Brucellosis Essay

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Brucellosis, which primarily affects mammals such as deer and elk, cattle, pigs, dogs, sheep, and goats, is an infectious disease caused by Brucella bacteria. Human cases of brucellosis are rare, but are more common in places where public health efforts are limited; unpasteurized milk and dairy products account for the most common route of infection.

Brucella abortis, a strain of the bacteria that generally affects cattle and bison, causes decreases in milk production and spontaneous abortions in infected individuals. In the United States, this is the most common agent causing brucellosis infections. Transmission of the bacteria is typically accomplished through direct exposure to infected animals, although cases of contamination through affected food and water sources have been documented. Contemporary losses to farmers, in the form of decreased milk production and aborted fetuses, are estimated at less than $1 million annually, compared to $400 million in 1952.

Control and Prevention

Prior to 1934, control of brucellosis in the United States was limited to individual herds and livestock owners. Since the mid-1930s, the Cooperative State Federal Brucellosis Eradication Program has eliminated occurrence of brucellosis in 44 states, with the other six states charting infection rates of less than 0.25 percent. Yellowstone National Park (YNP), which is comprised of land in Montana, Wyoming, and Idaho, is home to the last remaining free-range bison herds in North America, some of which carry brucellosis; about 50 percent of Yellowstone bison are estimated to carry the brucella abortis bacteria. Reintroduction of brucellosis from free-range herds could enormously economic impact the livestock industry, and potentially jeopardize export markets for American beef.

Because brucellosis prevention was historically focused on private herds nationwide, the YNP bison herds were controlled through border control activities and shot upon leaving the park. Problems arose during the winter of 1996-97, when record snowfalls limited forage for YNP bison. Some 1,079 bison that departed YNP in search of food were shot or sent to slaughter, while an additional 1,300 bison starved to death within the park. The winter of 2005 saw another 900 bison shot or slaughtered by the National Park Service. Concerns with this style of management include a potential reduction in genetic diversity and population viability of YNP bison. Environmental groups discount the theoretical risk to domestic livestock posed by bison and elk, and suggest that less heavy-handed management of wildlife in the YNP area could still protect livestock health.

Current management plans focus on managing a free-range bison herd, while also attempting to control brucellosis. To this end, a strain RB51 vaccine is being tested for use in bison, although delivery of the vaccine is often difficult, and would have to be delivered ballistically or to bison captured outside the YNP boundary. Another delivery option under study is microcapsules of oral vaccine that could be distributed in feeding areas in the park. If the YNP bison and elk herds were to become brucellosis-free, they could presumably be allowed unfettered access to the North American continent once again.


  1. S. Davis and P.H. Elzer, “Brucella Vaccines in Wildlife,” Veterinary Microbiology (v.90, 2002);
  2. Kleiner, “Oh Give Me a Home,” New Scientist (v.162/2190, 1999).

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