Historical context and background of brucellosis in the world

Brucellosis has infected humans for millennia and continues to be among the most important zoonotic diseases worldwide. Human brucellosis incidence is estimated to be in the millions of cases annually. Brucellosis incidence in animals, primarily livestock, is considerably higher, with rough estimates being in the tens of millions, perhaps hundreds of millions, of infected animals. With apparent origins in the Fertile Crescent in Southwest Asia, and hastened by the domestication of goats, sheep, cattle, and pigs in that same region, humans spread brucellosis through the expansion of farming. More recently, trade and movement of infected livestock have further contributed to its global distribution. The result has been the dissemination of this disease to the far reaches of the Earth, wherever livestock have been introduced. Although the hosts have not been identified, brucellosis likely originates in wildlife—perhaps the ancestors of domesticated animals, such as wild goats, ancient cattle-like aurochs, or possibly other sources, such as ungulates in Africa or Asia. This chapter examines the origins and spread of brucellosis to better understand how this infectious disease has come to conquer the world, with the ultimate goal of using this information to reduce the impacts of this pervasive disease across five continents.