National Academy of Sciences
National Academy of Engineering
Institute of Medicine
National Research Council
Office of News and Public Information
National Academy of Engineering
Back | Home
News from the National Academies
Date: December 11, 1997
Contacts: Molly Galvin, Media Relations Associate
Kristen Nye, Media Relations Assistant
(202) 334-2138; e-mail <news@nas.edu>
FOR IMMEDIATE RELEASE

Extra Measures Needed to Protect Cattle Around Yellowstone
Until Brucellosis Is Controlled in Bison and Elk

WASHINGTON -- The federal government should establish disease surveillance and quarantine zones around Yellowstone National Park to reduce the risk of bison or elk infecting cattle on neighboring ranches with brucellosis, says a new draft report* by the National Research Council released for public comment today. Although the likelihood is low that cattle could be infected, those in zones nearest the park should be vaccinated frequently and monitored closely until the disease can be eradicated in bison and elk.

In the long term, a vaccine for bison and elk must be developed and administered before the disease can be fully eradicated, the report says. And any effort to eliminate brucellosis from the park would require the testing and slaughtering of infected bison, elk, and cattle.

"The risk of bison or elk transmitting brucellosis to cattle is very small because ranchers already are vigilant about vaccinating their cattle and monitoring the disease," said Norman Cheville, one of the principal investigators for the study and chair of the department of veterinary pathology, College of Veterinary Medicine, Iowa State University, Ames. "But because brucellosis cannot be eradicated in bison and elk anytime soon, the government needs to take extra precautions while options for long-term control and elimination of the disease in wildlife are examined. Just one undetected case of a cow aborting its calf because of brucellosis could spread the disease throughout an entire herd."

Brucellosis, which can cause female bison, elk, and cattle to abort their calves, is passed to other animals through contact with infected aborted fetuses or afterbirth, or to calves through nursing. And though rare in humans, brucellosis is a potentially debilitating and chronic disease that can be transmitted by drinking unpasteurized milk or by handling infected cows.

Although the likelihood is low that brucellosis would be transmitted from bison or elk to cattle, the true prevalence of brucellosis in bison and elk is unknown. Better data on the number of infected animals and the risk of transmission to cattle are needed to design a long-term eradication program.

"To make the Yellowstone area brucellosis-free, the disease must be eradicated in all three species simultaneously," said co-investigator Dale McCullough, professor of wildlife biology, University of California at Berkeley. "A lot more research is needed to determine whether and how such an ambitious goal can be met. But in the meantime, steps can be taken to control the spread of the disease in wildlife and in domestic cattle."

The U.S. Department of the Interior asked the Research Council to address the scientific issues surrounding the transmission of brucellosis from bison and elk to cattle. The draft report has been reviewed extensively by a panel of independent experts, and is being issued to solicit public comment.

Reducing the Risk

As long as the National Park Service does not control bison population growth, the report says, the number of bison will grow beyond the park's capacity to supply food in hard winters. Bison in Yellowstone have high birth and low death rates, so bison populations will continue to expand. As bison stray from the park in search of food, they put nearby cattle at risk of getting the disease. Elk populations -- unlike bison -- gradually decrease as food becomes scarce, and elk are hunted when they migrate outside the park, which further controls the herd.

The U.S. Departments of Agriculture and the Interior should work together to establish and maintain a series of disease surveillance and quarantine zones around the perimeter of Yellowstone, the report says. In addition to increasing vaccination and monitoring of cattle in those areas, programs should be established for reporting bison or elk that stray into the zones. Both agencies should fund cooperative research and develop ways to analyze results and provide information to the public.

Controlling the Disease

Since 1934, the Department of Agriculture has enforced standards to protect domestic cattle from brucellosis -- including vaccination and testing, and slaughter of infected cattle. The agency's goal is to eradicate brucellosis from cattle by 1998. According to federal policy, if cattle are found to carry the disease in states that have been certified as brucellosis-free, the state's classification may be downgraded, neighboring herds must be tested, and ranchers could be prohibited from interstate transport of cattle.

Vaccines for bison and elk should be used to eradicate the disease, the report says. Eliminating brucellosis in Yellowstone without first trying to reduce the number of potentially infected bison and elk through vaccination would require the slaughter of many animals. Moreover, before any eradication program can be developed, multiple testing over a period of several months must be completed to determine how many bison and elk in Yellowstone are infected. Both blood tests and culture tests are needed to determine infection. Blood tests are not definitive in indicating chronic infection; and culture tests, which indicate disease organisms, are often inaccurate because it is difficult to obtain adequate tissue samples.

For these reasons, wildlife managers should consider an animal infected if blood tests indicate antibodies for the disease, the report says. Up to 40 percent of the approximately 2,000 bison in Yellowstone -- and as many as 77 percent in the Jackson, Wyo., herd -- have tested positive for brucellosis antibodies. Of the 120,000 elk in the greater Yellowstone area, 37 percent of those that frequent winter feeding grounds test positive. Only 2 percent of elk that do not use feeding grounds test positive.

Even after a vaccine for bison and elk is developed, a large-scale vaccination program will be difficult and costly to administer, the report says. A long-term study should be conducted to determine appropriate types and doses of vaccines and a strategy for administering them in the wild. Bison, for example, will probably need to receive the vaccines through food or via injection with darts, both of which would be difficult in Yellowstone. The amount of vaccine each animal would receive in food could not be controlled. Further, bison and free-ranging elk are not as approachable as elk on winter feeding grounds, making injection a challenge.

Some elk that frequent winter feeding grounds are receiving vaccines as part of an experimental study, but none of the bison in Yellowstone are being vaccinated. If the experimental vaccination program in elk is continued, a team of scientists should monitor its effectiveness and publish results in a peer-reviewed journal, the report says. The disease must be controlled in elk before vaccines will succeed in bison. The feeding grounds draw elk together in a small area, increasing the likelihood of spreading brucellosis in elk or bison that may wander into the area. Closing the feeding grounds would probably significantly reduce brucellosis in elk, the report concludes.

Last winter, when more than 3,400 bison were in Yellowstone, record numbers of bison left the park in search of food. Some of them wandered onto ranchland inhabited by cattle, increasing the risk of brucellosis transmission. The bison population reached a low of around 1,900 after many were shot outside the park's boundaries and some starved inside the park. Leaving the roads in the park unplowed during the winter would not prevent bison from leaving the park, the report says, because they have already discovered outside sources of food.

Comment on the draft report can be sent via the Internet at <www2.nas.edu./besthome/ bisonelk.htm> to Lee Paulson, study director and program director for the Research Council's Board on Environmental Studies in Toxicology, at the street address in the letterhead. A final report will be issued in January. The study is being sponsored by the U.S. Department of Interior. The National Research Council is the principal operating arm of the National Academy of Sciences and the National Academy of Engineering. It is a private, non-profit institution that provides independent advice on science and technology issues under a congressional charter.

*The draft report Brucellosis in the Greater Yellowstone Area is on the Internet at <www2.nas.edu./besthome/ bisonelk.htm>. The final report will be available in January from the National Academy Press at the mailing address in the letterhead; tel. (202) 334-3313 or 1-800-624-6242. The cost of the report will be $34.00 (estimated) plus shipping charges of $4.00 for the first copy and $.50 for each additional copy. Reporters may obtain copies of the draft and final reports from the Office of News and Public Information at the letterhead address (contacts listed above).