Brucellosis in cattle, bison and elk is caused by the bacteria Brucella abortus resulting in abortions, usually in the first pregnancy after infection. In some cases, however, abortions can occur in subsequent pregnancies or in stillbirths or poor calf survival in fetuses carried to full term.
Brucellosis is an infectious disease transmitted primarily through contact with infected birth tissues and fluids. It can cause disease in people. It was likely introduced into bison and elk populations through feeding and comingling with infected cattle in the early 1900’s, the disease can now be found in bison and elk populations within the Greater Yellowstone Area of Idaho, Montana, and Wyoming. Eradication efforts have nearly eliminated the disease in cattle with the exception of sporadic cases in the Greater Yellowstone Area. These cases are linked to transmission from wildlife, primarily elk.
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, FWP has not been able to document any measurable effects on the population due to brucellosis. 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 changes in exposure rates indicate that the prevalence, and possibly the geographical distribution, of the disease in elk is increasing. Even with the believed change in distribution, brucellosis in Montana has only been detected in elk populations within the Greater Yellowstone Area. Additional information on brucellosis programs for livestock is available on the Montana Department of Livestock website.
Brucellosis can negatively impact Montana livestock producers, influence the acceptability of elk on the landscape, impact the overall health of wildlife populations and is a health concern for people. In response, Montana Fish, Wildlife & Parks is working with the Montana Department of Livestock, livestock producers and sportsmen and -women to define the geographic distribution of the disease in elk. In this way, FWP seeks to measure its prevalence in elk populations and understand factors that may influence changes in the prevalence and distribution of the disease.
In past years, surveillance for brucellosis was largely dependent on samples collected from hunter-harvested animals. Recently, due to difficulties in obtaining a sufficient sample size from harvested elk, FWP embarked on an aggressive surveillance and research project to capture, test and radio collar elk near areas known to harbor brucellosis. Information gained from this effort will help FWP understand the distribution and prevalence of the disease, increase understanding of how the brucellosis is spread among elk and elk populations, and improve overall elk population management. Completion of this project is dependent on funding and landowner cooperation in high-priority areas.
FWP is entering the third year of this project which, to date, has been funded by FWP and grants from the U.S. Department of Agriculture, Animal and Plant Health Inspection Service.
In 2013, FWP embarked on its third year of a brucellosis research and surveillance project slated to occur in five areas within southwestern Montana. In one segment of the project, 100 adult cow elk were captured in the southern and western Pioneer Mountains and tested for exposure to brucellosis. All were considered negative for exposure. In addition, 30 cow elk received GPS collars to: (1) enhance the understanding of elk movement patterns within the population; (2) evaluate whether elk from the Pioneers have contact with elk populations in areas known to be exposed to brucellosis; and (3) improve overall elk population management.
Elk that tested positive for exposure to brucellosis in hunting districts 324, 326 and 325 during the first two years of the study were recaptured and, if pregnant, implanted with a Vaginal Implant Transmitter (VIT). The VIT will allow researchers to monitor for abortion or birth events, locate abortion or birth sites and evaluate if the Brucella bacteria is being shed on the landscape.
The research effort is aimed at evaluating the risk "seropositive" cow elk—those whose blood tests show exposure to brucellosis—pose for actually transmitting the disease to livestock or other elk.
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