The main goal of this chapter is to give an update on the worldwide distribution and prevalence of Brucella melitensis in animals and human populations, as well as the main risk factors of brucellosis occurrence in flocks. The current epidemiological data regarding brucellosis prevalence and incidence in small ruminants is still mainly based on indirect tests by the detection of antibodies anti-Brucella. Nevertheless, in the last years, a more progressive molecular characterization of B. melitensis, B. ovis and other Brucella species has been reported. As a consequence, new insights regarding the dynamics of Brucella were improved. Currently, several countries, mainly but not exclusively in socio-economic developed regions, e.g., USA, Oceania or Europe, are considered B. melitensis-free. In some other countries, normally with low socio-economic status, e.g., Africa or Asia, the situation remains unknown or with significantly high levels of brucellosis in small ruminants and people. According the data of the last five years, the true seroprevalence of brucellosis in small ruminant populations or flocks ranged from 2.7% to 70.4%, with Jordan and other Middle Eastern countries presenting the highest values. Animal movements, flock management, type and size, and environmental conditions are the most significant factors related to the prevalence of brucellosis
