BRUCELLOSIS IN THE GREATER YELLOWSTONE AREA

INTRODUCTION

At the onset of the harsh winter of 1996-1997 in the Greater Yellowstone Area (GYA)[fn1], the YNP bison population was more than 3,400. Record numbers of bison (Bison bison) left the park in search of forage, and others starved. As bison crossed into private lands and lands managed by federal agencies other than the National Park Service, national attention focused once again on management strategies—including shooting bison—used to prevent the potential spread of brucellosis to cattle that are grazed on land adjacent to the park.

Brucellosis in the GYA is a disease caused by Brucella abortus biovar 1, a bacterial organism transmitted primarily by contact with products of birth or abortion or by milk. In response to public discussion of whether brucellosis transmission by bison or elk (Cervus elaphus) is a threat to domestic livestock and whether vaccination or other management strategies might prove useful in controlling potential transmission, Secretary of the Interior Bruce Babbitt asked the National Academy of Sciences to undertake a 6-month study of brucellosis in the GYA. The Board on Agriculture and the Board on Environmental Studies and Toxicology began the study in May 1997. The study specifically addressed

1  

The GYA includes Yellowstone National Park (YNP), Grand Teton National Park (GTNP), and the surrounding areas in Montana, Wyoming, and Idaho (See Figures 1 and 2).



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BRUCELLOSIS IN THE GREATER YELLOWSTONE AREA INTRODUCTION At the onset of the harsh winter of 1996-1997 in the Greater Yellowstone Area (GYA)[fn1], the YNP bison population was more than 3,400. Record numbers of bison (Bison bison) left the park in search of forage, and others starved. As bison crossed into private lands and lands managed by federal agencies other than the National Park Service, national attention focused once again on management strategies—including shooting bison—used to prevent the potential spread of brucellosis to cattle that are grazed on land adjacent to the park. Brucellosis in the GYA is a disease caused by Brucella abortus biovar 1, a bacterial organism transmitted primarily by contact with products of birth or abortion or by milk. In response to public discussion of whether brucellosis transmission by bison or elk (Cervus elaphus) is a threat to domestic livestock and whether vaccination or other management strategies might prove useful in controlling potential transmission, Secretary of the Interior Bruce Babbitt asked the National Academy of Sciences to undertake a 6-month study of brucellosis in the GYA. The Board on Agriculture and the Board on Environmental Studies and Toxicology began the study in May 1997. The study specifically addressed 1   The GYA includes Yellowstone National Park (YNP), Grand Teton National Park (GTNP), and the surrounding areas in Montana, Wyoming, and Idaho (See Figures 1 and 2).

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FIGURE 1. Winter ranges and migration routes of the Greater Yellowstone Area bison herds. Source: GAO 1997.

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FIGURE 2. Winter ranges and migration routes of the Greater Yellowstone Area elk herds. Source: GAO 1997.

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The extent of bison infected with brucellosis in the Greater Yellowstone Area and the potential of developing a vaccine program. The transmission of B. abortus among cattle, bison, elk, and other wildlife species. The relationship, if any, between bison population dynamics and brucellosis. The ability of serologic testing to estimate true infectiousness. The efficacy and safety of existing vaccines for target and nontarget species and the need for new (including bison-specific) vaccines. The nature and likely successes or limitations of a wild animal vaccination program. Key factors in reducing risk of transmission from wildlife to cattle and among cattle. BACKGROUND Brucellosis is a zoonotic disease; in humans, it is manifested as a febrile, systemic disease, often characterized by an undulating body temperature. Although rarely fatal, human brucellosis is debilitating, and success of treating individuals varies widely. Lifelong infection is not unusual. The hallmark sign in cattle, bison, and elk is abortion or birth of nonviable calves. YNP bison have tested positive for infection since brucellosis first was detected by Mohler in 1917. Today, some 30-40% of bison in YNP test seropositive for B. abortus; 1-2% of non-feeding-ground elk are seropositive. Elk at the feeding grounds have a much higher rate—about 37%—because dense concentrations of animals create conditions favorable to disease transmission. Because of its potential to be transmitted to humans, brucellosis is one of the most regulated diseases of cattle in the United States. Cattle shipped interstate are tested routinely only for brucellosis and tuberculosis, although other diseases cause markedly more morbidity and mortality. Human brucellosis is uncommon today in North America because of efforts to eradicate brucellosis in cattle and the use of sanitary procedures (such as pasteurization) in milk processing, but it was a public-health concern in 1934. That year, the U.S. Department of Agriculture (USDA) established a national brucellosis eradication effort—which implemented standards for testing, quarantine, and elimination—that remains in place today. Since 1934, an estimated $3.5 billion in federal, state, and private funds has been spent on brucellosis eradication in domestic livestock. The National Brucellosis Program is run by the USDA Animal and Plant Health Inspection Service (APHIS), which has a

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goal of eradication of brucellosis from cattle and captive bison herds in the United States by 1998. Only 12 cattle herds were infected at the time of this report. As part of its efforts to eradicate brucellosis, APHIS certifies states as brucellosis-free, class A, class B, or class C, depending on the rate of infection in all cattle herds in a state. Cattle herds in brucellosis-free states have unrestricted interstate movement. Herds in class A states have an infection rate of no more than 0.25%, and cattle must be tested for B. abortus before export. Class B indicates an infection rate of no more than 1.5%, and cattle must be tested before and after interstate shipment. Class C designates an infection rate of more than 1.5%, and herds must be tested twice before and once after export; no states hold class B or C status at present, which is an indication of the success of eradication strategies. A state's classification is important if B. abortus is detected because of numerous costs incurred, such as those related to testing procedures, but perhaps the most important costs are those associated with the refusal of other states to accept a state's cattle because of the perception that B. abortus might be present. Many states prohibit importation of unvaccinated breeding cattle. STRUCTURE OF THIS STUDY The social and political issues underlying this study are thorny and controversial. Some claim that the possibility that bison or other wildlife transmit brucellosis to cattle is remote and that no management strategies are needed. Others claim that any risk of transmission is unacceptable and that brucellosis must be eradicated from the wild. This study looks at the scientific bases behind brucellosis research and related issues in wildlife biology and makes recommendations based on current scientific knowledge. By authorizing USDA to regulate brucellosis transmission in cattle, the federal government has demonstrated concern that brucellosis poses a low-risk, great-loss situation in terms of potential economic consequences and possible human health effects. This report was written with that in mind. The authors also are aware that the National Park Service must consider factors that are beyond the scope of this study but that might affect the ultimate management of brucellosis in the GYA, such as environmental safety of vaccines. The principal investigators for this study, Norman Cheville and Dale McCullough, were chosen because of their expertise in B. abortus and in wildlife (particularly ungulate) biology, respectively. Data collection for this

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study had many facets, including a review of the scientific literature. A questionnaire (see Appendix A) was sent to interested parties and experts to obtain current scientific information. Open meetings were held on July 24-25, 1997, in Bozeman, Montana, and on August 4, 1997, in Jackson Hole, Wyoming, to hear scientific presentations on current research and to provide a forum at which public opinion could be expressed (see Appendix B). Experts were contacted throughout the study process to aid in synthesizing current scientific thought on issues related to brucellosis. The NRC requested public comments after the prepublication copy of the study was released in December 1997. This final document reflects changes made in response to the comments received. Changes were made to clarify the authors' text but did not result in changes to the conclusions and recommendations made in the prepublication release. The report covers four subjects: infection, transmission of B. abortus, vaccination, and approaches to reducing the risk of transmission.