Applying an ecosystem approach to brucellosis control: can an old conflict between wildlife and agriculture be successfully managed?

and cattle is caused by Brucella abortus, a bacterium introduced to the US via European livestock. B abortus was first detected in bison in Yellowstone National Park (YNP) in 1917 (Cheville et al. 1998), and in elk as early as 1930. In wildlife and cattle, uninfected animals contract the disease primarily by licking birth exudates of infected herd members; however, bacteria localize in a variety of organs and can often be cultured from lymph nodes and mammary glands of infected animals on postmortem. Grazing on contaminated forage is a less likely intraspecies transmission route. Human brucellosis (known as undulant fever or Bang’s disease) is usually caused by consuming unpasteurized dairy products and/or handling infected animals. Brucella bacteria are well-adapted to, and have coevolved with, ungulates and rarely cause severe morbidity or mortality in these hosts. However, in humans the disease is painful, debilitating, and chronic. Prior to an intensive state–federal brucellosis eradication campaign initiated in 1934, infection was common among the general public as well as in slaughterhouse workers and veterinarians. Now, undulant fever rarely occurs in the US, although it remains a problem in countries with less reliable pasteurization systems (Young 1995). When the disease does appear in the US, it is usually caused by Brucella melitensis, a species that does not occur in bison or elk, and is traceable to consumption of unpasteurized dairy products from sheep and goats (Chomel et al. 1994). Cattle producers must vaccinate and test for brucellosis (at frequencies depending on the brucellosis classification of the state in which they are operating), and if a positive animal is identified, usually the entire herd is slaughtered.