Bison usually get the bulk of the blame for spreading a livestock disease around the Yellowstone ecosystem. A new study turns that assumption on its ear. It says elk are spreading the disease at an increased rate.
Researchers have long recognized elk carry brucellosis in the greater Yellowstone area:
"But really understanding how it’s being maintained on the landscape or that it actually could be spreading within elk populations, this is really the first time we can actually show that using genetic data.”
That's U.S. Geological Survey geneticist Pauline Kamath.
Kamath is the lead author of the new study produced by the U.S.G.S. and its partner agencies. It challenges the predominant theory that Yellowstone bison and Wyoming’s elk feeding grounds are responsible for the bulk of new brucellosis infections.
Brucellosis causes pregnant animals to prematurely abort. The disease can also cause undulant fever in humans. Kamath says the new genetic research shows only one of the disease’s five strains is primarily found in bison.
"And it’s pretty geographically localized, so it’s found in a very small area around Yellowstone and to the north of the park. There are four other strains that are found widespread throughout the system.” says Kamath.
Those four strains are now primarily associated with elk. They originated from the Wyoming feeding grounds. That’s where state and federal land managers provide feed for elk in the winter, meaning lots of elk are crammed together feeding during the brucellosis transmission period.
”Historically, we’ve had high levels of seroprevalence – exposure to brucellosis – on feed grounds. In our data set we showed four of the five of the elk-associated strains connect back to the feed grounds.” says Kamath.
Two of these elk-associated strains have spread at about four to eight kilometers per year. Kamath says this new study provides the most compelling evidence yet that brucellosis is now self-sustaining in Montana elk.
"'Self-sustaining' meaning that we’re seeing it being transmitted among elk in a local area. So in Montana, instead of having it spilling over continually from somewhere else, it’s being transmitted locally.” says Kamath.
The study found the fifth genetically-distinct brucellosis strain originated and was mainly found in Yellowstone National Park bison. That strain appears to be spreading less rapidly.
Thousands of bison infected with brucellosis have been slaughtered over the past two decades to prevent infection of domestic livestock. If it’s detected in those herds, that can lead to additional testing and trade restrictions, expensive consequences cattle producers want to avoid at all costs.
This study’s potential impact on land and bison management decisions is anyone’s guess right now.
For her part, U.S.G.S. scientist Dr. Pauline Kamath says the research will continue:
"Just trying to understand how the bacteria has potentially adapted to elk which has really not been shown in other areas because it [brucellosis] is a bovid-adapted species, meaning it’s adapted to cows and bison and other species in that family."
The study’s results are published in the May issue of Nature Communications.