Brucellosis is an infectious disease caused by the bacteria Brucella abortus that infects cattle, bison, and elk. In these species, brucellosis typically results in an abortion during the first pregnancy after infection, although it can also cause abortions during subsequent pregnancies, or the birth of weak calves with high mortality. B. abortus is primarily transmitted through contact with infected birth tissues and fluids. Brucellosis is a zoonotic disease, meaning that it can also cause disease in humans.

It is thought that brucellosis arrived in North America with infected European cattle sometime between the 16th and 18th centuries. Brucellosis arrived within the Greater Yellowstone Ecosystem sometime prior to 1917 when it was first detected in Yellowstone National Park, and subsequently spread to bison and elk throughout the region, including portions of Idaho, Montana, and Wyoming. Eradication efforts throughout North America have eliminated the disease in cattle with the exception of sporadic cases in the Greater Yellowstone Area caused by transmission from wildlife, primarily elk.

Brucellosis is a zoonotic disease, and in many places around the world, it still causes severe infections in humans. Brucellosis also causes decreased milk production, weight loss, abortion, and infertility in cattle. For these reasons, beginning in the mid-1950s, great efforts were made to eliminate the disease from all livestock within the United States. While these efforts were successful at eliminating transmission within cattle nation-wide, sporadic transmission from wildlife to cattle in and around the Greater Yellowstone Ecosystem has been on the increase. Brucellosis can result in serious financial burdens to cattle producers, potentially resulting in quarantine of a herd, increased testing and vaccination costs, and possible difficulty in trade with other states and countries.

Although the disease can cause abortions in elk, measurable population effects on population size or trend due to brucellosis have not been documented. However, the potential for transmission to livestock results in decreased acceptance of elk on private property which, in many areas, constitutes a large proportion of elk winter range. Historically, rates of exposure in elk (measured by blood tests) have been very low (below 2% in the early 1990’s) and limited in distribution. Recent research and surveillance efforts have indicated that the prevalence and geographical distribution of the disease in elk is likely increasing. Brucellosis now exists in elk populations outside of the Greater Yellowstone Area. Hunters and game processors should take precautions (gloves and good hygiene) when handling reproductive and/or fetal material from hunter-harvested elk and bison.

Additional information on brucellosis programs for livestock are available on the Montana Department of Livestock website.

Because brucellosis can negatively impact Montana livestock producers, influence the acceptability of elk on the landscape, impact the overall health of wildlife populations and remains a health concern for people, Montana Fish, Wildlife and Parks is working with the Montana Department of Livestock, livestock producers and sportsmen and women to better delineate the geographic distribution of the disease in elk, understand elk-cattle transmission risk and ways to mitigate that risk, measure its prevalence in elk populations and understand factors that may influence changes in prevalence and distribution of the disease.

Surveillance for brucellosis across Wyoming, Idaho, and Montana has largely relied on collection of samples from hunter harvested animals. Due to difficulties in obtaining a large enough sample size from harvested elk in Montana, since 2011, FWP has embarked on a surveillance and research project that involves capturing, testing, and radio collaring elk from areas on the edge of the known distribution of brucellosis. Information gained from this effort will help us update our estimates of the distribution and prevalence of the disease, predict elk-livestock transmission risk, increase our understanding of how brucellosis is spread among elk and elk populations, and improve our ability to manage elk to reduce the risk of brucellosis transmission to livestock. Long-term continuation of this project is dependent on future funding and landowner cooperation in areas identified as being a high priority for brucellosis surveillance and research. FWP is entering the sixth year of this project which, to date, has been funded by grants from the U.S. Department of Agriculture, Animal and Plant Health Inspection Service (USDA-APHIS), the Montana Department of Livestock, the sale of hunting and fishing licenses in Montana and matching Federal Aid in Wildlife Restoration funding from the US Fish and Wildlife Service.

In the winter of 2015/2016, FWP will embark on its sixth year of targeted brucellosis surveillance and research in southwestern Montana. Approximately one hundred adult cow elk will be captured across HDs 520 and 560 this winter. Blood from these elk will be tested for exposure to brucellosis. In total, 30 cow elk will receive GPS collars in an effort to enhance our understanding of elk movement patterns within these populations, evaluate the risk elk may pose for brucellosis transmission to cattle or other elk, and improve overall elk population management.

Part of our effort is also focused on obtaining a better understanding of the epidemiology of brucellosis and the actual risk posed by seropositive animals. For this, we are annually tracking the status pregnancies in seropositive elk identified in previous captures and examining whether Brucella bacteria are shed at birth or abortion sites. At the end of a 5-year monitoring period these elk will be collected and removed from the population to determine if they are actively infected with Brucella bacteria or are simply seropositive (which denotes they have been exposed to the bacteria at some point). We will be capturing elk in the Flying D/Red Mountain, Blacktail, Sage Creek, Tobacco Root Mountains, Mill Creek/North Absarokas, and Greely herds for this purpose in the winter of 2015/16 as well.

• Targeted Elk Brucellosis Surveillance Project 2016 Annual Report 1.1 MB
• Metcalf et al 2015_Acceptability of Brucellosis Management Tools for Elk Among MT Stakeholder Groups 3 MB
• 2011-2015 Targeted Elk Brucellosis Surveillance Project-Comprehensive Report 1 MB
• Hand et al 2014_Sex-biased Gene Flow Among Elk in the Greater Yellowstone Ecosystem 4 MB
• Brucellosis Working Group Proposed Recommendations for Commission Endorsement 54 KB
• Proffitt et al 2011_Elk Aggregation and Disease Risk in MT 422 KB
• Cross et al 2010_Probable Causes of Increasing Brucellosis in Free-ranging Elk 1 MB
• Proffitt et al 2010_Elk Distribution and Spatial Overlap with Livestock 712 KB
• 2010 MT Elk Brucellosis Survey Report 302 KB
• 2009 MT Elk Brucellosis Survey Report 473 KB
• 2008 MT Elk Brucellosis Survey Report 1 MB