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Microbiology, epidemiology, and pathogenesis of Brucella

Mile Bosilkovski, MD
Section Editors
Stephen B Calderwood, MD
Morven S Edwards, MD
Deputy Editor
Elinor L Baron, MD, DTMH


Brucellosis is a zoonotic infection transmitted to humans by contact with fluids from infected animals (sheep, cattle, goats, pigs, or other animals) or derived food products such as unpasteurized milk and cheese. It is one of the most widespread zoonoses worldwide [1]. Brucellosis has high morbidity both for humans and animals; it is an important cause of economic loss and public health problems in many developing countries [2]. The prevalence of brucellosis has been increasing due to growing international tourism and migration [3,4].

The microbiology, epidemiology, and pathogenesis of Brucella spp will be reviewed here. The clinical manifestations, diagnosis, and treatment of brucellosis are discussed separately. (See "Clinical manifestations, diagnosis, and treatment of brucellosis".)


Several species are recognized within the genus Brucella based on phenotypic characteristics, antigenic variation, and prevalence of infection in different animal hosts [5,6]. B. melitensis (small ruminants), B. abortus (cattle), B. suis (swine), and B. canis (dogs) are known to cause human disease. B. neotomae (desert wood rats) and B. ovis (sheep) are not pathogenic to humans. The majority of human cases worldwide are attributed to B. melitensis [7]. In general, B. melitensis and B. suis are more virulent for humans than B. abortus or B. canis [8]. B. melitensis, B. abortus, and B. suis have three, seven, and five biotypes, respectively [5,9].

Two additional Brucella species, B. pinipedialis and B. ceti, have been isolated from marine mammals and detected as sporadic human pathogens [10-12]. B. pinipedialis and B. ceti differ phenotypically from the other species by their pattern of metabolic activity [13]. Other relatively new species include B. microti (isolated from wildlife animals), B. papionis (isolated from baboons), and B. inopinata (isolated from a human breast implant wound) [14-16].

The genome of most Brucella species consists of two circular chromosomes [9]. Natural plasmids have not been detected [17]. Sequencing and annotation of the genomes of B. suis, B. melitensis, and B. abortus has been completed; the majority of the open reading frames share greater than 99 percent sequence identity between species [18-20].

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Literature review current through: Sep 2017. | This topic last updated: Sep 18, 2017.
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