Brucella is the cause of brucellosis, a true zoonotic disease (i.e. human-to-human transmission has not been identified). It is transmitted by ingesting infected food, direct contact with an infected animal, or inhalation of aerosols. Minimum infectious exposure is between 10 - 100 organisms. Brucellosis primarily occurs through occupational exposure (e.g. exposure to cattle, sheep, pigs), but also by consumption of unpasteurised milk products.
There are a few different species of Brucella, each with slightly different host specificity. B. melitensis which infects goats and sheep, B. abortus which infects cows, B. suis infects pigs, B. ovis infects sheeps and B. neotomae. Recently a new species was discovered in marine mammals: B. pinnipediae.
It's crucial to be able to differentiate Brucella from Salmonella which could also be isolated from blood cultures and are Gram negative. Testing for urease would successfully accomplish the task; as it is positive for the former and negative for the latter.
Brucella could also be seen in Bone marrow.
Laboratory acquired brucellosis is common. This most often happens when the disease is not thought of until cultures become positive, by which time the specimens have already been handled by a number of laboratory staff. The idea of preventative treatment is to stop people who have been exposed to Brucella from becoming unwell with the disease.
There are no clinical trials to be relied on as a guide for optimal treatment, but a three week course of rifampicin and doxycycline twice daily is the combination most often used, and appears to be efficacious; the advantage of this regimen is that it is oral medication and there are no injections, however, a high rate of side effects (nausea, vomiting, loss of appetite) has also been reported.