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. FWP is in the tenth 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 Rocky Mountain Elk Foundation (RMEF), 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 2019/2020, FWP will embark on its tenth year of targeted brucellosis surveillance and research in southwestern Montana. Approximately 100 adult cow elk will be captured in the Ruby Mountains of HD322 and 50 adult cow elk will be captured in the Bangtail Mountains of HD393. Blood from these elk will be tested for exposure to brucellosis. In total, 43 cow elk in the Ruby Mountains and 17 cow elk in the Bangtail Mountains 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 annually monitored the pregnancy outcome of seropositive elk captured between 2011 and 2015 and sampled birth sites for presence of Brucella bacteria. At the end of a 5-year monitoring period these elk were collected and removed from the population to determine if they were actively infected or were simply seropositive (which denotes they have been exposed to the bacteria at some point). We concluded this portion of the study in 2019. We detected Brucella bacteria at 3 out of 4 abortion and 2 out of 61 live birth sites. This data suggests that Brucella bacteria is typically found at abortions but not at live births. We performed necropsies on 18 seropositive elk, testing a total of 427 tissues, and detected Brucella bacteria in only 3 elk. Our limited detection suggests that Brucella is difficult to culture and that seropositive elk may not harbor widespread infections of Brucella bacteria. We worked with collaborators at the U.S. Geological Survey to develop a model of elk-to-livestock transmission risk across the Montana designated surveillance area (DSA) and identified the highest transmission risk areas. That report is available in the reports section.

Starting in 2017, we began to evaluate the effects of management hazing and lethal removal on elk distributions and spatial overlap with livestock. In 2017, we captured and collared 40 adult cow elk in the Sixmile Creek area of Paradise Valley. In 2018, we captured and collared 40 adult cow elk in the southeastern portion of the Madison Valley. Comparison of elk movements to the location and timing of known management actions and how long elk stay away from high-risk areas is ongoing. Data collection will be completed in Spring 2020.

• Elk Brucellosis Surveillance Project 2019 Annual Report 1.3 MB
• Elk Brucellosis Surveillance Project 2019 Update Report 1.8 MB
• Effects of Elk Density on Elk Aggregation Patterns and Exposure to Brucellosis 1.8 MB
• Targeted Elk Brucellosis Surveillance Project 2018 Annual Report 2.1 MB
• Targeted Elk Brucellosis Surveillance Project 2017 Annual Report 1.7 MB
• Estimating the risk of elk to livestock brucellosis transmission in Montana 1.6 MB
• 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
• Public Wildlife Management on Private Lands: Reciprocity, Population Status, and Stakeholders and Normative Beliefs
• 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