forth between cattle, bison and elk in the greater Yellowstone area.

Elk at a Wyoming feedground.
Elk grazing at a feedground in Wyoming.Public domain

The research focused on wildlife-livestock transmission pathways of a disease called 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.

Federal scientists developed and analyzed a genomic dataset of Brucella abortus, the bacteria that causes brucellosis, which spanned 30 years and included samples 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.

The fifth genetically-distinct strain originated and was mainly found in bison of Yellowstone National Park. This strain appeared to be spreading less rapidly.

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.

Cattle Grazing at Sunset in Montana
Cattle graze on a ranch in western Montana.Public domain

Brucellosis is a disease found in livestock and humans worldwide. Infected animals often experience a termination of pregnancy and further transmission occurs through direct contact with the fetuses and tissues.

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.

The study is a collaborative effort between 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.

More information about wildlife disease studies can found on the USGS Northern Rocky Mountain Science Center website.