Brucellosis

Abstract

Human brucellosis belongs to the most common bacterial zoonotic diseases with about 500,000 reported cases per year and is one of the most widespread zoonoses according to the World Health Organization. The disease is caused by Brucella species, a highly contagious bacterial agent causing severe infection in humans and economic loss in livestock. It is considered to be a bioterrorism organism due to its low infectious doses of 10 to 100 bacteria and its ease of transmission as an aerosol. Brucellosis is endemic worldwide but the Mediterranean region has been particularly affected. The species of the genus Brucella with the greatest importance as zoonotic pathogens are Brucella (B.) melitensis, B. abortus, and B. suis. Some species are further subdivided into biovars. The species differ in their animal host specificity and epidemiological occurrence depending on the livestock or the prevalence of the corresponding wild animals in the respective country. In addition, the species and, in the case of B. suis, even the biovars differ in their pathogenicity und thereby in the clinical picture caused in humans which is complex and often characterized by relapses or chronification and termed by the syndrome Mediterranean fever, among others. Since 2007, the genus Brucella has changed fundamentally. A series of new “atypical” species and Brucella-like organisms have been described infecting humans, rodents, amphibians, fish, and even reptiles, like the panther chameleon. The significance as a zoonosis of these rare species remains still unclear, but first cases caused by atypical Brucella spp. in humans have been reported. Diagnosis is based on the detection of the pathogen by means of cultivation and the detection of genus-specific nucleic acids in patient or animal samples. Unambiguous species differentiation and genotyping in case of outbreaks are challenging due to the close relationship between the species and can be achieved by multiplex PCRs, sequencing of single genes as well as by whole genome sequencing. The serological diagnosis in humans and livestock is based on the detection of antibodies against the Brucella lipopolysaccharide. It is hampered by different lipopolysaccharide types among the species and by cross-reactivities to other zoonotic Gram-negative bacteria. Prevention and control in livestock are achieved by regular testing and vaccination with live vaccines and in humans by avoiding contaminated food products and protection from infected animals and their secretions.