The role that pathogens play in structuring ecological communities needs to be examined from both a theoretical and empirical perspective. This paper provides a brief introduction to the ecology and epidemiology of brucellosis in Yellowstone National Park. Observed patterns of infection for brucellosis in bison in national parks in the United States suggest that Brucella has a relatively sharply defined threshold for establishment and that the proportion of the host population infected increases as a relatively simple function of population density. Unfortunately, the threshold population for Brucella establishment in bison is low, a herd of at least 200 individuals; this makes it very hard to eradicate Brucella from wild populations. Simple calculations based on observed prevalence and recruitment data for the Yellowstone bison herd suggest that unacceptably high levels of culling would be required to eradicate brucellosis in the park. A simple mathematical model is used to describe aspects of the population dynamics of Brucella. The analyses suggest that an understanding of infectious disease dynamics is crucial to the management and conservation of wild and domestic ungulate species in and around national parks and other nature reserves. The consequences of disease control for the maintenance of biodiversity in other natural and captive communities need to be better understood.

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Abstra~ Brucellosis caused by Brucella abortus occurs in the free-ranging bison (Bison bison) of Yellowstone and Wood Buffalo National Parks and in elk (Cervus elaphus) of the Greater Yellowstone Areg As a result of nationugde bovine brucellosis eradication programg states and provinces proximate to the national parks are considered free of bovine brucellosi& Thug increased attention has been focused on the wildlife within these areas us potenttal reservoirs for transmission to cattle Because the national parks are man. dated as natural area~ the question has been raised as to whether Bmcella abortus is endogenous or exogenous to bison, particularly for Yellowstone National Parl~ We synthesized diverse lines of inquiry, including the evolutionary history of both bison and Brucella, wild animals as Brucella host& biochemical and genetic information, behavioral characteristics of host and organisng and area history to develop an evaluation of the question for the National Park Service. All lines of inquiry indicated that the organism was introduced to North America with cattle~ and that the introduction into the Yellowstone bison probably was directly from cattle shortly before 1917. Fistulous withers of horses was a less likely possibllity. Elk on winter feedgrounds south of Yellowstone National Park apparently acquired the disease directly from cattle Bison presently using Grand Teton National Park probably acquired brucellosis from feedground elk Sobre el origen de la brucelosis en el bisonte del Parque Nacional Yellowstone: Una revisi6nResumen: La brucelosis causada por Brucella abortus afecta al btsonte (Bison bison) de los Parques Nacionales Yellowstone y "Wood Buffalo" y al alce (Cervus elaphus) de la Gran Area del Yellowstone Como resultado de programas de erradicaci6n de la brucelosis a 1o largo de toda la Naci6n, los estados y provincias pr6ximos a los parques nacionales son considerados como libres de brucelosis boring Como concecuencia de esto, se ha prestado mds atenci6n a la vida silvestre dentro de estas dreas como posibles resemo~os para la transmisibn de brucelosis al ganado. Dado que los parques nacionales son asignados por mandatos como dreas naturaleg ha surgldo el interds en determinar si Brucella abortus es end6gena o ex6gena al bisont~ en particular en lo que respecta al Parque Nacional Yellowstone Nosotros sintetizamos varias lineas de investigaci6n, que incluyen la historia evolativa tanto del bisonte como de Brucella, el estudio de animales saltctjes como portadores de Brucella,/a informacibn bioquimica y gen&tica~ las caracteristicas de comportamiento del portador y del organismo, y ia historia del drea a los efectos de desarrollar una evaluaci6n del problemapara el Servicio de Parques Nacionaleg Todas las lineas de investigaci6n indicaron que el organtsmo fue introducldo en Amdrica del Norte con el ganado, y que la transmisi6n al btsonte americano ocurri6 directamente a partir del ganado poco despues de 1917. La transmisi6n a partir de cru. zeras fistulosas de caballos fue una posibilida...

An epizootic of infectious keratoconjunctivitis occurred in bighorn sheep (Ovis canadensis) in Yellowstone National Park during the winter of 1981-82. The causative organism was identified as Chlamydia sp. Mortality related to the epizootic was approximately 60% of an estimated 500 bighorn sheep in the northern range population. The infection probably affected all sex and age classes, but field surveys of live animals and mortality suggested that mature rams died disproportionately. Limited field observations the following winter on individuals having both normal and cloudy-appearing eyes suggested that half of the bighorns then present on the core units of winter range had contracted the disease and survived. By 1988, there were about 300 bighorn sheep in the population.

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