BackgroundBrucella species include economically important zoonotic pathogens that can infect a wide range of animals. There are currently six classically recognised species of Brucella although, as yet unnamed, isolates from various marine mammal species have been reported. In order to investigate genetic relationships within the group and identify potential diagnostic markers we have sequenced multiple genetic loci from a large sample of Brucella isolates representing the known diversity of the genus.ResultsNine discrete genomic loci corresponding to 4,396 bp of sequence were examined from 160 Brucella isolates. By assigning each distinct allele at a locus an arbitrary numerical designation the population was found to represent 27 distinct sequence types (STs). Diversity at each locus ranged from 1.03–2.45% while overall genetic diversity equated to 1.5%. Most loci examined represent housekeeping gene loci and, in all but one case, the ratio of non-synonymous to synonymous change was substantially <1. Analysis of linkage equilibrium between loci indicated a strongly clonal overall population structure. Concatenated sequence data were used to construct an unrooted neighbour-joining tree representing the relationships between STs. This shows that four previously characterized classical Brucella species, B. abortus, B. melitensis, B. ovis and B. neotomae correspond to well-separated clusters. With the exception of biovar 5, B. suis isolates cluster together, although they form a more diverse group than other classical species with a number of distinct STs corresponding to the remaining four biovars. B. canis isolates are located on the same branch very closely related to, but distinguishable from, B. suis biovar 3 and 4 isolates. Marine mammal isolates represent a distinct, though rather weakly supported, cluster within which individual STs display one of three clear host preferences.ConclusionThe sequence database provides a powerful dataset for addressing ongoing controversies in Brucella taxonomy and a tool for unambiguously placing atypical, phenotypically discordant or newly emerging Brucella isolates. Furthermore, by using the phylogenetic backbone described here, robust and rationally selected markers for use in diagnostic assay development can be identified.

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Members of the genus Brucella infect many domesticated and wild animals and cause serious zoonotic infection in humans. The availability of discriminatory molecular typing tools to inform and assist conventional epidemiological approaches would be invaluable in controlling these infections, but efforts have been hampered by the genetic homogeneity of the genus. We report here on a molecular subtyping system based on 21 variable-number tandem-repeat (VNTR) loci consisting of 13 previously unreported loci and 8 loci previously reported elsewhere. This approach was applied to a collection of 121 Brucella isolates obtained worldwide and representing all six classically recognized Brucella species. The size of repeats selected for inclusion varied from 5 to 40 bp giving VNTR loci with a range of diversities. The number of alleles detected ranged from 2 to 21, and Simpson's diversity index values ranged from 0.31 to 0.92. This assay divides the 121 isolates into 119 genotypes, and clustering analysis results in groups that, with minor exceptions, correspond to conventional species designations. Reflecting this, the use of six loci in isolation was shown to be sufficient to determine species designation. On the basis of the more variable loci, the assay could also discriminate isolates originating from restricted geographical sources, indicating its potential as an epidemiological tool. Stability studies carried out in vivo and in vitro showed that VNTR profiles were sufficiently stable such that recovered strains could readily be identified as the input strain. The method described here shows great potential for further development and application to both epidemiological tracing of Brucella transmissions and in determining relationships between isolates worldwide.Brucellosis is a zoonotic disease of major public health, animal welfare, and economic significance worldwide. In humans, infection with Brucella can lead to a chronic debilitating infection; in domesticated animals, the main symptom is reproductive failure. Disease in humans usually reflects occupational exposure or the consumption of unpasteurized dairy products. Brucellosis remains a major problem in many parts of the world, particularly Mediterranean regions, western Asia, and parts of Africa and Latin America (11), although in many developed countries it has been eradicated or severely curtailed by a combination of strict veterinary hygiene measures, monitoring programs, and improved food safety measures. Brucella species have also long been considered potential biological warfare agents, and in 1954 Brucella became the first biological agent to be treated as a weapon and field tested on animals under the old U.S. offensive biological weapons program. Recent history has raised awareness in this area (28), and the organism remains on the list of Centers for Disease Control and Prevention category B potential biological warfare agents (25).Classical Brucella taxonomists developed a classification system that recognized six species based on subtle phenotypi...

BackgroundBrucellosis is a zoonosis of veterinary, public health and economic significance in most developing countries. Human brucellosis is a severely debilitating disease that requires prolonged treatment with a combination of antibiotics. The disease can result in permanent and disabling sequel, and results in considerable medical expenses in addition to loss of income due to loss of working hours. A study was conducted in Northern Tanzania to determine the risk factors for transmission of brucellosis to humans in Tanzania.MethodsThis was a matched case-control study. Any patient with a positive result by a competitive ELISA (c-ELISA) test for brucellosis, and presenting to selected hospitals with at least two clinical features suggestive of brucellosis such as headache, recurrent or continuous fever, sweating, joint pain, joint swelling, general body malaise or backache, was defined as a case. For every case in a district, a corresponding control was traced and matched by sex using multistage cluster sampling. Other criteria for inclusion as a control included a negative c-ELISA test result and that the matched individual would present to hospital if falls sick.ResultsMultivariable analysis showed that brucellosis was associated with assisted parturition during abortion in cattle, sheep or goat. It was shown that individuals living in close proximity to other households had a higher risk of brucellosis. People who were of Christian religion were found to have a higher risk of brucellosis compared to other religions. The study concludes that assisting an aborting animal, proximity to neighborhoods, and Christianity were associated with brucellosis infection. There was no association between human brucellosis and Human Immunodeficiency Virus (HIV) serostatus. Protecting humans against contact with fluids and tissues during assisted parturition of livestock may be an important means of reducing the risk of transferring brucellosis from livestock to humans. These can be achieved through health education to the communities where brucellosis is common.

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