Under present conditions there is a high risk of an epidemic of brucellosis associated with the threat of the spread of the pathogen from many natural sources, as well as artificially as a result of bioterrorist actions. In spite of the vast complex of brucellosis eradication activities around the world, it still remains endemic in many regions of the world. The situation is exacerbated by the ecological spreading of the causative agent of brucellosis on the previously unusual species of natural hosts, accompanied by the emergence of new Brucella species, some of which poses a risk to humans. This paper summarizes the data on the distribution area of human pathogenic Brucella species, structure and level of incidence of brucellosis in different regions of our country and abroad, pathogenicity of representatives of different species and biotypes of Brucella for humans.